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2022ApJ...934...41N | On the Energy Dependence of Galactic Cosmic Ray Anisotropies in the Very Local Interstellar Medium | We report on the energy dependence of Galactic cosmic rays (GCRs) in the very local interstellar medium (VLISM) as measured by the Low Energy Charged Particle (LECP) instrument on the Voyager 1 spacecraft. The LECP instrument includes a dual-ended solid-state detector particle telescope mechanically scanning through 360° across eight equally spaced angular sectors. As reported previously, LECP measurements showed a dramatic increase in GCR intensities for all sectors of the ≥211 MeV count rate (CH31) at the Voyager 1 heliopause (HP) crossing in 2012; however, since then the count rate data have demonstrated systematic episodes of intensity decrease for particles around 90° pitch angle. To shed light on the energy dependence of these GCR anisotropies over a wide range of energies, we use Voyager 1 LECP count rate and pulse height analyzer (PHA) data from ≥211 MeV channel together with lower-energy LECP channels. Our analysis shows that, while GCR anisotropies are present over a wide range of energies, there is a decreasing trend in the amplitude of second-order anisotropy with increasing energy during anisotropy episodes. A stronger pitch angle scattering at higher velocities is argued as a potential cause for this energy dependence. A possible cause for this velocity dependence arising from weak rigidity dependence of the scattering mean free path and resulting velocity-dominated scattering rate is discussed. This interpretation is consistent with a recently reported lack of corresponding GCR electron anisotropies. | [
567,
847,
711,
707,
845,
325
] | [
"galactic cosmic rays",
"interstellar medium",
"heliosphere",
"heliopause",
"interstellar magnetic fields",
"cosmic ray detectors"
] |
2024RNAAS...8...93S | The Recurrent Nova V745 Sco had a Classical Nova Eruption in 1897 July | Recurrent nova V745 Sco is discovered to have a long-lost nova eruption in 1897 July. Now with four known eruptions (in 1897, 1937, 1989, and 2014), plus two likely missed eruptions (around 1917 and 1963), the average recurrence time is 23 yr, with a fractional rms of 13%. | [
1366,
251,
1675
] | [
"recurrent novae",
"classical novae",
"symbiotic novae"
] |
2023ApJ...958..106F | Searching for Novel Chemistry in Exoplanetary Atmospheres Using Machine Learning for Anomaly Detection | The next generation of telescopes will yield a substantial increase in the availability of high-quality spectroscopic data for thousands of exoplanets. The sheer volume of data and number of planets to be analyzed greatly motivate the development of new, fast, and efficient methods for flagging interesting planets for reobservation and detailed analysis. We advocate the application of machine learning (ML) techniques for anomaly (novelty) detection to exoplanet transit spectra, with the goal of identifying planets with unusual chemical composition and even searching for unknown biosignatures. We successfully demonstrate the feasibility of two popular anomaly detection methods (local outlier factor and one-class support vector machine) on a large public database of synthetic spectra. We consider several test cases, each with different levels of instrumental noise. In each case, we use receiver operating characteristic curves to quantify and compare the performance of the two ML techniques. | [
487,
2021,
2133,
1908,
1934,
1936
] | [
"exoplanet atmospheres",
"exoplanet atmospheric composition",
"transmission spectroscopy",
"clustering",
"outlier detection",
"support vector machine"
] |
2023ApJ...954L..43K | A Dynamically Distinct Stellar Population in the Leading Arm of the Sagittarius Stream | We present a chemical and dynamical analysis of the leading arm (LA) and trailing arm (TA) of the Sagittarius (Sgr) stream, as well as for the Sgr dwarf galaxy core (SC), using red giant branch, main-sequence, and RR Lyrae stars from large spectroscopic survey data. The different chemical properties among the LA, TA, and SC generally agree with recent studies and can be understood by a radial metallicity gradient established in the progenitor of the Sgr dwarf, followed by preferential stellar stripping from the outer part of the Sgr progenitor. One striking finding is a relatively larger fraction of low-eccentricity stars (e < 0.4) in the LA than in the TA and SC. The TA and SC exhibit very similar distributions. Considering that a tidal tail stripped off from a dwarf galaxy maintains the orbital properties of its progenitor, we expect that the e-distribution of the LA should be similar to that of the TA and SC. Thus, the disparate behavior of the e-distribution of the LA is of particular interest. Following the analysis of Vasiliev et al., we attempt to explain the different e-distribution by introducing a time-dependent perturbation of the Milky Way by the Large Magellanic Cloud's (LMC) gravitational pull, resulting in substantial evolution of the angular momentum of the LA stars to produce the low-e stars. In addition, we confirm from RR Lyrae stars with high eccentricity (e > 0.6) that the TA stars farther away from the SC are also affected by disturbances from the LMC. | [
1051,
1423,
2166,
416,
1596,
1577
] | [
"milky way dynamics",
"sagittarius dwarf spheroidal galaxy",
"stellar streams",
"dwarf galaxies",
"stellar dynamics",
"stellar abundances"
] |
2020AJ....160....2B | Fear the Shadows of the Giants: On Secular Perturbations in Circumstellar Habitable Zones of Double Stars | After the detection of extrasolar planets in binary- and multiple-star systems, questions arose about their dynamics and habitability. In this study we investigate a five-dimensional parameter space for wide binary stars with a massive planet beyond the habitable zone (HZ). Our aim is to reveal those orbital and physical parameter combinations that expose bodies in the primary star's HZ to secular perturbations. Building on an established semianalytical model, we combine two separate analytical models into a new one to treat the restricted four-body problem. We apply this new Combined Analytical Model (CAM) to different synthetic systems and systematically map the occurrence of secular resonances (SRs). These maps are then visualized as two-dimensional sections of the parameter space. The CAM model has a median error below 3% relative to numerical reference simulations. We also derive a simplified CAM that performs well for hierarchical systems with moderate to large separations between the bodies. Our results show that SRs appear in the HZ even for large secondary-star distances (up to >1000 au) if either (i) the planet's distance is larger than Jupiter's or (ii) its mass is about Saturn's or lower. Changes in the secondary star's eccentricity by stellar flybys or galactic tides can push a formerly dynamically quiet HZ to a high-eccentricity state. Based on these results, we provide the easy-to-use online tool "SHaDoS" that evaluates the CAM for a given user input and traces the locations of SRs in the HZ in two-dimensional parameter space plots. | [
531,
695,
211,
490,
154,
62
] | [
"few-body systems",
"habitable planets",
"celestial mechanics",
"exoplanet dynamics",
"binary stars",
"apsidal motion"
] |
2024ApJ...961...40M | Differential Rotation of the Solar Chromosphere: A Century-long Perspective from Kodaikanal Solar Observatory Ca II K Data | Chromospheric differential rotation is a key component in comprehending the atmospheric coupling between the chromosphere and the photosphere at different phases of the solar cycle. In this study, we therefore utilize the newly calibrated multidecadal Ca II K spectroheliograms (1907-2007) from the Kodaikanal Solar Observatory (KoSO) to investigate the differential rotation of the solar chromosphere using the technique of image cross-correlation. Our analysis yields the chromospheric differential rotation rate Ω(θ) = (14.61 ± 0.04-2.18 ± 0.37 ${\sin }^{2}\theta -1.10\pm 0.61{\sin }^{4}\theta )^\circ $ day<SUP>-1</SUP>. These results suggest the chromospheric plages exhibit an equatorial rotation rate 1.59% faster than the photosphere when compared with the differential rotation rate measured using sunspots and also a smaller latitudinal gradient compared to the same. To compare our results to those from other observatories, we have applied our method on a small sample of Ca II K data from Rome, Meudon, and Mount Wilson observatories, which support our findings from KoSO data. Additionally, we have not found any significant north-south asymmetry or any systematic variation in chromospheric differential rotation over the last century. | [
1487,
1240,
1479,
1524,
1996
] | [
"solar cycle",
"plages",
"solar chromosphere",
"solar rotation",
"solar differential rotation"
] |
2020ApJ...896...83G | Discovery of a Universal Correlation for Long and Short GRBs and Its Application for the Study of Luminosity Function and Formation Rate | Gamma-ray bursts (GRBs) are known to be the most violent explosions in the universe, and a variety of correlations between observable GRB properties have been proposed in the literature, but none of these correlations are valid for both long and short GRBs. In this paper we report the discovery of a universal correlation that is suitable for both long and short GRBs using three prompt emission properties of GRBs, I.e., the isotropic peak luminosity L<SUB>iso</SUB>, the peak energy of the time-integrated prompt emission spectrum E<SUB>peak</SUB>, and the "high signal" timescale T<SUB>0.45</SUB>, ${L}_{\mathrm{iso}}\propto {E}_{\mathrm{peak}}^{1.94}{T}_{0.45}^{0.37}$ . This universal correlation involves properties of GRB prompt emission and does not require knowledge of the afterglow phase, which can be used as a relatively unbiased redshift estimator. Here we use this correlation to estimate the pseudoredshifts for short GRBs and then use the Lynden-Bell method to obtain a nonparametric estimate of their luminosity function and formation rate. The luminosity function is $\psi ({L}_{0})\propto {L}_{0}^{-0.63\pm 0.07}$ for dim SGRBs and $\psi ({L}_{0})\propto {L}_{0}^{-1.96\pm 0.28}$ for bright SGRBs, with the break point ${6.95}_{-0.76}^{+0.84}\times {10}^{50}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ . The local formation rate of SGRBs is about 15 events Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> . This universal correlation may have important implications for GRB physics, implying that the long and short GRBs should share similar radiation processes. | [
629,
187,
339,
343
] | [
"gamma-ray bursts",
"burst astrophysics",
"cosmological parameters",
"cosmology"
] |
2022ApJ...929...94A | Quenching and the UVJ Diagram in the SIMBA Cosmological Simulation | Over the past decade, rest-frame color-color diagrams have become popular tools for selecting quiescent galaxies at high redshift, breaking the color degeneracy between quiescent and dust-reddened star-forming galaxies. In this work, we study one such color-color selection tool-the rest-frame U - V versus V - J diagram-by employing mock observations of cosmological galaxy formation simulations. In particular, we conduct numerical experiments assessing both trends in galaxy properties in UVJ space and the color-color evolution of massive galaxies as they quench at redshifts z ~ 1-2. We find that our models broadly reproduce the observed UVJ diagram at z = 1-2, including (for the first time in a cosmological simulation) reproducing the population of extremely dust-reddened galaxies in the top right of the UVJ diagram. However, our models primarily populate this region with low-mass galaxies and do not produce as clear a bimodality between star-forming and quiescent galaxies as is seen in observations. The former issue is due to an excess of dust in low-mass galaxies and relatively gray attenuation curves in high-mass galaxies, while the latter is due to the overpopulation of the green valley in SIMBA. When investigating the time evolution of galaxies on the UVJ diagram, we find that the quenching pathway on the UVJ diagram is independent of the quenching timescale, and instead dependent primarily on the average specific star formation rate in the 1 Gyr prior to the onset of quenching. Our results support the interpretation of different quenching pathways as corresponding to the divergent evolution of post-starburst and green valley galaxies. | [
1724,
2040,
2176
] | [
"two-color diagrams",
"galaxy quenching",
"post-starburst galaxies"
] |
2020ApJ...890..144G | Why Radio Quiet Quasars are Preferred over Radio Loud Quasars Regardless of Environment and Redshift | Evidence has accumulated suggesting the clustering of radio loud quasars (RLQs) is greater than for radio quiet quasars. We interpret these results in a context in which the fraction of RLQ formation is f<SUB>RLQ</SUB> ≤ f<SUB>RQQ</SUB> compared to that for radio quiet quasars for all environments and redshifts. Because we assume that post-merger cold gas onto large black holes produces either a radio loud or a radio quiet quasar, we show that for the largest black hole masses that live in the largest dark matter halos, f<SUB>RLQ</SUB> approaches 0.5 from below but does not exceed it, such that in rich clusters the formation of an RLQ tends to be equally likely to occur as a radio quiet quasar. In dark matter halos with smaller mass, by contrast, radio quiet quasars are more likely to form and the likelihood increases inversely with dark matter halo mass. As a result, averaging over a population of radio loud and radio quiet quasars will necessarily generate lower average black hole masses for the radio quiet subgroup. Hence, despite the fact that the formation of radio quiet quasars is preferred over RLQs in any environment, at any mass scale, at any luminosity, or redshift, averaging over a range of RLQs will give the appearance that they are preferred in cluster environments over radio quiet quasars. We show how this also accounts for the order of magnitude difference in the total number of jetted active galaxies compared to nonjetted counterparts. | [
1349,
1354
] | [
"radio loud quasars",
"radio quiet quasars"
] |
2021ApJS..257....2C | Molecules with ALMA at Planet-forming Scales (MAPS). II. CLEAN Strategies for Synthesizing Images of Molecular Line Emission in Protoplanetary Disks | The Molecules with ALMA at Planet-forming Scales Large Program (MAPS LP) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0"15 and 0"30 beams for Bands 6 and 3, respectively) and sensitivity (spanning 0.3-1.3 mJy beam<SUP>-1</SUP> and 0.4-1.9 mJy beam<SUP>-1</SUP> for Bands 6 and 3, respectively). In this article, we describe the multistage workflow-built around the CASA tclean image deconvolution procedure-that we used to generate the core data product of the MAPS LP: the position-position-velocity image cubes for each spectral line. Owing to the expansive nature of the survey, we encountered a range of imaging challenges: some are familiar to the submillimeter protoplanetary disk community, like the need to use an accurate CLEAN mask, and others are less well known, like the incorrect default flux scaling of the CLEAN residual map first described by Jorsater & van Moorsel (the "JvM effect"). We distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. In particular, we describe how to produce image cubes with accurate fluxes via "JvM correction," a procedure that is generally applicable to any image synthesized via CLEAN deconvolution but is especially critical for low signal-to-noise ratio (S/N) emission. We further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of S/N when detecting molecular emission from protoplanetary disks. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement. | [
1300,
1647,
1346,
1910
] | [
"protoplanetary disks",
"submillimeter astronomy",
"radio interferometry",
"deconvolution"
] |
2023RNAAS...7..210Z | Variability Census of Legacy Catalogs. I. 1800+ New δ Scuti and γ Doradus Stars | Discovery of 1200+ new δ Scuti and 680+ new γ Doradus stars is presented as the preliminary results of a variability vetting census of the four legacy catalogs: BD, HD, SAO and PPM. This systematic screening of cataloged stars is part of a special survey project that aims to identify bright variable stars based on publicly accessible high-precision space photometry. Identification was performed using a Python program that involved human intervention and visual inspection. Successive results will be reported separately in a dynamic online catalog as the census progresses. *Dedicated to my wife Jingyun Zhang. | [
1307,
370,
2101
] | [
"pulsating variable stars",
"delta scuti variable stars",
"gamma doradus variable stars"
] |
2020ApJ...904L..23B | Near-infrared Spectroscopy of CK Vulpeculae: Revealing a Remarkably Powerful Blast from the Past | CK Vulpeculae (CK Vul), which erupted in AD 1670-71, was long considered to be a nova outburst; however, recent observations have required that alternative scenarios be considered. Long-slit infrared spectroscopy of a forbidden line of iron reported here has revealed high line-of-sight velocities (∼±900 km s<SUP>-1</SUP>) of the ansae at the tips of the bipolar lobes imaged in Hα in 2010. The deprojected velocities of the tips are approximately ±2130 km s<SUP>-1</SUP> assuming the previously derived inclination angle of 65° for the axis of cylindrical symmetry of the bipolar nebula. Such high velocities are in stark contrast to previous reports of much lower expansion velocities in CK Vul. Based on the deprojected velocities of the tips and their angular expansion measured over a 10 yr baseline, we derive a revised estimate, with estimated uncertainties, of ${3.2}_{-0.6}^{+0.9}$ kpc for the distance to CK Vul. This implies that the absolute visual magnitude at the peak of the 1670 explosion was ${M}_{V}=-{12.4}_{-2.4}^{+1.3}$ , indicating that the 1670 event was far more luminous than previous estimates and brighter than any classical nova or any Galactic stellar merger. We propose that CK Vul belongs to the class of intermediate-luminosity optical transients (ILOTs), objects which bridge the luminosity gap between novae and supernovae. While eruptions in lower luminosity ILOTs are attributed to merger events, the origin of the highly luminous ILOT outbursts is currently not known. | [
1619,
1636,
1613,
1609,
793
] | [
"stellar phenomena",
"stellar winds",
"stellar mass loss",
"stellar luminosities",
"infrared sources"
] |
2021ApJ...920L...3C | The Relative Contribution to Heavy Metals Production from Binary Neutron Star Mergers and Neutron Star-Black Hole Mergers | The origin of the heavy elements in the universe is not fully determined. Neutron star-black hole (NSBH) and binary neutron star (BNS) mergers may both produce heavy elements via rapid neutron-capture (r-process). We use the recent detection of gravitational waves from NSBHs, improved measurements of the neutron star equation of state (EoS), and the most modern numerical simulations of ejected material from binary collisions to measure the relative contribution of NSBHs and BNSs to the production of heavy elements. As the amount of r-process ejecta depends on the mass and spin distribution of the compact objects, as well as on the EoS of the neutron stars, we consider various models for these quantities, informed by gravitational-wave and pulsar data. We find that in most scenarios, BNSs have produced more r-process elements than NSBHs over the past 2.5 billion years. If black holes have preferentially small spins, BNSs can produce at least twice the amount of r-process elements than NSBHs. If black hole spins are small and there is a dearth of low-mass (<5M<SUB>⊙</SUB>) black holes within NSBH binaries, BNSs can account for the near totality of the r-process elements from binaries. For NSBH to produce a large fraction of r-process elements, black holes in NSBHs must have small masses and large aligned spins, which is disfavored by current data. | [
675,
678,
705
] | [
"gravitational wave astronomy",
"gravitational waves",
"heavy metal stars"
] |
2023PSJ.....4...74H | Toward 3D Retrieval of Exoplanet Atmospheres: Assessing Thermochemical Equilibrium Estimation Methods | Characterizing exoplanetary atmospheres via Bayesian retrievals requires assuming some chemistry model, such as thermochemical equilibrium or parameterized abundances. The higher-resolution data offered by upcoming telescopes enable more complex chemistry models within retrieval frameworks. Yet many chemistry codes that model more complex processes like photochemistry and vertical transport are computationally expensive, and directly incorporating them into a 1D retrieval model can result in prohibitively long execution times. Additionally, phase-curve observations with upcoming telescopes motivate 2D and 3D retrieval models, further exacerbating the lengthy runtime for retrieval frameworks with complex chemistry models. Here we compare thermochemical equilibrium approximation methods based on their speed and accuracy with respect to a Gibbs energy-minimization code. We find that, while all methods offer orders-of-magnitude reductions in computational cost, neural network surrogate models perform more accurately than the other approaches considered, achieving a median absolute dex error of <0.03 for the phase space considered. While our results are based on a 1D chemistry model, our study suggests that higher-dimensional chemistry models could be incorporated into retrieval models via this surrogate modeling approach. | [
2021,
487,
1933,
1914,
224
] | [
"exoplanet atmospheric composition",
"exoplanet atmospheres",
"neural networks",
"regression",
"chemical abundances"
] |
2024PASP..136e4503M | Robust 1-norm Periodograms for Analysis of Noisy Non-Gaussian Time Series with Irregular Cadences: Application to VLBI Astrometry of Quasars | Astronomical time series often have non-uniform sampling in time, or irregular cadences, with long gaps separating clusters of observations. Some of these data sets are also explicitly non-Gaussian with respect to the expected model fit, or the simple mean. The standard Lomb–Scargle periodogram is based on the least squares solution for a set of test periods and, therefore, is easily corrupted by a subset of statistical outliers or an intrinsically non-Gaussian population. It can produce completely misleading results for heavy-tailed distribution of residuals. We propose a robust 1-norm periodogram technique, which is based on the principles of robust statistical estimation. This technique can be implemented in weighted or unweighted options. The method is described in detail and compared with the classical least squares periodogram on a set of astrometric VLBI measurements of the ICRF quasar IERS B0642+449. It is uniformly applied to a collection of 259 ICRF3 quasars each with more than 200 epoch VLBI measurements, resulting in a list of 49 objects with quasi-periodic position changes above the 3σ level, which warrant further investigation. | [
80,
1959,
1858,
1883,
1319,
1769,
1955
] | [
"astrometry",
"lomb-scargle periodogram",
"astronomy data analysis",
"algorithms",
"quasars",
"very long baseline interferometry",
"period search"
] |
2022ApJ...941..131C | Vertical Equilibrium Model for Accretion Flow: An Exact General Relativistic Self-consistent Analysis | We provide a complete general relativistic and fluid dynamical treatment to derive an expression for the relativistic accretion rate in curved spacetime. We exploit the Killing symmetry of stationary axisymmetric spacetime to obtain the conserved current, using which we find an integral relation between mass flux and height of the accretion disk. In comparison with the existing different models of thin- and slim-disk approaches our analysis is self-consistent and mathematically rigorous. We reviewed the previous work and surveyed the recent status in this field. Our formula is different from the existing expression in the literature. The difference arises solely due to the rotation parameter of the compact star. The effect becomes important for slim/thick disks and for rapidly spinning compact stars. Thus one needs to alter the formula $\dot{M}=2\pi {rH}\rho {u}^{r}$ for Newtonian or spherically symmetric spacetime while studying the accretion flows around a Kerr black hole. Our formula can also be used to connect the variability of the vertical structure of the accretion disk through the luminosity variation of X-ray binaries, and can thereby explain the origin of the hysteresis loop of the spectral states. | [
14,
159,
1389,
1963,
1393
] | [
"accretion",
"black hole physics",
"relativistic fluid dynamics",
"hydrodynamics",
"relativity"
] |
2021ApJ...922...18O | Mixed Modes and Asteroseismic Surface Effects. II. Subgiant Systematics | Models of solar-like oscillators yield acoustic modes at different frequencies than would be seen in actual stars possessing identical interior structure, due to modeling error near the surface. This asteroseismic "surface term" must be corrected when mode frequencies are used to infer stellar structure. Subgiants exhibit oscillations of mixed acoustic (p-mode) and gravity (g-mode) character, which defy description by the traditional p-mode asymptotic relation. Since nonparametric diagnostics of the surface term rely on this description, they cannot be applied to subgiants directly. In Paper I, we generalized such nonparametric methods to mixed modes, and showed that traditional surface-term corrections only account for mixed-mode coupling to, at best, first order in a perturbative expansion. Here, we apply those results, modeling subgiants using asteroseismic data. We demonstrate that, for grid-based inference of subgiant properties using individual mode frequencies, neglecting higher-order effects of mode coupling in the surface term results in significant systematic differences in the inferred stellar masses, and measurable systematics in other fundamental properties. While these systematics are smaller than those resulting from other choices of model construction, they persist for both parametric and nonparametric formulations of the surface term. This suggests that mode coupling should be fully accounted for when correcting for the surface term in seismic modeling with mixed modes, irrespective of the choice of correction used. The inferred properties of subgiants, in particular masses and ages, also depend on the choice of surface-term correction, in a different manner from those of both main-sequence and red giant stars. | [
73,
1617,
1965,
1646
] | [
"asteroseismology",
"stellar oscillations",
"computational methods",
"subgiant stars"
] |
2024ApJ...963...10S | Magnetohydrodynamic Poynting Flux Vortices in the Solar Atmosphere and Their Role in Concentrating Energy | The nature of energy generation, transport, and effective dissipation responsible for maintaining a hot solar upper atmosphere is still elusive. The Poynting flux is a vital parameter for describing the direction and magnitude of the energy flow, which is mainly used in solar physics for estimating the upward energy generated by photospheric plasma motion. This study presents a pioneering 3D mapping of the magnetic energy transport within a numerically simulated solar atmosphere. By calculating the Finite Time Lyapunov Exponent of the energy velocity, defined as the ratio of the Poynting flux to the magnetic energy density, we precisely identify the sources and destinations of the magnetic energy flow throughout the solar atmosphere. This energy mapping reveals the presence of transport barriers in the lower atmosphere, restricting the amount of magnetic energy from the photosphere reaching the chromosphere and corona. Interacting kinematic and magnetic vortices create energy channels, breaking through these barriers and allowing three times more energy input from photospheric motions to reach the upper atmosphere than before the vortices formed. The vortex system also substantially alters the energy mapping, acting as a source and deposition of energy, leading to localized energy concentration. Furthermore, our results show that the energy is transported following a vortical motion: the Poynting flux vortex. In regions where these vortices coexist, they favor conditions for energy dissipation through ohmic and viscous heating, since they naturally create large gradients in the magnetic and velocity fields over small spatial scales. Hence, the vortex system promotes local plasma heating, leading to temperatures around a million Kelvins. | [
1989,
1986,
1503,
1964,
1966,
1987,
1498
] | [
"solar coronal heating",
"quiet solar chromosphere",
"solar magnetic fields",
"magnetohydrodynamics",
"magnetohydrodynamical simulations",
"solar chromospheric heating",
"solar granulation"
] |
2020ApJ...904L..20S | P/2019 LD2 (ATLAS): An Active Centaur in Imminent Transition to the Jupiter Family | The recently discovered object P/2019 LD2 (by the Asteroid Terrestrial-impact Last Alert System) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 yr. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ∼3 yr to less than once every 70 yr, if 2019 LD2's nucleus is ∼1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition. | [
215,
1452,
280,
272,
1184,
101
] | [
"centaur group",
"short period comets",
"comets",
"comet interiors",
"orbits",
"astrophysical fluid dynamics"
] |
2020ApJ...900...98G | Massive Black Holes Regulated by Luminous Blue Variable Mass Loss and Magnetic Fields | We investigate the effects of mass loss during the main-sequence (MS) and post-MS phases of massive star evolution on black hole (BH) birth masses. We compute solar metallicity Geneva stellar evolution models of an 85 ${M}_{\odot }$ star with mass-loss rate ( $\dot{M}$ ) prescriptions for MS and post-MS phases and analyze under which conditions such models could lead to very massive BHs. Based on the observational constraints for $\dot{M}$ of luminous stars, we discuss two possible scenarios that could produce massive BHs at high metallicity. First, if a massive BH progenitor evolves from the observed population of massive MS stars known as WNh stars, we show that its average post-MS mass-loss rate has to be less than $1\times {10}^{-5}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . However, this is lower than the typical observed mass-loss rates of luminous blue variables (LBV). Second, a massive BH progenitor could evolve from a yet undetected population of 80-85 ${M}_{\odot }$ stars with strong surface magnetic fields, which could quench mass loss during the evolution. In this case, the average mass-loss rate during the post-MS LBV phase has to be less than 5 × 10<SUP>-5</SUP> ${M}_{\odot }\,{\mathrm{yr}}^{-1}$ to produce 70 ${M}_{\odot }$ BHs. We suggest that LBVs that explode as SNe have large envelopes and small cores that could be prone to explosion, possibly evolving from binary interaction (either mergers or mass gainers that do not fully mix). Conversely, LBVs that directly collapse to BHs could have evolved from massive single stars or binary-star mergers that fully mix, possessing large cores that would favor BH formation. | [
732,
2046,
481,
774,
944
] | [
"massive stars",
"stellar evolutionary models",
"evolved stars",
"hypergiant stars",
"luminous blue variable stars"
] |
2020ApJ...899..163S | Softening of the Metagalactic Ionizing Background from Internal He II Absorption in Quasars | Quasars and other active galactic nuclei (AGN) are significant contributors to the metagalactic ionizing background at redshifts z < 3. Recent Hubble Space Telescope (HST)/Cosmic Origins Spectrograph (COS) composite spectra of AGN find a harder flux distribution in the Lyman continuum, ${F}_{\nu }\propto {\nu }^{-{\alpha }_{s}}$ (α<SUB>s</SUB> = 1.41 ± 0.15), compared to previous studies. This index appears to be inconsistent with observed He II/H I absorption ratios (η) in the Lyα forest. We explore the effects of internal AGN absorption in the He II (4 ryd) continuum using an analytic source-function model of the ionizing background in which the emissivity (j<SUB>ν</SUB>) arises from quasars, reprocessed by the opacity (κ<SUB>ν</SUB>) of the intervening Lyα forest and distinct AGN escape fractions ${f}_{\mathrm{esc}}^{({\rm{H}}\,{\rm{\small{I}}})}$ and ${f}_{\mathrm{esc}}^{(\mathrm{He}\,{\rm{\small{II}}})}$ at 1 ryd and 4 ryd, respectively. We also examine H I and He II photoelectric heating from the reprocessed background, whose spectral index (α<SUB>b</SUB> > α<SUB>s</SUB>) depends on α<SUB>s</SUB>, the H I column density slope β, and the ratio $R={f}_{\mathrm{esc}}^{({\rm{H}}\,{\rm{\small{I}}})}/{f}_{\mathrm{esc}}^{(\mathrm{He}\,{\rm{\small{II}}})}$. We compare the model to Lyα absorption lines of He II and H I toward the quasar HE 2347-4342. Internal AGN absorption with ${f}_{\mathrm{esc}}^{(\mathrm{He}\,{\rm{\small{II}}})}\approx 0.6\mbox{--}0.8$ but ${f}_{\mathrm{esc}}^{({\rm{H}}\,{\rm{\small{I}}})}\approx 1$ would increase the index by Δα<SUB>b</SUB> ≈ 0.3-1.0, corresponding to η = 60-200 for β ≈ 1.5-1.6, in agreement with HST/COS observations at z ≈ 2.5-2.9. The observed range of ratios, η < 200, constrains α<SUB>b</SUB> < 3.4 and ${f}_{\mathrm{esc}}^{(\mathrm{He}\,{\rm{\small{II}}})}\gt 0.4$. Individual AGN with softer spectra, α<SUB>s</SUB> > 1.7, and more internal He II absorption could produce a few absorbers with η > 300, in proximity to AGN transverse to the sight line. | [
1354,
813
] | [
"radio quiet quasars",
"intergalactic medium"
] |
2022ApJ...936...31U | Mid-infrared and Maser Flux Variability Correlation in Massive Young Stellar Object G036.70+00.09 | We present the discovery of the simultaneous flux variation of a massive young stellar object (MYSO) G036.70+00.09 (G036.70) both in the maser emission and mid-infrared (MIR; λ = 3-5 μm) bands. Using the ALLWISE and NEOWISE archival databases that cover a long time span of approximately 10 yr with a cadence of 6 months, we confirm that G036.70 indicates a stochastic year-long MIR variability with no signs of a WISE band color change of W1 (3.4 μm) -W2 (4.6 μm). Cross-matching the MIR data set with the high-cadence 6.7 GHz class II methanol maser flux using the Hitachi 32 m radio telescope that discovered its periodicity in the methanol maser of 53.0-53.2 days, we also determine the flux correlations between the two bands at two different timescales, year-long and day-long, both of which have never been reported in MYSOs, except when they are in the accretion burst phase. The results of our study support the scenario that a class II methanol maser is pumped up by infrared emission from accreting disks of MYSOs. We also discuss the possible origins of MIR and maser variability. To explain the two observed phenomena, a stochastic year-long MIR variability with no signs of significant color change and maser-MIR variability correlation or a change in mass accretion rate and line-of-sight extinction because of the nonaxisymmetric dust density distribution in a rotating accretion disk are possible origins. Observations through spectroscopic monitoring of accretion-related emission lines are essential for determining the origin of the observed variability in G036.70. | [
1761,
2109,
1834,
732,
786,
240
] | [
"variable stars",
"time domain astronomy",
"young stellar objects",
"massive stars",
"infrared astronomy",
"circumstellar masers"
] |
2023PSJ.....4...63G | Stereophotoclinometry on the OSIRIS-REx Mission: Mathematics and Methods | Stereophotoclinometry (SPC) makes it possible to extract the shapes of surfaces by combining information from images, namely stereo parallax data and surface shading from slopes, with knowledge of the location of a spacecraft. This technique has been used extensively in the past few decades to describe the shapes of planets and small bodies, such as asteroids and comets. It has also been used to carefully navigate spacecraft around very small bodies, as in the case of the OSIRIS-REx mission to the ~500 m diameter asteroid (101955) Bennu. This paper describes the mathematical foundation of SPC, with examples from the OSIRIS-REx mission. | [
1226,
72
] | [
"photogrammetry",
"asteroids"
] |
2020RNAAS...4..116V | A Recipe for Transforming ICRS Coordinates to a Cartesian Coordinate System Centered on a Cluster | For the purpose of studying internal kinematics of a star cluster it is often convenient to convert the astrometric parameters of its members into cluster-centered Cartesian coordinates. I provide a detailed and rigorous derivation of such a coordinate transformation and briefly compare it with a selection of published procedures from literature. | [
85
] | [
"astronomical location"
] |
2022ApJ...927...40H | Bayesian Rotation Inversion of KIC 11145123 | A scheme of Bayesian rotation inversion, which allows us to compute the probability of a model of a stellar rotational profile, is developed. The validation of the scheme with simple rotational profiles and the corresponding sets of artificially generated rotational shifts has been successfully carried out, and we can correctly distinguish the (right) rotational model, prepared beforehand for generating the artificial rotational shifts, from the other (wrong) rotational model. The Bayesian scheme is applied to a γ Dor-δ Sct-type hybrid star, KIC 11145123, leading to a result that the convective core of the star might be rotating much faster (~10 times faster) than the other regions of the star. The result is consistent with that previously suggested by Hatta et al. based on a three-zone modeling, further strengthening their argument from a Bayesian point of view. | [
73,
370,
1606,
1629,
1900,
1912
] | [
"asteroseismology",
"delta scuti variable stars",
"stellar interiors",
"stellar rotation",
"bayesian statistics",
"model selection"
] |
2023AJ....165..232B | Long-term 4.6 μm Variability in Brown Dwarfs and a New Technique for Identifying Brown Dwarf Binary Candidates | Using a sample of 361 nearby brown dwarfs, we have searched for 4.6 μm variability, indicative of large-scale rotational modulations or large-scale, long-term changes on timescales of over 10 yr. Our findings show no statistically significant variability in Spitzer's Infrared Array Camera (IRAC) channel 2 (ch2) or Wide-field Infrared Survey Explorer W2 photometry. For Spitzer the ch2 1σ limits are ~8 mmag for objects at 11.5 mag and ~22 mmag for objects at 16 mag. This corresponds to no variability above 4.5% at 11.5 mag and 12.5% at 16 mag. We conclude that highly variable brown dwarfs, at least two previously published examples of which have been shown to have 4.6 μm variability above 80 mmag, are very rare. While analyzing the data, we also developed a new technique for identifying brown dwarf binary candidates in Spitzer data. We find that known binaries have IRAC ch2 point response function (PRF) flux measurements that are consistently dimmer than aperture flux measurements. We have identified 59 objects that exhibit such PRF versus aperture flux differences and are thus excellent binary brown dwarf candidates. | [
185,
2050,
2119,
154,
896
] | [
"brown dwarfs",
"low mass stars",
"atmospheric variability",
"binary stars",
"l subdwarfs"
] |
2022AJ....163..109P | Hydrogen and Helium Shock Phenomena during Rising Light in RR Lyrae Fundamental Mode Pulsators | We present measurements of H and He emission and absorption lines produced in RRab fundamental mode pulsators during primary light rise. The lines define universal progressions of rise and decay in metal-poor RRab stars. Such a progression cannot be constructed for He in metal-rich RRab (those with [Fe/H] > -0.8) because weak He I emission is detected in only two of the six metal-rich RRab in our survey. Great variety exists in the phase variations of the blue- and red-shifted absorption components of the 5876 Å line during pre- and post-emission phases. Detection of measurable He II 4686 Å emission in eight RRab, three of them Blazhko variables, provides an additional constraint on ionization of helium. | [
1630,
746,
1410,
1307
] | [
"stellar spectral lines",
"horizontal branch stars",
"rr lyrae variable stars",
"pulsating variable stars"
] |
2020ApJ...889..187S | Hi-C 2.1 Observations of Small-scale Miniature-filament-eruption-like Cool Ejections in an Active Region Plage | We examine 172 Å ultra-high-resolution images of a solar plage region from the High-Resolution Coronal Imager, version 2.1 (Hi-C 2.1, or Hi-C) rocket flight of 2018 May 29. Over its five minute flight, Hi-C resolved a plethora of small-scale dynamic features that appear near noise level in concurrent Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 171 Å images. For 10 selected events, comparisons with AIA images at other wavelengths and with Interface Region Imaging Spectrograph (IRIS) images indicate that these features are cool (compared to the corona) ejections. Combining Hi-C 172 Å, AIA 171 Å, IRIS 1400 Å, and Hα, we see that these 10 cool ejections are similar to the Hα "dynamic fibrils" and Ca II "anemone jets" found in earlier studies. The front of some of our cool ejections are likely heated, showing emission in IRIS 1400 Å. On average, these cool ejections have approximate widths 3"2 ± 2"1, (projected) maximum heights and velocities 4"3 ± 2"5 and 23 ± 6 km s<SUP>-1</SUP>, and lifetimes 6.5 ± 2.4 min. We consider whether these Hi-C features might result from eruptions of sub-minifilaments (smaller than the minifilaments that erupt to produce coronal jets). Comparisons with SDO's Helioseismic and Magnetic Imager (HMI) magnetograms do not show magnetic mixed-polarity neutral lines at these events' bases, as would be expected for true scaled-down versions of solar filaments/minifilaments. But the features' bases are all close to single-polarity strong-flux-edge locations, suggesting possible local opposite-polarity flux unresolved by HMI. Or it may be that our Hi-C ejections instead operate via the shock-wave mechanism that is suggested to drive dynamic fibrils and the so-called type I spicules. | [
1980,
1975,
1478
] | [
"active solar chromosphere",
"solar active region magnetic fields",
"solar atmospheric motions"
] |
2023ApJ...954..216H | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm | We study the internal and external alignment of carbonaceous grains in the interstellar medium (ISM) within the Radiative Torque (RAT) paradigm. For internal alignment (IA), we find that hydrogenated amorphous carbon (HAC) grains having nuclear paramagnetism due to hydrogen protons have efficient nuclear relaxation, whereas both HAC and graphite grains can have efficient inelastic relaxation at both low-J and high-J attractors. For external alignment, HAC and pure graphite grains can align with the radiation direction (k-RAT) at low-J attractors but cannot have stable alignment at high-J attractors due to the suppression of radiative precession. However, HAC grains can align with the magnetic field (B-RAT) at high-J attractors due to fast Larmor precession compared to gas collisions. For HAC grains drifting through the ISM, they can align along the induced electric field (E-RAT) at low-J attractors due to the fast electric precession and only small HAC grains can align at high-J attractors. Nuclear paramagnetic relaxation is inefficient for HAC due to the suppression of nuclear susceptibility. We then study the alignment of carbon dust in the envelope of a C-rich Asymptotic Giant Branch star (IRC+10216) and find that grains aligned at low-J attractors may occur via k-RAT with the wrong IA in the inner region but via B-RAT in the outer region. However, grains aligned at high-J attractors have the right IA alignment via k-RAT due to efficient inelastic relaxation. The polarization pattern observed toward IRC+10216 by SOFIA/HAWC+ can be reproduced when only grains at low-J attractors are present due to the removal of grains at high-J attractors by the RAT disruption. | [
99,
236,
838,
2271,
1571,
481
] | [
"astrophysical dust processes",
"circumstellar dust",
"interstellar dust processes",
"dust composition",
"starlight polarization",
"evolved stars"
] |
2021RNAAS...5..253J | What is Exceptional about Solar Activity in the Early Phase of Cycle 25? | Solar Cycle 25 began in 2019 December and has been progressing nominally since. However, a closely associated pair of strong active regions, NOAA 12786 and 12785, emerged in 2020 November. The greater, northern component, 12786, attained a maximum sunspot area of 1000 μHemi. The sudden, uncharacteristic emergence of such a large concentration of intense magnetic flux in the early phase of the solar cycle has not been seen in previous cycles. Although the active region pair survived for two Carrington rotations, it did not produce any X- or M-class flares. Here we remark on the evolution of NOAA 12786 and 12785, first in the Sun's invisible and subsequently the visible hemispheres, and compare the irradiance and other characteristic profiles it manifested in the early ascending phase of cycle 25 with those of previous solar cycles. | [
1475,
1974,
1496,
1515,
1976
] | [
"solar activity",
"solar active regions",
"solar flares",
"solar oscillations",
"solar active region velocity fields"
] |
2021RNAAS...5...37M | The Large Far-ultraviolet Flux Deficiency of α Doradus (B8 IIIp Si) | The far-UV spectral energy distribution of α Dor recorded by IUE is compared to that of the constant and normal star ζ Dra, which has similar fundamental parameters. α Dor has much less flux than ζ Dra shortwards of 1800 Å, due to the accumulation of very strong absorption lines of Si II, in particular autoionization lines around 1400 Å. Two spectra of α Dor separated by 9 hr (i.e., much less than the rotational period) show evidence of modest variability shortwards of 1800 Å. | [
178
] | [
"bp stars"
] |
2023RNAAS...7...59M | Magneto-convective Modeling of Low-mass Pre-main Sequence Stars: Postponing the Depletion of Lithium | Standard evolutionary models of pre-main sequence (PMS) low-mass stars often predict radii R and Li abundances A(<SUP>7</SUP>Li) which are too small to agree with empirical data, while effective temperatures T <SUB>eff</SUB> are predicted to be too large. There are also discrepancies in replicating the stellar age. Discrepancies in R, T <SUB>eff</SUB>, and A(<SUP>7</SUP>Li) are reported by Stassun et al. for both components (A/B) of the eclipsing binary 2M1222-57 belonging to the young Lower Centaurus Crux association. Using the output of a magneto-convective stellar evolution model which we applied in an early study (in 2010) of PMS stars in a different young association, we show that the discrepancies reported by Stassun et al. in the 2M1222-57 system are alleviated. The models are instructive in showing why larger lithium abundances occur in magnetic PMS stars: it takes longer for the central gas in such a star to become hot enough to destroy lithium. | [
996,
982
] | [
"magnetic variable stars",
"m dwarf stars"
] |
2021ApJ...910..118P | Cepheids with Giant Companions. I. Revealing a Numerous Population of Double-lined Binary Cepheids | Masses of classical Cepheids of 3-11 M<SUB>⊙</SUB> are predicted by theory but those measured clump between 3.6-5 M<SUB>⊙</SUB>. As a result, their mass-luminosity relation is poorly constrained, impeding our understanding of basic stellar physics and the Leavitt Law. All Cepheid masses come from the analysis of 11 binary systems, including only five that are double lined and well suited for accurate dynamical mass determination. We present a project to analyze a new, numerous group of Cepheids in double-lined binary (SB2) systems to provide mass determinations in a wide mass interval and study their evolution. We analyze a sample of 41 candidate binary LMC Cepheids spread along the P-L relation, which are likely accompanied by luminous red giants, and present indirect and direct indicators of their binarity. In a spectroscopic study of a subsample of 18 brightest candidates, for 16 we detected lines of two components in the spectra, already quadrupling the number of Cepheids in SB2 systems. Observations of the whole sample may thus lead to quadrupling all the Cepheid mass estimates available now. For the majority of our candidates, erratic intrinsic period changes dominate over the light-travel-time effect due to binarity. However, the latter may explain the periodic phase modulation for four Cepheids. Our project paves the way for future accurate dynamical mass determinations of Cepheids in the LMC, Milky Way, and other galaxies, which will potentially increase the number of known Cepheid masses even 10-fold, hugely improving our knowledge about these important stars. <SUP>*</SUP> Based on observations collected at the European Southern Observatory, Chile. <SUP>†</SUP> This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile. | [
218,
368,
1557,
908
] | [
"cepheid variable stars",
"delta cepheid variable stars",
"spectroscopic binary stars",
"late-type giant stars"
] |
2023ApJ...945...38Z | A Semiblind PCA-based Foreground Subtraction Method for 21 cm Intensity Mapping | The principal component analysis (PCA) method and the singular value decomposition (SVD) method are widely used for foreground subtraction in 21 cm intensity mapping experiments. We show their equivalence, and point out that the condition for completely clean separation of foregrounds and cosmic 21 cm signal using the PCA/SVD is unrealistic. We propose a PCA-based foreground subtraction method, dubbed the "singular vector projection (SVP)" method, which exploits a priori information of the left and/or right singular vectors of the foregrounds. We demonstrate with simulation tests that this new, semiblind method can reduce the error of the recovered 21 cm signal by orders of magnitude, even if only the left and/or right singular vectors in the largest few modes are exploited. The SVP estimators provide a new, effective approach for 21 cm observations to remove foregrounds and uncover the physics in the cosmic 21 cm signal. | [
343,
1043,
690,
1944
] | [
"cosmology",
"astronomical methods",
"h i line emission",
"principal component analysis"
] |
2023PSJ.....4...70Z | Sodium Brightening of (3200) Phaethon near Perihelion | Sunskirting asteroid (3200) Phaethon has been repeatedly observed in Solar Terrestrial Relations Observatory (STEREO) Heliospheric Imager 1 (HI1) imagery to anomalously brighten and produce an antisunward tail for a few days near each perihelion passage, phenomena previously attributed to the ejection of micron-sized dust grains. Color imaging by the Solar and Heliospheric Observatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) during the 2022 May apparition indicates that the observed brightening and tail development instead capture the release of sodium atoms, which resonantly fluoresce at the 589.0/589.6 nm D lines. While HI1's design bandpass nominally excludes the D lines, filter degradation has substantially increased its D line sensitivity, as quantified by the brightness of Mercury's sodium tail in HI1 imagery. Furthermore, the expected fluorescence efficiency and acceleration of sodium atoms under solar radiation readily reproduce both the photometric and morphological behaviors observed by LASCO and HI1 during the 2022 apparition and the 17 earlier apparitions since 1997. This finding connects Phaethon to the broader population of sunskirting and sungrazing comets observed by SOHO, which often also exhibit bright sodium emission with minimal visible dust, but distinguishes it from other sunskirting asteroids without detectable sodium production under comparable solar heating. These differences may reflect variations in the degree of sodium depletion of near-surface material and thus the extent and/or timing of any past or present resurfacing activity. | [
274,
1092,
2162,
2197,
2198,
2203,
2209
] | [
"comet tails",
"near-earth objects",
"comet volatiles",
"sungrazers",
"sunskirters",
"comet origins",
"asteroid surfaces"
] |
2021PSJ.....2..217N | On the Fate of Interstellar Objects Captured by Our Solar System | With the recent discoveries of interstellar objects Oumuamua and Borisov traversing the solar system, understanding the dynamics of interstellar objects is more pressing than ever. These detections have highlighted the possibility that captured interstellar material could be trapped in our solar system. The first step in rigorously investigating this question is to calculate a capture cross section for interstellar objects as a function of hyperbolic excess velocity, which can be convolved with any velocity dispersion to compute a capture rate. Although the cross section provides the first step toward calculating the mass of alien rocks residing in our solar system, we also need to know the lifetime of the captured objects. We use an ensemble of N-body simulations to characterize a dynamical lifetime for captured interstellar objects and determine the fraction of surviving objects as a function of time (since capture). We also illuminate the primary effects driving their secular evolution. Finally, we use the resulting dynamical lifetime function to estimate the current inventory of captured interstellar material in the solar system. We find that capture from the field yields a steady-state mass of only ~10<SUP>-13</SUP> M<SUB>⊕</SUB>, whereas the mass remaining from capture events in the birth cluster is roughly 10<SUP>-9</SUP> M<SUB>⊕</SUB>. | [
1528,
421,
1469,
52,
893,
1157
] | [
"solar system",
"dynamical evolution",
"small solar system bodies",
"interstellar objects",
"kuiper belt",
"oort cloud"
] |
2020ApJ...898...83D | The Black Hole Mass-Color Relations for Early- and Late-type Galaxies: Red and Blue Sequences | The tight correlations between supermassive black hole (SMBH) mass (M<SUB>BH</SUB>) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and of the evolution of galaxies. Here, we present newly observed correlations between M<SUB>BH</SUB> and the host galaxy total UV-[3.6] color ( ${{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ , Pearson's r = 0.6-0.7) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured M<SUB>BH</SUB> in the Galaxy Evolution Explorer/S<SUP>4</SUP>G survey. The colors are carefully measured in a homogeneous manner using the far-UV, near-UV, and 3.6 μm magnitudes of the galaxies and their multicomponent structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ relations for the two morphological types have slopes that differ at ∼2σ level. Early-type galaxies define a red sequence in the ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by L<SUB>UV</SUB>/L<SUB>3.6</SUB>, it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ and M<SUB>BH</SUB> - L<SUB>3.6,tot</SUB> relations for the sample galaxies reveal a comparable level of vertical scatter in the log M<SUB>BH</SUB> direction, approximately 5%-27% more than the vertical scatter of the M<SUB>BH</SUB> - σ relation. Our ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios. These new relations offer the prospect of estimating SMBH masses reliably using the galaxy color alone. Furthermore, we show that they are capable of estimating intermediate black hole masses in low-mass early- and late-type galaxies. | [
1663,
209,
456,
915,
1560,
586,
611,
609,
622
] | [
"supermassive black holes",
"cd galaxies",
"elliptical galaxies",
"lenticular galaxies",
"spiral galaxies",
"galaxy colors",
"galaxy photometry",
"galaxy nuclei",
"galaxy structure"
] |
2024ApJ...961..220G | The Combined Effects of Vertical and Horizontal Shear Instabilities in Stellar Radiative Zones | Shear instabilities can be the source of significant amounts of turbulent mixing in stellar radiative zones. Past attempts at modeling their effects (either theoretically or using numerical simulations) have focused on idealized geometries, where the shear is either purely vertical or purely horizontal. In stars, however, the shear can have arbitrary directions with respect to gravity. In this work, we use direct numerical simulations to investigate the nonlinear saturation of shear instabilities in a stably stratified fluid, where the shear is sinusoidal in the horizontal direction and either constant or sinusoidal in the vertical direction. We find that in the parameter regime studied here (nondiffusive, fully turbulent flow), the mean vertical shear does not play any role in controlling the dynamics of the resulting turbulence, unless its Richardson number is smaller than 1 (approximately). As most stellar radiative regions have a Richardson number much greater than 1, our result implies that the vertical shear can essentially be ignored in the computation of the vertical mixing coefficient associated with shear instabilities for the purpose of stellar evolution calculations, even when it is much larger than the horizontal shear (as in the solar tachocline, for instance). | [
101,
1963,
1599,
1621,
767,
1629,
1524,
1623
] | [
"astrophysical fluid dynamics",
"hydrodynamics",
"stellar evolution",
"stellar physics",
"hydrodynamical simulations",
"stellar rotation",
"solar rotation",
"stellar processes"
] |
2020ApJ...898..160E | Low-albedo Surfaces of Lava Worlds | Hot super-Earths are exoplanets with short orbital periods (<10 days), heated by their host stars to temperatures high enough for their rocky surfaces to become molten. A few hot super-Earths exhibit high geometric albedos (>0.4) in the Kepler band (420-900 nm). We are motivated to determine whether reflection from molten lava and quenched glasses (a product of rapidly cooled lava) on the surfaces of hot super-Earths contribute to the observationally inferred high geometric albedos. We experimentally measure reflection from rough- and smooth-textured quenched glasses of both basalt and feldspar melts. For lava reflectance values, we use specular reflectance values of molten silicates from non-crystalline solids literature. Integrating the empirical glass reflectance function and non-crystalline solids reflectance values over the dayside surface of the exoplanet at secondary eclipse yields an upper limit for the albedo of a lava-quenched glass planet surface of ∼0.1. We conclude that lava planets with solid (quenched glass) or liquid (lava) surfaces have low albedos. The high albedos of some hot super-Earths are most likely explained by atmospheres with reflective clouds (or, for a narrow range of parameter space, possibly Ca/Al oxide melt surfaces). Lava planet candidates in TESS data can be identified for follow-up observations and future characterization. | [
496,
2078,
1655,
487,
2022,
804
] | [
"exoplanet surface characteristics",
"experimental techniques",
"super earths",
"exoplanet atmospheres",
"exoplanet surface composition",
"interdisciplinary astronomy"
] |
2022ApJ...941L...9N | Formation of Lunar Basins from Impacts of Leftover Planetesimals | The Moon holds important clues to the early evolution of the solar system. Some 50 impact basins (crater diameter D > 300 km) have been recognized on the lunar surface, implying that the early impact flux was much higher than it is now. The basin-forming impactors were suspected to be asteroids released from an inner extension of the main belt (1.8-2.0 au). Here we show that most impactors were instead rocky planetesimals left behind at ~0.5-1.5 au after the terrestrial planet accretion. The number of basins expected from impacts of leftover planetesimals largely exceeds the number of known lunar basins, suggesting that the first ~200 Myr of impacts are not recorded on the lunar surface. The Imbrium basin formation (age ≃3.92 Gyr; impactor diameter d ≳ 100 km) occurs with a 15%-35% probability in our model. Imbrium must have formed unusually late to have only two smaller basins (Orientale and Schrödinger) forming afterwards. The model predicts ≃20 d > 10 km impacts on the Earth 2.5-3.5 Gyr ago (Ga), which is comparable to the number of known spherule beds in the late Archean. | [
1530,
958
] | [
"solar system formation",
"lunar impacts"
] |
2024AJ....167..189C | Methods for the Detection of Stellar Rotation Periods in Individual TESS Sectors and Results from the Prime Mission | For ongoing studies of the role of rotation in stellar evolution, we require large catalogs of rotation periods for testing and refining gyrochronology. While there is a wealth of data from the Kepler and K2 missions, the Transiting Exoplanet Survey Satellite (TESS) presents both an opportunity and a challenge: despite its all-sky coverage, rotation periods remain hard to detect. We analyzed individual TESS sectors to detect short-period stellar rotation, using only parameters measured from light curves for a robust and unbiased method of evaluating detections. We used random forest classifiers for vetting, trained on a large corpus of period measurements in Kilodegree Extremely Little Telescope data from the Oelkers et al. catalog and using TESS full-frame image light curves generated by eleanor. Finally, using data from the first 26 sectors of TESS, we analyzed 432,704 2 minutes cadence single-sector light curves for FGKM dwarfs. We detected 16,800 periods in individual sector light curves, covering 10,909 distinct targets, and we present a catalog of the median period for each target as measured by a Lomb–Scargle periodogram. | [
1629,
1211,
1858,
1935
] | [
"stellar rotation",
"period determination",
"astronomy data analysis",
"random forests"
] |
2022AJ....164...86K | Kinematics of the Central Stars Powering Bowshock Nebulae and the Large Multiplicity Fraction of Runaway OB Stars | OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O-star population using Gaia EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocities v <SUB>2D</SUB>. For a subset of each sample, we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36% ± 6% among SBN central stars, consistent with >28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The median v <SUB>2D</SUB> of SBN central stars is v <SUB>2D</SUB> = 14.6 km s<SUP>-1</SUP>, larger than the median v <SUB>2D</SUB> = 11.4 km s<SUP>-1</SUP> for non-bowshock O stars. Central stars of SBNe have a runaway (v <SUB>2D</SUB> > 25 km s<SUP>-1</SUP>) fraction of 24 <?CDATA ${}_{-7}^{+9}$ %, consistent with the <?CDATA ${22}_{-3}^{+3}$ % for control-sample O stars. Most (76%) SBNe central stars are not runaways. Our analysis of alignment (Δ<SUB>PA</SUB>) between the nebular morphological and v <SUB>2D</SUB> kinematic position angles reveals two populations: a highly aligned (σ <SUB>PA</SUB> = 25°) population that includes stars with the largest v <SUB>2D</SUB> (31% of the sample) and a random (nonaligned) population (69%). SBNe that lie within or near H II regions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the solar local standard of rest motion, yielding [U <SUB>⊙</SUB>, V <SUB>⊙</SUB>, W <SUB>⊙</SUB>] = [5.5, 7.5,4.5] km s<SUP>-1</SUP>. | [
1417,
732,
430,
1608,
1141,
694,
236,
736
] | [
"runaway stars",
"massive stars",
"early-type stars",
"stellar kinematics",
"ob stars",
"h ii regions",
"circumstellar dust",
"high-velocity stars"
] |
2022ApJS..263...33C | An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher | We present a catalog (status 2022 July 1) of triple and higher-order systems identified containing exoplanets based on data from the literature, including various analyses. We explore statistical properties of the systems with a focus on both the stars and the planets. So far, about 30 triple systems and one to three quadruple systems, including (mildly) controversial cases, have been found. The total number of planets is close to 40. All planet-hosting triple-star systems are highly hierarchic, consisting of a quasi-binary complemented by a distant stellar component, which is in orbit about the common center of mass. Furthermore, the quadruple systems are in fact pairs of close binaries ("double-doubles"), with one binary harboring a planet. For the different types of star-planet systems, we introduce a template for the classifications of planetary orbital configurations in correspondence to the hierarchy of the system and the planetary host. The data show that almost all stars are main-sequence stars, as expected. However, the stellar primaries tend to be more massive (i.e., corresponding to spectral types A, F, and G) than expected from single-star statistics, a finding also valid for stellar secondaries but less pronounced. Tertiary stellar components are almost exclusively low-mass stars of spectral type M. Almost all planets have been discovered based on either the Radial Velocity method or the Transit method. Both gas giants (the dominant type) and terrestrial planets (including super-Earths) have been identified. We anticipate the expansion of this database in the light of future planetary search missions. | [
205,
498,
484,
1634,
839,
1621,
488,
1583,
486
] | [
"catalogs",
"exoplanets",
"exoplanet systems",
"stellar types",
"interstellar dynamics",
"stellar physics",
"exoplanet catalogs",
"stellar astronomy",
"exoplanet astronomy"
] |
2021ApJ...921...91D | Catastrophic Cooling in Superwinds. II. Exploring the Parameter Space | Superwinds and superbubbles driven by mechanical feedback from super star clusters (SSCs) are common features in many star-forming galaxies. While the adiabatic fluid model can well describe the dynamics of superwinds, several observations of starburst galaxies revealed the presence of compact regions with suppressed superwinds and strongly radiative cooling, i.e., catastrophic cooling. In the present study, we employ the nonequilibrium atomic chemistry and cooling package MAIHEM, built on the FLASH hydrodynamics code, to generate a grid of models investigating the dependence of cooling modes on the metallicity, SSC outflow parameters, and ambient density. While gas metallicity plays a substantial role, catastrophic cooling is more sensitive to high mass loading and reduced kinetic heating efficiency. Our hydrodynamic simulations indicate that the presence of a hot superbubble does not necessarily imply an adiabatic outflow and vice versa. Using CLOUDY photoionization models, we predict UV and optical line emission for both adiabatic and catastrophic cooling outflows, for radiation-bounded and partially density-bounded models. Although the line ratios predicted by our radiation-bounded models agree well with observations of star-forming galaxies, they do not provide diagnostics that unambiguously distinguish the parameter space of catastrophically cooling flows. Comparison with observations suggests the possibility of minor density bounding, nonequilibrium ionization, and/or observational bias toward the central outflow regions. | [
1656,
1657,
2028,
694,
1570,
459,
979
] | [
"superbubbles",
"superclusters",
"cooling flows",
"h ii regions",
"starburst galaxies",
"emission line galaxies",
"lyman-break galaxies"
] |
2021ApJ...918L..38F | Impact of Natal Kicks on Merger Rates and Spin-Orbit Misalignments of Black Hole-Neutron Star Mergers | The long wait for the detection of merging black hole-neutron star (BH-NS) binaries is finally over with the announcement by the LIGO/Virgo/Kagra collaboration of GW200105 and GW200115. Remarkably, the primary of GW200115 has a negative spin projection onto the orbital angular momentum, with about 90% probability. Merging BH-NS binaries are expected to form mainly through the evolution of massive binary stars in the field, since their dynamical formation in dense star clusters is strongly suppressed by mass segregation. In this Letter, we carry out a systematic statistical study of the binary stars that evolve to form a BH-NS binary, considering different metallicities and taking into account the uncertainties on the natal-kick distributions for BHs and NSs and on the common-envelope phase of binary evolution. Under the assumption that the initial stellar spins are aligned with the binary angular momentum, we show that both large natal kicks for NSs (≳150 km s<SUP>-1</SUP>) and high efficiencies for common-envelope ejection are required to simultaneously explain the inferred high merger rates and the large spin-orbit misalignment of GW200115. | [
98,
160,
162,
1611,
1108,
675,
676,
677,
678
] | [
"astrophysical black holes",
"black hole spin-flip",
"black holes",
"stellar mass black holes",
"neutron stars",
"gravitational wave astronomy",
"gravitational wave detectors",
"gravitational wave sources",
"gravitational waves"
] |
2022AJ....164...76P | Orbital Characterization of Superbolides Observed from Space: Dynamical Association with Near-Earth Objects, Meteoroid Streams, and Identification of Hyperbolic Meteoroids | There is an unceasing incoming flux of extraterrestrial materials reaching the Earth atmosphere. Some of these objects produce luminous columns when they ablate during the hypersonic encounter with air molecules. A few fireballs occur each year bright enough to be detected from space. The source of these events is still a matter of debate, but it is generally accepted that they are of sporadic origin. We studied the NASA-JPL Center for NEOs Studies (CNEOS) fireball database to infer the dynamic origin of large bolides produced by meter-sized projectiles that impacted our planet. These likely meteorite-dropping events were recorded by the US Government satellite sensors. We estimated the false-positive rate and analyzed the time evolution of multiple orbit dissimilarity criteria concerning potential associations with near-Earth objects and meteoroid streams. We found that at least 16% of the large bolides could be associated with meteoroid streams, about 4% are likely associated with near-Earth asteroids, and 4% may be linked to near-Earth comets. This implies that a significant fraction of meter-sized impactors producing large bolides may have an asteroidal or cometary origin. In addition, we found at least three bolides having hyperbolic orbits with high tensile strength values. Meter-sized meteoroids of interstellar origin could be more common than previously thought, representing about 1% of the flux of large bolides. The inferred bulk physical properties suggest that the interstellar medium could bias these projectiles toward high strength rocks with the ability to survive prolonged exposure to the harsh interstellar space conditions. | [
1040,
1035,
1092,
52
] | [
"meteoroids",
"meteor streams",
"near-earth objects",
"interstellar objects"
] |
2023ApJ...942....5B | On the Presence of Metallofullerenes in Fullerene-rich Circumstellar Envelopes | The presence of neutral C<SUB>60</SUB> fullerenes in circumstellar environments has been firmly established by astronomical observations as well as laboratory experiments and quantum-chemistry calculations. However, the large variations observed in the C<SUB>60</SUB> 17.4 μm/18.9 μm band ratios indicate that either additional emitters should contribute to the astronomical infrared (IR) spectra or unknown physical processes exist besides thermal and UV excitation. Fullerene-based molecules such as metallofullerenes and fullerene-adducts are natural candidate species as potential additional emitters, but no specific specie has been identified to date. Here we report a model based on quantum-chemistry calculations and IR spectra simulation of neutral and charged endo(exo)hedral metallofullerenes, showing that they have a significant contribution to the four strongest IR bands commonly attributed to neutral C<SUB>60</SUB>. These simulations may explain the large range of 17.4 μm/18.9 μm band ratios observed in very different fullerene-rich circumstellar environments like those around planetary nebulae and chemically peculiar R Coronae Borealis stars. Our proposed model also reveals that the 17.4 μm/18.9 μm band ratio in the metallofullerenes simulated IR spectra mainly depends on the metal abundances, ionization level, and endo/exoconcentration in the circumstellar envelopes. We conclude that metallofullerenes are potential emitters contributing to the observed IR spectra in fullerene-rich circumstellar envelopes. Our simulated IR spectra indicate also that the James Webb Space Telescope has the potential to confirm or refute the presence of metallofullerenes (or even other fullerene-based species) in circumstellar environments. | [
75,
241,
2285,
1249,
1327
] | [
"astrochemistry",
"circumstellar matter",
"infrared spectroscopy",
"planetary nebulae",
"r coronae borealis variable stars"
] |
2023ApJ...944..127C | Making the Solar System | We model the early stages of planet formation in the solar system, including continual planetesimal formation, and planetesimal and pebble accretion onto planetary embryos in an evolving disk driven by a disk wind. The aim is to constrain aspects of planet formation that have large uncertainties by matching key characteristics of the solar system. The model produces a good fit to these characteristics for a narrow range of parameter space. Planetary growth beyond the ice line is dominated by pebble accretion. Planetesimal accretion is more important inside the ice line. Pebble accretion inside the ice line is slowed by higher temperatures, partial removal of inflowing pebbles by planetesimal formation and pebble accretion further out in the disk, and increased radial velocities due to gas advection. The terrestrial planets are prevented from accreting much water ice because embryos beyond the ice line reach the pebble-isolation mass before the ice line enters the terrestrial-planet region. When only pebble accretion is considered, embryos typically remain near their initial mass or grow to the pebble-isolation mass. Adding planetesimal accretion allows Mars-sized objects to form inside the ice line, and allows giant-planet cores to form over a wider region beyond the ice line. In the region occupied by Mercury, pebble Stokes numbers are small. This delays the formation of embryos and stunts their growth, so that only low-mass planets can form here. | [
1241,
1528,
1191,
797,
1508,
1024,
1259
] | [
"planet formation",
"solar system",
"solar system gas giant planets",
"solar system terrestrial planets",
"solar nebulae",
"mercury (planet)",
"planetesimals"
] |
2021RNAAS...5...29D | Transient Terrestrial Trojans: Comparative Short-term Dynamical Evolution of 2010 TK<SUB>7</SUB> and 2020 XL<SUB>5</SUB> | The Trojan asteroids of Mars and Jupiter are long-term stable, those of Earth are expected to be just transient companions. The first Trojan of our planet, 2010 TK<SUB>7</SUB>, was discovered in 2010 and its resonant state was found to be transient. Here, we provide a preliminary assessment of the current dynamical status and short-term orbital evolution of 2020 XL<SUB>5</SUB>, a recently discovered near-Earth asteroid that might be the second known representative of this elusive population. Our calculations show that the current orbit determination of 2010 TK<SUB>7</SUB> is consistent with that of a robust, present-day, yet transient, L<SUB>4</SUB> Earth Trojan. In sharp contrast, the current orbit determination of 2020 XL<SUB>5</SUB> is still too uncertain and its orbital evolution too chaotic to confirm a current Trojan engagement with Earth, although the nominal orbit shows such a behavior. More observations are required to provide a conclusive answer. | [
1528,
72,
1092,
1715
] | [
"solar system",
"asteroids",
"near-earth objects",
"trojan asteroids"
] |
2021RNAAS...5...99M | SDSS-IV MaNGA: Characterizing E+A Galaxy Candidates in the Coma Cluster | Using data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, we examined a subsample of 29 E+A galaxy candidates in the Coma Cluster. We created spatially-resolved maps of spectral features and the kinematics of the underlying stellar population by utilizing the Marvin toolkit. We rule out star formation in the entire subsample, and do not find evidence for AGN activity. For the majority of the subsample, stellar rotation is coherent. | [
424,
2176,
2016,
270
] | [
"e+a galaxies",
"post-starburst galaxies",
"quenched galaxies",
"coma cluster"
] |
2024PASP..136b4101R | Median Statistics Estimate of the Distance to M87 | de Grijs & Bono compiled 211 independent measurements of the distance to galaxy M87 in the Virgo cluster from 15 different tracers and reported 31.03 ± 0.14 mag as the arithmetic mean of a subset of this compilation as the best estimate of the distance. We compute three different central estimates—the arithmetic mean, weighted mean, and the median—and corresponding statistical uncertainty for the full data set as well as three sub-compilations. We find that for all three central estimates the error distributions show that the data sets are significantly non-Gaussian. As a result, we conclude that the median is the most reliable of the three central estimates, as median statistics do not assume Gaussianity. We use median statistics to determine the systematic error on the distance by analyzing the scatter in the 15 tracer subgroup distances. From the 211 distance measurements, we recommend a summary M87 distance modulus of ${31.08}_{-0.04}^{+0.05}$ (statistical) ${}_{-0.06}^{+0.04}$ (systematic) mag, or combining the two errors in quadrature ${31.08}_{-0.07}^{+0.06}$ mag, rounded to 16.4 ± 0.5 Mpc, all at 68.27% significance. | [
395,
1858,
1146,
1886,
1116
] | [
"distance measure",
"astronomy data analysis",
"observational cosmology",
"astrostatistics techniques",
"non-gaussianity"
] |
2023AJ....166..212A | The Cycles of Alpha Centauri: Double Dipping of AB | In mid-2023, the Sunlike dwarfs of nearby α Centauri (HD 128620 ("A"): G2 V; HD 128621 ("B"): K1 V; hereafter "AB") coincidentally both entered coronal (T ≈ 1-3 MK) low states in their long-term X-ray cycles, as captured by the Chandra Observatory and its High Resolution Camera (HRC-I). The assessment benefited from a sensitivity degradation model for HRC-I based on a "check star," the F subgiant Procyon (α Canis Minoris A; HD 61421: F5 IV-V), further validated by Hubble Space Telescope time series of the Fe XII 1241.985 Å and 1349.396 Å coronal forbidden lines (T ≈ 1.6 MK) of all three stars. The AB starspot-cycle periods noted previously, 19 and 8 yr, appear to be holding. These deviate substantially from the 11 yr solar example, despite only modest differences in the stellar properties. The new cycle-minimum L <SUB>X</SUB>/L <SUB>BOL</SUB> of α Cen A is similar to that of the previous minimum observed by Chandra in 2005-2010, and close to solar-MIN X-ray levels in 2009 and 2019, with implications for the "basal" coronal flux of low-activity early G stars. The recent α Cen B X-ray MIN is similar to that in 2016 but higher than an earlier one in 2007-2009. Significantly, the B X-ray minima (in L <SUB>X</SUB>/L <SUB>BOL</SUB>) are comparable to the solar Cycle 24 maximum, suggesting plentiful starspots at the B-cycle MIN (contrary to the solar case). Tangentially, the current AB low states favor Doppler-reflex detections of planets, as opposed to the coronal high states, when elevated chromospheric activity can add nuisance signals to radial velocity time series. | [
1825,
1461,
2284,
1741,
1743,
1572,
1487
] | [
"x-ray telescopes",
"single x-ray stars",
"ultraviolet spectroscopy",
"ultraviolet sources",
"ultraviolet telescopes",
"starspots",
"solar cycle"
] |
2020ApJ...903L..34K | A Framework for Multiphase Galactic Wind Launching Using TIGRESS | Galactic outflows have density, temperature, and velocity variations at least as large as those of the multiphase, turbulent interstellar medium (ISM) from which they originate. We have conducted a suite of parsec-resolution numerical simulations using the TIGRESS framework, in which outflows emerge as a consequence of interaction between supernovae (SNe) and the star-forming ISM. The outflowing gas is characterized by two distinct thermal phases, cool (T ≲ 10<SUP>4</SUP> K) and hot (T ≳ 10<SUP>6</SUP> K), with most mass carried by the cool phase and most energy and newly injected metals carried by the hot phase. Both components have a broad distribution of outflow velocity, and especially for cool gas this implies a varying fraction of escaping material depending on the halo potential. Informed by the TIGRESS results, we develop straightforward analytic formulae for the joint probability density functions (PDFs) of mass, momentum, energy, and metal loading as distributions in outflow velocity and sound speed. The model PDFs have only two parameters, star formation rate surface density ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ and the metallicity of the ISM, and fully capture the behavior of the original TIGRESS simulation PDFs over ${{\rm{\Sigma }}}_{\mathrm{SFR}}\in ({10}^{-4},1)\,{M}_{\odot }\,{\mathrm{kpc}}^{-2}\,{\mathrm{yr}}^{-1}$ . Employing PDFs from resolved simulations will enable implementations of subgrid models for galaxy formation with wind velocity and temperature (as well as total loading factors) that are based on theoretical predictions rather than empirical tuning. This is a critical step to incorporate advances from TIGRESS and other high-resolution simulations in future cosmological hydrodynamics and semi-analytic galaxy formation models. We release a Python package to prototype our model and to ease its implementation. | [
572,
626,
596,
595,
1602
] | [
"galactic winds",
"galaxy winds",
"galaxy fountains",
"galaxy formation",
"stellar feedback"
] |
2021ApJ...908..135S | The Fundamental Plane of Massive Quiescent Galaxies at z ∼ 2 | We examine the Fundamental Plane (FP) and mass-to-light ratio (M/L) scaling relations using the largest sample of massive quiescent galaxies at 1.5 < z < 2.5 to date. The FP (r<SUB>e</SUB>, σ<SUB>e</SUB>, I<SUB>e</SUB>) is established using 19 UVJ quiescent galaxies from COSMOS with Hubble Space Telescope H<SUB>F160W</SUB> rest-frame optical sizes and X-shooter absorption line-measured stellar velocity dispersions. For a very massive, $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 11.26$ , subset of eight quiescent galaxies at z > 2, from Stockmann et al., we show that they cannot passively evolve to the local Coma cluster relation alone and must undergo significant structural evolution to mimic the sizes of local massive galaxies. The evolution of the FP and M/L scaling relations, from z = 2 to present day, for this subset are consistent with passive aging of the stellar population and minor merger structural evolution into the most massive galaxies in the Coma cluster and other massive elliptical galaxies from the MASSIVE Survey. Modeling the luminosity evolution from minor merger-added stellar populations favors a history of merging with "dry" quiescent galaxies. | [
591,
594,
612,
456,
651,
2016,
2031,
608,
2040,
761,
2096
] | [
"galaxy dynamics",
"galaxy evolution",
"galaxy physics",
"elliptical galaxies",
"giant elliptical galaxies",
"quenched galaxies",
"scaling relations",
"galaxy mergers",
"galaxy quenching",
"hubble space telescope",
"high resolution spectroscopy"
] |
2024ApJ...967..171S | Keck Primary Mirror Closed-loop Segment Control Using a Vector-Zernike Wavefront Sensor | We present the first on-sky segmented primary mirror closed-loop piston control using a Zernike wavefront sensor (ZWFS) installed on the Keck II telescope. Segment cophasing errors are a primary contributor to contrast limits on Keck and will be necessary to correct for the next generation of space missions and ground-based extremely large telescopes, which will all have segmented primary mirrors. The goal of the ZWFS installed on Keck is to monitor and correct primary mirror cophasing errors in parallel with science observations. The ZWFS is ideal for measuring phase discontinuities such as segment cophasing errors and is one of the most sensitive WFSs, but has limited dynamic range. The vector-ZWFS at Keck works on the adaptive-optics-corrected wavefront and consists of a metasurface focal plane mask that imposes two different phase shifts on the core of the point-spread function to two orthogonal light polarizations, producing two pupil images. This design extends the dynamic range compared with the scalar ZWFS. The primary mirror segment pistons were controlled in closed loop using the ZWFS, improving the Strehl ratio on the NIRC2 science camera by up to 10 percentage points. We analyze the performance of the closed-loop tests, the impact on NIRC2 science data, and discuss the ZWFS measurements. | [
2281,
2369
] | [
"adaptive optics",
"high contrast techniques"
] |
2022ApJ...935..178B | On the Effects of Planetary Oblateness on Exoplanet Studies | When studying transiting exoplanets it is common to assume a spherical planet shape. However, short rotational periods can cause a planet to bulge at its equator, as is the case with Saturn, whose equatorial radius is almost 10% larger than its polar radius. As a new generation of instruments comes online, it is important to continually assess the underlying assumptions of models to ensure robust and accurate inferences. We analyze bulk samples of known transiting planets and calculate their expected signal strength if they were to be oblate. We find that for noise levels below 100 ppm, as many as 100 planets could have detectable oblateness. We also investigate the effects of fitting spherical planet models to synthetic oblate lightcurves. We find that this biases the retrieved parameters by several standard deviations for oblateness values >0.1-0.2. When attempting to fit an oblateness model to both spherical and oblate lightcurves, we find that the sensitivity of such fits is correlated with both the signal-to-noise ratio as well as the time sampling of the data, which can mask the oblateness signal. For typical values of these quantities for Kepler observations, it is difficult to rule out oblateness values less than ~0.25. This results in an accuracy wall of 10%-15% for the density of planets which may be oblate. Finally, we find that a precessing oblate planet has the ability to mimic the signature of a long-period companion via transit-timing variations, inducing offsets at the level of tens of seconds. | [
489,
498,
1143,
2113,
1256,
1257
] | [
"exoplanet detection methods",
"exoplanets",
"oblateness",
"planetary surfaces",
"planetary structure",
"planetary system formation"
] |
2020ApJS..248...29A | Unraveling the Complex Behavior of Mrk 421 with Simultaneous X-Ray and VHE Observations during an Extreme Flaring Activity in 2013 April | We report on a multiband variability and correlation study of the TeV blazar Mrk 421 during an exceptional flaring activity observed from 2013 April 11 to 19. The study uses, among others, data from GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), Swift, Nuclear Spectroscopic Telescope Array (NuSTAR), Fermi Large Area Telescope, Very Energetic Radiation Imaging Telescope Array System (VERITAS), and Major Atmospheric Gamma Imaging Cherenkov (MAGIC). The large blazar activity and the 43 hr of simultaneous NuSTAR and MAGIC/VERITAS observations permitted variability studies on 15 minute time bins over three X-ray bands (3-7 keV, 7-30 keV, and 30-80 keV) and three very-high-energy (VHE; >0.1 TeV) gamma-ray bands (0.2-0.4 TeV, 0.4-0.8 TeV, and >0.8 TeV). We detected substantial flux variations on multi-hour and sub-hour timescales in all of the X-ray and VHE gamma-ray bands. The characteristics of the sub-hour flux variations are essentially energy independent, while the multi-hour flux variations can have a strong dependence on the energy of the X-rays and the VHE gamma-rays. The three VHE bands and the three X-ray bands are positively correlated with no time lag, but the strength and characteristics of the correlation change substantially over time and across energy bands. Our findings favor multi-zone scenarios for explaining the achromatic/chromatic variability of the fast/slow components of the light curves, as well as the changes in the flux-flux correlation on day-long timescales. We interpret these results within a magnetic reconnection scenario, where the multi-hour flux variations are dominated by the combined emission from various plasmoids of different sizes and velocities, while the sub-hour flux variations are dominated by the emission from a single small plasmoid moving across the magnetic reconnection layer. <SUP>*</SUP> Contact MAGIC Collaboration ([email protected]) for queries. Corresponding authors are D. Paneque, A. Babic, J. Finke, T. Hassan, and M. Petropoulou. | [
158,
164,
17,
1006,
630,
637,
1390,
739,
1145
] | [
"bl lacertae objects",
"blazars",
"active galaxies",
"markarian galaxies",
"gamma-ray detectors",
"gamma-rays",
"relativistic jets",
"high energy astrophysics",
"observational astronomy"
] |
2022AJ....164..258W | The Detectability of Rocky Planet Surface and Atmosphere Composition with the JWST: The Case of LHS 3844b | The spectroscopic characterization of terrestrial exoplanets over a wide spectral range from the near- to the mid-infrared will be made possible for the first time with the JWST. One challenge is that it is not known a priori whether such planets possess optically thick atmospheres or even any atmospheres altogether. However, this challenge also presents an opportunity, the potential to detect the surface of an extrasolar world. This study explores the feasibility of characterizing with the JWST the atmosphere and surface of LHS 3844b, the highest signal-to-noise rocky thermal emission target among planets that are cool enough to have nonmolten surfaces. We model the planetary emission, including the spectral signal of both the atmosphere and surface, and we explore all scenarios that are consistent with the existing Spitzer 4.5 μm measurement of LHS 3844b from Kreidberg et al. In summary, we find a range of plausible surfaces and atmospheres that are within 3σ of the observationless reflective metal-rich, iron-oxidized, and basaltic compositions are allowed, and atmospheres are restricted to a maximum thickness of 1 bar, if near-infrared absorbers at ≳100 ppm are included. We further make predictions on the observability of surfaces and atmospheres and find that a small number (~3) of eclipse observations should suffice to differentiate between surface and atmospheric features. We also perform a Bayesian retrieval analysis on simulated JWST data and find that the surface signal may make it harder to precisely constrain the abundance of atmospheric species and may falsely induce a weak H<SUB>2</SUB>O detection. | [
487,
2118,
2107,
2285
] | [
"exoplanet atmospheres",
"exoplanet surfaces",
"theoretical models",
"infrared spectroscopy"
] |
2023AJ....166..123K | Refining the Stellar Parameters of τ Ceti: a Pole-on Solar Analog | To accurately characterize the planets a star may be hosting, stellar parameters must first be well determined. τ Ceti is a nearby solar analog and often a target for exoplanet searches. Uncertainties in the observed rotational velocities have made constraining τ Ceti's inclination difficult. For planet candidates from radial velocity (RV) observations, this leads to substantial uncertainties in the planetary masses, as only the minimum mass ( $m\sin i$ ) can be constrained with RV. In this paper, we used new long-baseline optical interferometric data from the CHARA Array with the MIRC-X beam combiner and extreme precision spectroscopic data from the Lowell Discovery Telescope with EXPRES to improve constraints on the stellar parameters of τ Ceti. Additional archival data were obtained from a Tennessee State University Automatic Photometric Telescope and the Mount Wilson Observatory HK project. These new and archival data sets led to improved stellar parameter determinations, including a limb-darkened angular diameter of 2.019 ± 0.012 mas and rotation period of 46 ± 4 days. By combining parameters from our data sets, we obtained an estimate for the stellar inclination of 7° ± 7°. This nearly pole-on orientation has implications for the previously reported exoplanets. An analysis of the system dynamics suggests that the planetary architecture described by Feng et al. may not retain long-term stability for low orbital inclinations. Additionally, the inclination of τ Ceti reveals a misalignment between the inclinations of the stellar rotation axis and the previously measured debris disk rotation axis (i <SUB>disk</SUB> = 35° ± 10°). | [
1941,
1624,
1558,
932,
556
] | [
"solar analogs",
"stellar properties",
"spectroscopy",
"long baseline interferometry",
"g dwarf stars"
] |
2023AJ....166..197C | Mitigating Worst-case Exozodiacal Dust Structure in High-contrast Images of Earth-like Exoplanets | Detecting Earth-like exoplanets in direct images of nearby Sun-like systems brings a unique set of challenges that must be addressed in the early phases of designing a space-based direct imaging mission. In particular, these systems may contain exozodiacal dust, which is expected to be the dominant source of astrophysical noise. Previous work has shown that it may be feasible to subtract smooth, symmetric dust from observations; however, we do not expect exozodiacal dust to be perfectly smooth. Exozodiacal dust can be trapped into mean-motion resonances with planetary bodies, producing large-scale structures that orbit in lock with the planet. This dust can obscure the planet, complicate noise estimation, or be mistaken for a planetary body. Our ability to subtract these structures from high-contrast images of Earth-like exoplanets is not well understood. In this work, we investigate exozodi mitigation for Earth-Sun-like systems with significant mean-motion resonant disk structures. We find that applying a simple high-pass filter allows us to remove structured exozodi to the Poisson noise limit for systems with inclinations <60° and up to 100 zodis. However, subtracting exozodiacal disk structures from edge-on systems may be challenging, except for cases with densities <5 zodis. For systems with three times the dust of the solar system, which is the median of the best fit to survey data in the habitable zones of nearby Sun-like stars, this method shows promising results for mitigating exozodiacal dust in future Habitable Worlds Observatory observations, even if the dust exhibits significant mean-motion resonance structure. | [
500,
313,
696,
511
] | [
"exozodiacal dust",
"coronagraphic imaging",
"habitable zone",
"extrasolar rocky planets"
] |
2022AJ....164..104R | A Tendency Toward Alignment in Single-star Warm-Jupiter Systems | The distribution of spin-orbit angles for systems with wide-separation, tidally detached exoplanets offers a unique constraint on the prevalence of dynamically violent planetary evolution histories. Tidally detached planets provide a relatively unbiased view of the primordial stellar obliquity distribution, as they cannot tidally realign within the system lifetime. We present the third result from our Stellar Obliquities in Long-period Exoplanet Systems (SOLES) survey: a measurement of the Rossiter-McLaughlin effect across two transits of the tidally detached warm Jupiter TOI-1478 b with the WIYN/NEID and Keck/HIRES spectrographs, revealing a sky-projected spin-orbit angle $\lambda ={6.2}_{-5.5}^{+5.9^\circ} $ . Combining this new measurement with the full set of archival obliquity measurements, including two previous constraints from the SOLES survey, we demonstrate that, in single-star systems, tidally detached warm Jupiters are preferentially more aligned than closer-orbiting hot Jupiters. This finding has two key implications: (1) planets in single-star systems tend to form within aligned protoplanetary disks, and (2) warm Jupiters form more quiescently than hot Jupiters, which, in single-star systems, are likely perturbed into a misaligned state through planet-planet interactions in the post-disk-dispersal phase. We also find that lower-mass Saturns span a wide range of spin-orbit angles, suggesting a prevalence of planet-planet scattering and/or secular mechanisms in these systems. | [
1243,
490,
491,
2177,
498,
1258,
484,
486,
2173,
753,
1300
] | [
"planetary alignment",
"exoplanet dynamics",
"exoplanet evolution",
"star-planet interactions",
"exoplanets",
"planetary theory",
"exoplanet systems",
"exoplanet astronomy",
"planetary dynamics",
"hot jupiters",
"protoplanetary disks"
] |
2023ApJ...956...29Q | Prospects for Cryovolcanic Activity on Cold Ocean Planets | We have estimated total internal heating rates and depths to possible subsurface oceans for 17 planets that may be cold ocean planets, low-mass exoplanets with equilibrium surface temperatures and/or densities that are consistent with icy surfaces and a substantial H<SUB>2</SUB>O content. We have also investigated the potential for tidally driven cryovolcanism and exosphere formation on these worlds. Estimated internal heating rates from tidal and radiogenic sources are large enough that all planets in our study may harbor subsurface oceans, and their geological activity rates are likely to exceed the geological activity rates on Jupiter's moon Europa. Several planets are likely to experience enhanced volcanic activity rates that exceed that of Io. Owing to their relatively thin ice shells and high rates of internal heating, Proxima Cen b and LHS 1140 b are the most favorable candidates for telescopic detection of explosive, tidally driven cryovolcanism. Estimates for thin ice shells on Proxima Cen b, LHS 1140 b, Trappist-1f, and several Kepler planets suggest that any H<SUB>2</SUB>O vented into space during explosive cryovolcanic eruptions on these worlds could be sourced directly from their subsurface oceans. Like the icy moons in our outer solar system, cold ocean planets may be astrobiologically significant worlds that harbor habitable environments beneath their icy surfaces. These possibilities should be considered during analyses of observational data for small exoplanets from current and upcoming telescopes and during planning for a future space telescope mission aimed at characterization of potentially habitable exoplanets (e.g., Habitable Worlds Observatory). | [
497,
2118,
2174,
496,
487,
695,
498,
1655,
1151
] | [
"exoplanet tides",
"exoplanet surfaces",
"volcanism",
"exoplanet surface characteristics",
"exoplanet atmospheres",
"habitable planets",
"exoplanets",
"super earths",
"ocean planets"
] |
2021ApJ...914L..29B | Discovery of a Radio Halo (and Relic) in a M<SUB>500</SUB><2×10<SUP>14</SUP> M<SUB>⊙</SUB> Cluster | Radio halos are diffuse synchrotron sources observed in dynamically unrelaxed galaxy clusters. Current observations and models suggest that halos trace turbulent regions in the intracluster medium where mildly relativistic particles are reaccelerated during cluster mergers. Due to the higher luminosities and detection rates with increasing cluster mass, radio halos have been mainly observed in massive systems ( ${M}_{500}\gtrsim 5\times {10}^{14}$ ${M}_{\odot }$ ). Here, we report the discovery of a radio halo with a largest linear scale of750 kpc in PSZ2G145.92-12.53 (z0.03) using LOw Frequency ARray (LOFAR) observations at 120168 MHz. With a mass of ${M}_{500}=(1.9\pm 0.2)\times {10}^{14}$ ${M}_{\odot }$ and a radio power at 150MHz of ${P}_{150}=(3.5\pm 0.7)\times {10}^{23}$ W Hz<SUP>1</SUP>, this is the least powerful radio halo in the least massive cluster discovered to date. Additionally, we discover a radio relic with a mildly convex morphology at 1.7 Mpc from the cluster center. Our results demonstrate that LOFAR has the potential to detect radio halos even in low-mass clusters, where the expectation to form them is very low (5) based on turbulent reacceleration models. Together with the observation of large samples of clusters, this opens the possibility to constrain the low end of the powermass relation of radio halos. | [
584,
858,
508,
1338,
1346,
504,
1119
] | [
"galaxy clusters",
"intracluster medium",
"extragalactic radio sources",
"radio astronomy",
"radio interferometry",
"extended radiation sources",
"non-thermal radiation sources"
] |
2023PSJ.....4...91L | Mineralogical Characterization and Phase Angle Study of Two Binary Near-Earth Asteroids, Potential Targets for NASA's Janus Mission | Ground-based characterization of spacecraft targets prior to mission operations is critical to properly plan and execute measurements. Understanding surface properties, such as mineralogical composition and phase curves (expected brightness at different viewing geometries), informs data acquisition during the flybys. Binary near-Earth asteroids (NEAs) (35107) 1991 VH and (175706) 1996 FG3 were selected as potential targets of the National Aeronautics and Space Administration's (NASA) dual spacecraft Janus mission. We observed 1991 VH using the 3 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, on 2008 July 26. 1996 FG3 was observed with the IRTF for seven nights during the spring of 2022. Compositional analysis of 1991 VH revealed that this NEA is classified as an Sq-type in the Bus-DeMeo taxonomy classification, with a composition consistent with LL ordinary chondrites. Using thermal modeling, we computed the thermally corrected spectra for 1996 FG3 and the corresponding best-fit albedo of about 2%-3% for the best spectra averaged for each night. Our spectral analysis indicates that this NEA is a Ch-type. The best possible meteorite analogs for 1996 FG3, based on curve matching, are two carbonaceous chondrites, Y-86789 and Murchison. No rotational variation was detected in the spectra of 1996 FG3, which means there may not be any heterogeneities on the surface of the primary. However, a clear phase reddening effect was observed in our data, confirming findings from previous ground-based studies. | [
1092,
2209,
1093,
2304,
1038,
1217,
2285,
2115,
686
] | [
"near-earth objects",
"asteroid surfaces",
"near infrared astronomy",
"planetary mineralogy",
"meteorites",
"phase angle",
"infrared spectroscopy",
"surface composition",
"ground-based astronomy"
] |
2020ApJ...895L..50C | Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three Dimensions | We report microwave spectral imaging observations of an erupting magnetic flux rope during the early impulsive phase of the X8.2-class limb flare on 2017 September 10, obtained by the Expanded Owens Valley Solar Array. A few days prior to the eruption, when viewed against the disk, the flux rope appeared as a reverse S-shaped dark filament along the magnetic polarity inversion line. During the eruption, the rope exhibited a "hot channel" structure in extreme ultraviolet and soft X-ray passbands sensitive to ∼10 MK plasma. The central portion of the flux rope was nearly aligned with the line of sight, which quickly developed into a teardrop-shaped dark cavity during the early phase of the eruption. A long and thin plasma sheet formed below the cavity, interpreted as the reconnection current sheet viewed edge on. A nonthermal microwave source was present at the location of the central current sheet, which extended upward encompassing the dark cavity. A pair of nonthermal microwave sources were observed for several minutes on both sides of the main flaring region. They shared a similar temporal behavior and spectral property to the central microwave source below the cavity, interpreted as the conjugate footpoints of the erupting flux rope. These observations are broadly consistent with the magnetic topology and the associated energy release scenario suggested in the three-dimensional standard model for eruptive solar flares. In particular, our detection of nonthermal emission at conjugate flux rope footpoints provides solid evidence of particle transport along an erupting magnetic flux rope. | [
1496,
310,
1119,
1504,
1342,
1523
] | [
"solar flares",
"solar coronal mass ejections",
"non-thermal radiation sources",
"solar magnetic reconnection",
"solar radio flares",
"solar radio telescopes"
] |
2022PASP..134h4501H | Pattern Recognition Using SVM for the Classification of the Size and Distance of Trans-Neptunian Objects Detected by Serendipitous Stellar Occultations | We present a new pipeline based on the Support Vector Machine algorithm to confirm the detection and perform classification of small solar system objects by serendipitous stellar occultations. This pipeline is designed to analyze light curves and to identify the occultation events and the classification of the occulting bodies according to their size, typically from a fraction to a few kilometers, and their distance from the Sun, typically a few tens of astronomical units. The input light curves for this pipeline were obtained from the event simulator for the Trans-Neptunian Automated Occultation Survey (TAOS II). We explore parameters affecting occultation light curves such as spectral type, apparent magnitude and finite angular size of the occulted star, angle from opposition, and readout cadence for the observations; also we assumed a Poisson noise distribution as expected from the TAOS II project. We find that occultation events, especially by trans-Neptunian objects with diameters ≥2 km are detected with 99.99%, 99.53%, and 86% efficiency for stars with a visual apparent magnitude of 12, 14, and 16, respectively at 0.05 s of exposure time. In terms of size and distance classification the overall accuracy is 94%. However, for smaller objects the confirmation and classification depends mostly upon the signal-to-noise ratio. | [
893,
1858,
1148,
1671
] | [
"kuiper belt",
"astronomy data analysis",
"occultation",
"surveys"
] |
2022ApJ...937..100S | Exploring the Limits of Synthetic Creation of Solar EUV Images via Image-to-image Translation | The Solar Dynamics Observatory (SDO), a NASA multispectral decade-long mission that has been daily producing terabytes of observational data from the Sun, has been recently used as a use case to demonstrate the potential of machine-learning methodologies and to pave the way for future deep space mission planning. In particular, the idea of using image-to-image translation to virtually produce extreme ultraviolet channels has been proposed in several recent studies, as a way to both enhance missions with fewer available channels and to alleviate the challenges due to the low downlink rate in deep space. This paper investigates the potential and the limitations of such a deep learning approach by focusing on the permutation of four channels and an encoder-decoder based architecture, with particular attention to how morphological traits and brightness of the solar surface affect the neural network predictions. In this work we want to answer the question: can synthetic images of the solar corona produced via image-to-image translation be used for scientific studies of the Sun? The analysis highlights that the neural network produces high-quality images over 3 orders of magnitude in count rate (pixel intensity) and can generally reproduce the covariance across channels within a 1% error. However, the model performance drastically diminishes in correspondence to extremely high energetic events like flares, and we argue that the reason is related to the rareness of such events posing a challenge to model training. | [
1475,
1493,
1969,
1974,
1531,
1938
] | [
"solar activity",
"solar extreme ultraviolet emission",
"gpu computing",
"solar active regions",
"solar telescopes",
"convolutional neural networks"
] |
2021ApJ...908..112B | Formation of Dust Filaments in the Diffuse Envelopes of Molecular Clouds | The path to understanding star formation processes begins with the study of the formation of molecular clouds. The outskirts of these clouds are characterized by low column densities that allow the penetration of ultraviolet radiation, resulting in a nonnegligible ionization fraction and the charging of the small dust grains that are mixed with the gas; this diffuse phase is then coupled to the ambient magnetic field. Despite the general assumption that dust and gas are tightly correlated, several observational and theoretical studies have reported variations in the dust-to-gas ratio toward diffuse and cold clouds. In this work, we present the implementation of a new charged particles module for analyzing the dust dynamics in molecular cloud envelopes. We study the evolution of a single population of small charged grains (0.05 μm) in the turbulent, magnetized molecular cloud envelope using this module. We show that variations in the dust-to-gas ratio arise due to the coupling of the grains with the magnetic field, forming elongated dust structures decoupled from the gas. This emphasizes the importance of considering the dynamics of charged dust when simulating the different phases of the interstellar medium, especially for star formation studies. | [
834,
836,
1569,
1789
] | [
"interstellar clouds",
"interstellar dust",
"star formation",
"warm neutral medium"
] |
2024RNAAS...8..168E | Gnuastro: Generating Polar Plots in Astronomical Images | When a structure displays dependence on distance and azimuthal angle from a center (for example the spiral arms of galaxies or the diffraction spikes of stars), projecting the pixels to polar coordinates greatly simplifies their study. This projection from one pixel grid to another is known as a "polar plot." For this purpose, a new option has been added to the GNU Astronomy Utilities (Gnuastro) in version 0.23 to "astscript-radial-profile" script, which we describe in this research note. The figures of this research note are reproducible with Maneage, on the Git commit 5d34243. | [
1855,
1866,
1684,
1561,
1559
] | [
"astronomy software",
"open source software",
"astronomical techniques",
"spiral pitch angle",
"spiral arms"
] |
2021PSJ.....2..171L | Lucy Mission to the Trojan Asteroids: Science Goals | The Lucy Mission is a NASA Discovery-class mission to send a highly capable and robust spacecraft to investigate seven primitive bodies near both the L<SUB>4</SUB> and L<SUB>5</SUB> Lagrange points with Jupiter: the Jupiter Trojan asteroids. These planetesimals from the outer planetary system have been preserved since early in solar system history. The Lucy mission will fly by and extensively study a diverse selection of Trojan asteroids, including all the recognized taxonomic classes, a collisional family member, and a near equal-mass binary. It will visit objects with diameters ranging from roughly 1 km to 100 km. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. Additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will supplement imaging during closest approach and the telecommunication subsystem will be used to measure the mass of the Trojans. The science goals are derived from the 2013 Planetary Decadal Survey and include determining the surface composition, assessing the geology, determining the bulk properties, and searching for satellites and rings. | [
874,
545
] | [
"jupiter trojans",
"flyby missions"
] |
2023ApJ...959..105D | Star-forming Main Sequence of Giant Low Surface Brightness Galaxies | Giant low surface brightness galaxies (GLSBGs) are fundamentally distinct from normal galaxies and other types of LSBGs in terms of star formation and evolution. In this work, we collected 27 local GLSBGs from the literature. They have high stellar masses (M <SUB>*</SUB> > 10<SUP>10</SUP> M <SUB>⊙</SUB>) and low far-ultraviolet-based star formation rates (SFRs). With specific star formation rates (sSFRs) lower than the characteristic value of local star-forming galaxies (SFGs) of M <SUB>*</SUB> = 10<SUP>10</SUP> M <SUB>⊙</SUB> (sSFR < 0.1 Gyr<SUP>-1</SUP>), GLSBGs deviate from the star formation main sequence (MS) defined for local SFGs respectively by Elbaz et al. (E07) and Saintonge et al. (S16) at the high-M <SUB>*</SUB> regime. They are H I-rich systems with H I gas mass fractions (f <SUB>H I</SUB>) higher than the S16 MS galaxies, but have little molecular gas (H<SUB>2</SUB>), implying a quite low efficiency of H I-to-H<SUB>2</SUB> transition due to low H I surface densities (Σ H I) that are far lower than the minimum Σ H I of 6-8 M <SUB>⊙</SUB> pc<SUP>-2</SUP> required for shielding the formed H<SUB>2</SUB> from photodissociation. For GLSBGs, the inner, bulge-dominated parts with lower SFRs and higher M <SUB>*</SUB> are the main force pulling the entire GLSBG sample off of the MS, while the outer, disk-dominated parts with relatively higher SFRs and lower M <SUB>*</SUB> reduce the deviation from the MS. For some cases, the outer, disk-dominated parts even tend to follow the MS. In the aspect of near-ultraviolet - r versus g - r colors, the outer, disk-dominated parts are blue and behave similarly to normal SFGs while the inner, bulge-dominated parts are statistically redder, indicating an inside-out star formation mechanism for GLSBGs. They show few signs of external interactions in morphology, excluding the recent major merger scenario. | [
940,
652,
1569,
2031
] | [
"low surface brightness galaxies",
"giant galaxies",
"star formation",
"scaling relations"
] |
2020ApJ...903....3G | Probing the Physics of Mechanical AGN Feedback with Radial Elongations of X-Ray Cavities | Mechanical active galactic nucleus (AGN) feedback plays a key role in massive galaxies, galaxy groups, and clusters. However, the energy content of AGN jets that mediate this feedback process is still far from clear. Here we present a preliminary study of radial elongations τ of a large sample of X-ray cavities, which are apparently produced by mechanical AGN feedback. All of the cavities in our sample are elongated along the angular (type I) or jet directions (type II), or nearly circular (type III). The observed value of τ roughly decreases as the cavities rise buoyantly, confirming the same trend found in hydrodynamic simulations. For young cavities, both type-I and type-II cavities exist, and the latter dominates. Assuming a spheroidal cavity shape, we derive an analytical relation between the intrinsic radial elongation $\bar{\tau }$ and the inclination-angle-dependent value of τ, showing that projection effect makes cavities appear more circular, but does not change type-I cavities into type-II ones, or vice versa. We summarize radial elongations of young cavities in simulations, finding that $\bar{\tau }$ increases with the kinetic fraction of AGN jets. While mild jets always produce type-II cavities, thermal-energy-dominated strong jets produce type-I cavities, and kinetic-energy-dominated strong jets produce type-II cavities. Our results suggest that some AGN jets are strong and dominated by thermal energy (or cosmic rays). However, these jets do not dominate in AGN feedback. If most jets are dominated by nonkinetic energies, they should be mainly mild jets. If most jets are strong, they must be mainly dominated by the kinetic energy. | [
1347,
17,
739,
16,
1348,
767,
584,
858,
1810,
597
] | [
"radio jets",
"active galaxies",
"high energy astrophysics",
"active galactic nuclei",
"radio lobes",
"hydrodynamical simulations",
"galaxy clusters",
"intracluster medium",
"x-ray astronomy",
"galaxy groups"
] |
2023PSJ.....4..226P | Geometric Properties of Water-ice Clouds as Observed from Jezero Crater in the First 600 sols with the NavCam Instrument On Board the Mars2020 Rover, Perseverance | In the first 600 sols of the Mars2020 mission, L<SUB>S</SUB> 5.6<SUP>o</SUP> - 316.8<SUP>o</SUP>, 46 cloud movies and 145 cloud surveys were collected to observe clouds at Jezero Crater, the landing site of the Perseverance Rover. Cloud movies were processed using the Mean-Frame Subtraction (MFS) method for revealing cloud structures, which were subsequently analyzed using digital-image processing. Two-dimensional Fast Fourier Transforms (2D-FFT) were used to compute cloud structure sizes ranging from 2.90 to 15.25 km for clouds between 30 and 50 km altitude, based on coincident Mars Climate Sounder vertical profiles of atmospheric water-ice. Same-value thresholding was used to detect the cloud structures in MFS-processed and projected cloud movies. The resolution dependence that was needed to resolve these structures over various thresholds was examined to find multifractal scaling of Mars clouds for resolutions between 0.1 and 1.6 km. We characterize the multiscaling observed in the images and its implications for the design of cloud-tracking cameras from the surface as well as for cloud-resolving models. | [
1255,
1244,
2180,
1007,
1409
] | [
"planetary science",
"planetary atmospheres",
"atmospheric clouds",
"mars",
"rovers"
] |
2022ApJ...941..177Z | Accretion Variability of the Multiple T Tauri System VW Cha | Classical T Tauri stars are low-mass objects that are still accreting material from the surrounding circumstellar disk. The accretion process is essential in the formation of Sun-like stars and in setting the properties of the disk at the time when planet formation occurs. We constructed a complex data set in order to examine the accretion process of VW Cha, a classical T Tauri multiple system, with the aim of studying the physical origin of the photometric and spectroscopic variability of the system. The TESS space telescope observed VW Cha between 2019 April 22 and June 19, and we complemented these data with contemporaneous ground-based I <SUB>C</SUB>JHK-band photometric measurements. In addition, we obtained high-resolution optical spectra with the VLT/ESPRESSO and the 2.2 m/FEROS instruments. Analyzing these data, we found that the TESS light curve shows photometric variations on timescales from minutes to weeks with a peak-to-peak amplitude of ~0.8 mag. The near-infrared light curves follow the shape of the optical measurements; however, the peak-to-peak amplitudes are slightly increasing toward the longer wavelengths. We took spectra in both fainter and brighter photometric states of the system, allowing us to examine the origin of a photometric brightening event. Our results show that this brightening event can be explained by increased accretion. In addition, our spectroscopic data also suggest that the primary component of VW Cha is a spectroscopic binary, as was proposed in earlier works. | [
1578,
252,
1289,
1569,
1761,
235,
1290
] | [
"stellar accretion",
"classical t tauri stars",
"pre-main sequence",
"star formation",
"variable stars",
"circumstellar disks",
"pre-main sequence stars"
] |
2023ApJS..264...26M | Signature of Massive Neutrinos from the Clustering of Critical Points. I. Density-threshold-based Analysis in Configuration Space | Critical points represent a subset of special points tracing cosmological structures, carrying remarkable topological properties. They thus offer a richer high-level description of the multiscale cosmic web, being more robust to systematic effects. For the first time, we characterize here their clustering statistics in massive neutrino cosmologies, including cross-correlations, and quantify their simultaneous imprints on the corresponding web constituents-i.e., halos, filaments, walls, and voids-for a series of rarity levels. Our first analysis is centered on a density-threshold-based approach in configuration space. In particular, we show that the presence of massive neutrinos does affect the baryon acoustic oscillation peak amplitudes of all of the critical point correlation functions above/below the rarity threshold, as well as the positions of their correspondent inflection points at large scales: departures from analogous measurements carried out in the baseline massless neutrino scenario can reach up to ~7% in autocorrelations and ~9% in cross-correlations at z = 0 when M <SUB> ν </SUB> = 0.1 eV and are more pronounced for higher neutrino mass values. In turn, these combined multiscale effects can be used as a novel technique to set upper limits on the summed neutrino mass and infer the type of hierarchy. Our study is particularly relevant for ongoing and future large-volume redshift surveys such as the Dark Energy Spectroscopic Instrument and the Rubin Observatory Legacy Survey of Space and Time, which will provide unique data sets suitable for establishing competitive neutrino mass constraints. | [
1102,
338,
902,
343,
330
] | [
"neutrino masses",
"cosmological neutrinos",
"large-scale structure of the universe",
"cosmology",
"cosmic web"
] |
2023AJ....165..190N | Zwicky Transient Facility and Globular Clusters: The Period-Luminosity and Period-Wesenheit Relations for SX Phoenicis Variables in the gri Band | SX Phoenicis (SXP) variables are short-period pulsating stars that exhibit a period-luminosity (PL) relation. We derived the gri-band PL and extinction-free period-Wesenheit (PW) relations, as well as the period-color and reddening-free period-Q-index relations for 47 SXP stars located in 21 globular clusters, using the optical light curves taken from Zwicky Transient Facility. These empirical relations were derived for the first time in the gri filters except for the g-band PL relation. We used our gi-band PL and PW relations to derive a distance modulus to Crater II dwarf spheroidal which hosts one SXP variable. Assuming that the fundamental and first-overtone pulsation mode for the SXP variable in Crater II, we found distance moduli of 20.03 ± 0.23 mag and 20.37 ± 0.24 mag, respectively, using the PW relation, where the latter is in excellent agreement with independent RR Lyrae based distance to Crater II dwarf galaxy. | [
1673,
394,
1800,
1464,
656
] | [
"sx phoenicis variable stars",
"distance indicators",
"wide-field telescopes",
"sky surveys",
"globular star clusters"
] |
2020ApJ...894..115P | Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia | The orbits of binary stars and planets, particularly eccentricities and inclinations, encode the angular momentum within these systems. Within stellar multiple systems, the magnitude and (mis)alignment of angular momentum vectors among stars, disks, and planets probes the complex dynamical processes guiding their formation and evolution. The accuracy of the Gaia catalog can be exploited to enable comparison of binary orbits with known planet or disk inclinations without costly long-term astrometric campaigns. We show that Gaia astrometry can place meaningful limits on orbital elements in cases with reliable astrometry, and discuss metrics for assessing the reliability of Gaia DR2 solutions for orbit fitting. We demonstrate our method by determining orbital elements for three systems (DS Tuc AB, GK/GI Tau, and Kepler-25/KOI-1803) using Gaia astrometry alone. We show that DS Tuc AB's orbit is nearly aligned with the orbit of DS Tuc Ab, GK/GI Tau's orbit might be misaligned with their respective protoplanetary disks, and the Kepler-25/KOI-1803 orbit is not aligned with either component's transiting planetary system. We also demonstrate cases where Gaia astrometry alone fails to provide useful constraints on orbital elements. To enable broader application of this technique, we introduce the python tool lofti_gaiaDR2 to allow users to easily determine orbital element posteriors. | [
1175,
1184,
1177,
1257,
492,
1569,
79,
154,
1801
] | [
"orbit determination",
"orbits",
"orbital elements",
"planetary system formation",
"exoplanet formation",
"star formation",
"astrometric binary stars",
"binary stars",
"wide binary stars"
] |
2023RNAAS...7..160M | The Behavior of Bp He-weak Stars in the Far-UV-Paper XII: HD 175156 | The analysis of four spectra of the B5 He-variable star HD 175156 recorded by the SWP camera on board the International Ultraviolet Explorer reveals one possible instance of variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å in spectra separated by 5 yr. Spectra collected over 4 consecutive days with identical exposure times do not vary, which probably rules out the possibility that HD 175156 be a rotational variable. The modeling of the Space Telescope Imaging Spectrograph spectrum reveals the presence of interesting resonance or low lying transitions of C I, N I, S I, P II and several iron-peak elements, which provide interesting diagnostics of the atmosphere of this evolved sub-giant. | [
226,
717
] | [
"chemically peculiar stars",
"helium-weak stars"
] |
2023ApJ...958L..40W | Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: The Low-luminosity Cases and an Application to Sgr A* | In this paper, we investigate the astrophysical processes of stellar-mass black holes (sMBHs) embedded in advection-dominated accretion flows (ADAFs) of supermassive black holes (SMBHs) in low-luminosity active galactic nuclei. The sMBH is undergoing Bondi accretion at a rate lower than the SMBH. Outflows from the sMBH-ADAF dynamically interact with their surroundings and form a cavity inside the SMBH-ADAF, thereby quenching the accretion onto the sMBH. Rejuvenation of the Bondi accretion is rapidly done by turbulence. These processes give rise to quasi-periodic episodes of sMBH activities and create flickerings from relativistic jets developed by the Blandford-Znajek mechanism if the sMBH is maximally rotating. Accumulating successive sMBH-outflows trigger a viscous instability of the SMBH-ADAF, leading to a flare following a series of flickerings. Recently, the similarity of near-infrared flare's orbits has been found by GRAVITY/VLTI astrometric observations of Sgr A<SUP>∗</SUP>: their loci during the last 4 yr consist of a ring in agreement with the well-determined SMBH mass. We apply the present model to Sgr A*, which shows quasi-periodic flickerings. An sMBH of ~40M <SUB>⊙</SUB> is preferred orbiting around the central SMBH of Sgr A* from fitting radio to X-ray continuum. Such an extreme mass ratio inspiraling provides an excellent laboratory for LISA/Taiji/Tianqin detection of mHz gravitational waves with strains of ~10<SUP>-17</SUP>, as well as their polarization. | [
17
] | [
"active galaxies"
] |
2023PSJ.....4..223S | Spectroscopic Links among Giant Planet Irregular Satellites and Trojans | We collect near-infrared spectra (~0.75-2.55 μm) of four Jovian irregular satellites and visible spectra (~0.32-1.00 μm) of two Jovian irregular satellites, two Uranian irregular satellites, and four Neptune Trojans. We find close similarities between the observed Jovian irregular satellites and previously characterized Jovian Trojans. However, irregular satellites' unique collisional histories complicate comparisons to other groups. Laboratory study of CM and CI chondrites shows that grain size and regolith packing conditions strongly affect spectra of dark, carbonaceous materials. We hypothesize that different activity histories of these objects, which may have originally contained volatile ices that subsequently sublimated, could cause differences in regolith grain size or packing properties and therefore drive spectral variation. The Uranian satellites Sycorax and Caliban appear similar to TNOs. However, we detect a feature near 0.7 μm on Sycorax, suggesting the presence of hydrated materials. While the sample of Neptune Trojans have more neutral spectra than the Uranian satellites we observe, they remain consistent with the broad color distribution of the Kuiper Belt. We detect a possible feature near 0.65-0.70 μm on Neptune Trojan 2006 RJ103, suggesting that hydrated material may also be present in this population. Characterizing hydrated materials in the outer solar system may provide critical context regarding the origins of hydrated CI and CM chondrite meteorites. We discuss how the hydration state(s) of the irregular satellites constrains the thermal histories of the interiors of their parent bodies, which may have formed among the primordial Kuiper Belt. | [
2285,
1558,
72,
1715,
215,
2027,
1705,
872,
1750,
1097,
200
] | [
"infrared spectroscopy",
"spectroscopy",
"asteroids",
"trojan asteroids",
"centaur group",
"irregular satellites",
"trans-neptunian objects",
"jovian satellites",
"uranian satellites",
"neptune trojans",
"carbonaceous chondrites"
] |
2021ApJ...907...90S | Quality Metric for Spitzer-Braginskii and Grad 8 Moment Heat Flux Closures | Quality metrics for Spitzer-Härm and Grad closures are presented based on the percentage of the heat flux moment supported only by nonnegative, physical, phase space densities ${\mathbb{F}}\gt 0$ underlying the closure. The Spitzer and Grad qualities exceed 95% for the perturbative regimes where Spitzer's formulation is analytically known to be convergent. Beyond this regime both heat flux qualities fall about 30% per decade increase of ɛ > 0.01. In the solar corona the first decade's decrease in quality straddles the radius of the coronal temperature maximum and spans the initial acceleration of the solar wind. By the end of the second decade of increase of ɛ the observer is between 5 and 10R<SUB>⊙</SUB>, already in conditions comparable to those at 1 au with ≃60% degradation of quality. These strong radial decays of closure quality show that integrating the fluid equations using such closures must represent a very poor assay of the role and effects of ∇ · q had the heat flux been described throughout with a uniformly high quality closure procedure. For small ɛ, $\,{\mathbb{F}}\lt 0$ occurs for cosine of pitch angle μ < 0 opposed to q at speeds above 2 thermal speeds and are omnipresent (but ignorable) for truly perturbative closures. Above a computed threshold in ɛ unphysical ${\mathbb{F}}\lt 0$ occurs for speeds below 2 thermal speeds with μ > 0. The present work graphically shows ${\mathbb{F}}\lt 0$ regimes becoming increasingly pervasive as ɛ increases, first crossing ≃4 thermal speeds at μ < 0 and then representing ever larger unphysical incursions within the needed velocity sphere required to accurately determine the heat flux. | [
86,
101,
767,
1000,
2089,
1989,
1483,
1534,
1636
] | [
"astronomical models",
"astrophysical fluid dynamics",
"hydrodynamical simulations",
"main sequence stars",
"plasma physics",
"solar coronal heating",
"solar corona",
"solar wind",
"stellar winds"
] |
2021AJ....162..109S | Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22 | While most moving groups are young and nearby, a small number have been identified in the Galactic halo. Understanding the origin and evolution of these groups is an important piece of reconstructing the formation history of the halo. Here we report on our analysis of three putative halo moving groups: G03-37, G18-39, and G21-22. Based on Gaia EDR3 data, the stars associated with each group show some scatter in velocity (e.g., Toomre diagram) and integrals of motion (energy, angular momentum) spaces, counter to expectations of moving-group stars. We choose the best candidate of the three groups, G21-22, for follow-up chemical analysis based on high-resolution spectroscopy of six presumptive members. Using a new Python code that uses a Bayesian method to self-consistently propagate uncertainties from stellar atmosphere solutions in calculating individual abundances and spectral synthesis, we derive the abundances of α- (Mg, Si, Ca, Ti), Fe-peak (Cr, Sc, Mn, Fe, Ni), odd-Z (Na, Al, V), and neutron-capture (Ba, Eu) elements for each star. We find that the G21-22 stars are not chemically homogeneous. Based on the kinematic analysis for all three groups and the chemical analysis for G21-22, we conclude the three are not genuine moving groups. The case for G21-22 demonstrates the benefit of combining kinematic and chemical information in identifying conatal populations when either alone may be insufficient. Comparing the integrals of motion and velocities of the six G21-22 stars with those of known structures in the halo, we tentatively associate them with the Gaia-Enceladus accretion event. <SUP>*</SUP> Based on observations collected at the European Southern Observatory under ESO program 090.B-0605(A). | [
224,
1577,
1621,
699,
1076,
2096,
80,
1855
] | [
"chemical abundances",
"stellar abundances",
"stellar physics",
"halo stars",
"moving clusters",
"high resolution spectroscopy",
"astrometry",
"astronomy software"
] |
2021ApJ...911...54B | Probing the Solar Meridional Circulation Using Fourier Legendre Decomposition | We apply the helioseismic methodology of Fourier Legendre decomposition to 88 months of Dopplergrams obtained by the Helioseismic and Magnetic Imager (HMI) as the basis of inferring the depth variation of the mean meridional flow, as averaged between 20° and 60° latitude and in time, in both the northern and southern hemispheres. We develop and apply control procedures designed to assess and remove center-to-limb artifacts using measurements obtained by performing the analysis with respect to artificial poles at the east and west limbs. Forward modeling is carried out using sensitivity functions proportional to the mode kinetic energy density to evaluate the consistency of the corrected frequency shifts with models of the depth variation of the meridional circulation in the top half of the convection zone. The results, taken at face value, imply substantial differences between the meridional circulation in the northern and southern hemispheres. The inferred presence of a return (equatorward propagating) flow at a depth of approximately 40 Mm below the photosphere in the northern hemisphere is surprising and appears to be inconsistent with many other helioseismic analyses. This discrepancy may be the result of the inadequacy of our methodology to remove systematic errors in HMI data. Our results appear to be at least qualitatively similar to those by Gizon et al., which point to an anomaly in HMI data that is not present in MDI or GONG data. | [
709,
1874,
1500
] | [
"helioseismology",
"solar meridional circulation",
"solar interior"
] |
2022PSJ.....3..128R | Global-scale Reshaping and Resurfacing of Asteroids by Small-scale Impacts, with Applications to the DART and Hera Missions | We use a novel approach to model the entire cratering process resulting from impacts on small, weak asteroids that uses shock physics code calculations directly. We found that small-scale impacts (with a projectile size less than 1/150 of the target size) can significantly deform weak asteroids, causing global resurfacing at the same time. As a result, the collisional lifetime of the overall asteroid shapes is significantly lower than the traditionally used lifetime based on catastrophic disruption events. We also show that even very low asteroid cohesions can drastically influence the outcome of an impact. Consequently, if the target is homogeneous and weaker than ≈10 Pa, then NASA's Double Asteroid Redirection Test impact on Dimorphos may not lead to a cratering event, as originally anticipated. Rather, the impact may change the global morphology of the asteroid. Our results, together with future observations by the ESA's Hera mission, will provide constraints regarding the evolution of the shapes and structures of small asteroids by subcatastrophic impacts. | [
72,
779,
1255,
2065,
1469,
1092
] | [
"asteroids",
"impact phenomena",
"planetary science",
"collision physics",
"small solar system bodies",
"near-earth objects"
] |
2024ApJS..272...16S | Infrared Properties of Carbon Stars in Our Galaxy | We explore the characteristics of carbon stars within our Galaxy through a comprehensive analysis of observational data spanning visual and infrared (IR) bands. Leveraging data sets from IRAS, the Infrared Space Observatory, Akari, the Midcourse Space Experiment, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer (WISE), Gaia DR3, AAVSO, and the SIMBAD object database, we conduct a detailed comparison between the observational data and theoretical models. To facilitate this comparison, we introduce various IR two-color diagrams (2CDs), IR color–magnitude diagrams (CMDs), and spectral energy distributions (SEDs). We find that the CMDs, which utilize the latest distance and extinction data from Gaia DR3 for a substantial number of carbon stars, are very useful for distinguishing carbon-rich asymptotic giant branch (CAGB) stars from extrinsic carbon stars that are not in the AGB phase. To enhance the accuracy of our analysis, we employ theoretical radiative transfer models for dust shells around CAGB stars. These theoretical dust shell models demonstrate a commendable ability to approximate the observations of CAGB stars across various SEDs, 2CDs, and CMDs. We present the infrared properties of known pulsating variables and explore the infrared variability of the sample stars by analyzing WISE photometric data spanning the last 14 years. Additionally, we present a novel catalog of CAGB stars, offering enhanced reliability and a wealth of additional information. | [
2100,
199,
236,
935,
786,
1335
] | [
"asymptotic giant branch stars",
"carbon stars",
"circumstellar dust",
"long period variable stars",
"infrared astronomy",
"radiative transfer"
] |
2024ApJ...969..140R | The Long-period Spectroscopic Orbit and Dust Creation in the Wolf–Rayet Binary System WR 125 | Several long-period binaries with a carbon-rich Wolf–Rayet star and an OB star produce dust in their wind collisions. In eccentric binaries, this is seen most strongly near periastron passage. The exact conditions leading to dust creation require the orbital properties to be determined, which is difficult owing to their long periods. Recently, the binary system WR 125 (WC7 + O9III) began a dust-creation episode seen through an infrared outburst first detected by NEOWISE-R, which was the first outburst detected since 1991. We present new near- and mid-infrared photometry, which we use to show consistency between the two outbursts and derive an orbital period of yr. We use a long time series of optical spectra to place the first constraints on its orbital elements, on the assumption that this system will produce dust near periastron. The orbit has a mild eccentricity of 0.29 ± 0.12 and is only derived for the Wolf–Rayet component, as the O star's radial velocities have noise that is likely larger than the expected semiamplitude of the orbit. We also present SOFIA/FORCAST grism spectroscopy to examine the infrared spectral energy distribution of the dust during this outburst, comparing its properties to other WCd binaries, and deriving a dust temperature of 580 K in 2021. This collection of observations will allow us to plan future observations of this system and place the system in the context of dust-creating Wolf–Rayet binaries. | [
1793,
154,
1557
] | [
"wc stars",
"binary stars",
"spectroscopic binary stars"
] |
2021ApJ...918...25P | Observation of the Apoapsis of S62 in 2019 with NIRC2 and SINFONI | Given the increased attention toward the detection of faint stars in the Galactic center, we would like to address the detectability of S62 in its apoapsis with the Spectrograph for INtegral Field Observations in the Near Infrared at the Very Large Telescope (SINFONI; VLT) and the Near-Infrared Camera 2 (NIRC2; KECK) in this work. Because of the nearby stars and the chance of confusion, we are using Lucy-Richardson deconvolved images to detect S62 on its Keplerian orbit around Sgr A* with a period of less than 10 yr. We use the same data set as for S62 to trace additionally the S-cluster star S29 at the expected position based on the orbital elements presented in this work. To verify the results of the filtering technique, we are analyzing K-band continuum data of the same epoch independently observed with NIRC2/KECK. Based on the well-derived orbit of S62, we find the star in projection at the expected position in 2019.4 and 2019.5. By analyzing the SINFONI data of 2019.5, we confirm the 16.1 ± 0.2 mag for S62 that was formerly derived with NAOS-CONICA (NACO; VLT). We base our NACO imaging analysis on the robust data set that was previously used to investigate the Schwarzschild precision of S2. We also present a critical discussion of the elsewhere proposed linear trajectory of S62 and its disputed identification with a 19 mag star found with GRAVITY mounted at the VLT Interferometer. | [
565,
884,
162
] | [
"galactic center",
"keplerian orbit",
"black holes"
] |
2021ApJ...920...64G | New Hydrodynamic Solutions for Line-driven Winds of Hot Massive Stars Using the Lambert W-function | Hot massive stars present strong stellar winds that are driven by absorption, scattering, and reemission of photons by the ions of the atmosphere (line-driven winds). A better comprehension of this phenomenon, and a more accurate calculation of hydrodynamics and radiative acceleration, is Required to reduce the number of free parameters in spectral fitting and to determine accurate wind parameters such as mass-loss rates and velocity profiles. We use the non-LTE model-atmosphere code CMFGEN to numerically solve the radiative transfer equation in the stellar atmosphere and to calculate the radiative acceleration g<SUB>rad</SUB>(r). Under the assumption that the radiative acceleration depends only on the radial coordinate, we solve analytically the equation of motion by means of the Lambert W-function. An iterative procedure between the solution of the radiative transfer and the equation of motion is executed in order to obtain a final self-consistent velocity field that is no longer based on any β-law. We apply the Lambert-procedure to three O supergiant stars (ζ Puppis, HD 165763, and α Cam) and discuss the Lambert solutions for the velocity profiles. It is found that, even without recalculation of the mass-loss rate, the Lambert-procedure allows the calculation of consistent velocity profiles that reduce the number of free parameters when a spectral fitting using CMFGEN is performed. Synthetic spectra calculated from our Lambert solutions show significant differences compared to the initial β-law CMFGEN models. The results indicate the importance of consistent velocity profile calculation in the CMFGEN code and its use in a fitting procedure and interpretation of observed spectra. | [
1636,
1963,
430,
1137,
1335,
1584
] | [
"stellar winds",
"hydrodynamics",
"early-type stars",
"o stars",
"radiative transfer",
"stellar atmospheres"
] |
2023ApJ...955L..22L | Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra | TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique. | [
511,
498,
982,
1580,
1572,
1601,
487,
2133
] | [
"extrasolar rocky planets",
"exoplanets",
"m dwarf stars",
"stellar activity",
"starspots",
"stellar faculae",
"exoplanet atmospheres",
"transmission spectroscopy"
] |
2023ApJ...954...78N | Shadow Geometry of Kerr Naked Singularities | Direct imaging of supermassive black holes (SMBHs) at event horizon-scale resolutions, as recently done by the Event Horizon Telescope, allows for testing alternative models to SMBHs such as Kerr naked singularities (KNSs). We demonstrate that the KNS shadow can be closed, open, or vanishing, depending on the spins and observational inclination angles. We study the critical parameters where the KNS shadow opens a gap, a distinctive phenomenon that does not happen with the black hole shadow. We show that the KNS shadow can only be closed for dimensionless spin a ≲ 1.18 and vanishing for a ≳ 1.18 for certain ranges of inclination angles. We further analyze the effective angular momentum of photon orbits to demonstrate the fundamental connections between light geodesics and the KNS shadow geometry. We also perform numerical general relativistic ray-tracing calculations, which reproduce the analytical topological change in the KNS shadow, and illustrate other observational features within the shadow due to the lack of an event horizon. By comparing the geometric features of the KNS shadow with black hole shadow observations, the topological change in the shadow of KNSs can be used to test the cosmic censorship hypothesis and KNSs as alternative models to SMBHs. | [
886,
1087,
641,
661,
645
] | [
"kerr black holes",
"naked singularities",
"general relativity",
"gravitation",
"geodesics"
] |
2022AJ....164..102M | OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax | We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ( ${M}_{1}={170}_{-50}^{+40}{M}_{J}$ and ${M}_{2}={110}_{-30}^{+20}{M}_{J}$ ), or well below ( ${M}_{1}={22.5}_{-0.4}^{+0.7}{M}_{J}$ and ${M}_{2}={13.3}_{-0.3}^{+0.4}{M}_{J}$ ) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope. | [
2136,
672,
2148,
185,
1930
] | [
"binary lens microlensing",
"gravitational microlensing",
"satellite microlensing parallax",
"brown dwarfs",
"gaussian processes regression"
] |
2023ApJ...957...24C | A Severe Challenge to the Modified Newtonian Dynamics Phenomenology in Our Galaxy | Modified Newtonian dynamics (MOND) is one of the most popular alternative theories of dark matter to explain the missing mass problem in galaxies. Although it remains controversial regarding MOND as a fundamental theory, MOND phenomenology has been shown to widely apply in different galaxies, which poses challenges to the standard Lambda cold dark matter model. In this article, we derive analytically the galactic rotation curve gradient in the MOND framework and present a rigorous analysis to examine the MOND phenomenology in our Galaxy. By assuming a benchmark baryonic disk density profile and two popular families of MOND interpolating functions, we show for the first time that the recent discovery of the declining Galactic rotation curve in the outer region (R ≈ 17-23 kpc) can almost rule out the MOND phenomenology at more than 5σ. This strongly supports some of the previous studies claiming that MOND is neither a fundamental theory nor a universal description of galactic properties. | [
1069,
1059
] | [
"modified newtonian dynamics",
"milky way rotation"
] |
2020ApJ...891...42W | Equilibrium Tidal Response of Jupiter: Detectability by the Juno Spacecraft | An observation of Jupiter's tidal response is anticipated for the ongoing Juno spacecraft mission. We combine self-consistent, numerical models of Jupiter's equilibrium tidal response with observed Doppler shifts from the Juno gravity science experiment to test the sensitivity of the spacecraft to tides raised by the Galilean satellites and the Sun. The concentric Maclaurin spheroid (CMS) method finds the equilibrium shape and gravity field of a rotating, liquid planet with the tide raised by a satellite, expanded in Love numbers (k<SUB>nm</SUB>). We present improvements to the CMS theory that eliminate an unphysical center-of-mass offset and study in detail the convergence behavior of the CMS approach. We demonstrate that the dependence of k<SUB>nm</SUB> with orbital distance is important when considering the combined tidal response for Jupiter. Conversely, the details of the interior structure have a negligible influence on k<SUB>nm</SUB> for models that match the zonal harmonics J<SUB>2</SUB>, J<SUB>4</SUB>, and J<SUB>6</SUB>, already measured to high precision by Juno. As the mission continues, improved coverage of Jupiter's gravity field at different phases of Io's orbit is expected to yield an observed value for the degree-two Love number (k<SUB>22</SUB>) and potentially select higher-degree k<SUB>nm</SUB>. We present a test of the sensitivity of the Juno Doppler signal to the calculated k<SUB>nm</SUB>, which suggests the detectability of k<SUB>33</SUB>, k<SUB>42</SUB>, and k<SUB>31</SUB>, in addition to k<SUB>22</SUB>. A mismatch of a robust Juno observation with the remarkably small range in calculated Io equilibrium, k<SUB>22</SUB> = 0.58976 ± 0.0001, would indicate a heretofore uncharacterized dynamic contribution to the tides. | [
873,
1702,
1191,
872,
1248,
1697
] | [
"jupiter",
"tides",
"solar system gas giant planets",
"jovian satellites",
"planetary interior",
"tidal distortion"
] |
2023ApJ...951L..44T | When the Stars Align: A 5σ Concordance of Planetary Nebulae Major Axes in the Center of Our Galaxy | We report observations of a remarkable major axes alignment nearly parallel to the Galactic plane of 5σ significance for a subset of bulge "planetary nebulae" (PNe) that host, or are inferred to host, short-period binaries. Nearly all are bipolar. It is solely this specific PN population that accounts for the much weaker statistical alignments previously reported for the more general bulge PNe. It is clear evidence of a persistent, organized process acting on a measurable parameter at the heart of our galaxy over perhaps cosmologically significant periods of time for this very particular PN sample. Stable magnetic fields are currently the only plausible mechanism that could affect multiple binary star orbits as revealed by the observed major axes orientations of their eventual PNe. Examples are fed into the current bulge PN population at a rate determined by their formation history and mass range of their binary stellar progenitors. | [
461,
1249,
1250,
154
] | [
"emission nebulae",
"planetary nebulae",
"planetary nebulae nuclei",
"binary stars"
] |
2022PSJ.....3...66G | Blue Marble, Stagnant Lid: Could Dynamic Topography Avert a Waterworld? | Topography on a wet rocky exoplanet could raise land above its sea level. Although land elevation is the product of many complex processes, the large-scale topographic features on any geodynamically active planet are the expression of the convecting mantle beneath the surface. This so-called "dynamic topography" exists regardless of a planet's tectonic regime or volcanism; its amplitude, with a few assumptions, can be estimated via numerical simulations of convection as a function of the mantle Rayleigh number. We develop new scaling relationships for dynamic topography on stagnant lid planets using 2D convection models with temperature-dependent viscosity. These scalings are applied to 1D thermal history models to explore how dynamic topography varies with exoplanetary observables over a wide parameter space. Dynamic topography amplitudes are converted to an ocean basin capacity, the minimum water volume required to flood the entire surface. Basin capacity increases less steeply with planet mass than does the amount of water itself, assuming a water inventory that is a constant planetary mass fraction. We find that dynamically supported topography alone could be sufficient to maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 10<SUP>-4</SUP> times their mass, in the most favorable thermal states. By considering only dynamic topography, which has ~1 km amplitudes on Earth, these results represent a lower limit to the true ocean basin capacity. Our work indicates that deterministic geophysical modeling could inform the variability of land propensity on low-mass planets. | [
491,
2023,
2022,
511,
1151,
695
] | [
"exoplanet evolution",
"exoplanet surface variability",
"exoplanet surface composition",
"extrasolar rocky planets",
"ocean planets",
"habitable planets"
] |
2023ApJ...950...23W | Properties of Forbush Decreases with AMS-02 Daily Proton Flux Data | A Forbush decrease (FD) is a sudden reduction of Galactic Cosmic Rays (GCRs) that is usually caused by intense solar wind transients, such as Interplanetary Coronal Mass Ejections (ICMEs) and Corotating Interaction Regions (CIRs). Using daily proton fluxes measured by AMS-02 between 2011 May and 2019 October, we identified 142 FD events with an automatic systematic analysis method. The properties of 47 FDs caused by ICMEs and of 54 FDs caused by CIRs were analyzed. We found that the rigidity dependence of the GCR flux decrease is generally better described by an exponential function for both ICME and CIR FDs. We also found that the FD Amplitude of ICME FDs has a moderate correlation with the minimum Dst index and a number of solar wind parameters, such as maximum temperature, pressure, and magnetic field. For CIR FD events, neither FD Amplitude nor Maximum Affected Rigidity had a significant correlation with solar wind parameters. | [
546,
567,
310,
314,
1475
] | [
"forbush effect",
"galactic cosmic rays",
"solar coronal mass ejections",
"corotating streams",
"solar activity"
] |
2024ApJ...967L...9Z | What Is the Black Hole Spin in Cyg X-1? | We perform a detailed study of the black hole spin of Cyg X-1, using accurate broadband X-ray data obtained in the soft spectral state by simultaneous NICER and NuSTAR observations, supplemented at high energies by INTEGRAL data. We use the relativistic disk model kerrbb together with different models of the Comptonization high-energy tail and the relativistically broadened reflection features. Unlike most previous studies, we tie the spin parameters of the disk and relativistic broadening models, thus combining the continuum and reflection methods of spin determination. We also consider a likely increase of the disk color correction due to a partial support of the disk by large-scale magnetic fields. We find that such models yield a spin parameter of ${a}_{* }={0.87}_{-0.03}^{+0.04}$ if the disk inclination is allowed to be free, with $i=39{^\circ }_{-1}^{+1}$ . Assuming i = 27.°5, as determined by optical studies of the binary, worsens the fit but leads to similar values of the spin, ${a}_{* }={0.90}_{-0.01}^{+0.01}$ . In addition, we consider the presence of a warm Comptonization layer on top of the disk, motivated by successful modeling of soft X-ray excesses in other sources with such a model. This dramatically lowers the spin, to a <SUB>*</SUB> ≲ 0.1, consistent with the spin measurements from black hole mergers. On the other hand, if the natal spin of Cyg X-1 was low but now a <SUB>*</SUB> ≈ 0.9, a period of effective supercritical accretion had to take place in the past. Such accretion could be facilitated by photon advection, as proposed for ultraluminous X-ray sources. | [
1811,
1822,
14,
98,
1406
] | [
"x-ray binary stars",
"x-ray sources",
"accretion",
"astrophysical black holes",
"rotating black holes"
] |
2020ApJ...893..132H | The Broad-lined Ic Supernova ZTF18aaqjovh (SN 2018bvw): An Optically Discovered Engine-driven Supernova Candidate with Luminous Radio Emission | We present ZTF18aaqjovh (SN 2018bvw), a high-velocity ("broad-lined") stripped-envelope (Type Ic) supernova (Ic-BL SN) discovered in the Zwicky Transient Facility one-day cadence survey. ZTF18aaqjovh shares a number of features in common with engine-driven explosions: the photospheric velocity and the shape of the optical light curve are very similar to those of the Type Ic-BL SN 1998bw, which was associated with a low-luminosity gamma-ray burst (LLGRB) and had relativistic ejecta. However, the radio luminosity of ZTF18aaqjovh is almost two orders of magnitude fainter than that of SN 1998bw at the same velocity phase, and the shock velocity is at most mildly relativistic (V = 0.06-0.4c). A search of high-energy catalogs reveals no compelling gamma-ray burst (GRB) counterpart to ZTF18aaqjovh, and the limit on the prompt GRB luminosity of ${L}_{\gamma ,\mathrm{iso}}\approx 1.6\times {10}^{48}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ excludes a classical GRB but not an LLGRB. Altogether, ZTF18aaqjovh represents another transition event between engine-driven SNe associated with GRBs and "ordinary" Ic-BL SNe. | [
304,
1730,
1668,
775,
2008,
1851,
739,
2109,
1464
] | [
"core-collapse supernovae",
"type ic supernovae",
"supernovae",
"hypernovae",
"radio transient sources",
"transient sources",
"high energy astrophysics",
"time domain astronomy",
"sky surveys"
] |
2021ApJ...911L..12M | The Inner Accretion Flow in the Resurgent Seyfert-1.2 AGN Mrk 817 | Accretion disks and coronae around massive black holes have been studied extensively, and they are known to be coupled. Over a period of 30 yr, however, the X-ray (coronal) flux of Mrk 817 increased by a factor of 40 while its UV (disk) flux remained relatively steady. Recent high-cadence monitoring finds that the X-ray and UV continua in Mrk 817 are also decoupled on timescales of weeks and months. These findings could require mechanical beaming of the innermost accretion flow, and/or an absorber that shields the disk and/or broad line region (BLR) from the X-ray corona. Herein, we report on a 135 ks observation of Mrk 817 obtained with NuSTAR, complemented by simultaneous X-ray coverage via the Neil Gehrels Swift Observatory. The X-ray data strongly prefer a standard relativistic disk reflection model over plausible alternatives. Comparable fits with related models constrain the spin to lie in the range of 0.5 ≤ a ≤ 1, and the viewing angle to lie between 10° ≤ θ ≤ 22° (including 1σ statistical errors and small systematic errors related to differences between the models). The spectra also reveal strong evidence of moderately ionized absorption, similar to but likely less extreme than obscuring events in NGC 5548 and NGC 3783. Archival Swift data suggest that the absorption may be variable. Particularly if the column density of this absorber is higher along the plane of the disk, it may intermittently mask or prevent coupling between the central engine, disk, and BLR in Mrk 817. | [
17
] | [
"active galaxies"
] |
2022AJ....164..235K | Simulating Reflected Light Coronagraphy of Earth-like Exoplanets with a Large IR/O/UV Space Telescope: Impact and Calibration of Smooth Exozodiacal Dust | Observing Earth-like exoplanets orbiting within the habitable zone of Sun-like stars and studying their atmospheres in reflected starlight requires contrasts of ~1e-10 in the visible. At such high contrast, starlight reflected by exozodiacal dust is expected to be a significant source of contamination. Here, we present high-fidelity simulations of coronagraphic observations of a synthetic solar system located at a distance of 10 pc and observed with a 12 m and an 8 m circumscribed aperture diameter space telescope operating at 500 nm wavelength. We explore different techniques to subtract the exozodi and stellar speckles from the simulated images in the face-on, the 30 deg inclined, and the 60 deg inclined case and quantify the remaining systematic noise as a function of the exozodiacal dust level of the system. We find that in the face-on case, the exozodi can be subtracted down to the photon noise limit for exozodi levels up to ~1000 zodi using a simple toy model for the exozodiacal disk, whereas in the 60 deg inclined case this only works up to ~50 zodi. We also investigate the impact of larger wave front errors and larger system distance, finding that while the former has no significant impact, the latter has a strong (negative) impact. Ultimately, we derive a penalty factor as a function of the exozodi level and system inclination that should be considered in exoplanet yield studies as a realistic estimate for the excess systematic noise from the exozodi. | [
489,
486,
387,
500,
313,
2369,
1547
] | [
"exoplanet detection methods",
"exoplanet astronomy",
"direct imaging",
"exozodiacal dust",
"coronagraphic imaging",
"high contrast techniques",
"space telescopes"
] |
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