bibcode
stringlengths 19
19
| title
stringlengths 13
334
| abstract
stringlengths 103
2.97k
⌀ | verified_uat_ids
sequencelengths 1
12
| verified_uat_labels
sequencelengths 1
12
|
|---|---|---|---|---|
2020ApJ...892..144R | A Catalog of M-dwarf Flares with ASAS-SN | We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to search for white-light flares using photometry from the All-Sky Automated Survey for Supernovae. We identified 480 M dwarfs with at least one potential flare employing a simple statistical algorithm that searches for sudden increases in V-band flux. After more detailed evaluation, we identified 62 individual flares on 62 stars. The event amplitudes range from 0.12 lt; Δ V < 2.04 mag. Using classical flare models, we place lower limits on the flare energies and obtain V-band energies spanning 2.0× 10<SUP>30</SUP> ≲ E<SUB>V</SUB> ≲ 6.9× 10<SUP>35</SUP> erg. The fraction of flaring stars increases with spectral type, and most flaring stars show moderate to strong Hα emission. Additionally, we find that 14 of the 62 flaring stars are rotational variables, and they have shorter rotation periods and stronger Hα emission than nonflaring rotational variable M dwarfs. | [
1367,
2050,
1580,
1629
] | [
"red dwarf flare stars",
"low mass stars",
"stellar activity",
"stellar rotation"
] |
2023ApJ...946...10P | Correlating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4 | We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted non-accreting T Tauri star. Using SpeX at NASA's Infrared Telescope Facility (IRTF), 12 spectra were collected over five consecutive nights, spanning ≈1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we constructed empirical composite models of spotted stars by combining a warmer (photosphere) standard star spectrum with a cooler (spot) standard weighted by the spot filling factor, f <SUB>spot</SUB>. The best-fit models spanned two photospheric component temperatures, T <SUB>phot</SUB> = 4100 K (K7V) and 4400 K (K5V), and one spot component temperature, T <SUB>spot</SUB> = 3060 K (M5V) with an A <SUB> V </SUB> of 0.3. We find values of f <SUB>spot</SUB> to vary between 0.77 and 0.94 with an average uncertainty of ~0.04. The variability of f <SUB>spot</SUB> is periodic and correlates with its 3.374 day rotational period. Using a mean value for f <SUP>mean</SUP> <SUB>spot</SUB> to represent the total spot coverage, we calculated spot corrected values for T <SUB>eff</SUB> and L <SUB>⋆</SUB>. Placing these values alongside evolutionary models developed for heavily spotted young stars, we infer mass and age ranges of 0.45-0.6 M <SUB>⊙</SUB> and 0.50-1.25 Myr, respectively. These inferred values represent a twofold increase in the mass and a twofold decrease in the age as compared to standard evolutionary models. Such a result highlights the need for constraining the contributions of cool and warm regions of young stellar atmospheres when estimating T <SUB>eff</SUB> and L <SUB>⋆</SUB> to infer masses and ages as well as the necessity for models to account for the effects of these regions on the early evolution of low-mass stars. | [
1681,
1569,
434,
1572,
1290,
1600
] | [
"t tauri stars",
"star formation",
"early stellar evolution",
"starspots",
"pre-main sequence stars",
"stellar evolutionary tracks"
] |
2020ApJ...901...12B | Time Delay between Outer Heliosheath Crossing and Observation of Interstellar Neutral Atoms | In situ measurements of the heliospheric particle populations by the Voyager spacecraft can only be put in an appropriate context with remote-sensing observations of energetic and interstellar neutral atoms (ENAs and ISN, respectively) at 1 au when the time delay between the production and the observation times is taken into account. ENA times of flight from the production regions in the heliosheath are relatively easy to estimate because these atoms follow almost constant speed, force-free trajectories. For the ISN populations, dynamical and ballistic selection effects are important, and times of flight are much longer. We estimate these times for ISN He and H atoms observed by IBEX and in the future by IMAP using the WTPM model with synthesis method. We show that for the primary population atoms, the times of flight are on the order of three solar cycle periods, with a spread equivalent to one solar cycle. For the secondary populations, the times of flight are on the order of ten solar cycle periods, and during the past ten years of observations, IBEX has been collecting secondary He atoms produced in the outer heliosheath during almost the entire 19th century. ISN atoms penetrating the heliopause at the time of Voyager crossing will become gradually visible about 2027, during the planned IMAP observations. Hypothetical variations in the ISN flow in the Local Interstellar Medium are currently not detectable. Nevertheless, we expect steady-state heliosphere models used with appropriately averaged solar wind parameters to be suitable for understanding the ISN observations. | [
711,
710,
106,
707,
1635
] | [
"heliosphere",
"heliosheath",
"astrosphere interstellar medium interactions",
"heliopause",
"stellar wind bubbles"
] |
2024PSJ.....5..160C | Accretion of Meteoric Organic Matter at the Surface of Mars and Potential Production of Methane by Ultraviolet Radiation | In this study, a comprehensive model of the meteoric organic cycle on Mars for the current geological period is developed, which characterizes the ablation of exogenous organic matter in the upper atmosphere, the accretion of intact carbon at the surface, and the potential production of methane by UV photolysis from the surface reservoir. The model accounts for both the latitudinal and seasonal variation of the meteoroids' input from the most relevant populations in the inner solar system. A recent version of the University of Leeds Chemical Ablation Model, which includes a semiempirical model to describe the pyrolysis kinetics of the meteoric organic matter, is then combined with this meteoroid input function and a semiempirical model that quantifies the UV production of methane. The minimum and maximum accretion rates of organics are between 18 and 90 kg sol<SUP>‑1</SUP> at aphelion and 45–134 kg sol<SUP>‑1</SUP> at the first crossing of the ecliptic plane. The resulting mixing ratios of carbon, in the top 200 μm of the surface layer, range from 0.09–0.43 ppm at 20°N to 4.8–8.9 ppm around the south pole. To be consistent with the methane upper limit of 0.02 ppbv measured by the NOMAD instrument on the ExoMars Trace Gas Orbiter, the UV photolysis yields for methane production need to be around 3% assuming a meteoric carbon content in comets of 25.6 wt% and an atmospheric lifetime of methane of 329 Earth yr. Alternatively, a laboratory estimate of 20% for the methane production yield would require a lifetime of 60 Earth yr. | [
1007,
1040,
1041,
1038,
1037,
280,
70,
933,
1042,
2256,
1845,
1452
] | [
"mars",
"meteoroids",
"meteors",
"meteorites",
"meteorite composition",
"comets",
"asteroid belt",
"long period comets",
"methane",
"complex organic molecules",
"zodiacal cloud",
"short period comets"
] |
2021RNAAS...5..257F | A Recipe for Estimating the Frequency of Asteroid Close Approaches to Earth | null | [
2210,
72,
1092,
255
] | [
"asteroid dynamics",
"asteroids",
"near-earth objects",
"close encounters"
] |
2023AJ....165...43L | Kepler K2 and TESS Observations of Two Magnetic Cataclysmic Variables: The New Asynchronous Polar SDSS J084617.11+245344.1 and Paloma | There have been relatively few published long-duration, uninterrupted light curves of magnetic cataclysmic variable stars in which the accreting white dwarf's rotational frequency is slightly desynchronized from the binary orbital frequency. We report Kepler K2 and TESS observations of two such systems. The first, SDSS J084617.11+245344.1, was observed by the Kepler spacecraft for 80 days during Campaign 16 of the K2 mission, and we identify it as a new asynchronous polar with a likely 4.64 hr orbital period. This is significantly longer than any other asynchronous polar, as well as all but several synchronous polars. Its spin and orbital periods beat against each other to produce a conspicuous 6.77-day beat period, across which the system's accretion geometry gradually changes. The second system in this study, Paloma, was observed by TESS for one sector and was already known to be asynchronous. Until now, there had been an ambiguity in its spin period, but the TESS power spectrum pinpoints a spin period of 2.27 hr. During the resulting 0.7-day spin-orbit beat period, the light curve phased on the spin modulation alternates between being single and double humped. We explore two possible explanations for this behavior: the accretion flow being diverted from one of the poles for part of the beat cycle, or an eclipse of the emitting region responsible for the second hump. | [
407,
32,
203,
1799
] | [
"dq herculis stars",
"am herculis stars",
"cataclysmic variable stars",
"white dwarf stars"
] |
2020AJ....159...24L | Absolute Properties of the Eclipsing γ Dor Star V404 Lyrae | We present the first high-resolution spectra for the eclipsing binary V404 Lyr showing γ Dor pulsations, which we use to study its absolute properties. By fitting models to the disentangling spectrum of the primary star, we found that it has an effective temperature of T <SUB>eff,1</SUB> = 7330 ± 150 K and a rotational velocity of v <SUB>1</SUB> sin i = 148 ± 18 km s<SUP>-1</SUP>. The simultaneous analysis of our double-lined radial velocities and the pulsation-subtracted Kepler data gives us accurate stellar and system parameters of V404 Lyr. The masses, radii, and luminosities are M <SUB>1</SUB> = 2.17 ± 0.06 M <SUB>⊙</SUB>, R <SUB>1</SUB> = 1.91 ± 0.02 R <SUB>⊙</SUB>, and L <SUB>1</SUB> = 9.4 ± 0.8 L <SUB>⊙</SUB> for the primary, and M <SUB>2</SUB> = 1.42 ± 0.04 M <SUB>⊙</SUB>, R <SUB>2</SUB> = 1.79 ± 0.02 R <SUB>⊙</SUB>, and L <SUB>2</SUB> = 2.9 ± 0.2 L <SUB>⊙</SUB> for the secondary. The tertiary component orbiting the eclipsing pair has a mass of M <SUB>3b </SUB> = 0.71 ± 0.15 M <SUB>⊙</SUB> in an orbit of P <SUB>3b </SUB> = 642 ± 3 days, e <SUB>3b </SUB> = 0.21 ± 0.04, and a <SUB>3b </SUB> = 509 ± 2 R <SUB>⊙</SUB>. The third light of l <SUB>3</SUB> = 4.1% ± 0.2% could be partly attributable to the K-type circumbinary object. By applying a multiple frequency analysis to the eclipse-subtracted light residuals, we detected 45 frequencies with signal-to-noise amplitude ratios larger than 4.0. Identified as independent pulsation modes, seven frequencies (f <SUB>1</SUB> - f <SUB>6</SUB>, f <SUB>9</SUB>), their new pulsation constants, and the location in the Hertzsprung-Russell diagram indicate that the pulsating primary is a γ Dor-type variable star. | [
444,
555,
1617,
1558,
1078,
73
] | [
"eclipsing binary stars",
"fundamental parameters of stars",
"stellar oscillations",
"spectroscopy",
"multi-periodic pulsation",
"asteroseismology"
] |
2020RNAAS...4..151M | The Flat Galactic Rotation Curves from First Principles: A Novel Logarithmic Potential Originating in Laplace's Equation | This note reports flat galactic rotation curves coinciding with observation and originating in Laplace's classical field equation. Dark matter, identified with a primordial fluid populating the entire universe, is represented by the homogeneous Klein-Gordon equation (KGE). The key element is the novel solution for the KGE discovered by the leading author in 1994, expressed as a permanent background ${ \mathcal B }$ -potential plus an entangled ${ \mathcal E }$ -potential where time and distance appear as a ratio. The ${ \mathcal B }$ -potential may be viewed as solution to a non-homogeneous Laplace equation, for which the general solution contains in addition to Newton's 1/r potential a new logarithmic Zwicky potential overlooked thus far. The ensuing 1/r-Zwicky force predicts the observed flat galatic rotation curves exhibiting the observed limiting speed at long distance. | [
619,
1110
] | [
"galaxy rotation curves",
"newtonian gravitation"
] |
2020ApJ...897...93B | The Beautiful Mess in Abell 2255 | We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby (z = 0.0806) merging galaxy cluster hosting one of the first radio halos ever detected in the intracluster medium (ICM). The deep LOFAR images at 144 MHz of the central ∼10 Mpc<SUP>2</SUP> region show a plethora of emission on different scales, from tens of kiloparsecs to above megaparsec sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and nonthermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by the turbulence generating the extended radio halo. | [
1346,
858,
504,
584,
1119,
1810,
1682,
508,
1338,
9
] | [
"radio interferometry",
"intracluster medium",
"extended radiation sources",
"galaxy clusters",
"non-thermal radiation sources",
"x-ray astronomy",
"tailed radio galaxies",
"extragalactic radio sources",
"radio astronomy",
"abell clusters"
] |
2024ApJ...969..162D | Chronicling the Reionization History at 6 ≲ z ≲ 7 with Emergent Quasar Damping Wings | The spectra of high-redshift (z ≳ 6) quasars contain valuable information on the progression of the Epoch of Reionization. At redshifts z < 6, the observed Lyman-series forest shows that the intergalactic medium is nearly ionized, while at z > 7 the observed quasar damping wings indicate high neutral gas fractions. However, there remains a gap in neutral gas fraction constraints at 6 ≲ z ≲ 7 where the Lyman-series forest becomes saturated but damping wings have yet to fully emerge. In this work, we use a sample of 18 quasar spectra at redshifts 6.0 < z < 7.1 to close this gap. We apply neural networks to reconstruct the quasars' continuum emission around the partially absorbed Lyα line to normalize their spectra, and stack these continuum-normalized spectra in three redshift bins. To increase the robustness of our results, we compare the stacks to a grid of models from two hydrodynamical simulations, ATON and CROC, and we measure the volume-averaged neutral gas fraction, , while jointly fitting for the mean quasar lifetime, t <SUB>Q</SUB>, for each stacked spectrum. We chronicle the evolution of neutral gas fraction using the ATON (CROC) models as follows: ( ) at <z> = 6.10, ( ) at <z> = 6.46, and ( ) at <z> = 6.87. At the same time, we constrain the average quasar lifetime to be t <SUB>Q</SUB> ≲ 7 Myr across all redshift bins, in good agreement with previous studies. | [
1319,
1663,
1383,
813,
812
] | [
"quasars",
"supermassive black holes",
"reionization",
"intergalactic medium",
"intergalactic gas"
] |
2024ApJ...966L..14D | An Efficient Tidal Dissipation Mechanism via Stellar Magnetic Fields | Recent work suggests that inwardly propagating internal gravity waves (IGWs) within a star can be fully converted to outward magnetic waves if they encounter a sufficiently strong magnetic field. The resulting magnetic waves dissipate as they propagate outward to regions with lower Alfvén velocity. While tidal forcing is known to excite IGWs, this conversion and subsequent damping of magnetic waves have not been explored as a tidal dissipation mechanism. In particular, stars with sufficiently strong magnetic fields could fully dissipate tidally excited waves, yielding the same tidal evolution as the previously studied "traveling wave regime." Here, we evaluate the viability of this mechanism using stellar models of stars with convective cores (F-type stars in the mass range of 1.2–1.6 M <SUB>⊙</SUB>), which were previously thought to be weakly tidally dissipative (due to the absence of nonlinear gravity-wave breaking). The criterion for wave conversion to operate is evaluated for each stellar mass using the properties of each star's interior along with estimates of the magnetic field produced by a convective core dynamo under the assumption of equipartition between kinetic (convective) and magnetic energies. Our main result is that this previously unexplored source of efficient tidal dissipation can operate in stars within this mass range for significant fractions of their lifetimes. This tidal dissipation mechanism appears to be consistent with the observed inspiral of WASP-12b and more generally could play an important role in the orbital evolution of hot Jupiters—and to lower-mass ultra-short-period planets—orbiting F-type stars. | [
1702,
819,
519,
994,
1178,
1698,
2205
] | [
"tides",
"internal waves",
"f stars",
"magnetic fields",
"orbital evolution",
"tidal friction",
"exoplanet migration"
] |
2021AJ....161..292S | BVR<SUB>c</SUB>I<SUB>c</SUB> Observations, Third-body Orbital Study, and Analysis of the UV Leo-type, Pre-W UMA Binary V642 Virginis | V642 Vir is a polar spotted, well-detached, UV Leo-type, low-mass, pre-WUMa (T1 ∼ 4250K, ∼K6V) eclipsing binary. It was observed in 2020 April, May, and June at the Dark Sky Observatory in North Carolina, USA with the 0.81 m reflector of Appalachian State University. A total of 88 timings were used in our 22-year period study which included 12 Transiting Exoplanet Survey Satellite (TESS) timings. The O - C plots show a low-amplitude oscillation of residuals that points to the existence of an orbiting third body, a dwarf of minimum mass, 0.15 M<SUB>⊙</SUB> in an eccentric orbit (e = 0.41), with an orbital period of 20.07 yr. The odd light curves of V642 Virginis indicate that it has polar spots similar to UV Leo and the recently published V1023 Per. Its present large polar spot region indicates that it must have a strong magnetic field and that it is synchronously rotating. The BVR<SUB>c</SUB>I<SUB>c</SUB> simultaneous Wilson-Devinney Program solution gives a detached binary (primary and secondary components are underfilling their respective Roche Lobes, with 76% and 78% fill outs respectively). The cool spot region models near the pole of the primary component (centered at 10° colatitude) and is angled toward the secondary component. Its large radius (68°) and T-fact (T<SUB>spot</SUB>/T<SUB>surface</SUB> = 0.69) also attest to the conclusion of the strength of the magnetic field. The small ΔT in the components (∼318 K) and mass ratio near unity (0.9542 ± 0.0005) show that the stars are similar in spectral type (secondary ∼K9V). The inclination is high, ∼86.87 ± 0.04°, yet there is no time of constant light due to the two stars' essentially equal radii. | [
444,
375,
1416
] | [
"eclipsing binary stars",
"detached binary stars",
"rs canum venaticorum variable stars"
] |
2023ApJ...954...79M | Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT | The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the >300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with "Prompt" and "Delayed" (SGRE) gamma-ray components. We found that "Delayed"-component-associated CMEs have higher initial accelerations and space speeds than "Prompt Only"-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6-0.8 au and their speeds were high enough (≈975 km s<SUP>-1</SUP> and ≈750 km s<SUP>-1</SUP>, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons. | [
1497,
310,
1491
] | [
"solar gamma-ray emission",
"solar coronal mass ejections",
"solar energetic particles"
] |
2024ApJ...966...10E | Oxygen Isotopic Variations in the Calcium, Aluminum-rich Inclusion–forming Region Recorded by a Single Refractory Inclusion from the CO3.1 Carbonaceous Chondrite Dar al Gani 083 | Calcium, aluminum-rich inclusions (CAIs) are the oldest solids dated that formed in the solar system. Most CAIs in unmetamorphosed chondritic meteorites (chondrites; petrologic type ≤3.0) have uniform solar-like <SUP>16</SUP>O-rich compositions (Δ<SUP>17</SUP>O ∼ ‑24‰) and a high initial <SUP>26</SUP>Al/<SUP>27</SUP>Al ratio [(<SUP>26</SUP>Al/<SUP>27</SUP>Al)<SUB>0</SUB>] of ∼(4–5) × 10<SUP>‑5</SUP>, consistent with their origin in a gas of approximately solar composition during a brief (<0.3 Ma) epoch at the earliest stage of our solar system. The nature of O-isotope heterogeneity in CAIs (Δ<SUP>17</SUP>O range from ∼‑24 up to ∼+5‰) from weakly metamorphosed chondrites (petrologic type >3.0) remains an open issue. This heterogeneity could have recorded fluctuations of O-isotope composition of nebular gas in the CAI-forming region and/or postcrystallization O-isotope exchange of CAI minerals with aqueous fluids on the chondrite parent asteroids. To obtain insights into possible processes resulting in this heterogeneity, we investigated the mineralogy, rare-earth element abundances, and O- and Mg-isotope compositions of a CAI from the CO3.1 chondrite Dar al Gani 083. This concentrically zoned inclusion has a Zn-hercynite core surrounded by layers of (from core to edge) grossite, spinel, melilite, and Al-diopside. The various phases have heterogeneous Δ<SUP>17</SUP>O (from core to edge): ‑2.2 ± 0.6‰, ‑0.9 ± 2.1‰, ‑13.7 ± 2.1‰, ‑2.6 ± 2.3‰, and ‑22.6 ± 2.1‰, respectively. Magnesium-isotope compositions of grossite, spinel, melilite, and Al-diopside define an undisturbed internal Al–Mg isochron with (<SUP>26</SUP>Al/<SUP>27</SUP>Al)<SUB>0</SUB> of (2.60 ± 0.29) × 10<SUP>‑6</SUP>. We conclude that the variations in Δ<SUP>17</SUP>O of spinel and diopside recorded fluctuations in O-isotope composition of nebular gas in the CAI-forming region prior to injection and/or homogenization of <SUP>26</SUP>Al at the canonical level. The <SUP>16</SUP>O depletion of grossite and melilite resulted from O-isotope exchange with asteroidal fluid, which did not disturb Al–Mg isotope systematics of the CAI primary minerals. | [
1037,
2204,
1038,
228,
200,
1301,
1300
] | [
"meteorite composition",
"planetary-disk interactions",
"meteorites",
"chondrites",
"carbonaceous chondrites",
"protoplanetary nebulae",
"protoplanetary disks"
] |
2024ApJ...968L...4G | Peas-in-a-pod across the Radius Valley: Rocky Systems Are Less Uniform in Mass but More Uniform in Size and Spacing | The ubiquity of "peas-in-a-pod" architectural patterns and the existence of the radius valley each presents a striking population-level trend for planets with R <SUB> p </SUB> ≤ 4 R <SUB>⊕</SUB> that serves to place powerful constraints on the formation and evolution of these subgiant worlds. As it has yet to be determined whether the strength of this peas-in-a-pod uniformity differs on either side of the radius valley, we separately assess the architectures of systems containing only small (R <SUB> p </SUB> ≤ 1.6 R <SUB>⊕</SUB>), rocky planets from those harboring only intermediate-sized (1.6 R <SUB>⊕</SUB> < R <SUB> p </SUB> ≤ 4 R <SUB>⊕</SUB>), volatile-rich worlds to perform a novel statistical comparison of intra-system planetary uniformity across compositionally distinct regimes. We find that, compared to their volatile-rich counterparts, rocky systems are less uniform in mass (2.6σ) but more uniform in size (4.0σ) and spacing (3.0σ). We provide further statistical validation for these results, demonstrating that they are not substantially influenced by the presence of mean-motion resonances, low-mass host stars, alternative bulk compositional assumptions, sample size effects, or detection biases. We also obtain tentative evidence (>2σ significance) that the enhanced size uniformity of rocky systems is dominated by the presence of super-Earths (1 R <SUB>⊕</SUB> ≤ R <SUB> p </SUB> ≤ 1.6 R <SUB>⊕</SUB>), while their enhanced mass diversity is driven by the presence of sub-Earth (R <SUB> p </SUB> < 1 R <SUB>⊕</SUB>) worlds. | [
486,
491,
492,
495,
498,
484,
1655,
1063,
2292
] | [
"exoplanet astronomy",
"exoplanet evolution",
"exoplanet formation",
"exoplanet structure",
"exoplanets",
"exoplanet systems",
"super earths",
"mini neptunes",
"planetary system evolution"
] |
2024ApJ...962...72O | A Survey of Lyα Emission around Damped Lyα Absorbers at z ≈ 2 with the Keck Cosmic Web Imager | We present Keck Cosmic Web Imager Lyα integral field spectroscopy of the fields surrounding 14 damped Lyα absorbers (DLAs) at z ≈ 2. Of these 14 DLAs, nine have high metallicities ([M/H] > ‑ 0.3), and four of those nine feature a CO-emitting galaxy at an impact parameter ≲30 kpc. Our search reaches median Lyα line flux sensitivities of ∼2 × 10<SUP>‑17</SUP> erg s<SUP>‑1</SUP> cm<SUP>‑2</SUP> over apertures of ∼6 kpc and out to impact parameters of ∼50 kpc. We recover the Lyα flux of three known Lyα-emitting H I-selected galaxies in our sample. In addition, we find two Lyα emitters at impact parameters of ≈50–70 kpc from the high-metallicity DLA at z ≈ 1.96 toward QSO B0551-366. This field also contains a massive CO-emitting galaxy at an impact parameter of ≈15 kpc. Apart from the field with QSO B0551-366, we do not detect significant Lyα emission in any of the remaining eight high-metallicity DLA fields. Considering the depth of our observations and our ability to recover previously known Lyα emitters, we conclude that H I-selected galaxies associated with high-metallicity DLAs at z ≈ 2 are dusty and therefore might feature low Lyα escape fractions. Our results indicate that complementary approaches—using Lyα, CO, Hα, and [C II] 158 μm emission—are necessary to identify the wide range of galaxy types associated with z ≈ 2 DLAs. | [
594,
595,
573,
1319,
1879,
809,
1099,
812,
813,
1316
] | [
"galaxy evolution",
"galaxy formation",
"galaxies",
"quasars",
"circumgalactic medium",
"intergalactic clouds",
"neutral hydrogen clouds",
"intergalactic gas",
"intergalactic medium",
"quasar-galaxy pairs"
] |
2022ApJ...939...47C | A Semianalytical Line Transfer Model. III. Galactic Inflows | We present calculations of ultraviolet spectra resulting from the scattering of photons by gas infalling onto an isotropically emitting source of radiation. The model is based on an adaptation of the semianalytical line transfer (SALT) code of Scarlata & Panagia, and designed to interpret the inverse P Cygni profiles observed in the spectra of partially ionized galactic inflows. In addition to presenting the model, we explore the parameter space of the inflowing SALT model and recreate various physically motivated scenarios including spherical inflows, inflows with covering fractions less than unity, and galactic fountains (i.e., galactic systems with both an inflowing and outflowing component). The resulting spectra from inflowing gas show spectral features that could be misinterpreted as interstellar medium features in low resolution spectroscopy (σ ≈ 120 km s<SUP>-1</SUP>), suggesting that the total number of galactic systems with inflows is undercounted. Our models suggest that observations at medium resolution (R = 6000 or σ ≈ 50 km s<SUP>-1</SUP>) that can be obtained with 8 m class telescopes will be able to resolve the characteristic inverse P Cygni profiles necessary to identify inflows. | [
1335,
599,
1736,
1879,
2171,
596,
602,
594
] | [
"radiative transfer",
"galaxy infall",
"ultraviolet astronomy",
"circumgalactic medium",
"galaxy spectroscopy",
"galaxy fountains",
"galaxy kinematics",
"galaxy evolution"
] |
2023ApJ...952...95D | Reinterpreting the Polluted White Dwarf SDSS J122859.93+104032.9 in Light of Thermohaline Mixing Models: More Polluting Material from a Larger Orbiting Solid Body | The polluted white dwarf (WD) system SDSS J122859.93+104032.9 (SDSS J1228) shows variable emission features interpreted as originating from a solid core fragment held together against tidal forces by its own internal strength, orbiting within its surrounding debris disk. Estimating the size of this orbiting solid body requires modeling the accretion rate of the polluting material that is observed mixing into the WD surface. That material is supplied via sublimation from the surface of the orbiting solid body. The sublimation rate can be estimated as a simple function of the surface area of the solid body and the incident flux from the nearby hot WD. On the other hand, estimating the accretion rate requires detailed modeling of the surface structure and mixing in the accreting WD. In this work, we present MESA WD models for SDSS J1228 that account for the thermohaline instability and mixing in addition to heavy element sedimentation to constrain accurately the sublimation and accretion rate necessary to supply the observed pollution. We derive a total accretion rate of ${\dot{M}}_{\mathrm{acc}}=1.8\times {10}^{11}\,{\rm{g}}\,{{\rm{s}}}^{-1}$ , several orders of magnitude higher than the ${\dot{M}}_{\mathrm{acc}}=5.6\times {10}^{8}\,{\rm{g}}\,{{\rm{s}}}^{-1}$ estimate obtained in earlier efforts. The larger mass accretion rate implies that the minimum estimated radius of the orbiting solid body is ${r}_{\min }$ = 72 km, which, although significantly larger than prior estimates, still lies within the upper bounds (a few hundred kilometers) for which the internal strength could no longer withstand the tidal forces from the gravity of the WD. | [
1799,
1579,
1593,
2292
] | [
"white dwarf stars",
"stellar accretion disks",
"stellar diffusion",
"planetary system evolution"
] |
2024AJ....168...90S | A Survey of Galaxy Pairs in the SDSS Photometric Images based on Faster-RCNN | Galaxy pairs hold significant importance in understanding the evolution of galaxies, and the extensive search for a large sample of galaxy pairs is meaningful. In this article, we develop a deep learning-based approach for the search of galaxy pairs and conduct a comprehensive search on Sloan Digital Sky Survey (SDSS) images. In nine million photometric images, 17,965 physical galaxy pairs with spectral or photometric redshifts are detected. Four sets of results are provided, including physical pairs determined by two spectral redshifts, two photometric redshifts, one spectral redshift, and one photometric redshift, and visual irregular pairs that have no precise redshift information but can be inferred as physical galaxy pairs based on the morphological changes. Then their morphological and physical characteristics are explored, the redshifts of most targets are around 0.1, and as the redshift difference between two galaxies increases, the number of galaxy pairs gradually reduces. The distributions of star formation rate (SFR) are not the same for different morphologies of galaxy pairs, irregular pairs have higher SFR than the other three types, and statistics indicate that the SFR of galaxies depends on both nearby galaxies and internal properties. Color and stellar mass are also key properties of galaxies which can reflect the status of galaxy pairs. Compared to other surveys, a greater number of galaxy pair targets are detected, and this is also the first extensive detection of galaxy pairs in SDSS images using photometric redshifts. These galaxy pair samples can greatly aid in the study of galaxy evolution. | [
610,
1911,
1861,
1883
] | [
"galaxy pairs",
"detection",
"astronomy data reduction",
"algorithms"
] |
2020ApJ...905...13O | Magnetogenesis by Wave-driven Momentum Exchange | When multiple species interact with an electrostatic ion acoustic wave, they can exchange momentum, despite the lack of momentum in the field itself. The resulting force on the electrons can have a curl, and thus give rise to compensating electric fields with curl on magnetohydrodynamic timescales. As a result, a magnetic field can be generated. Surprisingly, in some astrophysical settings, this mechanism can seed magnetic fields with growth rates even larger than through the traditional Biermann battery. | [
102,
321,
604,
1294,
2089,
1261,
845
] | [
"astrophysical magnetism",
"cosmic magnetic fields theory",
"galaxy magnetic fields",
"primordial magnetic fields",
"plasma physics",
"plasma astrophysics",
"interstellar magnetic fields"
] |
2023RNAAS...7..159M | The Behavior of Bp He-weak Stars in the far-UV-Paper XI: HD 35456 | The analysis of four spectra of the B7 He-weak star HD 35456 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal any variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over slightly more than one rotational period. There is no sign of variability in the numerous Si II, Si III and Si IV lines present in the far-ultraviolet. The profile of the resonance line of C II at 1335 Å remains constant too. | [
226,
717
] | [
"chemically peculiar stars",
"helium-weak stars"
] |
2021ApJ...907..123I | Spin Parity of Spiral Galaxies. III. Dipole Analysis of the Distribution of SDSS Spirals with 3D Random Walk Simulations | Observation has not yet determined whether the distribution of spin vectors of galaxies is truly random. It is unclear whether is there any large-scale symmetry-breaking in the distribution of the vorticity field in the universe. Here, we present a formulation to evaluate the dipole component D<SUB>max</SUB> of the observed spin distribution, whose statistical significance σ<SUB>D</SUB> can be calibrated by the expected amplitude for 3D random walk (random flight) simulations. We apply this formulation to evaluate the dipole component in the distribution of Sloan Digital Sky Survey (SDSS) spirals. Shamir published a catalog of spiral galaxies from the SDSS DR8, classifying them with his pattern recognition tool into clockwise and counterclockwise (Z-spiral and S-spiral, respectively). He found significant photometric asymmetry in their distribution. We have confirmed that this sample provides dipole asymmetry up to a level of σ<SUB>D</SUB> = 4.00. However, we also found that the catalog contains a significant number of multiple entries of the same galaxies. After removing the duplicated entries, the number of samples shrunk considerably to 45%. The actual dipole asymmetry observed for the "cleaned" catalog is quite modest, σ<SUB>D</SUB> = 0.29. We conclude that SDSS data alone do not support the presence of a large-scale symmetry-breaking in the spin vector distribution of galaxies in the local universe. The data are compatible with a random distribution. | [
316,
1560,
595,
205,
618
] | [
"cosmic anisotropy",
"spiral galaxies",
"galaxy formation",
"catalogs",
"galaxy rotation"
] |
2024AJ....168....9B | A Close Binary Lens Revealed by the Microlensing Event Gaia20bof | During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them. | [
2136
] | [
"binary lens microlensing"
] |
2023ApJ...946...97F | The Role of Electrons and Helium Atoms in Global Modeling of the Heliosphere | We present a new three-dimensional, MHD-plasma/kinetic-neutrals model of the solar wind (SW) interaction with the local interstellar medium (LISM), which self-consistently includes neutral hydrogen and helium atoms. This new model also treats electrons as a separate fluid and includes the effect of Coulomb collisions. While the properties of electrons in the distant SW and in the LISM are mostly unknown due to the lack of in situ observations, a common assumption for any global, single-ion model is to assume that electrons have the temperature of the ion mixture, which includes pickup ions. In the new model, electrons in the SW are colder, which results in a better agreement with New Horizons observations in the supersonic SW. In the LISM, however, ions and electrons are almost in thermal equilibrium. As for the plasma mixture, the major differences between the models are in the inner heliosheath, where the new model predicts a charge-exchange-driven cooling and a decrease of the heliosheath thickness. The filtration of interstellar neutral atoms at the heliospheric interface is discussed. The new model predicts an increase in the H density by ~2% at 1 au. However, the fraction of pristine H atoms decreases by ~12%, while the density of atoms born in the outer and inner heliosheath increases by 5% and ~35%, respectively. While at 1 au the density of He atoms remains unchanged, the contribution from the "warm breeze" increases by ~3%. | [
711,
1534,
847,
106,
851,
2056,
710,
833
] | [
"heliosphere",
"solar wind",
"interstellar medium",
"astrosphere interstellar medium interactions",
"interstellar plasma",
"charge exchange ionization",
"heliosheath",
"interstellar atomic gas"
] |
2023ApJ...958...29C | Varstrometry for Off-nucleus and Dual Sub-kiloparsec Active Galactic Nuclei (VODKA): Very Long Baseline Array Searches for Dual or Off-nucleus Quasars and Small-scale Jets | Dual and off-nucleus active supermassive black holes are expected to be common in the hierarchical structure formation paradigm, but their identification at parsec scales remains a challenge due to strict angular resolution requirements. We conducted a systematic study using the Very Long Baseline Array (VLBA) to examine 23 radio-bright candidate dual and off-nucleus quasars. The targets are selected by a novel astrometric technique (varstrometry) from Gaia, aiming to identify dual or off-nucleus quasars at (sub)kiloparsec scales. Among these quasars, eight exhibit either multiple radio components or significant (>3σ) positional offsets between the VLBA and Gaia positions. The radio emission from the three candidates, which exhibit multiple radio components, is likely to originate from small-scale jets based on their morphology. Among the remaining five candidates with significant VLBA-Gaia offsets, three are identified as potential dual quasars at parsec scales, one is likely attributed to small-scale jets, and the origin of the last candidate remains unclear. We explore alternative explanations for the observed VLBA-Gaia offsets. We find no evidence for optical jets at kiloparsec scales, nor any contamination to Gaia astrometric noise from the host galaxy; misaligned coordinate systems are unlikely to account for our offsets. Our study highlights the promise of the varstrometry technique in discovering candidate dual or off-nucleus quasars and emphasizes the need for further confirmation and investigation to validate and understand these intriguing candidates. | [
1319,
1349,
406,
2360,
1768,
80,
1684,
16,
1347
] | [
"quasars",
"radio loud quasars",
"double quasars",
"gaia",
"very long baseline interferometers",
"astrometry",
"astronomical techniques",
"active galactic nuclei",
"radio jets"
] |
2023ApJ...943..161V | The Distance to High-velocity Cloud Complex M | λ-21 cm HI4PI survey data are used to study the anomalous-velocity hydrogen gas associated with high-velocity cloud Complex M. These high-sensitivity, high-resolution, high-dynamic-range data show that many of the individual features, including MI, MIIa, and MIIb, are components of a long, arched filament that extends from about (l, b) = (105°, 53°) to (l, b) = (196°, 55°). Maps at different velocities, results from Gaussian analysis, and observations of associated high-energy emission make a compelling case that the MI cloud and the arched filament are physically interacting. If this is the case, we can use the distance to MI, 150 pc as reported by Schmelz & Verschuur, to set the distance to Complex M. The estimated mass of Complex M is then about 120 M <SUB>⊙,</SUB> and the energy implied using the observed line-of-sight velocity, -85 km s<SUP>-1</SUP>, is 8.4 × 10<SUP>48</SUP> erg. Integrating over 4π sr, the total energy for a spherically symmetrical explosion is estimated to be 1.9 × 10<SUP>50</SUP> erg, well within the energy budget of a typical supernova. | [
834,
735
] | [
"interstellar clouds",
"high-velocity clouds"
] |
2021ApJ...908...25B | The Host Galaxy of the Dwarf Seyfert UGC 06728 | We present multi-color high-resolution imaging of the host galaxy of the dwarf Seyfert UGC 06728. As the lowest-mass black hole to be described with both a direct mass constraint and a spin constraint, UGC 06728 is an important source for comparison with black hole evolutionary models, yet little is known about the host galaxy. Using Hubble Space Telescope imaging in the optical and near-infrared, we find that UGC 06728 is a barred lenticular (SB0) galaxy with prominent ansae at the ends of the bar. We cleanly separated the active galactic nucleus (AGN) from the resolved galaxy with two-dimensional image decompositions, thus allowing accurate surface brightness profiles to be derived in all filters from the outer edge of the galaxy all the way into the nucleus. Based on a sample of 51 globular cluster candidates identified in the images, the globular cluster luminosity function predicts a distance to UCG 06728 of 32.5 ± 3.5 Mpc. Combining the galaxy photometry with the distance estimate, we derive a starlight-corrected AGN luminosity, the absolute magnitude of the galaxy, and a constraint on the galaxy stellar mass of $\mathrm{log}{M}_{\star }/{M}_{\odot }=9.9\pm 0.2$ . | [
1447,
915,
2017,
1663,
611,
590
] | [
"seyfert galaxies",
"lenticular galaxies",
"agn host galaxies",
"supermassive black holes",
"galaxy photometry",
"galaxy distances"
] |
2022ApJ...941L..15H | Satellite Constellation Avoidance with the Rubin Observatory Legacy Survey of Space and Time | We investigate a novel satellite avoidance strategy to mitigate the impact of large commercial satellite constellations in low-Earth orbit on the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). We simulate the orbits of currently planned Starlink and OneWeb constellations (~40,000 satellites) to test how effectively an upgraded Rubin scheduler algorithm can avoid them, and assess how the overall survey is affected. Given a reasonably accurate satellite orbit forecast, we find it is possible to adjust the scheduler algorithm to effectively avoid some satellites. Overall, sacrificing 10% of LSST observing time to avoid satellites reduces the fraction of LSST visits with streaks by a factor of 2. Whether such a mitigation will be required depends on the overall impact of streaks on science, which is not yet well quantified. This is due to a lack of adequate information about satellite brightness distributions as well as the impact of glints and low surface brightness residuals on alert purity and systematic errors in cosmological parameter estimation. A significant increase in the number of satellites or their brightness during Rubin Operations may make implementing this satellite avoidance strategy worthwhile. | [
2318,
1464,
68,
686
] | [
"light pollution",
"sky surveys",
"artificial satellites",
"ground-based astronomy"
] |
2024AJ....167..198S | On an Application of the Hill Approach to the General Case of the Three-body Problem | In this work, we use the energy and angular momentum integrals as a resource for applying Hill's approach to the general three-body problem. As a result, we obtain theorems on the Lagrange stability and Hill stability in the general three-body problem. Also, specific features of the general and restricted three-body problems are discussed. | [
1082,
1695
] | [
"n-body problem",
"three-body problem"
] |
2021PSJ.....2..123S | Detection of OH 18 cm Emission from Comet C/2020 F3 NEOWISE Using the Arecibo Telescope | We report the detection of emission from the OH 18 cm Λ-doublet transitions toward Comet C/2020 F3 NEOWISE using the Arecibo Telescope. The antenna temperatures are 113 ± 3 mK for the 1667 MHz line and 57 ± 3 mK for the 1665 MHz line. The beam-averaged OH column density (centered on the comet nucleus) derived from the 1667 transition is N<SUB>OH</SUB> = (1.11 ± 0.06) × 10<SUP>13</SUP> cm<SUP>-2</SUP>. We implemented the Haser model to derive an OH production rate. The estimated OH production rate using the 1667 transition is Q<SUB>OH</SUB> = (3.6 ± 0.6) × 10<SUP>28</SUP> s<SUP>-1</SUP>, a factor of 2.4 lower than optically derived values for the same observing day, the difference of which is likely explained by quenching. | [
2162,
280,
772,
2095,
1359
] | [
"comet volatiles",
"comets",
"hydroxyl sources",
"molecular spectroscopy",
"radio spectroscopy"
] |
2020ApJ...895...35W | Constraints on the Circumnuclear Disk through Free-Free Absorption in the Nucleus of 3C 84 with KaVA and KVN at 43 and 86 GHz | The nearby bright radio galaxy 3C 84 at the center of the Perseus cluster is an ideal target to explore the jet in an active galactic nucleus and its parsec-scale environment. The recent research of Fujita & Nagai revealed the existence of the northern counter-jet component (N1) located 2 mas north from the central core in very long baseline interferometer (VLBI) images at 15 and 43 GHz and they are explained by the free-free absorption (FFA) due to an ionized plasma foreground. Here we report a new quasi-simultaneous observation of 3C 84 with the Korean VLBI Network (KVN) at 86 GHz and the KVN and VLBI Exploration of Radio Astrometry Array (KaVA) at 43 GHz in 2016 February. We succeeded the first detection of N1 at 86 GHz and the data show that N1 still has an inverted spectrum between 43 and 86 GHz with its spectral index &agr; ( ${S}_{\nu }\propto {\nu }^{\alpha }$ ) of 1.19 ± 0.43, while the approaching lobe component has a steep spectrum with an index of -0.54 ± 0.30. Based on the measured flux asymmetry between the counter and approaching lobes, we constrain the averaged number density of the FFA foreground n<SUB>e</SUB> as $1.8\times {10}^{4}\,{\mathrm{cm}}^{-3}\lesssim {n}_{{\rm{e}}}\lesssim 1.0\times {10}^{6}\,{\mathrm{cm}}^{-3}$ . Those results suggest that the observational properties of the FFA foreground can be explained by the dense ionized gas in the circumnuclear disk and/or assembly of clumpy clouds at the central ∼1 pc region of 3C 84. | [
16,
1214,
1340,
1343,
1348,
1768
] | [
"active galactic nuclei",
"perseus cluster",
"radio continuum emission",
"radio galaxies",
"radio lobes",
"very long baseline interferometers"
] |
2022ApJS..260...15R | Time-domain Deep-learning Filtering of Structured Atmospheric Noise for Ground-based Millimeter Astronomy | The complex physics involved in atmospheric turbulence makes it very difficult for ground-based astronomy to build accurate scintillation models and develop efficient methodologies to remove this highly structured noise from valuable astronomical observations. We argue that a deep-learning approach can bring a significant advance to treat this problem because of deep neural networks' inherent ability to abstract nonlinear patterns over a broad scale range. We propose an architecture composed of long short-term memory cells and an incremental training strategy inspired by transfer and curriculum learning. We develop a scintillation model and employ an empirical method to generate a vast catalog of atmospheric-noise realizations and train the network with representative data. We face two complexity axes: the signal-to-noise ratio (S/N) and the degree of structure in the noise. Hence, we train our recurrent network to recognize simulated astrophysical pointlike sources embedded in three structured-noise levels, with a raw-data S/N ranging from 3 to 0.1. We find that a slow and repetitive increase in complexity is crucial during training to obtain a robust and stable learning rate that can transfer information through different data contexts. We probe our recurrent model with synthetic observational data, designing alongside a calibration methodology for flux measurements. Furthermore, we implement traditional matched filtering (MF) to compare its performance with our neural network, finding that our final trained network can successfully clean structured noise and significantly enhance the S/N compared to raw data and in a more robust way than traditional MF. | [
1061,
117,
383,
764,
1916,
1956,
1933,
1859,
1886
] | [
"millimeter astronomy",
"atmospheric scintillation",
"diffuse radiation",
"humidity",
"time series analysis",
"red noise",
"neural networks",
"astronomy data modeling",
"astrostatistics techniques"
] |
2022ApJ...931...88C | Redshift Estimation and Constraints on Intergalactic and Interstellar Media from Dispersion and Scattering of Fast Radio Bursts | A sample of 14 FRBs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (IGM), galaxy halos, and the disks of host galaxies. The IGM and galaxy halos contribute significantly to dispersion measures (DMs) but evidently not to scattering, which is then dominated by host galaxies. This enables the usage of scattering times for estimating DM contributions from host galaxies and also for a combined scattering-dispersion redshift estimator. Redshift estimation is calibrated using the scattering of Galactic pulsars after taking into account different scattering geometries for Galactic and intergalactic lines of sight. The DM-only estimator has a bias of ~0.1 and rms error of ~0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm<SUP>-3</SUP> for the host galaxy's DM contribution. The combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%-40% smaller rms error. We find that values for the baryonic fraction of the ionized IGM f <SUB>igm</SUB> ≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. Our study suggests that 2 of the 14 candidate galaxy associations (FRB 20190523A and FRB 20190611B) should be reconsidered. | [
1353,
2008,
1339,
813,
854,
847,
139,
851
] | [
"radio pulsars",
"radio transient sources",
"radio bursts",
"intergalactic medium",
"interstellar scattering",
"interstellar medium",
"baryon density",
"interstellar plasma"
] |
2024ApJ...961..189N | Apache Point Observatory (APO)/SMARTS Flare Star Campaign Observations. I. Blue Wing Asymmetries in Chromospheric Lines during Mid-M-Dwarf Flares from Simultaneous Spectroscopic and Photometric Observation Data | We conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid-M-dwarf flare stars YZ CMi, EV Lac, and AD Leo. Spectroscopic observations were obtained using Apache Point Observatory 3.5 m and Small and Moderate Aperture Research Telescope System 1.5 m telescopes during 31 nights. Among the 41 detected flares, seven flares showed clear blue wing asymmetries in the Hα line, with various correspondences in flare properties. The duration of the blue wing asymmetries range from 20 minutes to 2.5 hr, including a flare showing the shift from blue to red wing asymmetry. Blue wing asymmetries can be observed during both white-light and candidate non-white-light flares. All of the seven flares showed blue wing asymmetries also in the Hβ line, but there are large varieties on which other chromospheric lines showed blue wing asymmetries. One among the 7 flares was also observed with soft X-ray spectroscopy, which enabled us to estimate the flare magnetic field and length of the flare loop. The line-of-sight velocities of the blueshifted components range from –73 to –122 km s<SUP>‑1</SUP>. Assuming that the blueshifts were caused by prominence eruptions, the mass of upward-moving plasma was estimated to be 10<SUP>15</SUP>–10<SUP>19</SUP> g, which are roughly on the relation between flare energy and erupting mass expected from solar coronal mass ejections (CMEs). Although further investigations are necessary for understanding the observed various properties, these possible prominence eruptions on M-dwarfs could evolve into CMEs, assuming the similar acceleration mechanism with solar eruptions. | [
1603,
1881,
1166,
1637,
982,
540,
1367,
230
] | [
"stellar flares",
"stellar coronal mass ejections",
"optical flares",
"stellar x-ray flares",
"m dwarf stars",
"flare stars",
"red dwarf flare stars",
"stellar chromospheres"
] |
2020AJ....159..241D | The TESS-Keck Survey. I. A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras | We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231 -- an F8 dwarf star with a V-band magnitude of 8.56 -- was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG telescopes. The orbital period we infer from radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size ( ${0.867}_{-0.025}^{+0.027}\ {R}_{{\rm{J}}} ), sub-Saturn-mass ( $0.244\pm 0.021\ {M}_{{\rm{J}}} ) exoplanet on a 18.71 day circular orbit. The low surface gravity of HD 332231 b and the relatively low stellar flux it receives make it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter-McLaughlin effect, an exciting prospect given the 0.14 au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for TESS Sectors 14-16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days. | [
486,
1332,
1709,
489,
498,
516,
1558,
387
] | [
"exoplanet astronomy",
"radial velocity",
"transit photometry",
"exoplanet detection methods",
"exoplanets",
"f dwarf stars",
"spectroscopy",
"direct imaging"
] |
2021ApJ...919L..25G | A Rotating Azimuthally Distributed Auroral Current System on Saturn Revealed by the Cassini Spacecraft | Stunning aurorae are mainly produced when accelerated electrons travel along magnetic field lines to collide with the atmosphere. The motion of electrons often corresponds to the evolution of a magnetic field-aligned current system. In the terrestrial magnetosphere, the current system is formed at the night-side sector, and thus produces an auroral bulge at night. Due to the different energy sources between Saturn and the Earth, it is expected that their auroral current systems are fundamentally different, although the specific auroral driver at Saturn is poorly understood. Using simultaneous measurements of the aurora, particles, magnetic fields, and energetic neutral atoms, we reveal that a chain of paired currents, each of which includes a downward and an upward current branch, is formed in Saturn's magnetosphere, which generates separated auroral patches. These findings inform similar auroral current structures between the Earth and Saturn, while the difference is that Saturn's unique mass and energy sources lead to a rotational characteristic. | [
997,
1426,
2192
] | [
"planetary magnetospheres",
"saturn",
"aurorae"
] |
2021ApJ...914...84A | Mass-Radius Relationships for Irradiated Ocean Planets | Massive and water-rich planets should be ubiquitous in the universe. Many of these worlds are expected to be subject to important irradiation from their host star, and display supercritical water layers surrounded by extended steam atmospheres. Irradiated ocean planets with such inflated hydrospheres have been recently shown to be good candidates for matching the mass-radius distribution of sub-Neptunes. Here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (EOS) for water, and an atmospheric model that takes into account radiative transfer. We find that the use of inappropriate EOSs can lead to the overestimation of the planetary radius by up to ~10%, depending on the planet size and composition. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- or Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction (WMF) of ~20% ± 10%. We also provide fits for the mass-radius relationships, allowing one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. Our calculations finally suggest that highly irradiated planets lost their H/He content through atmospheric loss processes, and that the leftover material led to either super-Earths or sub-Neptunes, depending on the WMF. | [
498,
770,
1248,
1258,
486,
495,
1965
] | [
"exoplanets",
"hydrosphere",
"planetary interior",
"planetary theory",
"exoplanet astronomy",
"exoplanet structure",
"computational methods"
] |
2022ApJ...941..128P | Central Star Formation in Early-type Galaxy I Zw 81 in the Bootes Void | The origin of star formation in customarily passively evolving early-type massive galaxies is poorly understood. We present a case study of a massive galaxy, I Zw 81, inside the Bootes void. The void galaxy is known to host active galactic nuclei (AGN). Our detailed 2D decomposition of the surface brightness distribution in the Canada France Hawaii Telescope (CFHT) g and r bands revealed multiple structural components such as a nuclear point source, a bar, a ring, and an inner exponential disk followed by an outer low surface brightness disk. I Zw 81 turns out to be a disk-dominated galaxy with lenticular morphology. The modeling of the multiwavelength spectral energy distribution shows that the galaxy is star-forming (SF), and belongs to the blue cloud. We find that the optical (g-r) color of the bar is bluer than the disks, and the far- and near-ultraviolet emission inside the galaxy observed with Imaging Telescope onboard AstroSat is concentrated in the central few kpc region enclosing the bar. The strong bar might be playing a pivotal role in driving the gas inflow and causing SF activity in tandem with the minor merger-like interactions as evident from the deep CFHT data. The low-luminosity AGN is insufficient to quench the central SF. The results are peculiar from the standpoint of a massive barred lenticular galaxy. | [
1736,
915,
1569,
594
] | [
"ultraviolet astronomy",
"lenticular galaxies",
"star formation",
"galaxy evolution"
] |
2024PSJ.....5..150H | Using Hydrodynamic Similarity as a Verification Method for Impact Cratering Simulations in the FLAG Hydrocode | Hydrodynamic codes (hydrocodes) are common tools for modeling hypervelocity impacts to provide insight into the physical phenomenon. Hydrocodes can simulate impacts from micrometer to kilometer spatial scales and reach impact velocities difficult to achieve in experimental settings. However, numerical models are approximations, and demonstrating that a numerical method is capable of providing physical results for these models is essential. In this work, we employ a hydrocode verification technique that leverages hydrodynamic similarity, a mathematical property of the conservation equations of fluid mechanics that form the basis for hydrocode models. Using the FLAG hydrocode, we simulate aluminum (Al) and basalt projectiles and targets at spatial scales spanning 7 orders of magnitude (hundreds of micrometers to kilometers). These materials were chosen because Al-6061 is a common material in spacecraft and satellites and basalt is a useful approximation of rocky astronomical bodies. Our results show that hydrodynamic similarity holds for each material model used and across spatial scales. We show that under certain conditions hydrodynamic similarity can apply in the presence of gravity and that similarity does not hold in the presence of strength models. We conclude that the FLAG hydrocode preserves important mathematical properties of fluid dynamics in hypervelocity impacts of Al-6061 and basalt. | [
2282,
779,
1038,
2113,
767,
1963,
1542
] | [
"craters",
"impact phenomena",
"meteorites",
"planetary surfaces",
"hydrodynamical simulations",
"hydrodynamics",
"space debris"
] |
2023ApJ...950...48L | Secular Spin-Orbit Resonances of Black Hole Binaries in AGN Disks | The spin-orbit misalignment of stellar-mass black hole (sBH) binaries provides important constraints on the formation channels of merging sBHs. Here, we study the role of secular spin-orbit resonance in the evolution of an sBH binary component around a supermassive BH (SMBH) in an AGN disk. We consider the sBH's spin precession due to the J <SUB>2</SUB> moment introduced by a circum-sBH disk within the warping/breaking radius of the disk. We find that the sBH's spin-orbit misalignment (obliquity) can be excited via spin-orbit resonance between the sBH binary's orbital nodal precession and the sBH spin precession driven by a massive circum-sBH disk. Using an α-disk model with Bondi-Hoyle-Lyttleton accretion, the resonances typically occur for sBH binaries with semimajor axis of 1 au and at a distance of ~1000 au around a 10<SUP>7 </SUP> M <SUB>⊙</SUB> SMBH. The spin-orbit resonances can lead to high sBH obliquities and a broad distribution of sBH binary spin-spin misalignments. However, we note that the Bondi-Hoyle-Lyttleton accretion is much higher than that of Eddington accretion, which typically results in spin precession being too low to trigger spin-orbit resonances. Thus, secular spin-orbit resonances can be quite rare for sBHs in AGN disks. | [
160,
421,
677,
1184
] | [
"black hole spin-flip",
"dynamical evolution",
"gravitational wave sources",
"orbits"
] |
2021ApJS..254....7K | 101 Trojans: A Tale of Period Bimodality, Binaries, and Extremely Slow Rotators from K2 Photometry | Various properties of Jovian Trojan asteroids such as composition, rotation periods, and photometric amplitudes, or the rate of binarity in the population, can provide information and constraints on the evolution of the group and of the solar system itself. Here we present new photometric properties of 45 Jovian Trojans from the K2 mission of the Kepler space telescope, and present phase-folded light curves for 44 targets, including (11351) Leucus, one of the targets of the Lucy mission. We extend our sample to 101 asteroids with previous K2 Trojan measurements, then compare their combined amplitude and frequency distributions to other ground-based and space data. We show that there is a dichotomy in the periods of Trojans with a separation at ∼100 hr. We find that 25% of the sample are slow rotators (P ≥ 30 hr), an excess that can be attributed to binary objects. We also show that 32 systems can be classified as potential detached binary systems. Finally, we calculate density and rotation constraints for the asteroids. Both the spin barrier and fits to strengthless ellipsoid models indicate low densities and thus compositions similar to populations of comets and trans-Neptunian objects throughout the sample. This supports the scenario of outer solar system origin for Jovian Trojans. | [
1234,
1715,
874
] | [
"photometry",
"trojan asteroids",
"jupiter trojans"
] |
2022PASP..134i4103G | Peculiar Black Hole Accretion Rates in AGN with Highest Star Formation Rates in the Universe | Pouliasis et al. explored star formation rates, black hole accretion rates, and stellar mass of active galaxies at redshift above 3.5, uncovering a leveling off of the star formation rate at high stellar mass, which they consider to be evidence of AGN feedback. Their data shows that as AGN approach the flattening of the curve in the star formation rate-stellar mass plane, the accretion rates begin to drop. We describe the nature of the AGN feedback responsible for this in terms of powerful FRII jets enhancing star formation rates but eventually also triggering a shift in accretion from near-Eddington rates to advection dominated. These systems are on the cusp of a dramatic transition where the active galaxy goes from strong enhancement to large suppression of star formation in a way that produces the steeper slope for radio AGN at low redshift compared to radio AGN at higher redshift and to jetless AGN. We argue, therefore, that the data of Pouliasis et al. constitute the high redshift objects predicted by Singh et al. that connect to the low redshift behavior of radio AGN shown in Comerford et al. | [
1319,
1349,
1354
] | [
"quasars",
"radio loud quasars",
"radio quiet quasars"
] |
2021PSJ.....2..200A | Collision Chains among the Terrestrial Planets. III. Formation of the Moon | In the canonical model of Moon formation, a Mars-sized protoplanet "Theia" collides with proto-Earth at close to their mutual escape velocity v<SUB>esc</SUB> and a common impact angle ~45°. The "graze-and-merge" collision strands a fraction of Theia's mantle into orbit, while Earth accretes most of Theia and its momentum. Simulations show that this produces a hot, high angular momentum, silicate-dominated protolunar system, in substantial agreement with lunar geology, geochemistry, and dynamics. However, a Moon that derives mostly from Theia's mantle, as angular momentum dictates, is challenged by the fact that O, Ti, Cr, radiogenic W, and other elements are indistinguishable in Earth and lunar rocks. Moreover, the model requires an improbably low initial velocity. Here we develop a scenario for Moon formation that begins with a somewhat faster collision, when proto-Theia impacts proto-Earth at ~ 1.2v<SUB>esc</SUB>, also around ~45°. Instead of merging, the bodies come into violent contact for a half hour and their major components escape, a "hit-and-run" collision. N-body evolutions show that the "runner" often returns ~0.1-1 Myr later for a second giant impact, closer to v<SUB>esc</SUB>; this produces a postimpact disk of ~2-3 lunar masses in smoothed particle hydrodynamics simulations, with angular momentum comparable to canonical scenarios. The disk ends up substantially inclined, in most cases, because the terminal collision is randomly oriented to the first. Moreover, proto-Earth contributions to the protolunar disk are enhanced by the compounded mixing and greater energy of a collision chain. | [
436,
1241,
966
] | [
"earth-moon system",
"planet formation",
"lunar origin"
] |
2023ApJ...950L..11R | A Time-efficient, Data-driven Modeling Approach for Predicting the Geomagnetic Impact of Coronal Mass Ejections | To understand the global-scale physical processes behind coronal mass ejection (CME)-driven geomagnetic storms and predict their intensity as a space weather forecasting measure, we develop an interplanetary CME flux rope-magnetosphere interaction module using 3D magnetohydrodynamics. The simulations adequately describe CME-forced dynamics of the magnetosphere including the imposed magnetotail torsion. These interactions also result in induced currents, which are used to calculate the geomagnetic perturbation. Through a suitable calibration, we estimate a proxy of geoeffectiveness-the Storm Intensity index (STORMI)-that compares well with the Dst/SYM-H index. Simulated impacts of two contrasting CMEs quantified by the STORMI index exhibit a high linear correlation with the corresponding Dst and SYM-H indices. Our approach is relatively simple, has fewer parameters to be fine-tuned, and is time efficient compared to complex fluid-kinetic methods. Furthermore, we demonstrate that flux rope erosion does not significantly affect our results. Thus our method has the potential to significantly extend the time window for predictability-an outstanding challenge in geospace environment forecasting-if early predictions of near-Earth CME flux rope structures based on near-Sun observations are available as inputs. This study paves the way for early warnings based on operational predictions of CME-driven geomagnetic storms. | [
310,
2320,
2037
] | [
"solar coronal mass ejections",
"magnetic storms",
"space weather"
] |
2024PSJ.....5....9H | Effect of Equation of State and Cutoff Density in Smoothed Particle Hydrodynamics Simulations of the Moon-forming Giant Impact | The amount of vapor in the impact-generated protolunar disk carries implications for the dynamics, devolatilization, and moderately volatile element isotope fractionation during lunar formation. The equation of state (EoS) used in simulations of the giant impact is required to calculate the vapor mass fraction (VMF) of the modeled protolunar disk. Recently, a new version of M-ANEOS (Stewart M-ANEOS) was released with an improved treatment of heat capacity and expanded experimental Hugoniot. Here, we compare this new M-ANEOS version with a previous version (N-SPH M-ANEOS) and assess the resulting differences in smoothed particle hydrodynamics (SPH) simulations. We find that Stewart M-ANEOS results in cooler disks with smaller values of VMF and in differences in disk mass that are dependent on the initial impact angle. We also assess the implications of the minimum "cutoff" density (ρ <SUB> c </SUB>), similar to a maximum smoothing length, that is set as a fast-computing alternative to an iteratively calculated smoothing length. We find that the low particle resolution of the disk typically results in >40% of disk particles falling to ρ <SUB> c </SUB>, influencing the dynamical evolution and VMF of the disk. Our results show that the choice of EoS, ρ <SUB> c </SUB>, and particle resolution can cause the VMF and disk mass to vary by tens of percent. Moreover, small values of ρ <SUB> c </SUB> produce disks that are prone to numerical instability and artificial shocks. We recommend that future giant impact SPH studies review smoothing methods and ensure the thermodynamic stability of the disk over simulated time. | [
436,
767,
779,
1692,
101,
2204,
1425
] | [
"earth-moon system",
"hydrodynamical simulations",
"impact phenomena",
"the moon",
"astrophysical fluid dynamics",
"planetary-disk interactions",
"natural satellite formation"
] |
2023PSJ.....4..193B | Masses and Densities of Dwarf Planet Satellites Measured with ALMA | We have used the Atacama Large Millimeter/submillimeter Array to measure precise absolute astrometric positions and detect the astrometric wobble of dwarf planet Orcus and its satellite Vanth over a complete orbit. We also place upper limits to the astrometric wobble induced by Dysnomia on dwarf planet Eris around its orbit. From the Vanth-Orcus barycentric motion, we find a Vanth-Orcus mass ratio of 0.16 ± 0.02-the highest of any known planet or dwarf planet. This large ratio is consistent with the hypothesis that Vanth is a largely intact impactor from a giant collision in the system and that the system has likely evolved to a double synchronous state. We find only an upper limit of the barycenter motion of Eris, which implies a 1σ upper limit to the Dysnomia-Eris mass ratio of 0.0085, close to the modeled transition region between giant impact generated satellites, which are largely intact remnants of the original impactor and those which form out of reaccreted disk material left over postimpact. The low albedo of Dysnomia leads us to marginally favor the intact impactor scenario. We find that Dysnomia has a density of <1.2 g cm<SUP>-3</SUP>, significantly lower than the 2.4 g cm<SUP>-3</SUP> of Eris. | [
419,
1337,
1425
] | [
"dwarf planets",
"radio astrometry",
"natural satellite formation"
] |
2021RNAAS...5..123V | Coaque: An Astronomical Icon in the Middle of the World | This study aims to contribute to the astronomical studies for the creation of the astronomical and archaeological museum in Ecuador. Coaque, a fishermen village in the north coastal of Ecuador, is an iconic place where astronomy and archeology converge and portrays the geodesic and astronomical history of Ecuador. The 16th Century ethnohistorical data is rich on descriptions about abundance of wealth and land fertility within equinoctial zones. This awoke the curiosity of Europeans on the geodesic position. Two centuries later, La Condamine and Bouguer of the French-Hispanic Geodesic Mission, first measured the zero-degrees latitude at Punta Palmar, just south of Coaque. We present the detectability of the Crab Nebula, a high energy TeV source revealing the potential for astroparticles field of study. Also, we clarified the wrong idea of the equilibrium of an egg at zero latitude, a popular misinterpreted physical phenomenon. * AAS 237 HDV on 2021 January, 5th. | [
96,
1868,
645
] | [
"particle astrophysics",
"history of astronomy",
"geodesics"
] |
2022ApJ...927L..34S | Gradual Sequestration of Water at Lunar Polar Conditions due to Temperature Cycles | Migration of water molecules into the porous lunar soil can lead to sequestration of adsorbed water or ice at depth. Here, this process is modeled at several potential landing sites in the south polar region of the Moon. Desorption times are parameterized based on the Brunauer-Emmett-Teller (BET) isotherm model. Water sequestration is significant at depths where subsurface temperatures remain below the cold-trapping threshold, a condition satisfied at one of three sites considered, west of Haworth Crater. Model calculations predict a hydrated layer below a desiccated layer. The thickness of the desiccated layer is on the scale of the thermal skin depth, which for dust is typically centimeters. The underlying layer, decimeters thick, can be hydrated over a timescale of a billion years, reaching abundances on the order of 1 wt%. This sequestration process potentially simultaneously explains excess hydrogen concentrations outside of cold traps and the observed presence of a desiccated layer above a hydrogenous layer. | [
972,
974,
1692,
2117,
2092
] | [
"lunar science",
"lunar surface",
"the moon",
"surface ices",
"ice formation"
] |
2024ApJ...963..155C | Two High-amplitude δ Scuti–γ Doradus Hybrids Constrained by the Radial Fundamental p and Equally Spaced g Modes | Based on 2 minutes cadence TESS data, we investigate pulsations of TIC 65138566 and TIC 139729335 and discover them to be two new high-amplitude δ Scuti stars with equally spaced g modes. We recognize the radial fundamental mode f <SUB>1</SUB> = 18.3334 c d<SUP>‑1</SUP> and the first overtone f <SUB>3</SUB> = 23.6429 c d<SUP>‑1</SUP> for TIC 65138566, and identify the highest peak f <SUB>1</SUB> = 19.0955 c d<SUP>‑1</SUP> as the radial fundamental mode for TIC 139729335. For g modes, both stars display a regular period spacing of 2413 s. Through detailed seismological analysis, we deduce that these period-spacing patterns correspond to modes with ℓ = 1. Moreover, our analysis reveals that with increases in masses and metallicities, the star should display a higher degree of evolution to match a specific period spacing Π<SUB>0</SUB>. Conversely, the star should have a lower extent of evolution to match the radial fundamental mode. These two contradictory behaviors allow us to precisely obtain stellar physical parameters. TIC 65138566 and TIC 139729335 are determined to be two main-sequence stars that have almost the same range of masses and metallicities, with M = 1.36 ± 0.06 M <SUB>⊙</SUB> and Z = 0.005 ± 0.002. The hydrogen abundance in the core of TIC 65138566 is estimated to be about 0.28, while TIC 139729335 has a slightly higher value of around 0.31. Finally, we suggest that the high-amplitude δ Scuti–γ Doradus star TIC 308396022 is a main-sequence star with M = 1.54 ± 0.08 M <SUB>⊙</SUB>, Z = 0.007 ± 0.001, and X <SUB>c</SUB> = 0.18 ± 0.02. | [
73,
370,
2101
] | [
"asteroseismology",
"delta scuti variable stars",
"gamma doradus variable stars"
] |
2021PSJ.....2..157E | A Recipe for the Geophysical Exploration of Enceladus | Orbital geophysical investigations of Enceladus are critical to understanding its energy budget. In this paper, we identified key science questions for the geophysical exploration of Enceladus, answering which would support future assessment of Enceladus' astrobiological potential. Using a Bayesian framework, we explored how science requirements map to measurement requirements. We performed mission simulations to study the sensitivity of single-spacecraft and dual-spacecraft configurations to static gravity and tidal Love numbers of Enceladus. We find that mapping Enceladus' gravity field, improving the accuracy of the physical libration amplitude, and measuring Enceladus' tidal response would provide critical constraints on the internal structure and establish a framework for assessing Enceladus' long-term habitability. This kind of investigation could be carried out as part of a life search mission at little additional resource requirements. | [
1248,
667,
1427,
1543,
76
] | [
"planetary interior",
"gravitational fields",
"saturnian satellites",
"space observatories",
"astrodynamics"
] |
2022RNAAS...6..221G | The Intermediate Polar FO Aquarii Has Not Been the Same Since Recovering from a Series of Low States | FO Aqr is a bright intermediate polar that has long displayed large amplitude photometric variations corresponding to the 20.9 minutes spin period of its white dwarf. Between 2016 and 2020, the system suffered a series of unprecedented low-states, but recent data shows that it has now recovered to its normal optical luminosity. We compare the light curves obtained by K2/Kepler in 2014 with photometry from the TESS mission obtained in 2021. We find that the spin pulse that had been the dominant feature of the light curve in 2014 is now weak over the second half of the binary orbit and that a beat pulse is enhanced in the TESS photometry. Variations at approximately twice the spin frequency are now seen over the second half of the orbit. These photometric properties may be the new normal for FO Aqr now that its white dwarf has begun to spin down. | [
203,
407,
1799,
996
] | [
"cataclysmic variable stars",
"dq herculis stars",
"white dwarf stars",
"magnetic variable stars"
] |
2021ApJ...906...22N | Gravitomagnetic Instabilities of Relativistic Magnetohydrodynamics | We study gravitomagnetic instabilities of a static homogeneous medium with an aligned magnetic field in the two contexts of relativistic magnetohydrodynamics (MHD): first, MHD with post-Newtonian (PN) corrections, and second, special relativistic (SR) MHD with weak gravity. The analysis in the PN MHD is made without taking the temporal gauge condition, thus results are gauge-invariant. The PN corrections of the internal energy, pressure, sound velocity, and the Alfvén velocity lower the critical (Jeans) wavelength. All relativistic effects tend to destabilize the system. Although the SR MHD with weak gravity is presented in the harmonic gauge, in the presence of gravity the stability analysis is strictly valid to Newtonian order. In the absence of gravity, the SR MHD is independent of the gauge condition. We present the plane wave velocities and the stability criteria in both cases. | [
661,
668,
1964,
1393
] | [
"gravitation",
"gravitational instability",
"magnetohydrodynamics",
"relativity"
] |
2024ApJ...969L..20S | Interstellar Neutral Hydrogen in the Heliosphere: New Horizons Observations in the Context of Models | Interstellar neutral (ISN) hydrogen is the most abundant species in the outer heliosheath and the very local interstellar medium (VLISM). Charge-exchange collisions in the outer heliosheath result in filtration, reducing the ISN hydrogen density inside the heliosphere. Additionally, these atoms are intensively ionized close to the Sun, resulting in a substantial reduction of their density within a few astronomical units from the Sun. The products of this ionization—pickup ions (PUIs)—are detected by charged particle detectors. The Solar Wind Around Pluto instrument on New Horizons provides, for the first time, PUI observations from the distant heliosphere. We analyze the observations collected between 22 and 52 au from the Sun to find the ISN hydrogen density profile and compare the results with predictions from global heliosphere models. We conclude that the density profile derived from the observations is inconsistent with steady-state model predictions. This discrepancy is not explained by time variations close to the Sun and thus may be related to the temporal evolution of the outer boundaries or VLISM conditions. Furthermore, we show that the cold and hot models of ISN hydrogen distribution are not a good approximation closer to the termination shock. Therefore, we recommend a new fiduciary point based on the available New Horizons observations at 40 au from the Sun, at ecliptic direction (285.°62, 1.°94), where the ISN hydrogen density is 0.11 cm<SUP>‑3</SUP>. The continued operation of New Horizons should give better insight into the source of the discussed discrepancy. | [
833,
847,
711,
848,
827,
1239,
1535,
2065,
2218
] | [
"interstellar atomic gas",
"interstellar medium",
"heliosphere",
"interstellar medium wind",
"interplanetary physics",
"pickup ions",
"solar wind termination",
"collision physics",
"charge transfer"
] |
2024PSJ.....5...93V | Catalog of Ultraviolet Bright Stars: Strategies for UV Occultation Measurements, Planetary Illumination Modeling, and Sky Map Analyses Using Hybrid IUE-Kurucz Spectra | Ultraviolet spectroscopy is a powerful method to study planetary surface composition through reflectance measurements, atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA's Jupiter Icy Moons Explorer and NASA's Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030s. This work presents a compilation of a detailed UV stellar catalog, named Catalog of Ultraviolet Bright Stars (CUBS), of targets with high intensity in the 50–210 nm wavelength range with applications relevant to planetary spectroscopy. These applications include (1) planning and simulating occultations, including calibration measurements; (2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and (3) studying the origin of diffuse Galactic UV light as mapped by existing data sets from Juno-UVS and others. CUBS includes observations from the International Ultraviolet Explorer (IUE) and additional information from the SIMBAD database. We have constructed model spectra at 0.1 nm resolution for almost 90,000 targets using interpolated Kurucz models (which have a resolution of 1 nm) and, when available, IUE spectra. CUBS also includes robust checks for agreement between the Kurucz models and the IUE data. We also present a tool for which our catalog can be used to identify the best candidates for stellar occultation observations, with applications for any UV instrument. We report on our methods for producing CUBS and discuss plans for its implementation during ongoing and upcoming planetary missions. | [
2284,
205,
2189,
2135
] | [
"ultraviolet spectroscopy",
"catalogs",
"europa",
"stellar occultation"
] |
2022AJ....164...44M | Environmental Effects in Herschel Observations of the Ionized Carbon Content of Star-forming Dwarf Galaxies in the Virgo Cluster | We use archival Herschel data to examine the singly ionized carbon ([C II]) content of 14 star-forming dwarf galaxies in the Virgo cluster. We use spectral energy distribution fits to far-infrared, mid-infrared, near-infrared, optical, and ultraviolet data to derive the total infrared continuum (TIR) for these galaxies. We compare the [C II]/TIR ratio for dwarf galaxies in the central part of Virgo to those in the southern part of the cluster and to galaxies with similar TIR luminosities and metallicities in the Herschel Dwarf Galaxy Survey (DGS) sample of field dwarf galaxies to look for signs of [C II] formation independent of star formation. Our analysis indicates that the sample of Virgo dwarfs in the central part of the cluster has significantly higher values of [C II]/TIR than the sample from the southern part of the cluster and the sample from the DGS, while the southern sample is consistent with the DGS. This [C II]/TIR excess implies that a significant fraction of the [C II] in the dwarf galaxies in the cluster center has an origin other than star formation and is likely to be due to environmental processes in the central part of the cluster. We also find a surprisingly strong correlation between [C II]/TIR and the local ram pressure felt by the dwarf galaxies in the cluster. In this respect, we claim that the excess [C II] we see in these galaxies is likely to be due to formation in ram-pressure shocks. <SUP>*</SUP> Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. | [
1772,
2126,
529,
232,
416
] | [
"virgo cluster",
"ram pressure stripped tails",
"far infrared astronomy",
"cii region",
"dwarf galaxies"
] |
2021ApJ...910..122S | Classification of Magnetohydrodynamic Simulations Using Wavelet Scattering Transforms | The complex interplay of magnetohydrodynamics, gravity, and supersonic turbulence in the interstellar medium (ISM) introduces a non-Gaussian structure that can complicate a comparison between theory and observation. In this paper, we show that the wavelet scattering transform (WST), in combination with linear discriminant analysis (LDA), is sensitive to non-Gaussian structure in 2D ISM dust maps. WST-LDA classifies magnetohydrodynamic (MHD) turbulence simulations with up to a 97% true positive rate in our testbed of 8 simulations with varying sonic and Alfvénic Mach numbers. We present a side-by-side comparison with two other methods for non-Gaussian characterization, the reduced wavelet scattering transform (RWST) and the three-point correlation function (3PCF). We also demonstrate the 3D-WST-LDA, and apply it to the classification of density fields in position-position-velocity (PPV) space, where density correlations can be studied using velocity coherence as a proxy. WST-LDA is robust to common observational artifacts, such as striping and missing data, while also being sensitive enough to extract the net magnetic field direction for sub-Alfvénic turbulent density fields. We include a brief analysis of the effect of point-spread functions and image pixelization on 2D-WST-LDA applied to density fields, which informs the future goal of applying WST-LDA to 2D or 3D all-sky dust maps to extract hydrodynamic parameters of interest. | [
847,
1966,
1116,
1938,
1858
] | [
"interstellar medium",
"magnetohydrodynamical simulations",
"non-gaussianity",
"convolutional neural networks",
"astronomy data analysis"
] |
2020AJ....160..144G | Transient Jupiter Co-orbitals from Solar System Sources | We demonstrate dynamical pathways from main-belt asteroid and Centaur orbits to those in co-orbital motion with Jupiter, including the retrograde (inclination i > 90°) state. We estimate that, at any given time, there should be ∼1 km-scale or larger escaped asteroid in a transient direct (prograde) orbit with semimajor axis near that of Jupiter's (a ≃ a<SUB>J</SUB>), with proportionally more smaller objects as determined by their size distribution. Most of these objects would be in the horseshoe dynamical state, and are hard to detect due to their moderate eccentricities (spending most of their time beyond 5 au) and longitudes relative to Jupiter being spread nearly all over the sky. We also show that ≈1% of the transient asteroid co-orbital population is on retrograde orbits with Jupiter. This population, like the recently identified asteroid (514107) 2015 BZ<SUB>509</SUB>, can spend millions of years with a ≃ a<SUB>J</SUB> including tens or hundreds of thousands of years formally in the retrograde 1:-1 co-orbital resonance. Escaping near-Earth asteroids (NEAs) are thus likely the precursors of the handful of known high-inclination objects with a ≃ a<SUB>J</SUB>. We compare the production of Jovian co-orbitals from escaping NEAs with those from incoming Centaurs. We find that temporary direct co-orbitals are likely dominated by Centaur capture, but we only find production of (temporary) retrograde Jovian co-orbitals (including very long-lived ones) from the NEA source. We postulate that the primordial elimination of the inner solar system's planetesimal population could provide a supply route for a metastable outer solar system reservoir for the high-inclination Centaurs. | [
211,
1181,
780,
1179,
72,
874
] | [
"celestial mechanics",
"orbital resonances",
"inclination",
"orbital motion",
"asteroids",
"jupiter trojans"
] |
2023PSJ.....4...39D | Functionality of Ice Line Latitudinal EBM Tenacity (FILLET). Protocol Version 1.0. A CUISINES Intercomparison Project | Energy balance models (EBMs) are 1D or 2D climate models that can provide insights into planetary atmospheres, particularly with regard to habitability. Because EBMs are far less computationally intensive than 3D general circulation models (GCMs), they can be run over large uncertain parameter spaces and can be used to explore long-period phenomena, like carbon and Milankovitch cycles. Because horizontal dimensions are incorporated in EBMs, they can explore processes that are beyond the reach of 1D radiative-convective models (RCMs). EBMs are, however, dependent on parameterizations and tunings to account for physical processes that are neglected. Thus, EBMs rely on observations and results from GCMs and RCMs. Different EBMs have included a wide range of parameterizations (for albedo, radiation, and heat diffusion) and additional physics, such as carbon cycling and ice sheets. This CUISINES exoplanet model intercomparison project (exoMIP) will compare various EBMs across a set of numerical experiments. The set of experiments will include Earth-like planets at different obliquities, parameter sweeps across obliquity, and variations in instellation and CO<SUB>2</SUB> abundance, to produce hysteresis diagrams. We expect a range of different results due to the choices made in the various codes, highlighting which results are robust across models and which are dependent on parameterizations or other modeling choices. Additionally, the project will allow developers to identify model defects and determine which parameterizations are most useful or relevant to the problem of interest. Ultimately, this exoMIP will allow us to improve the consistency between EBMs and accelerate the process of discovering habitable exoplanets. | [
487,
2118,
2184,
1965,
437
] | [
"exoplanet atmospheres",
"exoplanet surfaces",
"planetary climates",
"computational methods",
"earth atmosphere"
] |
2023ApJ...951...35S | Interstellar Bow Shocks around Fast Stars Passing through the Local Interstellar Medium | Bow shocks are produced in the local interstellar medium by the passage of fast stars from the Galactic thin-disk and thick-disk populations with velocities V <SUB>*</SUB> = 40-80 km s<SUP>-1</SUP>. Stellar transits of local H I clouds occur every 3500-7000 yr on average and last between 10<SUP>4</SUP> and 10<SUP>5</SUP> yr. There could be 10-20 active bow shocks around low-mass stars inside clouds within 15 pc of the Sun. At local cloud distances of 3-10 pc, their turbulent wakes have transverse radial extents R <SUB>wake</SUB> ≈ 100-300 au, angular sizes 10″-100″, and Lyα surface brightnesses of 2-8 R in gas with total hydrogen density n <SUB>H</SUB> ≈ 0.1 cm<SUP>-3</SUP> and V <SUB>*</SUB> = 40-80 km s<SUP>-1</SUP>. These transit wakes may cover an area fraction f <SUB>A</SUB> ≈ (R <SUB>wake</SUB>/R <SUB>cl</SUB>) ≈ 10<SUP>-3</SUP> of local H I clouds and be detectable in IR (dust), UV (Lyα, two-photon), or nonthermal radio emission. Turbulent heating in these wakes could produce the observed elevated rotational populations of H<SUB>2</SUB> (J ≥ 2) and influence the endothermic formation of CH<SUP>+</SUP> in diffuse interstellar gas at T > 10<SUP>3</SUP> K. | [
834,
1586
] | [
"interstellar clouds",
"stellar bow shocks"
] |
2024PSJ.....5..114A | Ejecta Blankets at Small Craters on the Moon | Impact-derived ejecta covers most of the lunar surface, originating from recent impacts through to the beginning of the geologic record. Despite how common ejecta is, accurate measurements of ejecta thickness are difficult to obtain, and existing estimates of ejecta thickness vary widely. This study uses excavation by meter-scale impacts on the fresh ejecta blankets of larger, kilometer-scale impacts to make point measurements of ejecta thickness. We estimate ejecta thickness at the rims of 73 lunar craters (0.1–4.8 km diameter) and create isopach maps of ejecta thickness for three craters. We derive an equation for ejecta thickness, <inline-formula> <tex-math> $t=0.14\pm 0.062{R}^{(0.77\pm 0.080)}{\left(r/R\right)}^{(-B)}$ </tex-math> </inline-formula>, where r is the horizontal distance from the center of the crater, R is the center-to-rim crater radius, and B describes the rate at which ejecta thickness decays with radial distance. Our average value for B (2.8 ± 0.1) is similar to previous work, though we observe that B can vary significantly within an ejecta blanket. | [
1692,
958,
453,
779
] | [
"the moon",
"lunar impacts",
"ejecta",
"impact phenomena"
] |
2021ApJ...914...38Y | How to Identify Exoplanet Surfaces Using Atmospheric Trace Species in Hydrogen-dominated Atmospheres | Sub-Neptunes (R<SUB>p</SUB> ~ 1.25-4 R<SUB>Earth</SUB>) remain the most commonly detected exoplanets to date. However, it remains difficult for observations to tell whether these intermediate-sized exoplanets have surfaces and where their surfaces are located. Here we propose that the abundances of trace species in the visible atmospheres of these sub-Neptunes can be used as proxies for determining the existence of surfaces and approximate surface conditions. As an example, we used a state-of-the-art photochemical model to simulate the atmospheric evolution of K2-18b and investigate its final steady-state composition with surfaces located at different pressures levels (P<SUB>surf</SUB>). We find that the surface location has a significant impact on the atmospheric abundances of trace species, making them deviate significantly from their thermochemical equilibrium and "no-surface" conditions. This result arises primarily because the pressure-temperature conditions at the surface determine whether photochemically produced species can be recycled back to their favored thermochemical equilibrium forms and transported back to the upper atmosphere. For an assumed H<SUB>2</SUB>-rich atmosphere for K2-18b, we identify seven chemical species that are most sensitive to the existence of surfaces: ammonia (NH<SUB>3</SUB>), methane (CH<SUB>4</SUB>), hydrogen cyanide (HCN), acetylene (C<SUB>2</SUB>H<SUB>2</SUB>), ethane (C<SUB>2</SUB>H<SUB>6</SUB>), carbon monoxide (CO), and carbon dioxide (CO<SUB>2</SUB>). The ratio between the observed and the no-surface abundances of these species can help distinguish the existence of a shallow surface (P<SUB>surf</SUB> < 10 bar), an intermediate surface (10 bar < P<SUB>surf</SUB> < 100 bar), and a deep surface (P<SUB>surf</SUB> > 100 bar). This framework can be applied together with future observations to other sub-Neptunes of interest. | [
487,
2021,
2118,
2172,
511
] | [
"exoplanet atmospheres",
"exoplanet atmospheric composition",
"exoplanet surfaces",
"extrasolar gaseous planets",
"extrasolar rocky planets"
] |
2024AJ....168...22A | Detection of Faint Sources by the UltraViolet Imaging Telescope Onboard AstroSat Using Poisson Distribution of Background | We present an improved approach for constructing the UV source catalogs using observations from the UltraViolet Imaging Telescope (UVIT) onboard AstroSat, by considering the Poisson distribution of the UV background. The method is tested extensively using fields that are not crowded, the Small Magellanic Cloud and M31 (Field 13). The results are compared with previous studies that used UVIT observations. This approach is successful in detecting fainter sources and produces a large number of new sources (∼15% –92% more). Most of the newly discovered UV sources fall in the faint end of the source distribution (m ≳ 22). The counterparts at other wavelengths are identified for most sources. This approach is more efficient for source detection and provides an opportunity to explore new classes of UV sources. | [
1736,
212,
1898,
1468,
39
] | [
"ultraviolet astronomy",
"celestial objects catalogs",
"poisson distribution",
"small magellanic cloud",
"andromeda galaxy"
] |
2023ApJ...956...55C | MAXI J0637-430: A Possible Candidate for Bulk Motion Comptonization? | The transient Galactic black hole candidate MAXI J0637-430 went through an outburst in 2019-2020 for the very first time. This outburst was active for almost 6 months from 2019 November to 2020 May. We study the spectral properties of this source during that outburst using archival data from NICER/XTI, Swift/XRT, and NuSTAR/FPM satellites/instruments. We have analyzed the source during six epochs on which simultaneous NICER-NuSTAR and Swift/XRT-NuSTAR data were available. Using both phenomenological and physical model fitting approaches, we analyzed the spectral data in the broad 0.7-70 keV energy band. We first used a combination of disk blackbody with power-law, disk blackbody with broken power-law, and disk blackbody with power-law and bulk motion Comptonization (BMC) models. For a better understanding of the accretion picture, e.g., understanding how the accretion rates change with the changing size of the perceived Compton cloud, we used the two-component advective flow (TCAF) model with the broken power-law, and TCAF with the combined power-law, BMC models. For the last three epochs, the diskbb+power-law and TCAF models were able to spectrally fit the data for acceptable χ <SUP>2</SUP>/degrees of freedom (dof). However, for the first three epochs, we needed an additional component to fit spectra for acceptable χ <SUP>2</SUP>/dof. From our analysis, we reported on the possible presence of another component during these first three epochs when the source was in the high soft state. This additional component in this state is best described by the BMC phenomenon. From the TCAF model fitting, we estimated the average mass of the source as ${8.1}_{-2.7}^{+1.3}\,{M}_{\odot }$ . | [
1811,
162,
1579,
2086,
289
] | [
"x-ray binary stars",
"black holes",
"stellar accretion disks",
"shocks",
"compact radiation sources"
] |
2024AJ....168...17S | The Utility of Infrasound in Global Monitoring of Extraterrestrial Impacts: A Case Study of the 2008 July 23 Tajikistan Bolide | Among the various observational techniques used for the detection of large bolides on a global scale is a low-frequency sound known as infrasound. Infrasound, which is also one of the four sensing modalities used by the International Monitoring System, offers continuous global monitoring and can be leveraged for planetary defense. Infrasonic records can provide an additional dimension for event characterization and a distinct perspective that might not be available through any other observational method. This paper describes the infrasonic detection and characterization of the bolide that disintegrated over Tajikistan on 2008 July 23. This event was detected by two infrasound stations at distances of 1530 and 2130 km. Propagation paths to one of the stations were not predicted by the model, despite being clearly detected. The presence of the signal is attributed to the acoustic energy being trapped in a weak but leaky stratospheric AtmoSOFAR channel. The infrasound signal analysis indicates that the shock originated at the point of the main breakup at an altitude of 35 km. The primary mode of the shock production of the signal detected at the two stations was a spherical blast resulting from the main gross fragmentation episode. The energy estimate, based on the signal period, is 0.17–0.51 kt of TNT equivalent, suggesting a mass of 6.6–23.5 tons. The corresponding object radius, assuming the chondritic origin, was 0.78–1.18 m. | [
172,
538,
1244,
779,
2086,
1246,
72,
1092
] | [
"bolides",
"fireballs",
"planetary atmospheres",
"impact phenomena",
"shocks",
"planetary bow shocks",
"asteroids",
"near-earth objects"
] |
2022PSJ.....3..113C | OSSOS XXV: Large Populations and Scattering-Sticking in the Distant Trans-Neptunian Resonances | There have been 77 TNOs discovered to be librating in the distant trans-Neptunian resonances (beyond the 2:1 resonance, at semimajor axes greater than 47.7 au) in four well-characterized surveys: the Outer Solar System Origins Survey (OSSOS) and three similar prior surveys. Here, we use the OSSOS Survey Simulator to measure their intrinsic orbital distributions using an empirical parameterized model. Because many of the resonances had only one or very few detections, j:k resonant objects were grouped by k in order to have a better basis for comparison between models and reality. We also use the Survey Simulator to constrain their absolute populations, finding that they are much larger than predicted by any published Neptune migration model to date; we also find population ratios that are inconsistent with published models, presenting a challenge for future Kuiper Belt emplacement models. The estimated population ratios between these resonances are largely consistent with scattering-sticking predictions, though further discoveries of resonant TNOs with high-precision orbits will be needed to determine whether scattering-sticking can explain the entire distant resonant population or not. | [
1396
] | [
"resonant kuiper belt objects"
] |
2022RNAAS...6...53M | The Far UV Variability of τ Her (HD 147394) Recorded by IUE | Evidence is presented that the far-ultraviolet flux of τ Her recorded by the International Ultraviolet Explorer is variable in a series of six spectra taken consecutively over 4 hr and 45 minutes The centroids of the resonance lines of O I, C II and Si II are blueshifted in several spectra and resume their original positions over a timescale of 3 hr 5 minutes. The FUV flux also varies over the same timescale. The far-ultraviolet variability is discussed in light of the recent TESS lightcurve observed for τ Her. | [
128
] | [
"b stars"
] |
2020ApJ...895...26B | A Magnetic White Dwarf Accretion Model for the Anomalous X-Ray Pulsar 4U 0142+61 | The quiescent emission of the anomalous X-ray pulsar (AXP) 4U 0142+61 extends over a broad range of energy, from radio up to hard X-rays. In particular, this object is unique among soft gamma-ray repeaters (SGRs) and AXPs in presenting simultaneously mid-infrared emission and pulsed optical emission. In spite of the many propositions to explain this wide range of emission, it still lacks one that reproduces all of the observations. Filling this gap, we present a model to reproduce the quiescent spectral energy distribution of 4U 0142+61 from mid-infrared up to hard X-rays using plausible physical components and parameters. We propose that the persistent emission comes from a magnetic accreting white dwarf (WD) surrounded by a debris disk. This model assumes that (I) the hard X-rays are due to the bremsstrahlung emission from the postshock region of the accretion column, (II) the soft X-rays are originated by hot spots on the WD surface, and (III) the optical and infrared emissions are caused by an optically thick dusty disk, the WD photosphere, and the tail of the postshock region emission. In this scenario, the fitted model parameters indicate that 4U 0142+61 harbors a fast-rotator magnetic near-Chandrasekhar WD, which is very hot and hence young. Such a WD can be the recent outcome of a merger of two less massive WDs. In this case, 4U 0142+61 can evolve into a supernova Ia and hence give hints of the origin of these important astrophysical events. Additionally, we also present a new estimate of 4U 0142+61's distance, ${3.78}_{-0.18}^{+0.12}$ kpc, based on the measured hydrogen column density and new interstellar extinction 3D maps. | [
1306,
1173,
1799,
221,
363,
1579,
1471,
992,
995,
994
] | [
"pulsars",
"optical pulsars",
"white dwarf stars",
"chandrasekhar limit",
"debris disks",
"stellar accretion disks",
"soft gamma-ray repeaters",
"magnetars",
"magnetic stars",
"magnetic fields"
] |
2023ApJ...956...67Y | Implications of Narrow Spectra of Fast Radio Bursts | Fast radio bursts (FRBs) are millisecond-duration radio transients with extremely high brightness temperatures at cosmological distances, and the physical origin and the radiation mechanism of FRBs are still unknown. The observed spectral bandwidth of some FRBs appeared narrow compared with their peak frequencies, which could be used to constrain the radiation mechanism and the astrophysical environment of FRBs. In this work, we investigate some of the possible physical origins of the narrow spectra from the perspectives of intrinsic radiation mechanisms, coherent processes, radiative transfers, and interference processes. We find that: (1) If the observed narrow spectra of FRBs are attributed to the intrinsic radiation mechanism by a single charged particle, the particle's deflection angle should be much smaller than the radiation beaming angle. (2) Coherent process can cause narrow spectra. For the bunching mechanism, the narrow spectra might arise from the radiating bunches with a quasiperiodic distribution. For the maser mechanism, the negative absorption process can naturally cause a narrow spectrum. (3) Most absorption and scattering processes seem not to significantly change the observed spectra based on the current observation of some FRB repeaters. (4) Scintillation and plasma lensing in the FRB source environment can modulate the spectra, leading to the narrow spectra and the burst-to-burst variation of spectra. A planet-like object can generate the spectral modulation via gravitational lensing at the gigahertz band, but the observed burst-to-burst variation of the spectra does not support this scenario. | [
289,
2008,
1339,
2055,
1108
] | [
"compact radiation sources",
"radio transient sources",
"radio bursts",
"radiative processes",
"neutron stars"
] |
2020AJ....160..273L | A Likely Magnetic Activity Cycle for the Exoplanet Host M Dwarf GJ 3512 | Current radial velocity data from specialized instruments contain a large amount of information that may pass unnoticed if their analysis is not accurate. The joint use of Bayesian inference tools and frequency analysis has been shown as effective in revealing exoplanets but they have been used less frequently to investigate stellar activity. We intend to use radial velocity data of the exoplanet host star GJ 3512 to investigate its magnetic activity. Our study includes the analysis of the photometric data available. The main objectives of our work are to constrain the orbital parameters of the exoplanets in the system, to determine the current level of activity of the star and to derive an activity cycle length for it. An adaptive importance sampling method was used to determine the parameters of the exoplanets orbit. Generalized Lomb-Scargle periodograms were constructed with both radial velocity curve and photometric data. A careful analysis of the harmonic frequencies was conducted in each periodogram. Our fit to multiple Keplerian orbits constrained the orbital parameters of two giant gas planets orbiting the star GJ 3512. The host star showed an increase of its magnetic activity during the last observing campaign. The accurate fit of the radial velocity curve data to the multi-Keplerian orbit permitted to reveal the star rotation in the residuals of the best fit and estimate an activity cycle length of ∼14 yr. | [
1580,
982,
484,
1572,
1965,
906,
1900,
1892
] | [
"stellar activity",
"m dwarf stars",
"exoplanet systems",
"starspots",
"computational methods",
"late-type dwarf stars",
"bayesian statistics",
"importance sampling"
] |
2021ApJ...921...94D | Igniting Weak Interactions in Neutron Star Postmerger Accretion Disks | The merger of two neutron stars or a neutron star and a black hole typically results in the formation of a postmerger accretion disk. Outflows from disks may dominate the overall ejecta from mergers and be a major source of r-process nuclei in our universe. We explore the parameter space of such disks and their outflows and r-process yields by performing 3D general-relativistic magnetohydrodynamic simulations with weak interactions and approximate neutrino transport. We discuss the mapping between the initial binary parameters and the parameter space of the resulting disks, chiefly characterized by their initial accretion rate. We demonstrate the existence of an ignition threshold for weak interactions at around ~10<SUP>-3</SUP> M<SUB>⊙</SUB> s<SUP>-1</SUP> for typical parameters by means of analytic calculations and numerical simulations. We find a degenerate, self-regulated, neutrino-cooled regime above the threshold and an advection-dominated regime below the threshold. Excess heating in the absence of neutrino cooling below the threshold leads to ≳60% of the initial disk mass being ejected in outflows, with typical velocities of ~(0.1-0.2)c, compared to ≲40% at ~(0.1-0.15)c above the threshold. While disks below the threshold show suppressed production of light r-process elements, disks above the threshold can produce the entire range of r-process elements, in good agreement with the observed solar system abundances. Disks below the ignition threshold may produce an overabundance of actinides seen in actinide-boost stars. As gravitational-wave detectors start to sample the neutron star merger parameter space, different disk realizations may be observable via their associated kilonova emission. | [
14,
1964,
661,
1128,
1131,
1108,
162
] | [
"accretion",
"magnetohydrodynamics",
"gravitation",
"nuclear abundances",
"nucleosynthesis",
"neutron stars",
"black holes"
] |
2023ApJ...947...66F | A 3D View of Orion. I. Barnard's Loop | Barnard's Loop is a famous arc of Hα emission located in the Orion star-forming region. Here, we provide evidence of a possible formation mechanism for Barnard's Loop and compare our results with recent work suggesting a major feedback event occurred in the region around 6 Myr ago. We present a 3D model of the large-scale Orion region, indicating coherent, radial, 3D expansion of the OBP-Near/Briceño-1 (OBP-B1) cluster in the middle of a large dust cavity. The large-scale gas in the region also appears to be expanding from a central point, originally proposed to be Orion X. OBP-B1 appears to serve as another possible center, and we evaluate whether Orion X or OBP-B1 is more likely to have caused the expansion. We find that neither cluster served as the single expansion center, but rather a combination of feedback from both likely propelled the expansion. Recent 3D dust maps are used to characterize the 3D topology of the entire region, which shows Barnard's Loop's correspondence with a large dust cavity around the OPB-B1 cluster. The molecular clouds Orion A, Orion B, and Orion λ reside on the shell of this cavity. Simple estimates of gravitational effects from both stars and gas indicate that the expansion of this asymmetric cavity likely induced anisotropy in the kinematics of OBP-B1. We conclude that feedback from OBP-B1 has affected the structure of the Orion A, Orion B, and Orion λ molecular clouds and may have played a major role in the formation of Barnard's Loop. | [
1602,
414,
1668,
1569,
1565
] | [
"stellar feedback",
"dust shells",
"supernovae",
"star formation",
"star forming regions"
] |
2022RNAAS...6..270V | Spectral Characterization of the Low-mass Companion μ Virgenes B | We report optical and near-infrared spectral characterization of an M dwarf companion to the bright F2 star μ Virgenes. Data from Shane/Kast and IRTF/SpeX yield identical spectral types of M5, and spectral features indicate solar metallicity ([Fe/H] = -0.05 ± 0.20) with no evidence of low surface gravity features at optical or near-infrared bands. Strong Hα emission ( ${\mathrm{log}}_{10}{L}_{{\rm{H}}\alpha }/{L}_{\mathrm{bol}}$ = -3.80 ± 0.09) is consistent with an active source at saturation, while the lack of Li I absorption and low surface gravity features constrains the system's age to ≳200 Myr. Both metallicity and age estimates of the companion are consistent with its primary. As a well-resolved companion to an exceptionally well-characterized bright star, μ Virgenes B serves as a useful benchmark at the transition between partially and fully convective stars. | [
291,
982,
1509,
1589
] | [
"companion stars",
"m dwarf stars",
"solar neighborhood",
"stellar classification"
] |
2023ApJ...942...77B | Low-energy Electron-track Imaging for a Liquid Argon Time-projection-chamber Telescope Concept Using Probabilistic Deep Learning | The GammaTPC is an MeV-scale single-phase liquid argon time-projection-chamber gamma-ray telescope concept with a novel dual-scale pixel-based charge-readout system. It promises to enable a significant improvement in sensitivity to MeV-scale gamma rays over previous telescopes. The novel pixel-based charge readout allows for imaging of the tracks of electrons scattered by Compton interactions of incident gamma rays. The two primary contributors to the accuracy of a Compton telescope in reconstructing an incident gamma-ray's original direction are its energy and position resolution. In this work, we focus on using deep learning to optimize the reconstruction of the initial position and direction of electrons scattered in Compton interactions, including using probabilistic models to estimate predictive uncertainty. We show that the deep-learning models are able to predict locations of Compton scatters of MeV-scale gamma rays from simulated 500 μm pixel-based data to better than 1 mm rms error and are sensitive to the initial direction of the scattered electron. We compare and contrast different deep-learning uncertainty estimation algorithms for reconstruction applications. Additionally, we show that event-by-event estimates of the uncertainty of the locations of the Compton scatters can be used to select those events that were reconstructed most accurately, leading to improvement in locating the origin of gamma-ray sources on the sky. | [
634,
1853,
1938,
630,
2306
] | [
"gamma-ray telescopes",
"gamma-ray transient sources",
"convolutional neural networks",
"gamma-ray detectors",
"astronomy image processing"
] |
2023AJ....166..231E | Prospects from TESS and Gaia to Constrain the Flatness of Planetary Systems | The mutual inclination between planets orbiting the same star provides key information to understand the formation and evolution of multiplanet systems. In this work, we investigate the potential of Gaia astrometry in detecting and characterizing cold Jupiters in orbits exterior to the currently known Transiting Exoplanet Survey Satellite (TESS) planet candidates. According to our simulations, out of the ~3350 systems expected to have cold Jupiter companions, Gaia, by its nominal 5 yr mission, should be able to detect ~200 cold Jupiters and measure the orbital inclinations with a precision of ${\sigma }_{\cos i}\lt 0.2$ in ~120 of them. These numbers are estimated under the assumption that the orbital orientations of the CJs follow an isotropic distribution, but these only vary slightly for less broad distributions. We also discuss the prospects from radial velocity follow-ups to better constrain the derived properties and provide a package to do quick forecasts using our Fisher matrix analysis. Overall, our simulations show that Gaia astrometry of cold Jupiters orbiting stars with TESS planets can distinguish dynamically cold (mean mutual inclination ≲5°) from dynamically hot systems (mean mutual inclination ≳20°), placing a new set of constraints on their formation and evolution. | [
498,
2172,
488,
1541,
2205
] | [
"exoplanets",
"extrasolar gaseous planets",
"exoplanet catalogs",
"space astrometry",
"exoplanet migration"
] |
2023ApJ...954...12H | Galactic Bar Resonances with Diffusion: An Analytic Model with Implications for Bar-Dark Matter Halo Dynamical Friction | The secular evolution of disk galaxies is largely driven by resonances between the orbits of "particles" (stars or dark matter) and the rotation of non-axisymmetric features (spiral arms or a bar). Such resonances may also explain kinematic and photometric features observed in the Milky Way and external galaxies. In simplified cases, these resonant interactions are well understood: for instance, the dynamics of a test particle trapped near a resonance of a steadily rotating bar is easily analyzed using the angle-action tools pioneered by Binney, Monari, and others. However, such treatments do not address the stochasticity and messiness inherent to real galaxies-effects that have, with few exceptions, been previously explored only with complex N-body simulations. In this paper, we propose a simple kinetic equation describing the distribution function of particles near an orbital resonance with a rigidly rotating bar, allowing for diffusion of the particles' slow actions. We solve this equation for various values of the dimensionless diffusion strength Δ, and then apply our theory to the calculation of bar-halo dynamical friction. For Δ = 0, we recover the classic result of Tremaine and Weinberg that friction ultimately vanishes, owing to the phase mixing of resonant orbits. However, for Δ > 0, we find that diffusion suppresses phase mixing, leading to a finite torque. Our results suggest that stochasticity-be it physical or numerical-tends to increase bar-halo friction, and that bars in cosmological simulations might experience significant artificial slowdown, even if the numerical two-body relaxation time is much longer than a Hubble time. | [
2365,
136,
1880,
422,
1181,
1608,
2089
] | [
"galactic bar",
"barred spiral galaxies",
"galaxy dark matter halos",
"dynamical friction",
"orbital resonances",
"stellar kinematics",
"plasma physics"
] |
2023ApJ...953...69C | High-resolution Observations of Plume Footpoints in a Solar Coronal Hole | Plumes are bright structures in coronal holes extending from the solar surface into the corona and are considered as a possible source of the solar wind. Plumes are thought to be rooted in strong unipolar photospheric flux patches (network/plage region). The magnetic activities at the base of plumes may play a crucial role in producing outflows and propagating disturbances (PDs). However, the role of photospheric/chromospheric activities (e.g., jets/spicules) at the base of plumes and their connection to PDs is poorly understood. Using high-resolution observations of a plume taken on 2020 July 23 with the 1.6 m Goode Solar Telescope (GST), Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we analyzed chromospheric/transition region activities at the base of the plume and their connection to outflows/PDs in the plume. The GST Visible Imaging Spectrometer images reveal repetitive spicules with blueshifted emission (pseudo-Doppler maps) at the plume's footpoint. In addition, the photospheric magnetograms provide evidence of mixed polarities at the base of the plume. The IRIS Mg II k Dopplergrams show strong blueshifted emission (~50 km s<SUP>-1</SUP>) and a high brightness temperature (Mg II k2 line) at the footpoint of the plume. The long-period PDs (P ≈ 20-25 minutes) along the plume (AIA 171 Å) match the periodicity of spicules in the chromospheric images, suggesting a close connection between the spicules and the PDs. We suggest that the interchange reconnection between the closed and open flux of the coronal bright point at the plume's footpoint is the most likely candidate to produce upflows and associated PDs along the plume. | [
2039
] | [
"solar coronal plumes"
] |
2020AJ....160..234D | Time-variable Radio Recombination Line Emission in W49A | We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6 cm and at 7 mm at resolutions of 0"15 (1650 au) and 0"04 (440 au), respectively. The 3.6 cm data reveal new morphological detail in the ultracompact H II region population, as well as several previously unknown and unresolved sources. In particular, source A shows elongated, edge-brightened bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components. We also present VLA observations of radio recombination lines at 3.6 cm and 7 mm, and IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2 mm. Three of the smallest ultracompact H II regions (sources A, B2, and G2) all show broad kinematic linewidths, with ΔV<SUB>FWHM</SUB> ≳ 40 km s<SUP>-1</SUP>. A multi-line analysis indicates that broad linewidths remain after correcting for pressure broadening effects, suggesting the presence of supersonic flows. Substantial changes in linewidth over the 21 yr time baseline at both 3.6 cm and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from 31.7 ± 1.8 km s<SUP>-1</SUP> to 55.6 ± 2.7 km s<SUP>-1</SUP>, an increase of +23.9 ± 3.4 km s<SUP>-1</SUP>. The G2 source was previously reported to have shown a 3.6 cm continuum flux density decrease of 40% between 1994 and 2015. This source sits near the center of a very young bipolar outflow whose variability may have produced these changes. | [
286,
571
] | [
"compact h ii region",
"galactic radio sources"
] |
2023ApJ...959...57M | Surface Volatile Composition as Evidence for Hydrothermal Processes Lasting Longer in Triton's Interior than Pluto's | Ocean worlds, or icy bodies in the outer solar system that have or once had subsurface liquid water oceans, are among the most compelling topics of astrobiology. Typically, confirming the existence of a subsurface ocean requires close spacecraft observations. However, combining our understanding of the chemistry that takes place in a subsurface ocean with our knowledge of the building blocks that formed potential ocean worlds provides an opportunity to identify tracers of endogenic activity in the surface volatiles of Pluto and Triton. We show here that the current composition of the volatiles on the surfaces and in the atmospheres of Pluto and Triton are deficient in carbon, which can only be explained by the loss of CH<SUB>4</SUB> through a combination of aqueous chemistry and atmospheric processes. Furthermore, we find that the relative nitrogen and water abundances are within the range observed in building block analogs, comets, and chondrites. A lower limit for N/Ar in Pluto's atmosphere also suggests source building blocks that have a cometary or chondritic composition, all pointing to an origin for their nitrogen as NH<SUB>3</SUB> or organics. Triton's lower abundance of CH<SUB>4</SUB> compared to Pluto, and the detection of CO<SUB>2</SUB> at Triton but not at Pluto points to aqueous chemistry in a subsurface ocean that was more efficient at Triton than Pluto. These results have applications to other large Kuiper Belt objects as well as the assessment of formation locations and times for the four giant planets given future probe measurements of noble gas abundances and isotope ratios. | [
1530,
1241,
1267,
2187
] | [
"solar system formation",
"planet formation",
"pluto",
"triton"
] |
2020ApJ...905..127D | Constraints on Primordial Non-Gaussianity Using the Multitracer Technique for Skew Spectra | Extracting the bispectrum information from large-scale structure observations is challenging due to the complex models and the computational costs involved in measuring the signal and its covariance. Recently, the skew spectrum was proposed to access parts of the bispectrum information in a more effective manner and was confirmed to provide complementary information to that available in power spectrum measurements. In this work, we generalize the theory to apply the multitracer technique and explore its ability to constrain the local-type primordial non-Gaussianity. Using the spectra and their covariance estimated from N-body simulations, we find that the multitracer approach is effective in reducing the cosmic variance noise. The 1σ marginalized errors for ${b}_{1}^{2}{A}_{s},{n}_{s}$, and ${f}_{\mathrm{NL}}^{\mathrm{loc}}$ are reduced by 50%, 52%, and 73% compared with the results achieved using only the power spectrum obtained from a single tracer. These results indicate that both the skew spectrum and the multitracer technique are useful in constraining the primordial non-Gaussianity with the forthcoming wide-field galaxy surveys. | [
1116,
340
] | [
"non-gaussianity",
"cosmological parameters from large-scale structure"
] |
2020ApJ...888...54M | Discovery of a Rare Late-type, Low-mass Wolf-Rayet Star in the LMC | We report the serendipitous discovery of an object, UVQS J060819.93-715737.4, with a spectrum dominated by extremely intense, narrow C II emission lines. The spectrum is similar to those of the very rare, late-type [WC11] low-mass Wolf-Rayet stars. Despite the recognition of these stars as a distinct class decades ago, there remains barely a handful of Galactic members, all of which are also planetary-nebula central stars. Although no obvious surrounding nebulosity is present in J0608, [O II], [N II], and [S II] emission suggest the presence of an inconspicuous, low-excitation nebula. There is low-amplitude incoherent photometric variability on timescales of days to years, as well as numerous prominent P Cygni profiles, implying mass loss. There are indications of a binary companion. The star is located on the outskirts of the LMC, and the observed radial velocity (∼+250 km s<SUP>-1</SUP>) and proper motion strongly suggest membership. If indeed an LMC member, this is the first extragalactic late [WC] star, and the first with an accurately determined luminosity, as the Galactic examples are too distant for precise parallax determinations. A high-quality, broad-coverage spectrum of the prototype of the late [WC] class, CPD -56° 8032, is also presented. We discuss different excitation mechanisms capable of producing the great strength of the C II emission. Numerous autoionizing levels of C II are definitely populated by processes other than dielectronic recombination. Despite the spectacular emission spectra, observational selection makes objects such as these difficult to discover. Members of the [WC11] class may in fact be considerably more common than the handful of previously known late [WC] stars. | [
1793,
1250,
1249
] | [
"wc stars",
"planetary nebulae nuclei",
"planetary nebulae"
] |
2023RNAAS...7..163W | Hidden Companions to Intermediate-mass Stars. VIII. Discovery of a 0.6 M <SUB>⊙</SUB>, 1.7 au Companion to Albali = ϵ Aquarii | A large portion of the visually brightest stars in the night sky are late B to early A-type stars yet our knowledge of their multiplicity is incomplete. Here we report the discovery of a companion to the nearby star Albali (HIP 102618 = ϵ Aquarii), based on a VLTI/GRAVITY interferometric observation. The companion is at a projected separation ρ = 26 mas ↔ 1.7 au and has a K band flux ratio of 0.7%. Through isochrone fitting we find that Albali A is a 400 Myr old 2.8M <SUB>⊙</SUB> subgiant that has recently evolved off the main sequence, while the newly discovered Albali B is a 0.6 M <SUB>⊙</SUB> K dwarf. Further astrometric monitoring is needed in order to assess how strongly the stars are expected to interact as the primary expands. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001. | [
1081,
5,
128,
1168
] | [
"multiple stars",
"a stars",
"b stars",
"optical interferometry"
] |
2020ApJ...905...82H | Gamma-Ray Burst Triangulation with a Near-Earth Network | We study the characteristics of near-Earth networks (NENs) of gamma-ray burst (GRB) detectors, with the objective of defining a network with all-sky, full-time localization capability for multimessenger astrophysics. We show that a minimum network consisting of nine identical spacecraft in two orbits with different inclinations provides a good combination of sky coverage with several-degree localization accuracy with detector areas of 100 cm<SUP>2</SUP>. In order to achieve this, careful attention must be paid to systematics. This includes accurate photon timing (∼0.1 ms), good energy resolution (∼10%), and reduction of Earth albedo, which are all within current capabilities. Such a network can be scaled in both the number and size of detectors to produce increased accuracy. We introduce a new method of localization that does not rely on on-board trigger systems or on the cross-correlation of time histories, but rather it tests positions in ground processing over the entire sky and assigns probabilities to them to detect and localize events. We demonstrate its capabilities with simulations. If the NEN spacecraft can downlink at least several hundred time- and energy-tagged events per second, and the data can be ground-processed as they are received, it can in principle derive GRB positions in near-real time over the entire sky. | [
629,
2078,
630
] | [
"gamma-ray bursts",
"experimental techniques",
"gamma-ray detectors"
] |
2021ApJ...910...98L | Consistency Analysis of a Dark Matter Velocity-dependent Force as an Alternative to the Cosmological Constant | A range of cosmological observations demonstrate an accelerated expansion of the universe, and the most likely explanation of this phenomenon is a cosmological constant. Given the importance of understanding the underlying physics, it is relevant to investigate alternative models. This article uses numerical simulations to test the consistency of one such alternative model. Specifically, this model has no cosmological constant; instead, the dark matter particles have an extra force proportional to the velocity squared, somewhat reminiscent of the magnetic force in electrodynamics. The constant strength of the force is the only free parameter. Because bottom-up structure formation creates cosmological structures whose internal velocity dispersions increase in time, this model may mimic the temporal evolution of the effect from a cosmological constant. It is shown that models with force linearly proportional to internal velocities, or models proportional to velocity to power 3 or more, cannot mimic the accelerated expansion induced by a cosmological constant. However, models proportional to velocity squared are still consistent with the temporal evolution of a universe with a cosmological model. | [
353,
343,
12
] | [
"dark matter",
"cosmology",
"accelerating universe"
] |
2021ApJS..252....2M | Astromers: Nuclear Isomers in Astrophysics | We develop a method to compute thermally mediated transition rates between the ground state and long-lived isomers in nuclei. We also establish criteria delimiting a thermalization temperature above which a nucleus may be considered a single species and below which it must be treated as two separate species: a ground-state species and an astrophysical isomer ("astromer") species. Below the thermalization temperature, the destruction rates dominate the internal transition rates between the ground state and the isomer. If the destruction rates also differ greatly from one another, the nuclear levels fall out of or fail to reach thermal equilibrium. Without thermal equilibrium, there may not be a safe assumption about the distribution of occupation probability among the nuclear levels when computing nuclear reaction rates. In these conditions, the isomer has astrophysical consequences and should be treated as a separate astromer species which evolves separately from the ground state in a nucleosynthesis network. We apply our transition-rate methods and perform sensitivity studies on a few well-known astromers. We also study transitions in several other isomers of likely astrophysical interest. <SUP>*</SUP> This article is intended for unlimited release under LA-UR-20-22828. | [
1131,
1616,
1419,
1324
] | [
"nucleosynthesis",
"stellar nucleosynthesis",
"s-process",
"r-process"
] |
2023ApJ...949...74R | Infrared Ejecta and Cold Dust in the Young Supernova Remnant N132D | We present Spitzer, Wide-field Infrared Survey Explorer (WISE), and Herschel observations of the young supernova remnant (SNR) N132D in the Large Magellanic Cloud, including 3-40 μm Spitzer Infrared Spectrograph (IRS) mapping, 12 μm WISE and 70, 100, 160, 250, 350, and 500 μm Herschel images. The high-velocity lines of [Ne II] at 12.8 μm, [Ne III] at 15.5 μm, and [O IV] 26 μm reveal infrared ejecta concentrated in a central ring and coincide with the optical and X-ray ejecta. Herschel images reveal far-IR emission coinciding with the central ejecta, which suggests that the IR emission is freshly formed, cold dust in the SN ejecta. The infrared spectra are remarkably similar to those of another young SNR of 1E0102 with Ne and O lines. Shock modeling of the Ne ejecta emission suggests a gas temperature of 300-600 K and densities in the range 1000-2 × 10<SUP>4</SUP> cm<SUP>-3</SUP> in the postshock photoionized region. The IR continuum from the ejecta shows an 18 μm peak dust feature. We performed spectral fitting to the IRS dust continuum and Herschel photometry. The dust mass associated with the central ejecta is 1.25 ± 0.65 M <SUB>⊙</SUB>, while the 18 μm dust feature requires forsterite grains. The dust mass of the central ejecta region in N132D is higher than those of other young SNRs, which is likely associated with its higher progenitor mass. We discuss the dust productivity in the ejecta of N132D and infer its plausible implications for dust in the early universe. | [
412,
304,
1729,
435,
1667,
903,
1186,
529,
840
] | [
"dust continuum emission",
"core-collapse supernovae",
"type ib supernovae",
"early universe",
"supernova remnants",
"large magellanic cloud",
"origin of the universe",
"far infrared astronomy",
"interstellar emissions"
] |
2022ApJ...940..181S | Measuring He I Stark Line Shapes in the Laboratory to Examine Differences in Photometric and Spectroscopic DB White Dwarf Masses | Accurate helium White Dwarf (DB) masses are critical for understanding the star's evolution. DB masses derived from the spectroscopic and photometric methods are inconsistent. Photometric masses agree better with currently accepted DB evolutionary theories and are mostly consistent across a large range of surface temperatures. Spectroscopic masses rely on untested He I Stark line-shape and Van der Waals broadening predictions, show unexpected surface temperature trends, and are thus viewed as less reliable. To test this conclusion, we present in this paper detailed He I Stark line-shape measurements at conditions relevant to DB atmospheres (T <SUB>electron</SUB> ≈12,000-17,000 K, n <SUB>electron</SUB> ≈ 10<SUP>17</SUP> cm<SUP>-3</SUP>). We use X-rays from Sandia National Laboratories' Z-machine to create a uniform ≈120 mm long hydrogen-helium mixture plasma. Van der Waals broadening is negligible at our experimental conditions, allowing us to measure He I Stark profiles only. Hβ, which has been well-studied in our platform and elsewhere, serves as the n <SUB>e</SUB> diagnostic. We find that He I Stark broadening models used in DB analyses are accurate within errors at tested conditions. It therefore seems unlikely that line-shape models are solely responsible for the observed spectroscopic mass trends. Our results should motivate the WD community to further scrutinize the validity of other spectroscopic and photometric input parameters, like atmospheric structure assumptions and convection corrections. These parameters can significantly change the derived DB mass. Identifying potential weaknesses in any input parameters could further our understanding of DBs, help elucidate their evolutionary origins, and strengthen confidence in both spectroscopic and photometric masses. | [
1799,
358,
2004,
2063,
2089
] | [
"white dwarf stars",
"db stars",
"laboratory astrophysics",
"atomic physics",
"plasma physics"
] |
2022PSJ.....3...59S | New Constraints on Titan's Stratospheric n-Butane Abundance | Curiously, n-butane has yet to be detected at Titan, though it is predicted to be present in a wide range of abundances that span over 2.5 orders of magnitude. We have searched infrared spectroscopic observations of Titan for signals from n-butane (n-C<SUB>4</SUB>H<SUB>10</SUB>) in Titan's stratosphere. Three sets of Cassini Composite Infrared Spectrometer Focal Plane 4 (1050-1500 cm<SUP>-1</SUP>) observations were selected for modeling, having been collected from different flybys and pointing latitudes. We modeled the observations with the Nonlinear Optimal Estimator for MultivariatE Spectral AnalySIS radiative transfer tool. Temperature profiles were retrieved for each of the data sets by modeling the ν <SUB>4</SUB> emission from methane near 1305 cm<SUP>-1</SUP>. Then, incorporating the temperature profiles, we retrieved abundances of all of Titan's known trace gases that are active in this spectral region, reliably reproducing the observations. We then systematically tested a set of models with varying abundances of n-butane, investigating how the addition of this gas affected the fits. We did this for several different photochemically predicted abundance profiles from the literature, as well as for a constant-with-altitude profile. Ultimately, though we did not produce any firm detection of n-butane, we derived new upper limits on its abundance specific to the use of each profile and to multiple different ranges of stratospheric altitudes. These results will tightly constrain the C<SUB>4</SUB> chemistry of future photochemical modeling of Titan's atmosphere and also motivate the continued search for n-butane and its isomer, isobutane. | [
2186,
1427,
1528,
1255,
1244,
2120,
2214
] | [
"titan",
"saturnian satellites",
"solar system",
"planetary science",
"planetary atmospheres",
"atmospheric composition",
"natural satellite atmospheres"
] |
2021RNAAS...5..135A | How Cost Impacts Equitable Participation in Astronomy Outreach Events | The International Astronomical Youth Camp (IAYC) is an astronomy education outreach event with more than 50 yr of history and over 1700 unique participants from 81 nationalities. The International Workshop for Astronomy e.V. is the non-profit organization behind the IAYC, established in 1979 and based in Germany. The IAYC's unprecedented longevity in a rapidly globalizing world has meant that financial inequities decreases the reach of the camp to people from the Global South compared to Global North countries. Though nationalities represented per camp has increased steadily since its inception, the share of participants from eastern Europe and Africa has dropped, while those from western Europe and North America have increased. This note examines how camp cost, location, and leadership affects nationality diversity among participants, and how astronomy outreach events must reckon with funding for less privileged participants with limited access to resources. | [
2165
] | [
"astronomy education"
] |
2024ApJ...962L..21K | Eccentricity Distribution beyond the Snow Line and Implications for Planetary Habitability | A fundamental question in the study of planetary system demographics is: how common is the solar system architecture? The primary importance of this question lies in the potential of planetary systems to create habitable environments, and dissecting the various components of solar system evolution that contributed to a sustainable temperate surface for Earth. One important factor in that respect is volatile delivery to the inner system and the dependence on giant planets beyond the snow line as scattering agents, particularly as such cold giant planets are relatively rare. Here, we provide an investigation of the eccentricity distribution for giant planet populations both interior and exterior to their system snow lines. We show that the median eccentricity for cold giants is 0.23, compared with a far more circular orbital regime for inner planets. We further present the results of a dynamical simulation that explores the particle scattering potential for a Jupiter analog in comparison with a Jupiter whose eccentricity matches that of the median cold giant eccentricity. These simulations demonstrate that the capacity for such an eccentric cold giant system to scatter volatiles interior to the snow line is significantly increased compared with the Jupiter analog case, resulting in a far greater volume of Earth-crossing volatiles. Thus, many of the known systems with cold giant planets may harbor water worlds interior to the snow line. | [
696,
498,
484,
490,
491,
1184,
1178,
1528,
1191,
2293
] | [
"habitable zone",
"exoplanets",
"exoplanet systems",
"exoplanet dynamics",
"exoplanet evolution",
"orbits",
"orbital evolution",
"solar system",
"solar system gas giant planets",
"solar system evolution"
] |
2021ApJ...908..181M | Tracing Dark Energy History with Gamma-Ray Bursts | Observations of gamma-ray bursts up to z ∼ 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble's diagram and then we estimate the set (Ω<SUB>m</SUB>, Ω<SUB>Λ</SUB>) in the framework of flat and non-flat ΛCDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4σ, i.e., H<SUB>0</SUB> = (67.4 ± 0.5) km s<SUP>-1</SUP> Mpc<SUP>-1</SUP> and H<SUB>0</SUB> = (74.03 ± 1.42) km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>. We show our new sample provides tighter constraints on Ω<SUB>m</SUB> since at z ≤ 1.2 we see that w(z) agrees within 1σ with the standard value w = -1. The situation is the opposite at larger z, where gamma-ray bursts better fix w(z) that seems to deviate from w = -1 at 2σ and 4σ level, depending on the redshift bins. In particular, we investigate the w(z) evolution through a piecewise formulation over seven redshift intervals. From our fitting procedure we show that at z ≥ 1.2 the case w < -1 cannot be fully excluded, indicating that dark energy's influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper. | [
1563,
351,
629
] | [
"standard candles",
"dark energy",
"gamma-ray bursts"
] |
2021ApJS..255...10M | A Search for Rapid Mid-infrared Variability in Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies | Fermi-LAT's detection of γ-rays from narrow-line Seyfert 1 galaxies (NLS1s) has received increasing attention. Understanding these γ-NLS1s is of interest because they have some properties similar to blazars, which are known to show rapid and large-amplitude variability. Based on the largest sample of γ-NLS1s (25 sources), we carried out a systematic search for rapid mid-infrared (MIR, 3.4 and 4.6 μm) variability using the multiepoch data of the Wide-field Infrared Survey Explorer (WISE). We also compared a few variability properties between γ-NLS1s and γ-ray blazars. Our main results are as follows. (1) Thirteen γ-NLS1s showed significant (>3σ) rapid variability in at least one of the two MIR bands. The MIR emission of these sources is dominated by the synchrotron emission of relativistic electrons in the jet. (2) The γ-NLS1s with flat radio spectra are more variable than those not detected in γ-rays. (3) The γ-NLS1s tend to show smaller amplitude of variability as well as lower duty cycle relative to γ-ray blazars. (4) The γ-NLS1s tend to show a trend of bluer-when-brighter on both intraday and long timescales, similar to γ-ray blazars. (5) The γ-NLS1s that are more variable on long timescales have larger amplitudes of variability and higher duty cycles on intraday timescales. (6) In the majority of cases, the γ-NLS1s fall in the WISE Gamma-ray Blazar Strip (WGS). However, we noted migrations outside of the WGS due to significant variability. | [
1447,
785,
792,
633
] | [
"seyfert galaxies",
"infrared astronomical satellite",
"infrared photometry",
"gamma-ray sources"
] |
2021ApJ...919..101P | The Ultraviolet Deep Imaging Survey of Galaxies in the Bootes Void. I. Catalog, Color-Magnitude Relations, and Star Formation | We present a deep far and near-ultraviolet (FUV and NUV) wide-field imaging survey of galaxies in the Bootes void using the Ultraviolet Imaging Telescope on board AstroSat. Our data reach 5σ limiting magnitudes for point sources at 23.0 and 24.0 AB mag in the FUV and NUV, respectively. We report a total of six star-forming galaxies residing in the Bootes void alongside the full catalog, and of these, three are newly detected in our FUV observation. Our void galaxy sample spans a range of UV colors (-0.35 mag ≤ FUV-NUV ≤ 0.68 mag) and absolute magnitudes (-14.16 mag ≤ M<SUB>NUV</SUB> ≤ -18.65 mag). In addition, Sloan Digital Sky Survey and Two Micron All Sky Survey archival data are being used to study UV, optical, and infrared color-magnitude relations for our galaxies in the void. We investigate the nature of bimodal color distribution, morphologies, and star formation of the void galaxies. Most of the galaxies in our sample are fainter and less massive than L<SUP>*</SUP> galaxies, with M<SUB>r</SUB> > -20 mag. Our analysis reveals a dominant fraction of bluer galaxies over the red ones in the void region probed. The internal and Galactic extinction corrected FUV star formation rates (SFRs) in our void galaxy catalog varies in a large range of 0.05-51.01 M<SUB>⊙</SUB> yr<SUP>-1</SUP>, with a median of 3.96 M<SUB>⊙</SUB> yr<SUP>-1</SUP>. We find a weak effect of the environment on the SFRs of galaxies. Implications of our findings are discussed. | [
1569,
1742,
205,
1779,
615
] | [
"star formation",
"ultraviolet surveys",
"catalogs",
"voids",
"galaxy properties"
] |
2022ApJ...927..201A | Magnetohydrodynamic Wave Mode Identification in Circular and Elliptical Sunspot Umbrae: Evidence for High-order Modes | In this paper, we provide clear direct evidence of multiple concurrent higher-order magnetohydrodynamic (MHD) modes in circular and elliptical sunspots by applying both proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques on solar observational data. These techniques are well documented and validated in the areas of fluid mechanics, hydraulics, and granular flows but are relatively new to the field of solar physics. While POD identifies modes based on orthogonality in space and provides a clear ranking of modes in terms of their contribution to the variance of the signal, DMD resolves modes that are orthogonal in time. The clear presence of the fundamental slow sausage and kink body modes, as well as higher-order slow sausage and kink body modes, have been identified using POD and DMD analysis of the chromospheric Hα line at 6562.808 Å for both the circular and elliptical sunspots. Additionally, for the various slow body modes, evidence for the presence of the fast surface kink mode was found in the circular sunspot. All of the MHD mode patterns were cross-correlated with their theoretically predicted counterparts, and we demonstrated that ellipticity cannot be neglected when interpreting MHD wave modes. The higher-order MHD wave modes are even more sensitive to irregularities in umbral cross-sectional shapes; hence, this must be taken into account for more accurate modeling of the modes in sunspots and pores. | [
1653,
1476,
1918,
1744
] | [
"sunspots",
"solar physics",
"wavelet analysis",
"umbra"
] |
2021PSJ.....2...35M | Constraints on Sub-Neptune Planet Candidate KOI-972.01 via Joint Variability/Gravity-darkening Analysis | We analyze Kepler photometry of transiting planet candidate KOI-972.01, accounting for both stellar variability and gravity darkening. KOI-972.01 stands out because of its small radius, less than that of Neptune, and because of its intermediate orbit period at 13.12 days, long enough to avoid significant tidal evolution, and thus it represents an underexplored exoplanet class. The parent star of KOI-972.01 is a rapidly rotating δ-Scuti variable, complicating transit lightcurve interpretation but also offering a potential independent source of stellar parameters. We measure the stellar rotation period (16.2 hr) by identifying the stellar rotation frequency and subsequently place a constraint on the stellar obliquity of no greater than 10°, but have difficulty isolating individual oscillation modes in the periodogram owing to time variation of the δ-Scuti oscillations. After subtracting the stellar oscillations, lightcurve fits place the transiting object radius at 3.07 ± 0.09 R<SUB>⊕</SUB>, but the shallow transit prevents useful constraints on the system's spin-orbit alignment. | [
492,
486,
491,
484,
1063,
1243,
680
] | [
"exoplanet formation",
"exoplanet astronomy",
"exoplanet evolution",
"exoplanet systems",
"mini neptunes",
"planetary alignment",
"gravity darkening"
] |
2022ApJ...929L..17E | Limiting the Abundance of LIGO/Virgo Black Holes with Microlensing Observations of Quasars of Finite Size | We present a simple but general argument that strongly limits the abundance of primordial black holes (PBHs) (or other unknown population of compact objects) with masses similar to those determined by LIGO/Virgo from BH binary mergers. We show that quasar microlensing can be very sensitive to the mass of the lenses, and that it is able to distinguish between stars and BHs of high mass, when the finite size of the source is taken into account. A significant presence of massive BHs would produce frequent high-flux magnifications (except for unrealistically large sources), which have been very rarely observed. On the contrary, a typical stellar population would induce flux magnifications consistent with the observations. This result excludes PBHs (or any type of compact object) in the mass range determined by LIGO/Virgo as the main dark matter constituents in the lens galaxies. | [
343,
353,
1292,
98,
1318,
670
] | [
"cosmology",
"dark matter",
"primordial black holes",
"astrophysical black holes",
"quasar microlensing",
"gravitational lensing"
] |
2021ApJ...908...85M | Observational Evidence for Enhanced Black Hole Accretion in Giant Elliptical Galaxies | We present a study of the relationship between black hole accretion rate (BHAR) and star formation rate (SFR) in a sample of giant elliptical galaxies. These galaxies, which live at the centers of galaxy groups and clusters, have star formation and black hole activity that is primarily fueled by gas condensing out of the hot intracluster medium. For a sample of 46 galaxies spanning five orders of magnitude in BHAR and SFR, we find a mean ratio of ${\mathrm{log}}_{10}(\mathrm{BHAR}/\mathrm{SFR})=-1.45\pm 0.2$ , independent of the methodology used to constrain both SFR and BHAR. This ratio is significantly higher than most previously published values for field galaxies. We investigate whether these high BHAR/SFR ratios are driven by high BHAR, low SFR, or a different accretion efficiency in radio galaxies. The data suggest that the high BHAR/SFR ratios are primarily driven by boosted black hole accretion in spheroidal galaxies compared to their disk counterparts. We propose that the angular momentum of the cool gas is the primary driver in suppressing BHAR in lower-mass galaxies, with massive galaxies accreting gas that has condensed out of the hot phase on nearly radial trajectories. Additionally, we demonstrate that the relationship between specific BHAR and SFR (sBHAR and sSFR) has much less scatter over six orders of magnitude in both parameters, due to competing dependence on morphology between the M<SUB>BH</SUB>-M<SUB>*</SUB> and BHAR-SFR relations. In general, active galaxies selected by typical techniques have sBHAR/sSFR ∼ 10, while galactic nuclei with no clear AGN signatures have sBHAR/sSFR ∼ 1, consistent with a universal M<SUB>BH</SUB>-M<SUB>spheroid</SUB> relation. | [
181,
584,
597,
16,
2134,
2035,
159,
1663,
651
] | [
"brightest cluster galaxies",
"galaxy clusters",
"galaxy groups",
"active galactic nuclei",
"radio active galactic nuclei",
"x-ray active galactic nuclei",
"black hole physics",
"supermassive black holes",
"giant elliptical galaxies"
] |
2022ApJS..262...45S | A Dynamic Deep-learning Model for Generating a Magnetogram Sequence from an SDO/AIA EUV Image Sequence | The solar magnetic field dominates solar activities in the solar atmosphere, such as solar flares and coronal mass ejections (CMEs). The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) has been in operation from 2010, providing a full-disk photospheric magnetogram. However, with a single view of observation, SDO/HMI cannot provide a global view of the Sun at the same time, so the farside of the Sun is blind to us. The Solar Terrestrial Relations Observatory (STEREO) provides two different views of the Sun with complementary viewing angles relative to SDO/HMI. However, it did not carry a magnetograph, but an extreme-ultraviolet (EUV) imager. Fortunately, deep learning has been proved to generate a solar farside magnetogram from STEREO farside EUV observation. Although a single generated magnetogram is morphologically very similar to ground truth, the sequence of the generated magnetogram has noticeable magnetic field fluctuation, which cannot be ignored when it is displayed as a time series, especially at an active region. This fluctuation is represented by sudden magnetic polarity reversal and drifting of magnetic field distribution. To mitigate this problem, a novel dynamic deep-learning model by integrating a convolutional gated recurrent units (convGRU) model into a pix2pix baseline is proposed in this paper. It can generate a sequence of a magnetogram with smooth transition among consecutive magnetograms by exploring spatio-temporal information of an input EUV image sequence. From both quantitative and qualitative comparisons, the proposed model can generate a magnetogram sequence more close to real observation. | [
1974,
1938,
1911
] | [
"solar active regions",
"convolutional neural networks",
"detection"
] |
2023AJ....166..210Y | Star Photometry for DECam Legacy Survey and Sloan Digital Sky Survey Images Based on Convolutional Neural Networks | Flux is one of the most fundamental parameters in astrophysics, and aperture photometry and point-spread function (PSF) photometry are commonly used methods to obtain the flux. With the continuous development of astronomical equipment that has generated massive data, researchers have to find more effective methods to obtain stellar fluxes. However, current photometric software such as SExtractor are very sensitive to the configuration parameters and are difficult to configure. We propose a new photometric model based on deep learning called sf-convolutional neural network (CNN) to extract aperture fluxes and PSF fluxes. For the simulated data including 5727 stars, the experimental results show that sf-CNN can predict fluxes better than SExtractor. The mean absolute error (MAE) values of sf-CNN and SExtractor for predicting PSF fluxes are 0.0034 and 0.0134, respectively. On the 6293 mixed stars in DECam Legacy Survey Data Release (DR) 9, the MAE values of the predicted PSF fluxes are 0.0075 and 0.0177, respectively. The PSF accuracy of the sf-CNN model is significantly higher than that of SExtractor. Additionally, the MAE values of the predicted aperture fluxes on 6215 mixed stars and 1341 blends of stars in Sloan Digital Sky Survey DR 12 illustrate that the accuracy of sf-CNN is still the highest. Meanwhile, the results indicate that sf-CNN outperforms VGG16 and ResNet50. Furthermore, sf-CNN is 100-200 times faster than Photutils on RTX 3070 GPU and 20-40 times faster than Photutils on I7 12700 CPU. sf-CNN can calculate fluxes efficiently and accurately only by setting a few parameters and may thus become a fundamental tool for the era of big data in astronomy. | [
1620,
1938,
1670,
555,
208
] | [
"stellar photometry",
"convolutional neural networks",
"surface photometry",
"fundamental parameters of stars",
"ccd photometry"
] |
2022PSJ.....3...92W | Large-scale Volcanism and the Heat Death of Terrestrial Worlds | Large-scale volcanism has played a critical role in the long-term habitability of Earth. Contrary to widely held belief, volcanism, rather than impactors, has had the greatest influence on and bears most of the responsibility for large-scale mass extinction events throughout Earth's history. We examine the timing of large igneous provinces (LIPs) throughout Earth's history to estimate the likelihood of nearly simultaneous events that could drive a planet into an extreme moist or runaway greenhouse, leading to the end of volatile cycling and causing the heat death of formerly temperate terrestrial worlds. In one approach, we make a conservative estimate of the rate at which sets of near-simultaneous LIPs (pairs, triplets, and quartets) occur in a random history statistically the same as Earth's. We find that LIPs closer in time than 0.1-1 million yr are likely; significantly, this is less than the time over which terrestrial LIP environmental effects are known to persist. In another approach, we assess the cumulative effects with simulated time series consisting of randomly occurring LIP events with realistic time profiles. Both approaches support the conjecture that environmental impacts of LIPs, while narrowly avoiding grave effects on the climate history of Earth, could have been responsible for the heat death of our sister world Venus. | [
2174,
2184,
1763,
439
] | [
"volcanism",
"planetary climates",
"venus",
"earth (planet)"
] |
2023ApJ...958..191S | The Third Fermi Large Area Telescope Catalog of Gamma-Ray Pulsars | We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to ≤11 known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with six undetected in radio. Overall, ≥236 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot{E}$ decreases to its observed minimum near 10<SUP>33</SUP> erg s<SUP>‑1</SUP>, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties, and fit results to guide and be compared with modeling results. | [
153,
1062,
1305,
1408,
1306,
637,
212,
1108,
1353
] | [
"binary pulsars",
"millisecond pulsars",
"pulsar timing method",
"rotation powered pulsars",
"pulsars",
"gamma-rays",
"celestial objects catalogs",
"neutron stars",
"radio pulsars"
] |
Subsets and Splits