adsabs/SciX_UAT_keywords huggingface dataset:
T-matrix and Hapke Modeling of the Thermal Infrared Spectra of Trojan Asteroids and (944) Hidalgo: Implications for Their Regolith Particle Size and Porosity

Trojan asteroids (911) Agamemnon, (1172) Aneas, and (624) Hektor and primitive asteroid (944) Hidalgo share a common thermal infrared spectral feature: a prominent 10 μm plateau that is also present in cometary comae spectra. To fit these asteroid spectra, we modeled individual minerals using the light-scattering multiple sphere T-matrix (MSTM) and Hapke reflectance models. Modeled mineral spectra were then combined using a weighted least-squares (WLS) model that included a spectral library of varied particle sizes and porosities. We later refined our method by using the mineral abundances, particle sizes, and porosities computed by WLS as an input to rerun the MSTM and Hapke models. We were able to model the asteroid spectral features using a mixture of olivine components, fine particles, and lunar-like porosities. The Trojan asteroids and (944) Hidalgo are comparable in mineral composition and particle size to spectrally similar bodies such as comet Hale-Bopp and CO3 and CY chondrite meteorites. While the required porosities for modeling are like those present on the lunar surface, they are lower than those in the meteorites and higher than those in comets.

Keywords: jupiter trojans; astronomy data modeling; spectroscopy
Planetesimal Dynamics in the Presence of a Giant Planet

Standard models of planet formation explain how planets form in axisymmetric, unperturbed disks in single star systems. However, it is possible that giant planets could have already formed when other planetary embryos start to grow. We investigate the dynamics of planetesimals under the perturbation of a giant planet in a gaseous disk. Our aim is to understand the effect of the planet's perturbation on the formation of giant planet cores outside the orbit of the planet. We calculate the orbital evolution of planetesimals ranging from 1013 to 1020 g, with a Jupiter-mass planet located at 5.2 au. We find orbital alignment of planetesimals distributed at ≃9-15 au, except for the mean motion resonance (MMR) locations. The degree of alignment increases with increasing distance from the planet and decreasing planetesimal mass. Aligned orbits lead to low encounter velocity and thus faster growth. The typical velocity dispersion for identical-mass planetesimals is $\sim { \mathcal O }(10)\,{\rm{m}}\,{{\rm{s}}}^{-1}$ except for the MMR locations. The relative velocity decreases with increasing distance from the planet and decreasing mass ratio of planetesimals. When the eccentricity vectors of planetesimals reach equilibrium under the gas drag and secular perturbation, the relative velocity becomes lower when the masses of two planetesimals are both at the larger end of the mass spectrum. Our results show that with a giant planet embedded in the disk, the growth of another planetary core outside the planet's orbit might be accelerated in certain locations.

Keywords: protoplanetary disks; orbital evolution; planetesimals; planet formation
Fuzzy Dark Matter as a Solution to Reconcile the Stellar Mass Density of High-z Massive Galaxies and Reionization History

The JWST early release data show unexpected high stellar mass densities of massive galaxies at 7 < z < 11. A high star formation efficiency is probably needed to explain this. However, such a high star formation efficiency would greatly increase the number of ionizing photons, which would be in serious conflict with current cosmic microwave background (CMB) and other measurements of cosmic reionization history. To solve this problem, we explore fuzzy dark matter (FDM), which is composed of ultra-light scalar particles, e.g., ultra-light axions, and calculate its halo mass function and stellar mass density for different axion masses. We find that a FDM model with m a ≃ 5 × 10-23 eV and a possible uncertainty range ~3 × 10-23-10-22 eV can effectively suppress the formation of small halos and galaxies, so that with higher star formation efficiency both the JWST data at z ~ 8 and the reionization history measurements from optical depth of CMB scattering and ionization fraction can be simultaneously matched. We also find that the JWST data at z ~ 10 are still too high to fit in this scenario. We note that the estimated mean redshift of the sample may have large uncertainty, that it can be as low as z ~ 9 depending on adopted spectral energy distribution templates and photometric-redshift code. In addition, warm dark matter with ~keV mass can also be an alternative choice, since it should have similar effects on halo formation as FDM.

Keywords: cosmology; dark matter; large-scale structure of the universe
Temperature and Differential Emission Measure Profiles in Turbulent Solar Active Region Loops

We examine the temperature structure of static coronal active region loops in regimes where thermal conductive transport is driven by Coulomb collisions, by turbulent scattering, or by a combination of the two. (In the last case collisional scattering dominates the heat transport at lower levels in the loop where temperatures are low and densities are high, while turbulent scattering dominates the heat transport at higher temperatures/lower densities.) Temperature profiles and their corresponding differential emission measure distributions are calculated and compared to observations, and earlier scaling laws relating the loop apex temperature and volumetric heating rate to the loop length and pressure are revisited. Results reveal very substantial changes, compared to the wholly collision-dominated case, to both the loop scaling laws and the temperature/density profiles along the loop. They also show that the well-known excess of differential emission measure at relatively low temperatures in the loop may be a consequence of the flatter temperature gradients (and so increased amount of material within a specified temperature range) that results from the predominance of turbulent scattering in the upper regions of the loop.

Keywords: active solar corona; solar active regions; solar activity; solar coronal loops; solar physics; solar ultraviolet emission
Identification of a White Dwarf Companion in the V* HP Dra System

We present Gaia DR2 2144465183642117888, a previously unknown, wide white dwarf companion to the HP Dra eclipsing binary system. This companion was discovered through the Backyard Worlds: Planet 9 citizen science collaboration. It has separation of 14"4 on the sky from the central eclipsing pair, translating to a projected separation of ~1140 au. We present a review of the orbit and physical parameters of all the components in this now triple system.

Keywords: white dwarf stars; eclipsing binary stars; multiple stars
The Distribution of Silicon and Magnesium over the Surface of 21 Com

Inspection of 10 individual spectra taken over the 24 hr monitoring of 21 Com with International Ultraviolet Explorer on 1991 April 17 reveals variations of low excitation lines of Si II between rotational phases φ = 0.18 and φ = 0.65 of the 2 days period, suggesting a inhomogeneous repartition of silicon over the surface of 21 Com. The silicon lines are weaker at rotational phase φ = 0.18. More recent optical high resolution high signal-to-noise ELODIE spectra taken in 2004 April confirm the variations of silicon lines from phase φ = 0.99 to φ = 0.47. The synthesis of the optical Si II lines yields estimates of the abundances of silicon: 8 times solar at phase 0.99 and 10 times solar at phase 0.47. The large FUV variations of 21 Com appear then to be partly due to changes in the silicon line and continuous opacity as the star rotates. In contrast, the Mg II lines do not show convincing variations between the two rotational phases observed in the optical.

Keywords: chemically peculiar stars; chemical abundances
Insights on the Origin of Odd Radio Circles from Cosmological Simulations

We investigate shock structures driven by merger events in high-resolution simulations that result in a galaxy with a virial mass M ≈ 1012 M ⊙. We find that the sizes and morphologies of the internal shocks resemble remarkably well those of the newly detected class of odd radio circles (ORCs). This would highlight a so-far overlooked mechanism to form radio rings, shells, and even more complex structures around elliptical galaxies. Mach numbers of ${ \mathcal M }$ = 2-3 for such internal shocks are in agreement with the spectral indices of the observed ORCs. We estimate that ~5% of galaxies could undergo merger events, which occasionally lead to such prominent structures within the galactic halo during their lifetime, explaining the low number of observed ORCs. At the time when the shock structures are matching the physical sizes of the observed ORCs, the central galaxies are typically classified as early-type galaxies, with no ongoing star formation, in agreement with observational findings. Although the energy released by such mergers could potentially power the observed radio luminosity already in Milky Way-like halos, our predicted luminosity from a simple, direct shock acceleration model is much smaller than the observed one. Considering the estimated number of candidates from our cosmological simulations and the higher observed energies, we suggest that the proposed scenario is more likely for halo masses around 1013 M ⊙ in agreement with the observed stellar masses of the galaxies at the center of ORCs. Such shocks might be detectable with next-generation X-ray instruments like the Line Emission Mapper (LEM).

Keywords: galaxies; hydrodynamical simulations; radio continuum emission; galaxy mergers
Variability Timescales of Hα on Active Mid-to-late M dwarfs

We present a study of the variation timescales of the chromospheric activity indicator Hα on a sample of 13 fully convective, active mid-to-late M stars with masses between 0.1 and 0.3 solar masses. Our goal was to determine the dominant variability timescale and, by inference, a possible mechanism responsible for the variation. We gathered 10 or more high-resolution spectra each of 10 stars using the TRES spectrograph at times chosen to span all phases of stellar rotation, as determined from photometric data from the MEarth Observatories. All stars varied in their Hα emission. For nine of these stars, we found no correlation between Hα and rotational phase, indicating that constant emission from fixed magnetic structures, such as star spots and plage, are unlikely to be the dominant source of Hα emission variability. In contrast, one star, G 7-34, shows a clear relationship between Hα and stellar rotational phase. Intriguingly, we found that this star is a member of the AB Doradus moving group and hence has the young age of 149 Myr. High-cadence spectroscopic observations of three additional stars revealed that they are variable on timescales ranging from 20 to 45 minutes, which we posit may be due to flaring behavior. For one star, GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in Hα emission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in Hα on the timescales we observe and thus may be the dominant source of Hα variability on active fully convective M dwarfs.

Keywords: stellar flares; m dwarf stars; stellar activity; stellar rotation
Radial Migration of Gap-opening Planets in Protoplanetary Disks. II. The Case of a Planet Pair

When two planets are born in a protoplanetary disk, they may enter into mean-motion resonance as a consequence of convergent planetary migration. The formation of mean-motion resonances is important for understanding how planetary systems are shaped in disk environments. Motivated by recent progress in the comprehension of the migration of partial gap-opening planets, we have investigated the orbital evolution of planet pairs in a wide range of masses and disk properties with the aim to find out when resonance capture is likely to happen. Using the formula for the migration timescale of a gap-opening planet developed in our previous work, we have derived a simple criterion that allows us to predict when the migration will be convergent (divergent). Further, we have verified the criterion using two-dimensional hydrodynamic simulations. We have found that the resonant pair of planets formed at the early phase of evolution can depart from resonance at later times because the migration speed of the outer planet slows down due to gap formation. Moreover, adopting our formula for the migration timescale, we have also carried out three-body simulations, which confirm the results of hydrodynamic simulations. Finally, we have compared our predictions with observations, selecting a sample of known two-planet systems.

Keywords: protoplanetary disks; planet formation; planetary system formation
Kinetic Alfvén Waves in Space Plasma Environment with κ-electrons

A resonant instability of kinetic Alfvén waves (KAWs) driven by ion beam is discussed through a theoretical model encompassing Maxwellian background ions and beam ions and non-Maxwellian κ-electrons. The ion beam velocity alone as a source is able to excite the KAWs up to a significant growth. The non-Maxwellian parameter κ impedes the growth of KAWs by restricting the wave unstable region. The effects of other plasma parameters such as propagation angle, temperature of the plasma species, and ion plasma beta on the excitation of KAWs are also examined. The present model can generate waves with frequencies in the range of ≈6.6-51.2 mHz, which are relevant to explaining the observed ultralow frequency waves at auroral ionospheric altitudes. Theoretical model predictions will also be applicable to other planetary environments where ion beams and non-Maxwellian κ-electrons are present.

Keywords: solar wind; space plasmas; alfven waves
Very Metal-poor Stars in the Solar Vicinity: Age Determination

The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and superimpose isochrones from different sources on the stars' color-magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low-metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be 13.9 ± 0.5 Gyr using Padova isochrones, and 13.7 ± 0.4 Gyr using BASTI isochrones. We found also a group of very metal-poor stars ([Fe/H] = -2.7 to -2.0 dex) with relatively young ages, in the range 8-10 Gyr.

Keywords: metallicity; population ii stars; stellar ages
Information Theoretical Approach to Understanding Flare Waiting Times

There is not currently a consensus on the process responsible for producing the waiting time distribution of solar flares. This study presents an information theoretical approach to determining whether solar flare data are significantly distinguishable from a nonstationary Poisson process. A study of solar flares stronger than C1 class detected by the Geostationary Operational Environmental Satellite from 1975 to 2017 was performed. A sequence of waiting times (time elapsed between adjacent X-ray flare peaks) was constructed from the data. Surrogate waiting time sequences were produced using a time-varying Poisson firing rate from the Bayesian block procedure. Utilizing Shannon entropy, the mutual information of time-lagged waiting time distributions was computed for both the original data and the surrogates using a method of discretization by binning. When the entire period is considered, we see that when compared to carefully constructed surrogates, there is a significant elevation of mutual information on a timescale of approximately 30 hr, demonstrating that flares are confidently related to subsequent flares, contradicting the null hypothesis that flares are produced by a nonstationary Poisson process. When only 4 yr subsets of the data are considered, we see that at relatively small timescales (on the order of 10-30 hr), solar flare waiting times have a significant impact on subsequent flares. When corrected for the number of points in each considered time window, there is no correlation between the magnitude of significance and position in the solar cycle.

Keywords: solar flares; poisson distribution; solar activity
A Statistical Study of Propagating MHD Kink Waves in the Quiescent Corona

The Coronal Multi-channel Polarimeter (CoMP) has opened up exciting opportunities to probe transverse MHD waves in the Sun's corona. The archive of CoMP data is utilized to generate a catalog of quiescent coronal loops that can be used for studying propagating kink waves. The catalog contains 120 loops observed between 2012 and 2014. This catalog is further used to undertake a statistical study of propagating kink waves in the quiet regions of the solar corona, investigating phase speeds, loop lengths, footpoint power ratio (a measure of wave power entering the corona through each footpoint of a loop) and equilibrium parameter (which provides a measure of the change in wave amplitude) values. The statistical study enables us to establish the presence of a relationship between the rate of damping and the length of the coronal loop, with longer coronal loops displaying weaker wave damping. We suggest the reason for this behavior is related to a decreasing average density contrast between the loop and ambient plasma as loop length increases. The catalog presented here will provide the community with the foundation for the further study of propagating kink waves in the quiet solar corona.

Keywords: magnetohydrodynamics; quiet solar corona; solar coronal loops; solar coronal heating; quiet sun; solar activity
Acceleration of Relativistic Particles in Counterpropagating Circularly Polarized Alfvén Waves

Counterpropagating Alfvén waves are ubiquitously observed in many astrophysical environments, such as a star surface and a planetary foreshock. We discuss an efficient particle acceleration mechanism in two counterpropagating circularly polarized Alfvén waves. Phase transitions of particle behavior occur when wave amplitudes exceed two critical values. Above the critical amplitudes, the numerical simulation shows that any particles irreversibly gain relativistic energy within a short time regardless of their initial position and energy once the coherent waveform is formed. The accelerated particles have spatial coherence. Higher wave phase velocity requires smaller critical amplitudes, while the maximum attainable energy increases as the wavenumber and the frequency decrease. The results may be applicable in some astrophysical phenomena, as well as a future laboratory experiment using high-power lasers.

Keywords: heliosphere; cosmic rays; magnetars; solar wind
The Direct-method Oxygen Abundance of Typical Dwarf Galaxies at Cosmic High Noon

We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲ z ≲ 2.6 (z mean = 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of $\mathrm{log}{({M}_{* }/{M}_{\odot })}_{\mathrm{med}}={8.29}_{-0.43}^{+0.51}$ and a median star formation rate of ${{\rm{S}}{\rm{F}}{\rm{R}}}_{{\rm{H}}\alpha }^{{\rm{m}}{\rm{e}}{\rm{d}}}={2.25}_{-1.26}^{+2.15}\,{M}_{\odot }\,{{\rm{y}}{\rm{r}}}^{-1}$ . We measure the faint electron-temperature-sensitive [O III] λ4363 emission line at 2.5σ (4.1σ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of $12+\mathrm{log}{({\rm{O}}/{\rm{H}})}_{\mathrm{direct}}={7.88}_{-0.22}^{+0.25}$ ( ${0.15}_{-0.06}^{+0.12}\ {Z}_{\odot }$ ). We investigate the applicability at high z of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixed M *, our composite is well represented by the z ~ 2.3 direct-method stellar mass-gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories $(\mathrm{log}{({M}_{* }/{M}_{\odot })}_{\mathrm{med}}={8.92}_{-0.22}^{+0.31})$ , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixed M * and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [O II] λ3729/[O II] λ3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ${n}_{e}={1}_{-0}^{+215}\ {\mathrm{cm}}^{-3}$ ( ${n}_{e}={1}_{-0}^{+74}\ {\mathrm{cm}}^{-3}$ ) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies at z ~ 2. ∗ The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs #9289, #11710, #11802, #12201, #12931, #13389, #13498, #13504.

Keywords: galaxy abundances; dwarf galaxies; high-redshift galaxies; galaxy evolution; interstellar medium; scaling relations
A VLA View of the Flared, Asymmetric Disk around the Class 0 Protostar L1527 IRS

We present high-resolution Karl G. Jansky Very Large Array (VLA) observations of the protostar L1527 IRS at 7 mm, 1.3 cm, and 2 cm wavelengths. We detect the edge-on dust disk at all three wavelengths and find that it is asymmetric, with the southern side of the disk brighter than the northern side. We confirm this asymmetry through analytic modeling and also find that the disk is flared at 7 mm. We test the data against models including gap features in the intensity profile, and though we cannot rule such models out, they do not provide a statistically significant improvement in the quality of fit to the data. From these fits, we can, however, place constraints on allowed properties of any gaps that could be present in the true, underlying intensity profile. The physical nature of the asymmetry is difficult to associate with physical features owing to the edge-on nature of the disk, but it could be related to spiral arms or asymmetries seen in other imaging of more face-on disks.

Keywords: star formation; planet formation; protoplanetary disks; planetary system formation; protostars