adsabs/SciX_UAT_keywords huggingface dataset:
3D Radiation Hydrodynamic Simulations of Gravitational Instability in AGN Accretion Disks: Effects of Radiation Pressure

We perform 3D radiation hydrodynamic local shearing-box simulations to study the outcome of gravitational instability (GI) in optically thick active galactic nuclei (AGNs) accretion disks. GI develops when the Toomre parameter Q T ≲ 1, and may lead to turbulent heating that balances radiative cooling. However, when radiative cooling is too efficient, the disk may undergo runaway gravitational fragmentation. In the fully gas-pressure-dominated case, we confirm the classical result that such a thermal balance holds when the Shakura-Sunyaev viscosity parameter (α) due to the gravitationally driven turbulence is ≲0.2, corresponding to dimensionless cooling times Ωt cool ≳ 5. As the fraction of support by radiation pressure increases, the disk becomes more prone to fragmentation, with a reduced (increased) critical value of α (Ωt cool). The effect is already significant when the radiation pressure exceeds 10% of the gas pressure, while fully radiation-pressure-dominated disks fragment at t cool ≲ 50 Ω-1. The latter translates to a maximum turbulence level α ≲ 0.02, comparable to that generated by magnetorotational instability. Our results suggest that gravitationally unstable (Q T ~ 1) outer regions of AGN disks with significant radiation pressure (likely for high/near-Eddington accretion rates) should always fragment into stars, and perhaps black holes.

Keywords: galaxy accretion disks; star formation; gravitational instability; supermassive black holes; accretion
Mid-infrared Studies of HD 113766 and HD 172555: Assessing Variability in the Terrestrial Zone of Young Exoplanetary Systems

We present multiepoch infrared photometry and spectroscopy obtained with warm Spitzer, Subaru, and the Stratospheric Observatory for Infrared Astronomy to assess variability for the young (∼20 Myr) and dusty debris systems around HD 172555 and HD 113766A. No variations (within 0.5%) were found for the former at either 3.6 or 4.5 μm, while significant nonperiodic variations (peak to peak of ∼10%-15% relative to the primary star) were detected for the latter. Relative to the Spitzer Infrared Spectrograph spectra taken in 2004, multiepoch mid-infrared spectra reveal no change in either the shape of the prominent 10 μm solid-state features or the overall flux levels (no more than 20%) for both systems, corroborating the fact that the population of submicron-size grains that produce the pronounced solid-state features is stable over a decadal timescale. We suggest that these submicron-size grains were initially generated in an optically thick clump of debris of millimeter-size vapor condensates resulting from a recent violent impact between large asteroidal or planetary bodies. Because of the shielding from the stellar photons provided by this clump, intense collisions led to an overproduction of fine grains that would otherwise be ejected from the system by radiation pressure. As the clump is sheared by its orbital motion and becomes optically thin, a population of very fine grains could remain in stable orbits until Poynting-Robertson drag slowly spirals them into the star. We further suggest that the 3-5 μm disk variation around HD 113766A is consistent with a clump/arc of such fine grains on a modestly eccentric orbit in its terrestrial zone.

Keywords: circumstellar matter; debris disks; exozodiacal dust; infrared excess; early-type stars; extrasolar rocky planets
Possible Detection of the Progenitor of the Type II Supernova SN 2023ixf

Stellar evolution theory predicts multiple pathways to the explosive deaths of stars as supernovae. Locating and characterizing the progenitors of well-studied supernovae is important to constrain the theory and to justify and design future surveys to improve on progenitor detections. Here we report the serendipitous preexplosion imaging, by the Hubble Space Telescope, of SN 2023ixf, one of the nearest extragalactic supernovae ever discovered, in the galaxy M101. The extremely red color and absolute magnitude ${M}_{{\rm{F}}814{\rm{W}}}=-{5.11}_{-0.47}^{+0.65}$ mag suggest that the progenitor was a red supergiant. Comparison with stellar evolutionary isochrones suggests it is within the relatively low initial mass range of ~8-10 M ⊙ and that there is likely a lot of dust present at the supernova site.

Keywords: type ii supernovae; supernovae; core-collapse supernovae
The Cross-sectional Shape and Height Expansion of Coronal Loops: High-resolution Coronal Imager (Hi-C) Analysis of AR 12712

Coronal loop observations have existed for many decades yet the precise shape of these fundamental coronal structures is still widely debated since the discovery that they appear to undergo negligible expansion between their footpoints and apex. In this work a selection of eight EUV loops and their 22 sub-element strands are studied from the second successful flight of NASA's High-resolution Coronal Imager (Hi-C 2.1). Four of the loops correspond to open fan structures with the other four considered to be magnetically closed loops. Width analysis is performed on the loops and their sub-resolution strands using our method of fitting multiple Gaussian profiles to cross-sectional intensity slices. It is found that while the magnetically closed loops and their sub-element strands do not expand along their observable length, open fan structures may expand an additional 150% of their initial width. Following recent work, the Pearson correlation coefficient between peak intensity and loop/strand width are found to be predominantly positively correlated for the loops (≈88%) and their sub-element strands (≈80%). These results align with the hypothesis of Klimchuk & DeForest that loops and-for the first time-their sub-element strands have approximately circular cross-sectional profiles.

Keywords: solar coronal loops; solar corona; solar active regions
Mass-shedding Activities of Asteroid (3200) Phaethon Enhanced by Its Rotation

Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of 3.60 hr and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of 6.25 km. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is 0.5-1.5 g cm-3 (a typical bulk density of a B-type asteroid). We found that in this condition, the structure of Phaethon is sensitive to failure unless the cohesive strength is ∼ 50 - ∼ 260 Pa. This result implies that if there are some surface processes driven by, for example, thermal waves, large-scaled deformation may happen and cause mass shedding. From this interpretation, we propose the processes that produced the Geminid meteor stream in the past and dust tails recently. Phaethon initially rotated at a spin period shorter than the current period. The magnitude of structural deformation at this stage was higher than the present spin condition, and a large mass-shedding event, I.e., the Geminid meteor stream, occurred. After this deformation process, the body became more oblate, and its spin slowed down. At this point, while the spin was high enough for the body to have mass-shedding events, the magnitude of these events became small.

Keywords: near-earth objects; asteroids; planetary structure; planetary science; planetary surfaces; meteor streams; meteors
SMC-Last Mosaic Images

We present mosaic images of the Small Magellanic Cloud (SMC) observed with the Spitzer IRAC 3.6 μm and 4.5 μm bands over two epochs, 2017 August 25-2017 September 13 and 2017 November 24-2018 February 12. The survey region comprises ~30 deg2 covering the SMC and the Bridge to the Large Magellanic Cloud. The region is covered by 52 ~ 1.°1 × 1.°1 tiles, with each tile including images in each band for both separate and combined epochs. The mosaics are made in individual tangent projections in J2000 coordinates. The angular pixel size is 0.″6 with a resolution (FWHM) of ~2.″0. We describe processing to correct or mitigate residual artifacts and remove background discontinuities. The mosaic images are publicly available at the Infrared Science Archive.

Keywords: small magellanic cloud; infrared astronomy
Optical Transmission Spectra of Hot Jupiters: Effects of Scattering

We present new grids of transmission spectra for hot Jupiters by solving the multiple-scattering radiative transfer equations with non-zero scattering albedo instead of using the Beer-Bouguer-Lambert law for the change in the transmitted stellar intensity. The diffused reflection and transmission due to scattering increase the transmitted stellar flux resulting, in a decrease in the transmission depth. Thus, we demonstrate that scattering plays a double role in determining the optical transmission spectra—increasing the total optical depth of the medium and adding the diffused radiation due to scattering to the transmitted stellar radiation. The resulting effects yield an increase in the transmitted flux and hence a reduction in the transmission depth. For a cloudless planetary atmosphere, Rayleigh scattering albedo alters the transmission depth up to about 0.6 μm, but the change in the transmission depth due to forward scattering by cloud or haze is significant throughout the optical and near-infrared regions. However, at wavelengths longer than about 1.2 μm, the scattering albedo becomes negligible, hence the transmission spectra match with that calculated without solving the radiative transfer equations. We compare our model spectra with existing theoretical models and find significant differences at wavelengths shorter than one micron. We also compare our models with observational data for a few hot Jupiters, which may help with constructing better retrieval models in the future.

Keywords: exoplanet atmospheres; transmission spectroscopy; radiative transfer; atmospheric effects
A Tale of Two Type Ia Supernovae: The Fast-declining Siblings SNe 2015bo and 1997cn

We present optical and near-infrared photometric and spectroscopic observations of the fast-declining Type Ia supernova (SN) 2015bo. SN 2015bo is underluminous (M B = -17.50 ± 0.15 mag) and has a fast-evolving light curve (Δm15(B) = 1.91 ± 0.01 mag and s BV = 0.48 ± 0.01). It has a unique morphology in the observed V - r color curve, where it is bluer than all other supernovae (SNe) in the comparison sample. A 56Ni mass of 0.17 ± 0.03 M ⊙ was derived from the peak bolometric luminosity, which is consistent with its location on the luminosity-width relation. Spectroscopically, SN 2015bo is a cool SN in the Branch classification scheme. The velocity evolution measured from spectral features is consistent with 1991bg-like SNe. SN 2015bo has a SN twin (similar spectra) and sibling (same host galaxy), SN 1997cn. Distance moduli of μ = 34.33 ± 0.01 (stat) ±0.11 (sys) mag and μ = 34.34 ± 0.04 (stat) ± 0.12 (sys) mag are derived for SN 2015bo and SN 1997cn, respectively. These distances are consistent at the 0.06σ level with each other, and they are also consistent with distances derived using surface-brightness fluctuations and redshift-corrected cosmology. This suggests that fast-declining SNe could be accurate distance indicators, which should not be excluded from future cosmological analyses.

Keywords: supernovae
AstroSat/UVIT Study of the Diffuse Ultraviolet Radiation in the Dwarf Galaxy Holmberg II

We present measurements of diffuse ultraviolet (UV) emission in the dwarf irregular galaxy Holmberg II obtained with the Ultra Violet Imaging Telescope (UVIT) instrument onboard AstroSat, India's first multiwavelength space mission. With a spatial resolution of 1.″2–1.″6, these are the highest resolution UV observations of the galaxy to date. We find that diffuse emission accounts for ∼70.6% of the total far-ultraviolet (FUV) and for ~58.1% of the total near-ultraviolet (NUV) emission. In the FUV, this is reasonably close to the fraction reported for the SMC bar. We perform a UV–IR correlation study of the diffuse emission in this galaxy using infrared (IR) observations from the Spitzer Space Telescope and Herschel Space Observatory for selected locations, free of detectable bright point sources. The strongest positive correlation between FUV and IR is observed at 70 μm for high H I density (N(H I) > 1 × 1021 cm‑2) locations, indicating that warm dust grains dominate the IR emission, in agreement with earlier studies, while NUV is better correlated with 160 μm emission associated with cold dust grains. Low H I density regions (N(H I) < 1 × 1021 cm‑2), or cavities, do not show any significant UV–IR correlation except at 160 μm, implying either the presence of colder dust grains in cavities being irradiated by the general radiation field, or insufficient amount of dust. The dust scattering contribution in high H I density regions, estimated using a single scattering model with foreground dust clouds with LMC reddening, gives best-fit albedo and asymmetry factor values of α = 0.2 and g = 0.5, respectively, in reasonable agreement with the theoretical predictions for LMC dust. Our model-derived scattering optical depths in the FUV range from 0.02 to 0.12, implying the medium is optically thin. Therefore, in high H I density regions, dust scattering can be one of the sources of the observed diffuse UV emission, apart from possible contributions from H2 fluorescence. However, the diffuse UV component in H I cavities can only be explained via other mechanisms, such as two-photon emission.

Keywords: galaxies; dwarf irregular galaxies
Thermal Evolution and Magnetic History of Rocky Planets

We present a thermal evolution model coupled with a Henyey solver to study the circumstances under which a rocky planet could potentially host a dynamo in its liquid iron core and/or magma ocean. We calculate the evolution of planet thermal profiles by solving the energy-balance equations for both the mantle and the core. We use a modified mixing length theory to model the convective heat flow in both the magma ocean and solid mantle. In addition, by including the Henyey solver, we self-consistently account for adjustments in the interior structure and heating (cooling) due to planet contraction (expansion). We evaluate whether a dynamo can operate using the critical magnetic Reynolds number. We run simulations to explore how the planet mass (M pl), core mass fraction (CMF), and equilibrium temperature (T eq) affect the evolution and lifetime of possible dynamo sources. We find that the T eq determines the solidification regime of the magma ocean, and only layers with melt fraction greater than a critical value of 0.4 may contribute to the dynamo source region in the magma ocean. We find that the mantle mass, determined by M pl and CMF, controls the thermal isolating effect on the iron core. In addition, we show that the liquid core lasts longer with increasing planet mass. For a core thermal conductivity of 40 Wm-1 K-1, the lifetime of the dynamo in the iron core is limited by the lifetime of the liquid core for 1 M ⊕ planets and by the lack of thermal convection for 3 M ⊕ planets.

Keywords: exoplanet evolution; exoplanet structure; extrasolar rocky planets; magnetic fields
The Orbital Geometries and Stellar Obliquities of Exoplanet-hosting Multistar Systems

The current orbital geometries of exoplanet systems offer a fossilized record of the systems' dynamical histories. A particularly rich set of dynamical mechanisms is available to exoplanets residing in multistar systems, which may have their evolution shaped by the gravitational influence of bound stellar companions. In this work, we examine the joint distribution of stellar obliquities and orbital orientations for transiting exoplanets residing within astrometrically resolved binary and triple-star systems. We leverage existing constraints on stellar obliquities in exoplanet systems, together with astrometric measurements from Gaia DR3, to uncover a set of fully aligned, "orderly" exoplanet systems that exhibit evidence of both spin–orbit and orbit–orbit alignment. We also find evidence that the observed distribution of orbit–orbit orientations in our sample is more strongly peaked toward alignment than an isotropic distribution. Our results may be indicative of efficient viscous dissipation by nodally recessing protoplanetary disks, demonstrating a regime in which stellar companions produce and maintain order in planetary systems, rather than enhancing misalignments.

Keywords: exoplanets; binary stars; planetary alignment; exoplanet astronomy; exoplanet dynamics; exoplanet systems; circumstellar disks; planetary-disk interactions; protoplanetary disks; star-planet interactions; orbit determination; orbital evolution
GRB Prompt Emission with Anisotropic Electron Distribution

The typical spectrum of the prompt emission of gamma-ray bursts (GRBs) indicates that the electron cooling is suppressed in spite of the strong magnetic field in the standard synchrotron model. Recent particle-in-cell simulations show that the particle acceleration by magnetic reconnection in a magnetically dominated plasma can lead to small pitch angles especially in a low-energy region. Such a small pitch angle prevents electrons from cooling via synchrotron radiation. In this paper, taking into account the effects of the synchrotron cooling and the adiabatic cooling, we numerically calculate the synchrotron spectra with anisotropic electron distributions. If we require a Poynting flux larger than 1050 erg s-1 as the model is motivated by magnetic reconnection, the bulk Lorentz factor of ~1000 and the electron minimum Lorentz factor of γ min ~ 104 are required to reproduce the typical GRB spectrum.

Keywords: gamma-ray bursts
Beyond the Drake Equation: A Time-dependent Inventory of Habitable Planets and Life-bearing Worlds in the Solar Neighborhood

We introduce a mathematical framework for statistical exoplanet population and astrobiology studies that may help direct future observational efforts and experiments. The approach is based on a set of differential equations and provides a time-dependent mapping between star formation, metal enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemo-population history of the solar neighborhood. Our results are summarized as follows: (1) the formation of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about 11 Gyr ago; (2) within 100 pc from the Sun, there are as many as 11,000(η ⊕/0.24) Earth-size planets in the habitable zone ("temperate terrestrial planets" or TTPs) of K-type stars. The solar system is younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and was triggered by an external agent; (3) the metallicity modulation of the giant planet occurrence rate results in a later typical formation time, with TTPs outnumbering giant planets at early times; and (4) the closest, life-harboring Earth-like planet would be ≲20 pc away if microbial life arose as soon as it did on Earth in ≳1% of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also old, as it would have emerged more than 8 Gyr ago in about one-third of all life-bearing planets today. Older Earth analogs are more likely to have developed sufficiently complex life capable of altering their environment and producing detectable oxygenic biosignatures.

Keywords: astrobiology; exoplanets; star formation; solar neighborhood; biosignatures
Reconstructing the Coronal Magnetic Field: The Role of Cross-field Currents in Solution Uniqueness

We present a new 3D magnetohydrostatic (MHS) direct elliptic solver for extrapolating the coronal magnetic field from photospheric boundary conditions in a manner consistent with an assumed plasma distribution. We use it to study the uniqueness of the reconstructed magnetic field as a function of how significant the plasma forcing is on the force balance of the magnetic field. To this end, we consider an analytic MHS model as ground truth. The model uses two free parameters to decompose the current into two parts: a magnetic-field-aligned component and a cross-field component. We perform a comprehensive study of the 2D parameter space to understand under what conditions the ground truth can be reproduced uniquely. We find that current oriented perpendicular to the magnetic field has a smaller solution space than the same amount of current oriented parallel to the magnetic field, and so MHS regimes with larger proportions of plasma-related forcing may be a promising avenue toward finding unique magnetic field reconstructions.

Keywords: solar corona; solar magnetic fields; computational methods; magnetohydrodynamics
The Geologic Impact of 16 Psyche's Surface Temperatures

NASA's Discovery mission Psyche will soon be launched to visit the asteroid 16 Psyche. In this work, we model the surface temperatures of 16 Psyche. Our modeling is focused on capturing the diurnal and seasonal surface temperature variations caused by 16 Psyche's large obliquity (95°) and moderately high eccentricity (0.134). Using a semianalytic framework, we predict that large thermal variations (including at the poles) can cause cracking of boulders leading to a porous surface regolith. This prediction is consistent with a high-porosity surface regolith inferred from thermal inertia measurements. We also find that water ice is not likely to be stable at any latitude.

Keywords: asteroid surfaces; asteroids
A Gaussian Process Regression Reveals No Evidence for Planets Orbiting Kapteyn's Star

Radial-velocity (RV) planet searches are often polluted by signals caused by gas motion at the star's surface. Stellar activity can mimic or mask changes in the RVs caused by orbiting planets, resulting in false positives or missed detections. Here we use Gaussian process regression to disentangle the contradictory reports of planets versus rotation artifacts from Kapteyn's star. To model rotation, we use joint quasiperiodic kernels for the RV and Hα signals, requiring that their periods and correlation timescales be the same. We find that the rotation period of Kapteyn's star is 125 days, while the characteristic active-region lifetime is 694 days. Adding a planet to the RV model produces a best-fit orbital period of 100 yr, or 10 times the observing time baseline, indicating that the observed RVs are best explained by star rotation only. We also find no significant periodic signals in residual RV data sets constructed by subtracting off realizations of the best-fit rotation model and conclude that both previously reported "planets" are artifacts of the star's rotation and activity. Our results highlight the pitfalls of using sinusoids to model quasiperiodic rotation signals.

Keywords: radial velocity; exoplanet detection methods; stellar activity; starspots; gaussian processes regression; stellar rotation
The Araucaria Project: Deep Near-infrared Photometric Maps of Local and Sculptor Group Galaxies. I. Carina, Fornax, and Sculptor

Deep near-infrared (NIR) J- and K-band photometry of three Local Group dwarf spheroidal galaxies—Fornax, Carina, and Sculptor—is made available for the community. Until now, these data have only been used by the Araucaria Project to determine distances using the tip of the red giant branch and RR Lyrae stars. Now, we present the entire data collection in the form of a database, consisting of accurate J- and K-band magnitudes, sky coordinates, ellipticity measurements, and timestamps of observations, complemented by stars' loci in their reference images. The depth of our photometry reaches about 22 mag at the 5σ level, and is comparable to NIR surveys, such as the UKIRT Infrared Deep Sky Survey (UKIDSS) or the VISTA Hemisphere Survey (VHS). Small overlap with VHS and no overlap with UKIDSS makes our database a unique source of quality photometry.

Keywords: observational astronomy; infrared photometry; astronomy databases; dwarf galaxies