adsabs/SciX_UAT_keywords huggingface dataset:
The Demographics of Terrestrial Planets in the Venus Zone

Understanding the physical characteristics of Venus, including its atmosphere, interior, and its evolutionary pathway with respect to Earth, remains a vital component for terrestrial planet evolution models and the emergence and/or decline of planetary habitability. A statistical strategy for evaluating the evolutionary pathways of terrestrial planets lies in the atmospheric characterization of exoplanets, where the sample size provides sufficient means for determining required runaway greenhouse conditions. Observations of potential exo-Venuses can help confirm hypotheses about Venus's past, as well as the occurrence rate of Venus-like planets in other systems. Additionally, the data from future Venus missions, such as DAVINCI, EnVision, and VERITAS, will provide valuable information regarding Venus, and the study of exo-Venuses will be complimentary to these missions. To facilitate studies of exo-Venus candidates, we provide a catalog of all confirmed terrestrial planets in the Venus zone, including transiting and nontransiting cases, and quantify their potential for follow-up observations. We examine the demographics of the exo-Venus population with relation to stellar and planetary properties, such as the planetary radius gap. We highlight specific high-priority exo-Venus targets for follow-up observations, including TOI-2285 b, LTT 1445 A c, TOI-1266 c, LHS 1140 c, and L98-59 d. We also discuss follow-up observations that may yield further insight into the Venus/Earth divergence in atmospheric properties.

Keywords: exoplanet astronomy; exoplanet catalogs; exoplanet atmospheres; exoplanet systems; exoplanets; venus; observational astronomy
Cooling Envelope Model for Tidal Disruption Events

We present a toy model for the thermal optical/UV/X-ray emission from tidal disruption events (TDEs). Motivated by recent hydrodynamical simulations, we assume that the debris streams promptly and rapidly circularize (on the orbital period of the most tightly bound debris), generating a hot quasi-spherical pressure-supported envelope of radius R v ~ 1014 cm (photosphere radius ~1015 cm) surrounding the supermassive black hole (SMBH). As the envelope cools radiatively, it undergoes Kelvin-Helmholtz contraction R v ∝ t -1, its temperature rising T eff ∝ t 1/2 while its total luminosity remains roughly constant; the optical luminosity decays as $\nu {L}_{\nu }\propto \,{R}_{v}^{2}{T}_{\mathrm{eff}}\propto {t}^{-3/2}$ . Despite this similarity to the mass fallback rate ${\dot{M}}_{\mathrm{fb}}\propto {t}^{-5/3}$ , envelope heating from fallback accretion is subdominant compared to the envelope cooling luminosity except near optical peak (where they are comparable). Envelope contraction can be delayed by energy injection from accretion from the inner envelope onto the SMBH in a regulated manner, leading to a late-time flattening of the optical/X-ray light curves, similar to those observed in some TDEs. Eventually, as the envelope contracts to near the circularization radius, the SMBH accretion rate rises to its maximum, in tandem with the decreasing optical luminosity. This cooling-induced (rather than circularization-induced) delay of up to several hundred days may account for the delayed onset of thermal X-rays, late-time radio flares, and high-energy neutrino generation, observed in some TDEs. We compare the model predictions to recent TDE light-curve correlation studies, finding both agreement and points of tension.

Keywords: tidal disruption; accretion
The Magnetic Sensitivity of the (250-278 nm) Fe II Polarization Spectrum

This paper presents a theoretical investigation of the polarization and magnetic sensitivity of the near-ultraviolet (near-UV) solar spectral lines of Fe II between 250 and 278 nm. In recent years, UV spectropolarimetry has become key to uncovering the magnetism of the upper layers of the solar chromosphere. The unprecedented data obtained by the CLASP2 suborbital space experiment across the Mg II h and k lines around 280 nm are a clear example of the capabilities of near-UV spectropolarimetry for magnetic field diagnostics throughout the whole solar chromosphere. Recent works have pointed out the possible complementary diagnostic potential of the many Fe II lines in the unexplored spectral region between 250 and 278 nm, but no quantitative analysis of the polarization and magnetic sensitivity of those spectral lines has been carried out yet. To study the polarization signals in these spectral lines, we create a comprehensive atomic model including all the atomic transitions resulting in strong spectral lines. We then study the magnetic sensitivity of the linear and circular polarization profiles in a semiempirical model representative of the quiet Sun. We present a selection of Fe II spectral lines with significant linear and circular polarization signals and evaluate their diagnostic capabilities by studying their formation heights and magnetic sensitivity through the action of the Hanle and Zeeman effects. We conclude that when combined with the CLASP2 spectral region these Fe II lines are of interest for the inference of magnetic fields throughout the solar chromosphere, up to near the base of the corona.

Keywords: spectropolarimetry; radiative transfer; solar magnetic fields; quiet sun; solar chromosphere
Scaling K2. VII. Evidence For a High Occurrence Rate of Hot Sub-Neptunes at Intermediate Ages

The NASA K2 mission obtained high-precision time-series photometry for four young clusters, including the near-twin 600-800 Myr old Praesepe and Hyades clusters. Hot sub-Neptunes are highly prone to mass-loss mechanisms, given their proximity to the host star and the weakly bound gaseous envelopes, and analyzing this population at young ages can provide strong constraints on planetary evolution models. Using our automated transit detection pipeline, we recover 15 planet candidates across the two clusters, including 10 previously confirmed planets. We find a hot sub-Neptune occurrence rate of 79%-107% for GKM stars in the Praesepe cluster. This is 2.5-3.5σ higher than the occurrence rate of ${16.54}_{-0.98}^{+1.00}$ % for the same planets orbiting the ~3-9 Gyr old GKM field stars observed by K2, even after accounting for the slightly supersolar metallicity ([Fe/H] ~ 0.2 dex) of the Praesepe cluster. We examine the effect of adding ~100 targets from the Hyades cluster and extending the planet parameter space under examination, and we find similarly high occurrence rates in both cases. The high occurrence rate of young, hot sub-Neptunes could indicate either that these planets are undergoing atmospheric evolution as they age, or that planetary systems that formed when the Galaxy was much younger are substantially different than from today. Under the assumption of the atmospheric mass-loss scenario, a significantly higher occurrence rate of these planets at the intermediate ages of Praesepe and Hyades appears more consistent with the core-powered mass-loss scenario for the origin of the planet radius valley, compared to the photoevaporation scenario.

Keywords: exoplanets; exoplanet atmospheric evolution
An In-depth Look at TOI-3884b: A Super-Neptune Transiting an M4Dwarf with Persistent Starspot Crossings

We perform an in-depth analysis of the recently validated TOI-3884 system, an M4-dwarf star with a transiting super-Neptune. Using high-precision light curves obtained with the 3.5 m Apache Point Observatory and radial velocity observations with the Habitable-zone Planet Finder, we derive a planetary mass of ${32.6}_{-7.4}^{+7.3}\,{M}_{\oplus }$ and radius of 6.4 ± 0.2 R ⊕. We detect a distinct starspot crossing event occurring just after ingress and spanning half the transit for every transit. We determine this spot feature to be wavelength dependent with the amplitude and duration evolving slightly over time. Best-fit starspot models show that TOI-3884b possesses a misaligned (λ = 75° ± 10°) orbit that crosses a giant pole spot. This system presents a rare opportunity for studies into the nature of both a misaligned super-Neptune and spot evolution on an active mid-M dwarf.

Keywords: exoplanet astronomy; exoplanets; exoplanet detection methods; starspots
A Recommendation to Retire VESPA for Exoplanet Validation

VESPA, the first open-source python package built to probabilistically validate exoplanet transit signals, has contributed to the validation of over a thousand exoplanets. However, since it is no longer maintained and has not been updated to account for the modern astronomy data landscape, we recommend retiring it in favor of the newer, actively maintained TRICERATOPS package.

Keywords: exoplanets; astronomy software
A Mid-infrared Flare in the Active Galaxy MCG-02-04-026: Dust Echo of a Nuclear Transient Event

We report the discovery of a mid-infrared (MIR) flare using Wide field Infrared Survey Explorer data in the center of the nearby Seyfert 1.9 galaxy MCG-02-04-026. The MIR flare began in the first half of 2014, peaked around the end of 2015, and faded in 2017. During these years, energy of more than 7 × 1050 erg was released in the infrared, and the flare's MIR color was generally turning red. We detected neither optical nor ultraviolet (UV) variation corresponding to the MIR flare based on available data. We explained the MIR flare using a dust echo model in which the radiative transfer is involved. The MIR flare can be well explained as thermal reradiation from dust heated by UV-optical photons of a primary nuclear transient event. Although the transient event was not seen directly owing to dust obscuration, we can infer that it may produce a total energy of at least ∼1051 erg, most of which was released in less than ∼3 yr. The nature of the transient event could be a stellar tidal disruption event by the central supermassive black hole (SMBH), or a sudden enhancement of the existing accretion flow onto the SMBH, or a supernova that was particularly bright.

Keywords: transient sources; infrared astronomy; active galaxies
A Binary Star in the Superbubble N160 in the Large Magellanic Cloud

We have made a spectroscopic investigation of the nature of 053949.17-693747.4, a blue star with mid-infrared excess, projected within a superbubble in the H II complex N160 in the Large Magellanic Cloud (LMC). Analyses of photometric and spectrophotometric data of this star indicate that it is an O7 ± 1 V in the LMC. The radial velocity of this star from a 2010 spectrum shows an offset of ∼150 km s-1 from that of the background interstellar medium (ISM), while the spectra taken in 2020 show stellar velocity similar to the ISM velocity. The velocity variations indicate that 053949.17-693747.4 must be a binary system. The lack of spectroscopic features from a stellar companion and the large radial velocity variations of the primary O7 star imply that the companion is most likely an early-type B star. Hubble Space Telescope Hα and [O III] images of 053949.17-693747.4 show a small nebula around the star with the southern rim resembling a blow-shock-like structure. While the physical nature as a bow shock cannot be robustly established, this small nebula is likely the cause of 053949.17-693747.4's mid-infrared excess. Spectroscopic monitoring over an entire binary period is needed to establish the period and systemic velocity to determine the properties of the binary companion and whether this binary system is a runaway.

Keywords: massive stars; large magellanic cloud; interstellar medium
Accessing the Host Galaxies of Long Gamma-Ray Bursts with Next-generation Telescopes

We present a method to estimate the detection expectations of host galaxies of long gamma-ray bursts (LGRBs) in the grizJHKL bands. It is found that given the same limiting magnitude ${m}_{{grizJHKL},\mathrm{lim}}$ in each band, the z band produces the largest number of overall LGRB hosts and low-mass hosts (M * ≤ 108 M ⊙) at ${m}_{{grizJHKL},\mathrm{lim}}\gtrsim 26$ mag. For the detection of high-redshift LGRB hosts (redshift ≥5), it is recommended to prioritize the L band, due to its good performance at both low and high limiting magnitudes. We specifically estimate the expectation of LGRB host detection with ${m}_{{grizJHKL},\mathrm{lim}}=28$ mag, which the James Webb Space Telescope can partially attain. We find that there may exist 116, 259, 277, 439, 266, 294, 274, and 316 LGRB hosts, including 0.54, 31, 28, 143, 12, 20, 14, and 35 low-mass ones in the grizJHKL bands and 13, 14, 15, 14, and 15 high-redshift ones in the zJHKL bands, for 15 yr Swift LGRBs with S ≥ 10‑6 erg cm‑2. The results show that the study of LGRB hosts under next-generation observational conditions holds significant potential, especially for low-mass host studies. However, it appears that the deeper sensitivities of galaxy telescopes may not significantly enhance statistical studies of high-redshift hosts. Strategies aimed at increasing the number of distant LGRB hosts may require the expansion of high-redshift LGRB detections.

Keywords: gamma-ray bursts; galaxies; stellar mass functions
Galactic Gamma-Ray Diffuse Emission at TeV Energies with HAWC Data

Galactic gamma-ray diffuse emission (GDE) is emitted by cosmic rays (CRs), ultra-relativistic protons, and electrons, interacting with gas and electromagnetic radiation fields in the interstellar medium. Here we present the analysis of teraelectronvolt diffuse emission from a region of the Galactic plane over the range in longitude of l ∈ [43°, 73°], using data collected with the High Altitude Water Cherenkov (HAWC) detector. Spectral, longitudinal, and latitudinal distributions of the teraelectronvolt diffuse emission are shown. The radiation spectrum is compatible with the spectrum of the emission arising from a CR population with an index similar to that of the observed CRs. When comparing with the DRAGON base model, the HAWC GDE flux is higher by about a factor of 2. Unresolved sources such as pulsar wind nebulae and teraelectronvolt halos could explain the excess emission. Finally, deviations of the Galactic CR flux from the locally measured CR flux may additionally explain the difference between the predicted and measured diffuse fluxes.

Keywords: gamma-ray astronomy; high energy astrophysics; galactic cosmic rays; milky way disk
The Streaming Instability in Two-dimensional Protoplanetary Disks

We conduct a two-dimensional (2D) stability analysis for the aerodynamically coupled system of gas and dust in protoplanetary disks using the WKB approximation. The 2D analysis may apply to a vertically integrated disk or a thin dust layer at the disk midplane. We show that the streaming instability exists in 2D and examine the growth rate and its dependence on the mean dust-to-gas ratio, $\bar{\epsilon }$ , and the Stokes number, St. For small $\bar{\epsilon }$ , the dust back reaction may be viewed as a perturbation to the wave system, and analytical results are successfully derived by the method of perturbation with respect to $\bar{\epsilon }$ . At a given azimuthal wavenumber, m, the growth rate as a function of the radial wavenumber, kr, shows a peak corresponding to the resonance between the relative drift velocity and the Rossby/trivial waves in the gas. For small $\bar{\epsilon }$ , the peak growth rate at resonant modes increases as m1/2 when the Rossby wave effect is negligible and the gas wave becomes trivial. With increasing St, the peak growth rate increases as St1/2 at St ≪ 1, peaks at St ∼ 1, and finally decreases as St-1/2 for St ≫ 1. We find that the growth rate scales with $\bar{\epsilon }$ as ${\bar{\epsilon }}^{1/2}$ at $\bar{\epsilon }\ll 1$ and peaks at $\bar{\epsilon }\sim 1$ . The instability is physically interpreted as a runaway process of dust trapping in relative drift-induced anticyclonic vortices. The effects of the compressibility and viscosity of the gas, the applicability of the WKB application, and the effects of the Keplerian shear are discussed.

Keywords: planet formation; protoplanetary disks; planetesimals; astrophysical fluid dynamics
Plasmoid Instability in the Multiphase Interstellar Medium

The processes controlling the complex clump structure, phase distribution, and magnetic field geometry that develop across a broad range of scales in the turbulent interstellar medium (ISM) remain unclear. Using unprecedentedly high-resolution 3D magnetohydrodynamic simulations of thermally unstable turbulent systems, we show that large current sheets unstable to plasmoid-mediated reconnection form regularly throughout the volume. The plasmoids form in three distinct environments: (i) within cold clumps, (ii) at the asymmetric interface of the cold and warm phases, and (iii) within the warm, volume-filling phase. We then show that the complex magnetothermal phase structure is characterized by a predominantly highly magnetized cold phase, but that regions of high magnetic curvature, which are the sites of reconnection, span a broad range in temperature. Furthermore, we show that thermal instabilities change the scale-dependent anisotropy of the turbulent magnetic field, reducing the increase in eddy elongation at smaller scales. Finally, we show that most of the mass is contained in one contiguous cold structure surrounded by smaller clumps that follow a scale-free mass distribution. These clumps tend to be highly elongated and exhibit a size versus internal velocity relation consistent with supersonic turbulence and a relative clump distance-velocity scaling consistent with subsonic motion. We discuss the striking similarity of cold plasmoids to observed tiny-scale atomic and ionized structures and H I fibers and consider how the presence of plasmoids will modify the motion of charged particles, thereby impacting cosmic-ray transport and thermal conduction in the ISM and other similar systems.

Keywords: interstellar magnetic fields; interstellar medium; interstellar plasma; galaxy formation; galaxy magnetic fields; plasma astrophysics; cosmic rays
Forming Gas Giants around a Range of Protostellar M-dwarfs by Gas Disk Gravitational Instability

Recent discoveries of gas giant exoplanets around M-dwarfs from transiting and radial velocity surveys are difficult to explain with core-accretion models. We present here a homogeneous suite of 162 models of gravitationally unstable gaseous disks. These models represent an existence proof for gas giants more massive than 0.1 Jupiter masses to form by the gas disk gravitational instability (GDGI) mechanism around M-dwarfs for comparison with observed exoplanet demographics and protoplanetary disk mass estimates for M-dwarf stars. We use the Enzo 2.6 adaptive mesh refinement (AMR) 3D hydrodynamics code to follow the formation and initial orbital evolution of gas giant protoplanets in gravitationally unstable gaseous disks in orbit around M-dwarfs with stellar masses ranging from 0.1 M ⊙ to 0.5 M ⊙. The gas disk masses are varied over a range from disks that are too low in mass to form gas giants rapidly to those where numerous gas giants are formed, therefore revealing the critical disk mass necessary for gas giants to form by the GDGI mechanism around M-dwarfs. The disk masses vary from 0.01 M ⊙ to 0.05 M ⊙ while the disk to star mass ratios explored the range from 0.04 to 0.3. The models have varied initial outer disk temperatures (10-60 K) and varied levels of AMR grid spatial resolution, producing a sample of expected gas giant protoplanets for each star mass. Broadly speaking, disk masses of at least 0.02 M ⊙ are needed for the GDGI mechanism to form gas giant protoplanets around M-dwarfs.

Keywords: extrasolar gaseous giant planets; protoplanetary disks; gravitational instability
Toward a Bias-free Selection Criterion in Shear Measurement

Sample selection is a necessary preparation for weak lensing measurement. It is well-known that selection itself may introduce bias to the measured shear signal. Using image simulation and the Fourier_Quad shear measurement pipeline, we quantify the selection bias in various commonly used selection criteria (signal-to-noise ratio, magnitude, etc.). We propose a new selection criterion defined in the power spectrum of the galaxy image. This new selection criterion has a low selection bias, and it is particularly convenient for shear measurement pipelines based on Fourier transformation.

Keywords: weak gravitational lensing; large-scale structure of the universe; astronomy data analysis; astronomical methods
An Informed and Systematic Method to Identify Variable Mid-L Dwarfs

Most brown dwarfs show some level of photometric or spectral variability. However, finding the most variable dwarfs more suited for a thorough variability monitoring campaign remained a challenge until a few years ago with the design of spectral indices to find the most likely L and T dwarfs using their near-infrared (NIR) single-epoch spectrum. In this work, we designed and tested NIR spectral indices to preselect the most likely variable L4–L8 dwarfs, complementing the indices presented by Ashraf et al. and Oliveros-Gomez et al. We used time-resolved NIR Hubble Space Telescope Wide Field Camera 3 spectra of an L6.0 dwarf, LP 261–75b, to design our novel spectral indices. We tested these spectral indices on 75 L4.0–L8.0 NIR SpeX/IRTF spectra, providing 27 new variable candidates. Our indices have a recovery rate of ∼80% and a false negative rate of ∼25%. All the known nonvariable brown dwarfs were found to be nonvariable by our indices. We estimated the variability fraction of our sample to be %, which agrees with the variability fractions provided by Buenzli et al., Radigan et al., and Metchev et al. for L4–L8 dwarfs. These spectral indices may support the future selection of the most likely variable directly imaged exoplanets for studies with the James Webb Space Telescope and as well as the 30 m telescopes.

Keywords: brown dwarfs; l dwarfs; atmospheric variability; spectral index
Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?

We present the color-magnitude diagrams and star formation histories (SFHs) of seven ultra-faint dwarf galaxies: Horologium 1, Hydra 2, Phoenix 2, Reticulum 2, Sagittarius 2, Triangulum 2, and Tucana 2, derived from high-precision Hubble Space Telescope photometry. We find that the SFH of each galaxy is consistent with them having created at least 80% of the stellar mass by z ~ 6. For all galaxies, we find quenching times older than 11.5 Gyr ago, compatible with the scenario in which reionization suppresses the star formation of small dark matter halos. However, our analysis also reveals some differences in the SFHs of candidate Magellanic Cloud satellites, i.e., galaxies that are likely satellites of the Large Magellanic Cloud and that entered the Milky Way potential only recently. Indeed, Magellanic satellites show quenching times about 600 Myr more recent with respect to those of other Milky Way satellites, on average, even though the respective timings are still compatible within the errors. This finding is consistent with theoretical models that suggest that satellites' SFHs may depend on their host environment at early times, although we caution that within the error bars all galaxies in our sample are consistent with being quenched at a single epoch. * Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

Keywords: dwarf galaxies; galaxy evolution; galaxy dynamics; galaxy stellar content; galaxy kinematics; star formation; local group; magellanic clouds