Sazuna/UAT_keywords huggingface dataset:
Zero Metallicity with Zero CPU Hours: Masses of the First Stars on the Laptop. We develop an analytic model for the mass of the first stars forming in the centers of primordial gas clouds as a function of host halo mass, redshift, and degree of rotation. The model is based on the estimation of key timescales determining the following three processes: the collapse of the gas cloud, the accretion onto the protostellar core, and the radiative feedback of the protostellar core. The final stellar mass is determined by the total mass accreted until the radiative feedback halts the accretion. The analytic estimation, motivated by the result of the full numerical simulations, leads to algebraic expressions allowing an extremely fast execution. Despite its simplicity, the model reproduces the stellar mass scale and its parameter dependencies observed in state-of-the-art cosmological zoom-in simulations. This work clarifies the basic physical principles undergirding such numerical treatments and provides a path to efficiently calibrating numerical predictions against eventual observations of the first stars.

Keywords: Cosmology, Population III stars, Star formation
Tidal Migration of Exoplanets around M Dwarfs: Frequency-dependent Tidal Dissipation. The orbital architectures of short-period exoplanet systems are shaped by tidal dissipation in their host stars. For low-mass M dwarfs whose dynamical tidal response comprises a dense spectrum of inertial modes at low frequencies, resolving the frequency dependence of tidal dissipation is crucial to capturing the effect of tides on planetary orbits throughout the evolutionary stages of the host star. We use nonperturbative spectral methods to calculate the normal mode oscillations of a fully convective M dwarf modeled using realistic stellar profiles from MESA. We compute the dissipative tidal response composed of contributions from each mode, as well as nonadiabatic coupling between the modes, which we find to be an essential component of the dissipative calculations. Using our results for dissipation, we then compute the evolution of circular, coplanar planetary orbits under the influence of tides in the host star. We find that orbital migration driven by resonance locking affects the orbits of Earth-mass planets at orbital periods P orb ≲ 1.5 days and of Jupiter-mass planets at P orb ≲ 2.5 days. Due to resonantly driven orbital decay and outward migration, we predict a dearth of small planets closer than P orb ∼ 1 day and similarly sparse numbers of more massive planets out to P orb ∼ 3 days.

Keywords: Tidal interaction, Exoplanet tides, Star-planet interactions
Influence of Ionization on the Polytropic Index of the Solar Atmosphere within Local Thermodynamic Equilibrium Approximation. An initial theoretical attempt to explain the observed decrease of the polytropic/adiabatic index γ in the solar corona has been accomplished. The chemical reactions of the ionization–recombination processes in local thermodynamic equilibrium (LTE) of a solar plasma cocktail containing heavy elements are found to cause 1.1 &lt; γ ≤ 5/3 in the quiet solar atmosphere. It is also shown that the quiet solar atmosphere is in LTE, justifying this theoretical study. This result is obtained by numerically solving the Saha equation and subsequently using a newly derived equation for calculation of the polytropic index from thermodynamic partial derivatives of the enthalpy and pressure with respect to density and temperature. In addition, a comparison measured from spectroscopic observations of propagating slow magnetohydrodynamic waves in coronal loops shows that LTE ionization accounts for a very small part of the observed decrease of γ, meaning that the solar plasma in the active region is not in LTE as expected. However, the observed dependency of higher polytropic index at higher temperatures is confirmed by the current theoretical approach. It is concluded that in order to account for the polytropic index decrease in the active regions of the solar corona, it is necessary for kinetic non-LTE ionization calculations to be performed.

Keywords: Chemical thermodynamics, Solar atmosphere, Polytropes, Ionization
Clouds and Seasonality on Terrestrial Planets with Varying Rotation Rates. Using an idealized climate model incorporating seasonal forcing, we investigate the impact of rotation rate on the abundance of clouds on an Earth-like aquaplanet, and the resulting impacts upon albedo and seasonality. We show that the cloud distribution varies significantly with season, depending strongly on the rotation rate, and is well explained by the large-scale circulation and atmospheric state. Planetary albedo displays nonmonotonic behavior with rotation rate, peaking at around 1/2ΩE. Clouds reduce the surface temperature and total precipitation relative to simulations without clouds at all rotation rates, and reduce the dependence of total precipitation on rotation rate, causing nonmonotonic behavior and a local maximum around 1/8ΩE; these effects are related to the impacts of clouds on the net atmospheric and surface radiative energy budgets. Clouds also affect the seasonality. The influence of clouds on the extent of the winter Hadley cell and the intertropical convergence zone is relatively minor at slow rotation rates (&lt;1/8ΩE), but becomes more pronounced at intermediate rotation rates, where clouds decrease their maximum latitudes. The timing of seasonal transitions varies with rotation rate, and the addition of clouds reduces the seasonal phase lag.

Keywords: Magnetopause, Planetary atmospheres, Seasonal phenomena, Planetary climates, Planetary science, Albedo, Atmospheric dynamics, Exoplanet atmospheres
Dwarf–Dwarf Interactions Can Both Trigger and Quench Star Formation. It is exceedingly rare to find quiescent low-mass galaxies in the field at low redshift. UGC 5205 is an example of such a quenched field dwarf (M ⋆ ∼ 3 × 108 M ⊙). Despite a wealth of cold gas (M HI ∼ 3.5 × 108 M ⊙) and UV emission that indicates significant star formation in the past few hundred megayears, there is no detection of Hα emission—star formation in the last ∼10 Myr—across the face of the galaxy. Meanwhile, the near equal-mass companion of UGC 5205, PGC 027864, is starbursting (which has an Hα equivalent width &gt; 1000 Å). In this work, we present new Karl G. Jansky Very Large Array 21 cm line observations of UGC 5205, showing that the lack of star formation is caused by an absence of H I in the main body of the galaxy. The H I of UGC 5205 is highly disturbed; the bulk of the H I resides in several-kiloparsec–long tails, while the H I of PGC 027864 is dominated by ordered rotation. We model the stellar populations of UGC 5205 to show that, as indicated by the UV and Hα emission, the galaxy underwent a coordinated quenching event ∼100–300 Myr ago. The asymmetry of outcomes for UGC 5205 and PGC 027864 demonstrate that major mergers can both quench and trigger star formation in dwarfs. However, because the gas remains bound to the system, we suggest that such mergers only temporarily quench star formation. We estimate a total quenched time of ∼560 Myr for UGC 5205, consistent with established upper limits on the quenched fraction of a few percent for dwarfs in the field.

Keywords: Interstellar atomic gas, Galaxy interactions, Tidal tails, Star formation, Galaxy quenching
Detection of Asymmetry in the Narrow Fe Kα Emission Line in MCG-5-23-16 with Chandra. Iron Kα (Fe Kα) emission is observed ubiquitously in active galactic nuclei (AGN), and it is a powerful probe of their circumnuclear environment. Examinations of the emission line play a pivotal role in understanding the disk geometry surrounding black holes. It has been suggested that the torus and the broad-line region (BLR) are the origins of emission. However, there is no universal location for the emitting region relative to the BLR. Here, we present an analysis of the narrow component of the Fe Kα line in the Seyfert AGN MCG-5-23-16, one of the brightest AGN in X-rays and in Fe Kα emission, to localize the emitting region. Spectra derived from Chandra/HETGS observations show asymmetry in the narrow Fe Kα line, which has only been confirmed before in the AGN NGC 4151. Models including relativistic Doppler broadening and gravitational redshifts are preferred over simple Gaussians and measure radii consistent with R ≃ 200–650 r  g . These results are consistent with those of NGC 4151 and indicate that the narrow Fe Kα line in MCG-5-23-16 is primarily excited in the innermost part of the optical BLR, or X-ray BLR. Characterizing the properties of the narrow Fe Kα line is essential for studying the disk geometries of the AGN population and mapping their innermost regions.

Keywords: X-ray astronomy, Active galactic nuclei, Black holes, Spectroscopy
Chondrule Survivability in the Solar Nebula. The lifetime of millimeter-sized dust grains, such as chondrules, in the nominal solar nebula model is limited to ∼105 yr, due to an inward drift driven by gas drag. However, isotopic and petrological studies of primitive meteorites indicate a discrepancy of ≳106 yr between the formation time of chondrules and that of chondritic parent bodies. Therefore, chondrules should survive for ≳106 yr in the solar nebula against the inward drift without subsequent growth (i.e., planetesimal formation). Here, we investigate the conditions of the solar nebula that are suitable for the long lifetime of chondrule-sized dust particles. We take the turbulent strength, the radial pressure gradient force, and the disk metallicity of the solar nebula as free parameters. For 1 mm radius chondrules to survive and keep their size for ≳106 yr, the suitable condition is a weak turbulence (α ∼ 10‑6), a flat radial profile (η ≲ 10‑3), and a high metallicity (Z ∼ 0.1). This condition is qualitatively consistent with the characteristics of protoplanetary disks suggested by recent observations. We eventually propose that planetesimal formation may be induced by disk evolution, e.g., the inside-out dispersal of the gas component due to the disk wind.

Keywords: Solar nebulae, Carbonaceous chondrites, Chondrules, Planetary system formation, Protoplanetary disks, Planetesimals
Deconstructing Photospheric Spectral Lines in Solar and Stellar Flares. During solar flares, spectral lines formed in the photosphere have been shown to exhibit changes to their profiles despite the challenges of energy transfer to these depths. Recent work has shown that deep-forming spectral lines are subject to significant contributions from regions above the photosphere throughout the flaring period, resulting in a composite emergent intensity profile from multiple layers of the atmosphere. We employ radiative–hydrodynamic and radiative transfer calculations to simulate the response of the solar/stellar atmosphere to electron beam heating and synthesize spectral lines of Fe I to investigate the line-of-sight velocity fields information available from Doppler shifts of the emergent intensity profile. By utilizing the contribution function to deconstruct the line profile shape into its constituent sources, we show that variations in the line profiles are primarily caused by changes in the chromosphere. Up-flows in this region were found to create blueshifts or false redshifts in the line core dependent on the relative contribution of the chromosphere compared to the photosphere. In extreme solar and stellar flare scenarios featuring explosive chromospheric condensations, redshifted transient components can dominate the temporal evolution of the profile shape, requiring a tertiary component consideration to fully characterize. We conclude that deep-forming lines require a multicomponent understanding and treatment, with different regions of the spectral line being useful for probing individual regions of the atmosphere's velocity flows.

Keywords: Solar flares, Solar photosphere, Stellar activity, Stellar flares, Solar activity, Radiative transfer simulations, Stellar photospheres
Global Chemical Transport on Hot Jupiters: Insights from the 2D VULCAN Photochemical Model. The atmospheric dynamics of tidally locked hot Jupiters is characterized by strong equatorial winds. Understanding the interaction between global circulation and chemistry is crucial in atmospheric studies and interpreting observations. Two-dimensional (2D) photochemical transport models shed light on how the atmospheric composition depends on circulation. In this paper, we introduce the 2D photochemical (horizontal and vertical) transport model, VULCAN 2D, which improves on the pseudo-2D approaches by allowing for nonuniform zonal winds. We extensively validate our VULCAN 2D with analytical solutions and benchmark comparisons. Applications to HD 189733 b and HD 209458 b reveal a transition in mixing regimes: horizontal transport predominates below ∼0.1 mbar, while vertical mixing is more important at higher altitudes above 0.1 mbar. Motivated by the previously inferred carbon-rich atmosphere, we find that HD 209458 b with supersolar carbon-to-oxygen ratio (C/O) exhibits pronounced C2H4 absorption on the morning limb but not on the evening limb, due to horizontal transport from the nightside. We discuss when a pseudo-2D approach is a valid assumption and its inherent limitations. Finally, we demonstrate the effect of horizontal transport in transmission observations and its impact on the morning‑evening limb asymmetry with synthetic spectra, highlighting the need to consider global transport when interpreting exoplanet atmospheres.

Keywords: Exoplanet atmospheric dynamics, Exoplanet atmospheric composition , Planetary atmospheres, Exoplanet atmospheres
A Transition Discovered in the Subcritical Regime of 1A 0535+262. We present NICER observations of the accreting X-ray pulsar 1A 0535+262 during its faint state (≲6 × 1036 erg s‑1), observed in several type I and type II outbursts. We discovered a transition of temporal and spectral properties around the luminosity L t = 3.3 × 1035 erg s‑1, below which spectra are relatively soft and the pulse profiles have only a narrow peak. The spectra are harder and a secondary hump gradually appears in the pulse profiles when L ≳ L t. We discuss possible physical mechanisms for this transition, including different Comptonization seed photons, the disappearance of gas shocks on the neutron star surface, and the combination of plasma and vacuum polarization effects.

Keywords: Accretion, High mass x-ray binary stars, Pulsars
On the Possibility of an Upper Limit on Magnetically Induced Radius Inflation in Low-mass Stars. The radii of low-mass stars are observed to be inflated above standard model predictions, especially in magnetically active stars. Typically, the empirical relative radius inflations ΔR/R are ≤10% but in (rare) cases may be ≥20%. Our magneto-convective stellar models have already replicated many empirical ΔR/R values. Here, we ask: is there any theoretical upper limit on the amount of such inflation? We use our magneto-convective model to compute ΔR/R using empirically plausible values of the surface field strength parameter δ. Inside each model, the maximum internal field is set to a particular value: B ceil = 10, or 100 kG, or 1 MG. When B ceil = 10 kG, peak inflation with ΔR/R ≈ 90% occurs in stars with masses of 0.7 M ⊙. With B ceil = 100 kG, peak inflation with ΔR/R ≈ 140% occurs in stars with M ≈ 0.5 M ⊙. But with B ceil = 1 MG, we find no peak in ΔR/R as a function of δ; instead, the larger δ is, the larger ΔR/R becomes, reaching 300%–350% in the case of the largest δ considered. Thus, magneto-convective modeling can accommodate ΔR/R values which are considerably larger than any reported empirical inflations. We find that a maximum occurs in ΔR/R as a function of δ only in model stars where the field reaches its maximum strength B ceil inside the convective envelope. Moreover, our models of completely convective stars undergo smaller amounts of relative radius inflation than models with radiative cores, a result consistent with some previous reports.

Keywords: M dwarf stars, Stellar interiors, Late-type dwarf stars, Magnetic stars
COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens. We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the "Epoch of Reionization," and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is $M(\lt 5\buildrel{\prime\prime}\over{.} \,77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{\odot }$ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is &lt;μ arc&gt; = ${76}_{-20}^{+40}$ , a factor of ${2.4}_{-0.7}^{+1.4}$ greater than previously estimated from ground-based data; the flux-weighted average magnification is &lt;μ arc&gt; = ${92}_{-31}^{+37}$ . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\mathrm{log}({M}_{\star }/{M}_{\odot })\,=$ 9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$ M ⊙ yr‑1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.

Keywords: Galaxy clusters, Strong gravitational lensing, Galaxy formation, Gravitational lensing
Cosmic Reionization on Computers: Statistics, Physical Properties, and Environments of Lyman Limit Systems at z ∼ 6. Lyman limit systems (LLSs) are dense hydrogen clouds with high enough H I column densities to absorb Lyman continuum photons emitted from distant quasars. Their high column densities imply an origin in dense environments; however, the statistics and distribution of LLSs at high redshifts still remain uncertain. In this paper, we use self-consistent radiative transfer cosmological simulations from the Cosmic Reionization on Computers (CROC) project to study the physical properties of LLSs at the tail end of cosmic reionization at z ∼ 6. We generate 3000 synthetic quasar sight lines to obtain a large number of LLS samples in the simulations. In addition, with the high physical fidelity and resolution of CROC, we are able to quantify the association between these LLS samples and nearby galaxies. Our results show that the fraction of LLSs spatially associated with nearby galaxies increases with H I column density. Moreover, we find that LLSs that are not near any galaxy typically reside in filamentary structures connecting neighboring galaxies in the intergalactic medium (IGM). This quantification of the distribution and association of LLSs to large-scale structure informs our understanding of the IGM–galaxy connection during the "Epoch of Reionization," and provides a theoretical basis for interpreting future observations.

Keywords: Reionization, Lyman limit systems, Intergalactic medium
Radial Distribution of Electron Quasi-thermal Noise in the Outer Heliosphere. Voyager 1 and 2 are only the two spacecraft that have arrived and passed through the heliospheric boundaries. Based on the plasma data from the Voyager 2 spacecraft, the electron quasi-thermal noise (QTN) is investigated by using of the electron population model consisting of a core with Maxwellian distribution and a halo with kappa distribution. The power spectra of the electron QTN is calculated at different heliocentric distances from 1 to 110 au. The parametric dependence of the QTN power spectra and the effective Debye length on the model parameters, such as the density ratio and temperature ratio of the halo to the core, kappa index and the antenna length, are discussed further. The results show that the electron QTN spectrum consists of a plateau in the low frequency band f &lt; f  pt , a prominent peak at the plasma frequency f  pt , and a rapid decreasing part in the high frequency band f &gt; f  pt . The QTN plateau level basically falls down outwards until the termination shock crossing at about 84 au, after which the plateau rebounds a little near the heliopause. Although the model parameters can be very variable, the QTN plateau level does not present more than the double change in a fairly wide range of the model parameters. The presented results can be useful for future deep-space explorations in the heliosphere and can provide valuable references for the design of onboard detectors.

Keywords: Heliosphere, Interstellar plasma
Very High-energy (&gt;50 GeV) Gamma-Ray Flux Variability of Bright Fermi Blazars. Understanding the high-energy emission processes and variability patterns are two of the most challenging research problems associated with relativistic jets. In particular, the long-term (months to years) flux variability at very high energies (VHE &gt;50 GeV) has remained an unexplored domain so far. This is possibly due to the decreased sensitivity of the Fermi Large Area Telescope (LAT) above a few GeV, hence low photon statistics, and observing constraints associated with the ground-based Cherenkov telescopes. This paper reports the results obtained from the 0.05‑2 TeV Fermi-LAT data analysis of a sample of 29 blazars with the primary objective to explore their months-to-year-long very high-energy (VHE) flux variability behavior. This systematic search has led to, for the first time, the detection of significant flux variations in five blazars at the &gt;99% confidence level, whereas eight of them exhibit variability, albeit at a lower confidence level (∼95%–99%). A comparison of the 0.05–2 TeV flux variations with that observed at 0.1–50 GeV band has revealed similar variability behavior for most of the sources. However, complex variability patterns that are not reflected contemporaneously in both energy bands were also detected, thereby providing tantalizing clues about the underlying radiative mechanisms. These results open up a new dimension to unravel the VHE emission processes operating in relativistic jets, hence sowing the seeds for their future observations with the upcoming Cherenkov Telescope Array.

Keywords: Gamma-ray astronomy, Active galaxies, BL Lacertae objects