Sazuna/UAT_keywords huggingface dataset:
Effects of Fully Relativistic Condition on Electron Cyclotron Maser Emission. The electron cyclotron maser (ECM) instability is a very important nonthermal radiation mechanism. It has been developed by proposing various electron distribution functions as well as the relativistic resonance condition, called the semirelativistic correction. Taking account of the relativistic effects of both the velocity distribution of energetic electrons and the resonance condition, called the fully relativistic correction, the present paper investigates the ECM instability driven by a power-law electron distribution with a low-energy cutoff. The results show that (1) both in the semirelativistic and fully relativistic cases, the growth rate and relative frequency bandwidth of ordinary (O) and extraordinary (X) modes show a positive correlation with cutoff energy E  c , i.e., the peak frequency decreases with increasing E  c ; (2) the peak frequency ratio (H peak/F peak) of the harmonic and fundamental waves is always ~2; (3) compared with the semirelativistic case, the fully relativistic case has a larger growth rate (for both the O and X mode) and a smaller peak frequency (only for the O mode) for energy &gt; 50 keV, and there is almost no difference at lower energy for the two cases; (4) the peak frequency of the X1 mode can be higher than its cutoff frequency in a strongly magnetized plasma, implying that the X1 mode emission may escape more easily for a higher E  c  and stronger magnetic field. These results can be helpful for us to understand better the physics of radio bursts from the Sun and other objects.

Keywords: Plasma astrophysics, Radio bursts, Solar radio emission, Non-thermal radiation sources, Astrophysical masers
Collisional Growth and Fragmentation of Dust Aggregates. II. Mass Distribution of Icy Fragments. By performing N-body simulations, we investigated the fundamental processes of collisions between dust aggregates composed of submicron-sized icy dust monomers. We examined the mass distribution of fragments in the collisional outcomes in a wide range of the mass ratio and the collision velocity between colliding dust aggregates. We derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a large target to a small projectile, which occurs for a mass ratio of ≳3 and is shown in a previous study. We found that the power-law index of the cumulative mass distribution of the small fragments is independent of the mass ratio and only weakly dependent on the collision velocity. On the other hand, the mass fraction of fragments of individual dust monomers decreases with an increasing total mass of colliding aggregates for a fixed mass ratio. This tendency implies that multiple hierarchical disruptive collisions (i.e., collisions between fragments, and collisions between fragments of fragments) are required for producing a large number of individual dust monomers via collisional fragmentation. Our fragment model suggests that the total geometric cross section integrated over the fragments is estimated to be about the same order as the geometric cross section of the target.

Keywords: Interstellar dust, Protoplanetary disks, N-body simulations
A Study of Stellar Spins in 15 Open Clusters. We analyze spectroscopic and photometric data to determine the projected inclinations of stars in 11 open clusters, placing constraints on the spin-axis distributions of six clusters. We combine these results with four additional clusters studied by Healy &amp; McCullough and Healy et al. to perform an ensemble analysis of their spins. We find that eight out of 10 constrained clusters (80%) have spin-axis orientations consistent with isotropy, and we establish a lower limit of four out of 10 (40%) isotropic clusters at 75% confidence, assuming no correlation of spins between clusters. We also identify two clusters whose spin-axis distributions can be better described by a model consisting of an aligned fraction of stars combined with an isotropic distribution. However, the inclination values of these stars may be influenced by systematic error, and the small number of stars modeled as aligned in these two clusters precludes the interpretation that their stellar subsets are physically aligned. Overall, no cluster displays an unambiguous signature of spin alignment, and 97% of the stars in our sample are consistent with isotropic orientations in their respective clusters. Our results offer support for the dominance of turbulence over ordered rotation in clumps and do not suggest the alignment of rotation axes and magnetic fields in protostars.

Keywords: Open star clusters, Stellar rotation, Star formation, Inclination
A Study of Primordial Very Massive Star Evolution. We present new evolutionary models of primordial very massive stars with initial masses ranging from 100 to 1000 M ⊙ that extend from the main sequence to the onset of dynamical instability caused by the creation of electron-positron pairs during core C, Ne, or O burning, depending on the star's mass and metallicity. Mass loss accounts for radiation-driven winds, as well as pulsation-driven mass loss on the main sequence and during the red supergiant phase. After examining the evolutionary properties, we focus on the final outcome of the models and associated compact remnants. Stars that avoid the pair instability supernova channel should produce black holes with masses ranging from ≈40 to ≈1000 M ⊙. In particular, stars with initial masses of about 100 M ⊙ could leave black holes of ≃85-90 M ⊙, values consistent with the estimated primary black hole mass of the GW190521 merger event. Overall, these results may contribute to explaining future data from next-generation gravitational-wave detectors, such as the Einstein Telescope and Cosmic Explorer, which will have access to an as-yet-unexplored black hole mass range of ≈102-104 M ⊙ in the early universe.

Keywords: Stellar winds, Stellar remnants, Population III stars, Stellar evolution
The SPHINX M-dwarf Spectral Grid. I. Benchmarking New Model Atmospheres to Derive Fundamental M-dwarf Properties. About 70%-80% of stars in our solar and Galactic neighborhood are M dwarfs. They span a range of low masses and temperatures relative to solar-type stars, facilitating molecule formation throughout their atmospheres. Standard stellar atmosphere models primarily designed for FGK stars face challenges when characterizing broadband molecular features in spectra of cool stars. Here, we introduce SPHINX-a new 1D self-consistent radiative-convective thermochemical equilibrium chemistry model grid of atmospheres and spectra for M dwarfs in low resolution (R ~ 250). We incorporate the latest precomputed absorption cross sections with pressure broadening for key molecules dominant in late-K, early/main-sequence-M stars. We then validate our grid models by determining fundamental properties (T eff, log g, [M/H], radius, and C/O) for 10 benchmark M+G binary stars with known host metallicities and 10 M dwarfs with interferometrically measured angular diameters. Incorporating the Gaussian process inference tool Starfish, we account for correlated and systematic noise in low-resolution (spectral stitching of SpeX, SNIFS, and STIS) observations and derive robust estimates of fundamental M-dwarf atmospheric parameters. Additionally, we assess the influence of photospheric heterogeneity on inferred [M/H] and find that it could explain some deviations from observations. We also probe whether the adopted convective mixing length parameter influences inferred radii, effective temperature, and [M/H] and again find that may explain discrepancies between interferometric observations and model-derived parameters for cooler M dwarfs. Mainly, we show the unique strength in leveraging broadband molecular absorption features occurring in low-resolution M dwarf spectra and demonstrate the ability to improve constraints on fundamental properties of exoplanet hosts and brown-dwarf companions.

Keywords: M dwarf stars, Theoretical models, Fundamental parameters of stars, Planet hosting stars, Stellar atmospheres
The Nominal Ranges of Rocky Planet Masses, Radii, Surface Gravities, and Bulk Densities. The two primary observable quantities of an exoplanet-its mass and radius-alone are not sufficient to probe a rocky exoplanet's interior composition and mineralogy. To overcome this, host-star abundances of the primary planet-building elements (Mg, Si, Fe) are typically used as a proxy for the planet's bulk composition. The majority of small exoplanet hosts, however, do not have available abundance data. Here we present the open-source ExoPlex mass-radius-composition solver. Unlike previous open-source mass-radius solvers, ExoPlex calculates the core chemistry and equilibrium mantle mineralogy for a bulk composition, including effects of mantle FeO content, core light elements, and surface water/ice. We utilize ExoPlex to calculate the planetary radii, surface gravities, and bulk densities for 106 model planets up to 2 R ⊕ across these geochemistries, adopting the distribution of FGK stellar abundances to estimate of the range of bulk exoplanet compositions. We outline the 99.7% distribution of radii, surface gravities, and bulk densities that define planets as "nominally rocky." Planets outside this range require compositions outside those expected from stellar abundance data, likely making them either Fe-enriched super-Mercuries, or volatile-enriched mini-Neptunes. We apply our classification scheme to a sample of 85 well-resolved exoplanets without available host-star abundances. We estimate only nine planets are within the "nominally rocky planet zone" at &gt;70% confidence, while ~20% and ~30% of this sample can be reasonably classified as super-Mercuries or volatile-rich, respectively. Our results provide observers with a self-consistent way to classify broadly a planet as likely rocky, Mercury-like, or volatile-enriched, using mass and radius measurements alone.

Keywords: Exoplanet structure, Exoplanet astronomy, Planetary interior, Planet hosting stars
Timing the r-process Enrichment of the Ultra-faint Dwarf Galaxy Reticulum II. The ultra-faint dwarf galaxy Reticulum II (Ret II) exhibits a unique chemical evolution history, with ${72}_{-12}^{+10}$ % of its stars strongly enhanced in r-process elements. We present deep Hubble Space Telescope photometry of Ret II and analyze its star formation history. As in other ultra-faint dwarfs, the color-magnitude diagram is best fit by a model consisting of two bursts of star formation. If we assume that the bursts were instantaneous, then the older burst occurred around the epoch of reionization, forming ~80% of the stars in the galaxy, while the remainder of the stars formed ~3 Gyr later. When the bursts are allowed to have nonzero durations, we obtain slightly better fits. The best-fitting model in this case consists of two bursts beginning before reionization, with approximately half the stars formed in a short (100 Myr) burst and the other half in a more extended period lasting 2.6 Gyr. Considering the full set of viable star formation history models, we find that 28% of the stars formed within 500 ± 200 Myr of the onset of star formation. The combination of the star formation history and the prevalence of r-process-enhanced stars demonstrates that the r-process elements in Ret II must have been synthesized early in its initial star-forming phase. We therefore constrain the delay time between the formation of the first stars in Ret II and the r-process nucleosynthesis to be less than 500 Myr. This measurement rules out an r-process source with a delay time of several Gyr or more, such as GW170817.

Keywords: Local Group, Nucleosynthesis, Stellar populations, R-process, Dwarf galaxies, HST photometry, Galaxy ages
The Hydrodynamic Evolution of Binary Black Holes Embedded within the Vertically Stratified Disks of Active Galactic Nuclei. Stellar-mass black holes can become embedded within the disks of active galactic nuclei (AGNs). Afterwards, their interactions are mediated by their gaseous surroundings. Here, we study the evolution of stellar-mass binary black holes (BBHs) embedded within AGN disks using three-dimensional hydrodynamic simulations and analytic methods, focusing on environments where the AGN disk scale height H is ≳ the BBH sphere of influence. We model the local surroundings of the embedded BBHs using a wind tunnel formalism and characterize different accretion regimes based on the local properties of the disk. We develop prescriptions for accretion and drag for embedded BBHs. Using these prescriptions with AGN disk models that can represent the Toomre-unstable outer regions of AGN disks, we study the long-term evolution of BBHs as they migrate through the disk. We find that BBHs typically merge within ≲1-30 Myr, increasing their mass significantly in the process, allowing BBHs to enter (or cross) the pair-instability supernova mass gap. The BBH accretion rate often exceeds the Eddington limit, sometimes by several orders of magnitude. Many embedded BBHs will merge before migrating significantly in the disk. We also discuss possible electromagnetic signatures during and following the inspiral, finding that it is generally unlikely for the bolometric luminosity of the BBH to exceed the AGN luminosity.

Keywords: Hydrodynamical simulations, Binary stars, Black holes, Hydrodynamics, Active galactic nuclei, Astrophysical black holes
Convection and Clouds under Different Planetary Gravities Simulated by a Small-domain Cloud-resolving Model. In this study, we employ a cloud-resolving model to investigate how gravity influences convection and clouds in a small-domain (96 × 96 km) radiative-convective equilibrium. Our experiments are performed with a horizontal grid spacing of 1 km, which can resolve large (&gt;1 km2) convective cells. We find that under a given stellar flux, sea surface temperature increases with decreasing gravity. This is because a lower-gravity planet has larger water vapor content and more clouds, resulting in a larger clear-sky greenhouse effect and a stronger cloud warming effect in the small domain. By increasing stellar flux under different gravity values, we find that the convection shifts from a quasi-steady state to an oscillatory state. In the oscillatory state, there are convection cycles with a period of several days, comprised of a short wet phase with intense surface precipitation and a dry phase with no surface precipitation. When convection shifts to the oscillatory state, the water vapor content and high-level cloud fraction increase substantially, resulting in rapid warming. After the transition to the oscillatory state, the cloud net positive radiative effect decreases with increasing stellar flux, which indicates a stabilizing climate effect. In the quasi-steady state, the atmospheric absorption features of CO2 are more detectable on lower-gravity planets because of their larger atmospheric heights. While in the oscillatory state, the high-level clouds mute almost all of the absorption features, making the atmospheric components hard to characterize.

Keywords: Atmospheric clouds, Surface gravity, Planetary atmospheres, Planetary science, Planetary climates, Habitable planets, Exoplanet atmospheres
Characteristic Scales of Complexity and Coherence within Interplanetary Coronal Mass Ejections: Insights from Spacecraft Swarms in Global Heliospheric Simulations. Many aspects of the 3D structure and evolution of interplanetary coronal mass ejections (ICMEs) remain unexplained. Here, we investigate two main topics: (1) the coherence scale of magnetic fields inside ICMEs, and (2) the dynamic nature of ICME magnetic complexity. We simulate ICMEs interacting with different solar winds using the linear force-free spheromak model incorporated into the EUHFORIA model. We place a swarm of ~20,000 spacecraft in the 3D simulation domain and characterize ICME magnetic complexity and coherence at each spacecraft based on the simulated time series. Our simulations suggest that ICMEs retain a lower complexity and higher coherence along their magnetic axis, but that a characterization of their global complexity requires crossings along both the axial and perpendicular directions. For an ICME of initial half angular width of 45° that does not interact with other large-scale solar wind structures, global complexity can be characterized by as little as 7-12 spacecraft separated by 25°, but the minimum number of spacecraft rises to 50-65 (separated by 10°) if interactions occur. Without interactions, ICME coherence extends for 45°, 20°-30°, 15°-30°, and 0°-10° for B, B  ϕ , B  θ , and B  r , respectively. Coherence is also lower in the ICME west flank compared to the east flank due to Parker spiral effects. Moreover, coherence is reduced by a factor of 3-6 by interactions with solar wind structures. Our findings help constrain some of the critical scales that control the evolution of ICMEs and aid in the planning of future dedicated multispacecraft missions.

Keywords: Solar wind, Corotating streams, Interplanetary magnetic fields, Solar coronal mass ejections
Untangling the Sources of Abundance Dispersion in Low-metallicity Stars. We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (-2 ≲ [Fe/H] ≲ -1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (&lt;0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ~ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ~6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

Keywords: High resolution spectroscopy, Chemical enrichment, Supernovae, Abundance ratios
Tidally Forced Planetary Waves in the Tachocline of Solar-like Stars. Can atmospheric waves in planet-hosting solar-like stars substantially resonate to tidal forcing, perhaps at a level of impacting the space weather or even being dynamo-relevant? In particular, low-frequency Rossby waves, which have been detected in the solar near-surface layers, are predestined to respond to sunspot cycle-scale perturbations. In this paper, we seek to address these questions as we formulate a forced wave model for the tachocline layer, which is widely considered as the birthplace of several magnetohydrodynamic planetary waves, i.e., Rossby, inertia-gravity (Poincaré), Kelvin, Alfvén, and gravity waves. The tachocline is modeled as a shallow plasma atmosphere with an effective free surface on top that we describe within the Cartesian β-plane approximation. As a novelty to former studies, we equip the governing equations with a conservative tidal potential and a linear friction law to account for viscous dissipation. We combine the linearized governing equations into one decoupled wave equation, which facilitates an easily approachable analysis. Analytical results are presented and discussed within several interesting free, damped, and forced wave limits for both midlatitude and equatorially trapped waves. For the idealized case of a single tide-generating body following a circular orbit, we derive an explicit analytic solution that we apply to our Sun for estimating leading-order responses to Jupiter. Our analysis reveals that Rossby waves resonating to low-frequency perturbations can potentially reach considerable velocity amplitudes on the order of 101-102 cm s-1, which, however, strongly rely on the yet unknown frictional damping parameter.

Keywords: Tidal interaction, Internal waves, Astrophysical fluid dynamics, Magnetic fields
300: An ACA 870 μm Continuum Survey of Orion Protostars and Their Evolution. We present an 870 μm continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales ≤8000 au (20″) and resolve the structure of envelopes with 1600 au (4″) resolution, a factor of 3-5 improvement in angular resolution over existing single-dish 870 μm observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 μm with ~0.″1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 μm flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios &lt;0.5. In contrast, Flat Spectrum protostars are primarily disk-dominated with ratios near 1, although with a number of face-on protostars dominated by their envelopes. Class I protostars span the range from envelope to disk-dominated. The increase in ratio is accompanied by a decrease in the envelope fluxes and estimated mass infall rates. We estimate that 80% of the mass is accreted during the envelope-dominated phase. We find that the 12 m/ACA flux ratio is an evolutionary indicator that largely avoids the inclination and foreground extinction dependence of spectral energy distribution-based indicators.

Keywords: Protostars, Young stellar objects, Star formation
An 8.0% Determination of the Baryon Fraction in the Intergalactic Medium from Localized Fast Radio Bursts. The dispersion measure (DM)-redshift relation of fast radio bursts (FRBs) has been proposed as a potential new tool for probing the intergalactic medium (IGM) and for studying cosmology. However, poor knowledge of the baryon fraction in the IGM (f IGM) and its degeneracy with cosmological parameters impose restrictions on the cosmological applications of FRBs. Furthermore, DMs contributed by the IGM (DMIGM) and host galaxy (DMhost), important cosmological quantities, cannot be exactly extracted from observations, which would bring uncontrolled systematic uncertainties in FRB cosmology. In this work, we use 17 localized FRBs to constrain f IGM and its possible redshift evolution. Other cosmological probes such as type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background radiation are combined to break parameter degeneracy. Taking into account the probability distributions of DMIGM and DMhost derived from the IllustrisTNG simulation, we obtain a robust measurement of f IGM = 0.927 ± 0.075, representing a precision of 8.0%. We find that there is no strong evidence for the redshift dependence of f IGM at the current observational data level. The rapid progress in localizing FRBs will significantly improve the constraints on f IGM.

Keywords: Intergalactic medium, Cosmological parameters, Observational cosmology, Radio transient sources