Sazuna/UAT_keywords huggingface dataset:
CHAOS. VII. A Large-scale Direct Abundance Study in M33. The dispersion in chemical abundances provides a very strong constraint on the processes that drive the chemical enrichment of galaxies. Due to its proximity, the spiral galaxy M33 has been the focus of numerous chemical abundance surveys to study the chemical enrichment and dispersion in abundances over large spatial scales. The CHemical Abundances Of Spirals project has observed ~100 H II regions in M33 with the Large Binocular Telescope (LBT), producing the largest homogeneous sample of electron temperatures (T  e ) and direct abundances in this galaxy. Our LBT observations produce a robust oxygen abundance gradient of -0.037 ± 0.007 dex kpc-1 and indicate a relatively small (0.043 ± 0.015 dex) intrinsic dispersion in oxygen abundance relative to this gradient. The dispersions in N/H and N/O are similarly small, and the abundances of Ne, S, Cl, and Ar relative to O are consistent with the solar ratio as expected for α-process or α-process-dependent elements. Taken together, the ISM in M33 is chemically well-mixed and homogeneously enriched from inside out, with no evidence of significant abundance variations at a given radius in the galaxy. Our results are compared to those of the numerous studies in the literature, and we discuss possible contaminating sources that can inflate abundance dispersion measurements. Importantly, if abundances are derived from a single T  e  measurement and T  e -T  e  relationships are relied on for inferring the temperature in the unmeasured ionization zone, this can lead to systematic biases that increase the measured dispersion up to 0.11 dex.

Keywords: Spiral galaxies, Chemical abundances, Triangulum Galaxy, Galaxy evolution, Interstellar medium, H II regions
Improved Models of R Coronae Borealis Stars. We present an improved numerical method to model subsolar He+CO-WD merger progenitors of R Corona Borealis stars that builds on our previous work. These improvements include a smooth entropy transition from the core to the envelope of the post-merger, inclusion of single-zone nucleosynthesis to mimic the effects of burning during the merger event, and post-processing the models with a larger nuclear network for analysis of s-process nucleosynthesis. We perform a parameter study to understand the effects of the entropy transition, peak temperature, and overshooting on our models. The models that best agree with observations of R Corona Borealis stars are processed with a much larger nuclear network to investigate s-process nucleosynthesis and the dredge-up of s-process products into the outer envelope in detail. We present a model with a significant enhancement in s-process elements, which also agrees with observed surface abundances and isotopic ratios of 16O/16O and C/O between 1 and 10. Finally, we find that the neutron exposure and initial neutron densities this model requires to obtain such an enhancement are much more consistent with i-process nucleosynthesis.

Keywords: Nucleosynthesis, Stellar mergers, Close binary stars, Stellar abundances, White dwarf stars, Stellar evolution
Star and Cluster Formation in the Sh2-112 Filamentary Cloud Complex. We present the star formation activity around the emission nebula Sh2-112. At a distance of ~2.1 kpc, this H II complex, itself 3 pc in radius, is illuminated by the massive star (O8 V) BD+45 3216. The associated molecular cloud extends in angular scales of 2.°0 × 0.°83, corresponding to linear sizes of 73 pc by 30 pc, along the Galactic longitude. The high-resolution (30″) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of A  V  ~ 2.78 mag, varying up to a maximum of ~17 mag. Our analysis led to identification of a rich population (~500) of young (average age of ~1 Myr) stars, plus a numerous number (~350) of Hα emitters, spatially correlated with the filamentary clouds. Located near the edge of the cloud, the luminous star BD+45 3216 has created an arc-like pattern as the ionizing radiation encounters the dense gas, forming a blister-shaped morphology. We found three distinct young stellar groups, all coincident with relatively dense parts of the cloud complex, signifying ongoing star formation. Moreover, the cloud filament (excitation temperature ~10 K) traced by the CO isotopologues and extending nearly ~80 pc is devoid of ionized gas except at the dense cores (excitation temperature ~28-32 K) wherein significant ionized emission excited by OB stars (dynamical age ~0.18-1.0 Myr) pertains. The radial velocity is dynamic (median ~-3.65 km s-1) along the main filament, increasing from Galactic east to west, indicating mass flow to form the massive stars/clusters at the central hubs.

Keywords: Stellar feedback, Star forming regions, Molecular clouds, Pre-main sequence stars, Star formation, Ionization, Interstellar extinction, H II regions
A Semianalytical Line Transfer Model. III. Galactic Inflows. We present calculations of ultraviolet spectra resulting from the scattering of photons by gas infalling onto an isotropically emitting source of radiation. The model is based on an adaptation of the semianalytical line transfer (SALT) code of Scarlata &amp; Panagia, and designed to interpret the inverse P Cygni profiles observed in the spectra of partially ionized galactic inflows. In addition to presenting the model, we explore the parameter space of the inflowing SALT model and recreate various physically motivated scenarios including spherical inflows, inflows with covering fractions less than unity, and galactic fountains (i.e., galactic systems with both an inflowing and outflowing component). The resulting spectra from inflowing gas show spectral features that could be misinterpreted as interstellar medium features in low resolution spectroscopy (σ ≈ 120 km s-1), suggesting that the total number of galactic systems with inflows is undercounted. Our models suggest that observations at medium resolution (R = 6000 or σ ≈ 50 km s-1) that can be obtained with 8 m class telescopes will be able to resolve the characteristic inverse P Cygni profiles necessary to identify inflows.

Keywords: Galaxy fountains, Galaxy infall, Ultraviolet astronomy, Galaxy kinematics, Radiative transfer, Galaxy evolution, Circumgalactic medium, Galaxy spectroscopy
Anatomy of a Slow Merger: Dissecting Secularly Driven Inspirals of LIGO/Virgo Gravitational Wave Sources. The dozens of compact object mergers detected by LIGO/Virgo raise a key theoretical question: how do initially wide binaries shrink sufficiently quickly that they are able to merge via gravitational wave (GW) radiation within a Hubble time? One promising class of answers involves secular driving of binary eccentricity by some external tidal perturbation. This perturbation can arise due to the presence of a tertiary point mass, in which case the system exhibits Lidov-Kozai (LK) dynamics, or it can stem from the tidal field of the stellar cluster in which the binary orbits. While these secular tide-driven mechanisms have been studied exhaustively in the case of no GW emission, when GWs are included the dynamical behavior is still incompletely understood. In this paper we consider compact object binaries driven to merger via high-eccentricity excitation by (doubly averaged, test-particle quadrupole level) cluster tides-which includes LK-driven mergers as a special case-and include the effects of both general relativistic precession and GW emission. We provide for the first time an analytical understanding of the different evolutionary stages of the binary's semimajor axis, secular oscillation timescale, and phase-space structure all the way to merger. Our results will inform future population synthesis calculations of compact object binary mergers from hierarchical triples and stellar clusters.

Keywords: Astrodynamics, Relativistic binary stars, Compact binary stars, Gravitational wave sources, Celestial mechanics, LIGO, Star clusters
Light Bridge and Magnetic Field in a Solar Active Region. Observational data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and the multiwavelength simultaneous imaging system attached to the New Vacuum Solar Telescope located at Fuxian Lake, China are employed for the study of light bridges and magnetic fields in the active region NOAA 12529. Coronal fields in this active region are computed with a boundary integration model and the field line connectivity in the dominant spot is investigated with the squashing factor Q. Quasi separatrix layer intersections in the CCD coordinate plane are determined according to values of Q. It is found that weak field lanes (WFLs) appear in the umbra and penumbra; open and closed flux systems are separated by QSLs in the dominant spot; and WFLs and QSLs look quite different from each other in the dominant spot but partially overlap in the umbra. Our study demonstrates that WFLs cannot be attributed to topological evolution of magnetic fields and might be regarded as rifts among splitting flux systems.

Keywords: Solar active region magnetic fields, Sunspots
Bridging the Gap between Intermediate and Massive Stars. I. Validation of MESA against the State-of-the-Art Monash Stellar Evolution Program for a 2M <SUB>⊙</SUB> AGB Star. One-dimensional stellar structure and evolution programs are built using different physical prescriptions and algorithms, which means there can be variations between models' predictions even when using identical input physics. This leads to questions about whether such deviations are physical or numerical; code validation studies are important and necessary tools for studying these questions. We provide the first direct comparison between the Monash stellar evolution program and MESA for a 2M ⊙ model evolved from the zero-age main sequence to the tip of the thermally pulsing asymptotic giant branch. We compare the internal structure of the two models at six critical evolutionary points and find that they are in excellent agreement with regard to characteristics like central temperature, central density, and the temperature at the base of the convective envelope during the thermally pulsing asymptotic giant branch. The H-exhausted core mass between the models differs by less than 4.2% throughout the entire evolution; the final values vary only by 1.5%. Surface quantities such as luminosity and radius vary by less than 0.2% prior to the asymptotic giant branch. During thermal pulses, the difference extends to 3.4%, largely due to uncertainties in mixing and the treatment of atmospheric boundary conditions. Given that the veteran Monash code is closed-source, the present work provides the first fully open-source computational analog. This increases accessibility to precision modeling on the asymptotic giant branch and lays the groundwork for higher-mass calculations that are performed with MESA but preserve the standards of the Monash code during the asymptotic giant branch.

Keywords: Asymptotic giant branch stars, Stellar evolutionary models, Stellar evolution
Angular-momentum Transport in Proto-neutron Stars and the Fate of Neutron Star Merger Remnants. Both the core collapse of rotating massive stars, and the coalescence of neutron star (NS) binaries result in the formation of a hot, differentially rotating NS remnant. The timescales over which differential rotation is removed by internal angular-momentum transport processes (viscosity) have key implications for the remnant's long-term stability and the NS equation of state (EOS). Guided by a nonrotating model of a cooling proto-NS, we estimate the dominant sources of viscosity using an externally imposed angular-velocity profile Ω(r). Although the magneto-rotational instability provides the dominant source of effective viscosity at large radii, convection and/or the Tayler-Spruit dynamo dominate in the core of merger remnants where dΩ/dr ≥ 0. Furthermore, the viscous timescale in the remnant core is sufficiently short that solid-body rotation will be enforced faster than matter is accreted from rotationally supported outer layers. Guided by these results, we develop a toy model for how the merger remnant core grows in mass and angular momentum due to accretion. We find that merger remnants with sufficiently massive and slowly rotating initial cores may collapse to black holes via envelope accretion, even when the total remnant mass is less than the usually considered threshold ≈1.2 M TOV for forming a stable solid-body rotating NS remnant (where M TOV is the maximum nonrotating NS mass supported by the EOS). This qualitatively new picture of the post-merger remnant evolution and stability criterion has important implications for the expected electromagnetic counterparts from binary NS mergers and for multimessenger constraints on the NS EOS.

Keywords: Neutron stars, High energy astrophysics, Core-collapse supernovae, Stellar physics, Gravitational waves, Time domain astronomy
A Meteor of Apparent Interstellar Origin in the CNEOS Fireball Catalog. The earliest confirmed interstellar object, 'Oumuamua, was discovered in the solar system by Pan-STARRS in 2017, allowing for a calibration of the abundance of interstellar objects of its size ~100 m. This was followed by the discovery of Borisov, which allowed for a similar calibration of its size ~0.4-1 km. One would expect a much higher abundance of significantly smaller interstellar objects, with some of them colliding with Earth frequently enough to be noticeable. Based on the CNEOS catalog of bolide events, we identify the ~0.45 m meteor detected at 2014 January 8 17:05:34 UTC as originating from an unbound hyperbolic orbit. The U.S. Department of Defense has released an official letter stating that "the velocity estimate reported to NASA is sufficiently accurate to indicate an interstellar trajectory," which we rely on here as confirmation of the object's interstellar trajectory. Based on the data provided by CNEOS, we infer that the meteor had an asymptotic speed of v ∞ ~ 42.1 ± 5.5 km s-1 outside of the solar system. Note that v ∞ here refers to the velocity of the meteor outside the solar system, not the velocity of the meteor outside the atmosphere. Its origin is approximately toward R.A. 49.°4 ± 4.°1 and decl. 11.°2 ± 1.°8, implying that its initial velocity vector was 58 ± 6 km s-1 away from the velocity of the local standard of rest (LSR).

Keywords: Meteors, Interstellar objects
The Emergence of Toroidal Flux Ropes with Different Twist Rising at the Same Speed. The role of twist in the emergence of magnetic flux ropes into the solar atmosphere has remained unclear for some time. Although many studies have investigated how the photospheric properties of active regions resulting from the simulated emergence of magnetic flux ropes from the convection zone with different twists compare to the observed properties of active regions, these simulations have a wide range of magnetic flux rope radii, depths, and initial configurations, making it challenging to form a complete picture of the role of any one variable in the emergence process. Twist, in particular, has been difficult to analyze because isothermally buoyant magnetic flux ropes with different twists also experience different accelerations. In this paper, we develop an analytical model of a toroidal magnetic flux rope in approximate vertical force balance in the convection zone. We numerically implement this model in a stratified atmosphere, and then subtract off a twist-independent density to make magnetic flux ropes buoyant in a twist-independent way, ensuring that the initial acceleration of each magnetic flux rope is approximately the same. We perform numerical simulations to obtain a parameter study of toroidal magnetic flux ropes with different twist rising at the same speed. We analyze the photospheric and coronal properties of the active regions resulting from the emergence of these magnetic flux ropes, and argue that the Parker instability is responsible for many of the features observed in the simulations.

Keywords: Emerging flux tubes, Solar magnetic flux emergence, Solar photosphere
On Detecting Nearby Nanohertz Gravitational Wave Sources via Pulsar Timing Arrays. Massive binary black holes (MBBHs) in nearby galactic centers, if any, may be nanohertz gravitational wave (GW) sources for pulsar timing arrays (PTAs) to detect. Normally the objective GWs for PTA experiments are approximated as plane waves because their sources are presumably located far away. For nearby GW sources, however, this approximation may be inaccurate due to the curved GW wave front and the GW strength changes along the paths of PTA pulsar pulses. In this paper, we analyze the near-field effect in the PTA detection of nearby sources and find it is important if the source distance is less than a few tens of megaparsecs, and ignoring this effect may lead to a significant signal-to-noise underestimation especially when the source distance is comparable to the pulsar distances. As examples, we assume a nanohertz MBBH source located at either the Galactic Center (GC) or the Large Magellanic Cloud (LMC) according to the observational constraints/hints on the MBBH parameter space, and estimate its detectability by current/future PTAs. We find that the GC MBBH may be detectable by the Square Kilometer Array PTA. Detecting the LMC MBBH is challenging; however, if a number (N ≳ 10) of stable millisecond pulsars can be found in the LMC center, the MBBH may be detectable via a PTA formed by these pulsars. We further illustrate the near-field effects on the PTA detection of an isotropic GW background contributed mainly by nearby GW sources, and the resulting angular correlation is similar to the Hellings-Downs curve.

Keywords: Black hole physics, Supermassive black holes, Galactic center, Pulsars, Gravitational waves, Magellanic Clouds
Millimeter Dust Emission and Planetary Dynamics in the HD 106906 System. Debris disks are dusty, optically thin structures around main-sequence stars. HD 106906AB is a short-period stellar binary, host to a wide-separation planet, HD 106906b, and a debris disk. Only a few known systems include a debris disk and a directly imaged planet, and HD 106906 is the only one in which the planet is exterior to the disk. The debris disk is edge-on and highly asymmetric in scattered light. Here we resolve the disk structure at a resolution of 0.″38 (39 au) with the Atacama Large Millimeter/submillimeter Array (ALMA) at a wavelength of 1.3 mm. We model the disk with both a narrow and broad ring of material, and find that a radially broad, axisymmetric disk between radii of ~50-100 au is able to capture the structure of the observations without evidence of any asymmetry or eccentricity, other than a tentative stellocentric offset. We place stringent upper limits on both the gas and dust contents of a putative circumplanetary disk. We interpret the ALMA data in concert with scattered-light observations of the inner ring and astrometric constraints on the planet's orbit, and find that the observations are consistent with a large-separation, low-eccentricity orbit for the planet. A dynamical analysis indicates that the central binary can efficiently stabilize planetesimal orbits interior to ~100 au, which somewhat relaxes the constraints on the eccentricity and semimajor axis. The observational constraints are consistent with in-situ formation via gravitational instability but cannot rule out a scattering event as the origin for HD 106906b's current orbit.

Keywords: Exoplanet dynamics, Millimeter astronomy, Circumstellar disks, Exoplanet formation, Debris disks
Pulse Timing Discovery of a Three-day Companion to the Hot Subdwarf BPM 36430. Hot subdwarf B stars are core-helium-burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBVrs pulsator exhibiting several low-amplitude g-modes and a strong p-mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 days. Using the CHIRON echelle spectrograph on the CTIO 1.5 m telescope, we confirm the reflex motion by detecting a radial-velocity variation with semiamplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of ≈0.42 M ⊙ orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.

Keywords: Binary stars, Stellar pulsations
ALMA Uncovers Highly Filamentary Structure toward the Sgr E Region. We report on the discovery of linear filaments observed in the CO(1-0) emission for a ~2' field of view toward the Sgr E star-forming region, centered at (l, b) = (358.°720, 0.°011). The Sgr E region is thought to be at the turbulent intersection of the "far dust lane" associated with the Galactic bar and the Central Molecular Zone (CMZ). This region is subject to strong accelerations, which are generally thought to inhibit star formation, yet Sgr E contains a large number of H II regions. We present 12CO(1-0), 13CO(1-0), and C18O(1-0) spectral line observations from the Atacama Large Millimeter/submillimeter Array and provide measurements of the physical and kinematic properties for two of the brightest filaments. These filaments have widths (FWHMs) of ~0.1 pc and are oriented nearly parallel to the Galactic plane, with angles from the Galactic plane of ~2°. The filaments are elongated, with lower-limit aspect ratios of ~5:1. For both filaments, we detect two distinct velocity components that are separated by about 15 km s-1. In the C18O spectral line data, with ~0.09 pc spatial resolution, we find that these velocity components have relatively narrow (~1-2 km s-1) FWHM line widths when compared to other sources toward the Galactic center. The properties of these filaments suggest that the gas in the Sgr E complex is being "stretched," as it is rapidly accelerated by the gravitational field of the Galactic bar while falling toward the CMZ, a result that could provide insights into the extreme environment surrounding this region and the large-scale processes that fuel this environment.

Keywords: Galactic center, Milky Way dynamics, Interstellar filaments
R-process Rain from Binary Neutron Star Mergers in the Galactic Halo. Compact binary mergers involving at least one neutron star are promising sites for the synthesis of the r-process elements found in stars and planets. However, mergers can take place at significant offsets from their host galaxies, with many occurring several kpc from star-forming regions. It is thus important to understand the physical mechanisms involved in transporting enriched material from merger sites in the galactic halo to the star-forming disk. We investigate these processes, starting from an explosive injection event and its interaction with the halo medium. We show that the total outflow mass in compact binary mergers is too low for the material to travel to the disk in a ballistic fashion. Instead, the enriched ejecta is swept into a shell, which decelerates over ≲10 pc scales and becomes corrugated by the Rayleigh-Taylor instability. The corrugated shell is denser than the ambient medium and breaks into clouds that sink toward the disk. These sinking clouds lose thermal energy through radiative cooling, and are also ablated by shearing instabilities. We present a dynamical heuristic that models these effects to predict the delay times for delivery to the disk. However, we find that turbulent mass ablation is extremely efficient and leads to the total fragmentation of sinking r-process clouds over ≲10 pc scales. We thus predict that enriched material from halo injection events quickly assimilates into the gas medium of the halo and that enriched mass flow to the disk could only be accomplished through turbulent diffusion or large-scale inflowing mass currents.

Keywords: Neutron stars, Nucleosynthesis, Galaxy chemical evolution, R-process, Chemical enrichment