adsabs/SciX_UAT_keywords huggingface dataset:
The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. I. Survey Overview and First Results for Andromeda I

An optical monitoring survey in nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. Fifty-five dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch (AGB) stars and red supergiants at the end-point of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star formation history, quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions (SEDs), and relate this to luminosity and radius variations. In this first of a series of papers, we present the methodology of the variability survey and describe the photometric catalog of the Andromeda I (And I) dwarf galaxy as an example of the survey, and we discuss the identified long period variable (LPV) stars. We detected 5581 stars and identified 59 LPV candidates within two half-light radii of the center of And I. The amplitudes of these candidates range from 0.2 to 3 mag in the I-band. Seventy-five percent of detected sources and 98% of LPV candidates are detected at mid-infrared wavelengths. We show evidence for the presence of dust-producing AGB stars in this galaxy including five extreme AGB (X-AGB) stars, and we model some of their SEDs. A distance modulus of 24.41 mag for And I was determined based on the tip of the red giant branch. Also, a half-light radius of 3'2 ± 0'3 was calculated.

Keywords: asymptotic giant branch stars; local group; stellar mass loss; stellar evolution; luminosity function; stellar mass functions; stellar oscillations; galaxy stellar content; dwarf galaxies; surveys; long period variable stars; galaxy distances
Reimagining the Water Snowline

Water is a molecule that is tightly related to many facets of star and planet formation. Water's abundance and distribution, especially the location of its snowline has thus been the subject of much study. While water is seen to be abundant in the inner region of protoplanetary disks in infrared spectroscopy, detections of water in the disk in the submillimeter are rare, with only one detection toward AS 205. Here we put the multitude of nondetections and the single detection into context of recent physicochemical models. We find that the 321.2257 GHz (102,9-93,6) line detection toward AS 205 is inconsistent with a normal inner disk temperature structure and that the observed line must be masing. Furthermore, the emitting area derived from the line width, together with published analyses on water in disks around T-Tauri stars implies that the water snowline in the disk surface is at the same location as the snowline in the midplane. We propose that this is caused by vertical mixing continuously sequestering water from the warm surface layers into the cold disk midplane.

Keywords: protoplanetary disks; astrochemistry; chemical abundances; submillimeter astronomy
Revisiting the Constraint on the Equation of State of Neutron Stars Based on Binary Neutron Star Mergers

The merger of a neutron star (NS)–NS binary can form different productions of compact remnants, among which a supramassive NS (SMNS) can create an internal plateau, and the following steep decay marks the collapse of the SMNS. The proportion of the SMNS and the corresponding collapse time are often used to constrain the NS equation of state (EOS). This paper revisits this topic by considering the effect of an accretion disk on a compact remnant, which is not considered in previous works. Compared with previous works, the collapse-time distribution (peaks ∼100 s) of SMNSs formed from an NS–NS merger is almost unaffected by the initial surface magnetic field (B s,i ) of the NS, but the total energy output of the magnetic dipole radiation from the SMNSs depends on B s,i significantly. Coupling the constraints from the SMNS fraction, we exclude some EOSs and obtain three candidate EOSs, i.e., DD2, ENG, and MPA1. By comparing the distributions of the collapse time and the luminosity of the internal plateau (in the short gamma-ray bursts) for observations obtained based on the three candidate EOSs, it is shown that only the EOS of ENG is favored. Our sample, based on the ENG EOS and a mass distribution motivated by Galactic systems, suggests that approximately 99% of NS–NS mergers collapse to form a black hole (BH) within 107s. This includes scenarios promptly forming a BH (36.5%), an SMNS (60.7%), or a stable NS that transitions into a BH or an SMNS following accretion (2.1%). It also indicates that the remnants for GW170817 and GW190425, and the second object of GW190814, are more likely to be BHs.

Keywords: neutron stars; gamma-ray bursts
Tracing the Dynamical Mass in Galaxy Disks Using H I Velocity Dispersion and Its Implications for the Dark Matter Distribution in Galaxies

We present a method to derive the dynamical mass of face-on galaxy disks using their neutral hydrogen (H I) velocity dispersion (σH I). We have applied the method to nearby, gas-rich galaxies that have extended H I gas disks and have low inclinations. The galaxy sample includes four large disk galaxies, NGC 628, NGC 6496, NGC 3184, and NGC 4214, and three dwarf galaxies, DDO 46, DDO 63, and DDO 187. We have used archival H I data from The H I Nearby Galaxy Survey (THINGS) and the LITTLE THINGS survey to derive the H I gas distributions and Spitzer mid-infrared images to determine the stellar disk mass distributions. We examine the disk dynamical and baryonic mass ratios in the extreme outer disks where there is H I gas but no visible stellar disk. We find that for the large galaxies, the disk dynamical and H I gas mass surface densities are comparable in the outer disks. But in the smaller dwarf galaxies, for which the total H I gas mass dominates the baryonic mass, I.e., M(H I) ≥ M(stars), the disk dynamical mass is much larger than the baryonic mass. For these galaxies, there must either be a very low-luminosity stellar disk which provides the vertical support for the H I gas disk or there is halo dark matter associated with their disks, which is possible if the halo has an oblate shape so that the inner part of the dark matter halo is concentrated around the disk. Our results are important for explaining the equilibrium of H I disks in the absence of stellar disks and is especially important for gas-rich, dwarf galaxies that appear to have significant dark matter masses associated with their disks.

Keywords: dwarf galaxies; spiral galaxies; h i line emission; galaxy dark matter halos; galaxy disks; dark matter distribution; galaxy stellar disks
A Sample of Am and Ap Candidates from LAMOST DR10 (v1.0) Based on the Ensemble Regression Model

Large samples of Am and Ap stars are helpful in studying the interplay between phenomena like atomic diffusion, magnetic fields, and stellar rotation in stellar astrophysics. Existing samples of Am and Ap stars, mostly obtained from spectral data with a signal-to-noise ratio in the g band (S/Ng) greater than 50, can benefit from expansion by exploring spectra with lower S/Ng. Therefore, this paper proposes an ensemble regression model applicable to spectra with a minimum S/Ng of 30. Using the model, we identify 21,361 Am candidates, of which 11,614 are new, and 6182 Ap candidates, of which 4978 are new, from LAMOST DR10. The Am sample size has increased by 60% and the Ap sample size has increased by 180% compared to the previous sample. In terms of effective temperature (T eff), the Am candidates range mainly from 6000 to 8500 K, while the Ap candidates range from 6000 to 11,700 K. The surface gravity ( ) distributions for Am and Ap candidates differ in the range of 3.25–4.75 dex. The number of Am candidates increases stepwise, in contrast to the relatively uniform distribution of Ap candidates across the entire surface gravity range. Regarding metallicity ([Fe/H]), Am candidates typically range from ‑0.75 to 0.38 dex, peaking near 0 dex, while Ap candidates are distributed from ‑1.38 to 0.38 dex, with a peak near ‑0.5 dex.

Keywords: chemically peculiar stars; am stars; ap stars
New Parameters for Star Cluster Dynamics: The Effect of Primordial Binaries and Dark Remnants

By studying the normalized cumulative radial distribution (nCRD) of the stars in the central region of a Monte Carlo-simulated globular cluster, we recently defined three parameters able to pinpoint the stage of internal dynamical evolution reached by the system: A 5 (i.e., the area subtended by the nCRD within 5% of the half-mass radius, r h ), P 5 (the value of the nCRD at 5% r h ), and S 2.5 (the slope of the nCRD at 2.5% r h ). Here we extend the analysis and explore the effects that different fractions (0%, 10%, and 20%) of primordial binaries and stellar mass black holes (BHs) induce on the dynamical history of the system. As expected, the gradual contraction of the cluster becomes milder and core collapse shallower for an increasing binary fraction. Nevertheless, the cluster dynamical evolution is still properly traced by the three parameters. For models with a larger initial retention of stellar mass BHs, the evolution depends on the timescale of their subsequent dynamical ejection. An early dynamical ejection of BHs results in a long-term evolution of the three parameters similar to that found in systems without initial BH retention. Conversely, in the model that retains a large number of BHs for an extended time (slow dynamical ejection of BHs), the system is characterized by a less concentrated structure and by the lack of significant temporal evolution of the three parameters. The lower values of the three parameters found in this case might be used to indirectly infer the possible presence of BHs in the cluster.

Keywords: globular star clusters; stellar dynamics
A Modeling Study of the Seasonal, Latitudinal, and Temporal Distribution of the Meteoroid Mass Input at Mars: Constraining the Deposition of Meteoric Ablated Metals in the Upper Atmosphere

This study provides a comprehensive description of the deposition of meteor-ablated metals in the upper atmosphere of Mars, accounting for the temporal, vertical, latitudinal, and seasonal distribution. For this purpose, the Leeds Chemical Ablation Model is combined with a meteoroid input function to characterize the size and velocity distributions of three distinctive meteoroid populations around Mars-the Jupiter-family comets (JFCs), main-belt asteroids, and Halley-type comets (HTCs). These modeling results show a significant midnight-to-noon enhancement of the total mass influx because of the orbital dynamics of Mars, with meteoroid impacts preferentially distributed around the equator for particles with diameters below 2000 μm. The maximum total mass input occurs between the northern winter and the first crossing of the ecliptic plane with 2.30 tons sol-1, with the JFCs being the main contributor to the overall influx with up to 56% around Mars' equator. Similarly, total ablated atoms mainly arise from the HTCs with a maximum injection rate of 0.71 tons sol-1 spanning from perihelion to the northern winter. In contrast, the minimum mass and ablated inputs occur between the maximum vertical distance above the ecliptic plane and aphelion with 1.50 and 0.42 tons sol-1, respectively. Meteoric ablation occurs approximately in the range altitude between 100 and 60 km with a strong midnight-to-noon enhancement at equatorial latitudes. The eccentricity and the inclination of Mars' orbit produces a significant shift of the ablation peak altitude at high latitudes as Mars moves toward, or away, from the northern/southern solstices.

Keywords: zodiacal cloud; comets; short period comets; long period comets; asteroid belt; meteoroids; meteors; meteor radiants; micrometeorites; meteorite composition; mars; planetary atmospheres
On the Three-dimensional Structure of Local Molecular Clouds

We leverage the 1 pc spatial resolution of the Leike et al. three-dimensional (3D) dust map to characterize the 3D structure of nearby molecular clouds (d ≲ 400 pc). We start by "skeletonizing" the clouds in 3D volume density space to determine their "spines," which we project on the sky to constrain cloud distances with ≈1% uncertainty. For each cloud, we determine an average radial volume density profile around its 3D spine and fit the profiles using Gaussian and Plummer functions. The radial volume density profiles are well described by a two-component Gaussian function, consistent with clouds having broad, lower-density outer envelopes and narrow, higher-density inner layers. The ratio of the outer to inner envelope widths is ≈3:1. We hypothesize that these two components may be tracing a transition between atomic and diffuse molecular gas or between the unstable and cold neutral medium. Plummer-like models can also provide a good fit, with molecular clouds exhibiting shallow power-law wings with density, n, falling off like n-2 at large radii. Using Bayesian model selection, we find that parameterizing the clouds' profiles using a single Gaussian is disfavored. We compare our results with two-dimensional dust extinction maps, finding that the 3D dust recovers the total cloud mass from integrated approaches with fidelity, deviating only at higher levels of extinction (AV ≳ 2-3 mag). The 3D cloud structure described here will enable comparisons with synthetic clouds generated in simulations, offering unprecedented insight into the origins and fates of molecular clouds in the interstellar medium.

Keywords: molecular clouds; solar neighborhood; interstellar reddening; astronomy data visualization
MeV Gamma Rays from Fission: A Distinct Signature of Actinide Production in Neutron Star Mergers

Neutron star mergers (NSMs) are the first verified sites of rapid neutron capture (r-process) nucleosynthesis, and could emit gamma rays from the radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma rays may provide a unique and direct probe of the NSM environment as well as insight into the nature of the r process, just as observed gammas from the 56Ni radioactive decay chain provide a window into supernova nucleosynthesis. In this work, we include the photons from fission processes for the first time in estimates of the MeV gamma-ray signal expected from an NSM event. We consider NSM ejecta compositions with a range of neutron richness and find a dramatic difference in the predicted signal depending on whether or not fissioning nuclei are produced. The difference is most striking at photon energies above ∼3.5 MeV and at a relatively late time, several days after the merger event, when the ejecta is optically thin. We estimate that a Galactic NSM could be detectable by a next generation gamma-ray detector such as AMEGO in the MeV range, up to ∼104 days after the merger, if fissioning nuclei are robustly produced in the event.

Keywords: r-process; nucleosynthesis; compact binary stars; gamma-rays; gamma-ray transient sources; supernovae
Searching for Supernovae in HETDEX Data Release 3

We have extracted 636 spectra taken at the positions of 583 transient sources from the third data release of the Hobby-Eberly Telescope Dark Energy eXperiment (HETDEX). The transients were discovered by the Zwicky Transient Facility (ZTF) during 2018-2022. The HETDEX spectra provide a potential means to obtain classifications for a large number of objects found by photometric surveys for free. We attempt to explore and classify the spectra by utilizing several template-matching techniques. We have identified two transient sources, ZTF20aatpoos = AT 2020fiz and ZTF19abdkelq, as supernova (SN) candidates. We classify AT 2020fiz as a Type IIP SN observed ~10 days after explosion, and we propose ZTF19abdkelq as a likely Type Ia SN caught ~40 days after maximum light. ZTF photometry of these two sources are consistent with their classifications as SNe. Beside these two objects, we have confirmed several ZTF transients as variable active galactic nuclei based on their spectral appearance, and determined the host galaxy types of several other ZTF transients. * Based on observations obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians-Universitaet Muenchen, and Georg-August Universitaet Goettingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

Keywords: supernovae; active galactic nuclei; spectroscopy
Quasiperiodic Variations of Coronal Mass Ejections with Different Angular Widths

Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasiperiodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 yr of observational data, we systematically analyzed the quasiperiodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 yr, and 3.3-4.3 yr. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2 (±0.01), 3.1 (±0.04), and ≈6.1 (±0.4) months, and 1.2 (±0.1) and 2.4 (±0.4) yr. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1 (±0.2) months and 4.1 (±0.2) yr in the northern hemisphere, 1 (±0.004) and 5.9 (±0.2) months and 1 (±0.1), 1.4 (±0.1), and 2.4 (±0.4) yr in the southern hemisphere, 6.1 (±0.4) months in solar cycle 23, and 6.1 (±0.4) months and 1.2 (±0.1) and 3.7 (±0.2) yr in solar cycle 24. The analysis shows that quasiperiodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.

Keywords: solar coronal mass ejections; solar-terrestrial interactions; solar magnetic fields
Constraining Baryon Loading Efficiency of Active Galactic Nuclei with Diffuse Neutrino Flux from Galaxy Clusters

Active galactic nuclei (AGNs) are widely believed to be one of the promising acceleration sites of ultrahigh-energy cosmic rays (CRs). Essentially, AGNs are powered by the gravitational energy of matter falling into supermassive black holes. However, the conversion efficiency of gravitational to kinetic energy of CRs in AGNs, which is defined as the baryon loading factor η p , is not well known yet. After being accelerated, high-energy CRs could escape the host galaxy and enter the intracluster medium (ICM). These CRs can be confined within the galaxy cluster and produce γ-rays and neutrinos through proton-proton collisions with the ICM. In this paper, we study the diffusion of CRs in galaxy clusters and calculate the diffuse neutrino flux from the galaxy cluster population. Using the latest upper limits on the cumulative unresolved TeV-PeV neutrino flux from galaxy clusters posed by the IceCube Neutrino Observatory, we derive the upper limit of the average baryon loading factor as η p,grav ≲ 2 × 10-3 - 0.1 for the population of galaxy clusters. This constraint is more stringent than the one obtained from γ-ray observation on the Coma cluster.

Keywords: cosmic rays; neutrino astronomy; gamma-rays; galaxy clusters
A Candidate Relativistic Tidal Disruption Event at 340 Mpc

We present observations of an extreme radio flare, VT J024345.70-284040.08, hereafter VT J0243, from the nucleus of a galaxy with evidence for historic Seyfert activity at redshift z = 0.074. Between NRAO Very Large Array (VLA) Sky Survey observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from a ~ GHz radio luminosity of ν L ν ≲ 1038 erg s-1 to ν L ν ~ 1040 erg s-1, and still continues to brighten. The radio spectral energy distribution evolution is consistent with a nascent jet that has slowed over ~3000 days with an average 0.1 <<β>< 0.6. The jet is energetic (~1051-52 erg), and had a radius ~0.7 pc in 2021 December. X-ray observations suggest a persistent or evolving corona, possibly associated with an accretion disk, and IR and optical observations constrain any high-energy counterpart to be sub-Eddington. VT J0243 may be an example of a young, off-axis radio jet from a slowly evolving tidal disruption event. Other more mysterious triggers for the accretion enhancement and jet launching are possible. In either case, VT J0243 is a unique example of a nascent jet, highlighting the unknown connection between supermassive black holes, the properties of their accretion flows, and jet launching.

Keywords: tidal disruption; active galactic nuclei; radio transient sources; relativistic jets; transient sources; high energy astrophysics
Stability Analysis for General Order Central Finite-difference Hyperdiffusivity with Time Integrators of Arbitrary Accuracy

Computational studies of astrophysical fluid dynamics often make use of explicit high-order artificial dissipation terms (i.e., hyperdiffusion and hyperviscosity), that behave as high-frequency filters, shortening the dissipation range while preserving numerical stability. In this contribution, I derive the Courant-Friedrichs-Lewy stability condition for general order hyperdiffusion, when discretized via central finite differences, to arbitrary order of accuracy in the Taylor expansion.

Keywords: astronomy software
Black Hole Mass Function of Coalescing Neutron Star Black Hole Binary Systems: The Prospect of Reconstruction with the Gravitational Wave Observations

The discovery of gravitational waves from compact objects coalescence opens a brand-new window to observe the universe. With more events being detected in the future, statistical examinations would be essential to better understand the underlying astrophysical processes. In this work we investigate the prospect of measuring the mass function of black holes that are merging with the neutron stars. Applying Bayesian parameter estimation for hundreds of simulated neutron star-black hole (NSBH) mergers, we find that the parameters for most of the injected events can be well recovered. We also take a Bayesian hierarchical model to reconstruct the population properties of the masses of black holes, in the presence of a low mass gap, both the mass gap and power-law index (α) of black hole mass function can be well measured, thus we can reveal where the α is different for binary black hole (BBH) and NSBH systems. In the absence of a low mass gap, the gravitational wave data as well as the electromagnetic data can be used to pin down the nature of the merger event and then measure the mass of these very light black holes. However, as a result of the misclassification of BBH into NSBH, the measurement of α is more challenging and further dedicated efforts are needed.

Keywords: gravitational waves; black holes; compact objects
SDSS-IV MaNGA: Variations in the N/O-O/H Relation Bias Metallicity Gradient Measurements

In this Letter we use strong line calibrations of the N/O and O/H in Mapping Galaxies at Apache Point Observatory (MaNGA) galaxy survey spaxel data to explore the systematics introduced by variations in N/O on various strong-line metallicity diagnostics. We find radial variations in N/O at fixed O/H that correlate with total galaxy stellar mass and that can induce ∼40% systematic uncertainties in oxygen abundance gradients when nitrogen-dependent abundance calibrations are used. Empirically, we find that departures from the expected N/O are associated with variation in the local star formation efficiency, as predicted by recent chemical evolution models for galaxies, but we cannot rule out other processes such as radial migration also playing a role.

Keywords: metallicity; chemical abundances; abundance ratios; galaxy chemical evolution; chemical enrichment