Sazuna/UAT_keywords huggingface dataset:
JWST Imaging of the Closest Globular Clusters. II. Discovery of Brown Dwarfs in NGC 6397 and Measurement of Age from the Brown Dwarf Cooling Sequence, Using SANDee—A New Grid of Model Isochrones across the Hydrogen-burning Limit. Globular clusters contain vast repositories of metal-poor stars that represent some of the oldest stellar generations in the Universe. The archaeological footprint of early Galactic evolution may be retained in the measurable properties of globular clusters, such as their ages, mass functions, and chemical abundances. Until recently, all photometric studies of globular clusters were restricted to stellar members. Now, the sensitivity of JWST can extend this analysis to the substellar regime. If detected in sufficient numbers, brown dwarf members can provide tight constraints on the properties of their parent population. We present SANDee—a new grid of stellar models that accurately represent the color–magnitude diagrams of globular clusters across the hydrogen-burning limit at a wide range of metallicities. Using JWST NIRCam photometry and the new models, we identify three brown dwarfs in the globular cluster NGC 6397 with T eff = 1300–1800 K, confirmed by both proper motion and model fitting. We use the observed luminosities of discovered brown dwarfs to obtain the first age estimate of a globular cluster from its substellar cooling sequence: 13.4 ± 3.3 Gyr. We also derive the local mass function of the cluster across the hydrogen-burning limit and find it to be top heavy, suggesting extensive dynamical evolution. We expect that the constraints on both age and mass function of NGC 6397 derived in this work can be greatly improved by a second epoch of NIRCam imaging in the same field.

Keywords: Globular star clusters, Brown dwarfs, Stellar populations, Stellar evolutionary models, Photometry
Cold Water Emission Cannot Be Used to Infer Depletion of Bulk Elemental Oxygen [O/H] in Disks. We reexamine the constraints provided by Herschel Space Observatory data regarding cold water emission from protoplanetary disks. Previous disk models that were used to interpret observed water emission concluded that oxygen (O/H) is depleted by at least 2 orders of magnitude if a standard, interstellar gas/dust mass ratio is assumed in the disk. In this work, we use model results from a recent disk parameter survey and show that most of the Herschel constraints obtained for cold water (i.e., for transitions with an upper energy level E up &lt; 200 K, where the bulk of the disk water lies) can be explained with disk models adopting interstellar medium-like oxygen elemental abundance (i.e., O/H = 3.2 × 10‑4) and the canonical gas/dust mass ratio of 100. We show that cold water vapor is mainly formed by photodesorption of water ice at the interface between the molecular layer and the midplane, and that its emission is relatively independent of the main disk properties like the disk gas mass and gas/dust mass ratio. We find that the abundance of water vapor in the outer disk is set by photoprocesses and depends on the (constant) vertical column density of water ice needed to attenuate the far-ultraviolet photon flux, resulting in roughly constant emission for the parameters (gas mass, dust mass, disk radius) varied in our survey. Importantly, water line emission is found to be optically thick and hence sensitive to temperature more than abundance, possibly driving previous inferences of large-scale oxygen depletion.

Keywords: Water vapor, Chemical abundances, Astrochemistry, Star formation, Protoplanetary disks
Effects of Halo Spin on the Formation and Evolution of Bars in Disk Galaxies. The spin of dark halos has been shown to significantly affect bar formation and evolution in disk galaxies. To understand the physical role of halo spin in bar formation, we run N-body simulations of isolated, Milky Way–sized galaxies by varying the halo spin parameter in the range ‑0.16 ≤ λ ≤ 0.16 and the bulge mass. We find that our adopted halo alone is subject to swing amplification of an m = 2 nonaxisymmetric mode rotating in the same sense as the halo, which assists or inhibits the bar formation in a disk depending on its sense of rotation. The m = 2 mode in the disk, growing via swing amplification, interacts constructively (destructively) with the m = 2 mode in the prograde (retrograde) halo, promoting (delaying) bar formation. A bar grows by losing its angular momentum primarily to a halo. Since the halo particles inside (outside) the corotation resonance with the bar can emit (absorb) angular momentum to (from) the bar, the bar pattern speed decays more slowly for larger λ &gt; 0, while it decreases relatively fast almost independent of λ ≤ 0. Models with a strong bar develop a boxy peanut-shaped bulge. In models without a bulge, this occurs rapidly via buckling instability, while bars with a bulge thicken gradually without undergoing buckling instability. Among the models considered in the present work, the bar in the λ = 0.06 model with a bulge of 10% of the disk mass best describes the Milky Way in terms of its length and pattern speed.

Keywords: Galaxy dark matter halos, Galaxy bars, Disk galaxies, Galaxy bulges, Galaxy disks, Barred spiral galaxies, Milky Way Galaxy
Active Dwarf Galaxy Database. I. Overlap between Active Galactic Nuclei Selected by Different Techniques. We assemble a sample of 733 dwarf galaxies (M * ≤ 109.5 M ⊙) with signatures of active galactic nuclei (AGN) and explore the intersection between different AGN-selection techniques. Objects in our database are compiled from previous studies that identify AGN in dwarf galaxies through spectroscopy, X-ray emission, infrared colors, and optical photometric variability. We apply a uniform set of AGN diagnostic tools to the database using archival data. We find that any single selection method captures no more than half of the overall AGN population, and there is a general disagreement among the AGN-selection methods in this stellar-mass regime. The largest overlap between methods is found when both methods use optical spectroscopic data. In contrast, the populations of AGN intersect the least when comparing those methods that use photometric data at different wavelengths. These results can be used to better constrain the active fraction in dwarf galaxies, which is in turn an important constraint for black hole seed formation models. In a follow-up paper, we will explore links between the effectiveness of each selection technique and host galaxy properties.

Keywords: Intermediate-mass black holes, Active galaxies, Dwarf galaxies, Active galactic nuclei, Astrophysical black holes
Dark Matter Distribution in Milky Way analog Galaxies. Our current understanding of how dark matter (DM) is distributed within the Milky Way (MW) halo, particularly in the solar neighborhood, is based on either careful studies of the local stellar orbits, model assumptions on the global shape of the MW halo, or from direct acceleration measurements. In this work, we undertake a study of external galaxies, with the intent of providing insight into the DM distribution in MW-analog galaxies. For this, we carefully select a sample of galaxies similar to the MW, based on maximum atomic hydrogen (H I) rotational velocity ( vmax,HI=200–280  km s‑1) and morphological type (Sab–Sbc) criteria. With a need for deep, highly resolved H I, our resulting sample is composed of five galaxies from the VLA Imaging of Virgo in Atomic Gas (VIVA) survey and The H I Nearby Galaxy Survey (THINGS). To perform our baryonic analysis, we use deep mid-IR images at 3.6 and 4.5 μm from the Spitzer Survey of Stellar Structures in Galaxies (S4G). Based on the dynamical three-dimensional modeling software 3D-Based Analysis of Rotating Objects via Line Observations (3D-BAROLO), we construct rotation curves (RCs) and derive the gas and stellar contributions from the galaxy's gaseous and stellar disks' mass surface density profiles. Through a careful decomposition of their RCs into their baryonic (stars, gas) and DM components, we isolate the DM contribution by using a Markov Chain Monte Carlo-based approach. Based on the Sun's location and the MW's R 25, we define the corresponding location of the solar neighborhood in these systems. We put forward a window for the DM density (ρ dm = 0.21–0.55 GeV cm‑3) at these galactocentric distances in our MW analog sample, consistent with the values found for the MW's local DM density, based on more traditional approaches found in the literature.

Keywords: Galaxy dark matter halos, Dark matter distribution, Galaxy dynamics, Galaxy kinematics
Modeling Blazar Broadband Emission with Convolutional Neural Networks. II. External Compton Model. In the context of modeling spectral energy distributions (SEDs) for blazars, we extend the method that uses a convolutional neural network (CNN) to include external inverse Compton processes. The model assumes that relativistic electrons within the emitting region can interact with and up-scatter external photons originating from the accretion disk, the broad-line region, and the torus, to produce the observed high-energy emission. We trained the CNN on a numerical model that accounts for the injection of electrons, their self-consistent cooling, and pair creation-annihilation processes, considering both internal and all external photon fields. Despite the larger number of parameters compared to the synchrotron self-Compton model and the greater diversity in spectral shapes, the CNN enables an accurate computation of the SED for a specified set of parameters. The performance of the CNN is demonstrated by fitting the SED of two flat-spectrum radio quasars, namely 3C 454.3 and CTA 102, and obtaining their parameter posterior distributions. For the first source, the available data in the low-energy band allowed us to constrain the minimum Lorentz factor of the electrons,  γmin , while for the second source, due to the lack of these data,  γmin=102  was set. We used the obtained parameters to investigate the energetics of the system. The model developed here, along with one from Bégué et al., enables self-consistent, in-depth modeling of blazar broadband emissions within a leptonic scenario.

Keywords: Blazars, Flat-spectrum radio quasars, Active galaxies
On the Determination of Stellar Mass and Binary Fraction of Open Clusters within 500 pc from the Sun. We investigated the stellar mass function and the binary fraction of 114 nearby open clusters (OCs) using the high-precision photometric data from Gaia Data Release 3 (Gaia DR3). We estimated the mass of member stars by using a ridge line that is better in line with the observed color–magnitude diagram, thus obtaining more accurate stellar mass and binary mass ratio (q) at the low-mass region. By analyzing the present-day mass function (PDMF) of star clusters, we found that 108 OCs follow a two-stage power-law distribution, whereas six OCs present a single power-law PDMF. Subsequently, we fitted the high(low)-mass index of PDMF ( dN/dm∝m‑α ), denoted as α h(α l), and segmentation point m c. For our cluster sample, the median values of α h and α l are 2.65 and 0.95, respectively, which are approximately consistent with the initial mass function results provided by Kroupa. We utilized the cumulative radial number distribution of stars with different masses to quantify the degree of mass segregation. We found a significant positive correlation between the state of dynamical evolution and mass segregation in OCs. We also estimated the fraction of binary stars with q ≥ 0.5, ranging from 6% to 34% with a median of 17%. Finally, we provided a catalog of 114 nearby cluster properties, including the total mass, the binary fraction, the PDMF, and the dynamical state.

Keywords: Binary stars, Surveys, Stellar mass functions, Stellar masses, Open star clusters
Experimental Study of Alfvén Wave Reflection from an Alfvén-speed Gradient Relevant to the Solar Coronal Holes. We report the first experimental detection of a reflected Alfvén wave from an Alfvén-speed gradient under conditions similar to those in coronal holes. The experiments were conducted in the Large Plasma Device at the University of California, Los Angeles. We present the experimentally measured dependence of the coefficient of reflection versus the wave inhomogeneity parameter, i.e., the ratio of the wavelength of the incident wave to the length scale of the gradient. Two-fluid simulations using the Gkeyll code qualitatively agree with and support the experimental findings. Our experimental results support models of wave heating that rely on wave reflection at low heights from a smooth Alfvén-speed gradient to drive turbulence.

Keywords: Plasma physics, Fast solar wind, The Sun, Solar coronal heating, Plasma astrophysics, Alfven waves, Solar corona, Solar coronal waves, Solar coronal holes
Polar Orbits around the Newly Formed Earth–Moon Binary System. We examine the dynamics and stability of circumbinary particles orbiting around the Earth–Moon binary system. The moon formed close to the Earth (semimajor axis a EM ≈ 3 R ⊕) and expanded through tides to its current day semimajor axis (a EM = 60 R ⊕). Circumbinary orbits that are polar or highly inclined to the Earth–Moon orbit are subject to two competing effects: (i) nodal precession about the Earth–Moon eccentricity vector and (ii) Kozai–Lidov oscillations of eccentricity and inclination driven by the Sun. While we find that there are no stable polar orbits around the Earth–Moon orbit with the current day semimajor axis, polar orbits were stable immediately after the formation of the Moon, at the time when there was a lot of debris around the system, up to when the semimajor axis reached about a EM ≈ 10 R ⊕. We discuss implications of polar orbits on the evolution of the Earth–Moon system and the possibility of polar orbiting moons around exoplanet–moon binaries.

Keywords: Solar system, Solar system astronomy
Investigating Optical Variability of the Blazar S5 0716+714 on Diverse Timescales. We present the results of the observational study of the blazar S5 0716+716 in the optical bands B, V, R, and I between 2019 March and 2023 August to investigate its variability on diverse timescales. The blazar was followed up by the T60 robotic telescope in Türkiye for 416 nights to obtain long-term variability during this period. In order to search for the intraday variability of the object, we have carried out 21 nights of observations with the T100 telescope for at least 1 hr. The blazar showed a ∼2.47 mag variation in the optical R band during our monitoring period, the brightest state on 2020 January 18 (MJD 58866) as R = 12.109 ± 0.011 mag and the faintest state on 2019 March 23 (MJD 58565) as R = 14.580 ± 0.013 mag. We employed the nested ANOVA test and the power-enhanced F-test to quantify intraday variability, which showed that the blazar was significantly variable in the R band on 12 out of 21 nights. Correlation analysis of the light curves shows that the emission in the BVRI optical bands was strongly correlated both in the short and long term without any time lag. The blazar has likely quasiperiods of 186 ± 30 and 532 ± 76 days in the optical R-band light curve according to the weighted wavelet Z-transform and Lomb–Scargle periodogram. The intraday variation and long-term variation features are discussed within the frame of prospective scenarios.

Keywords: Blazars, Active galactic nuclei, BL Lacertae objects
Cosmic Reionization in the JWST Era: Back to AGNs?. Deep surveys with the James Webb Space Telescope (JWST) have revealed an emergent population of moderate-luminosity, broad-line active galactic nuclei (AGNs) at 4 ≲ z ≲ 13 powered by accretion onto early massive black holes. The high number densities reported, together with the large Lyman-continuum (LyC) production efficiency and leakiness into the intergalactic medium that are typical of UV-selected AGNs, lead us to reassess a scenario where AGNs are the sole drivers of the cosmic hydrogen/helium reionization process. Our approach is based on the assumptions, grounded in recent observations, that (a) the fraction of broad-line AGNs among galaxies is around 10%–15%; (b) the mean escape fraction of hydrogen LyC radiation is high, at ≳80%, in AGN hosts and is negligible otherwise; and (c) internal absorption at 4 ryd or a steep ionizing EUV spectrum delay full reionization of He II until z ≃ 2.8–3.0, in agreement with observations of the He II Lyα forest. In our fiducial models, (1) hydrogen reionization is 99% completed by redshift z ≃ 5.3–5.5 and reaches its midpoint at z ≃ 6.5–6.7; (2) the integrated Thomson scattering optical depth to reionization is ≃0.05, consistent with constraints from cosmic microwave background anisotropy data; and (3) the abundant AGN population detected by JWST does not violate constraints on the unresolved X-ray background.

Keywords: Hot intergalactic medium, Reionization, High-redshift galaxies, Quasars
Shoulder of Dust Rings Formed by Planet–Disk Interactions. Recent analyses of millimeter-wavelength protoplanetary disk observations have revealed several emission excesses on the previously identified dust rings, referred to as dust shoulders. The prevalence of dust shoulders suggests that they trace a common but unclear mechanism. In this work, we combine 3D, multifluid hydrodynamic simulations with radiative transfer calculations to explain the formation of dust shoulders. We find that the ring-shoulder pairs can result from the 3D planet–disk interactions with massive, gap-opening planets. The key driver is the dust filtration effect at the local pressure maximum due to planet-driven outward gas flows. Our work provides a possible explanation for the outer dust shoulders in recent super-resolution analyses of Atacama Large Millimeter/submillimeter Array observations. It also provides insights into the formation of the inner dust shoulder in the PDS 70 disk and highlights the role of 3D effects in planet–disk interaction studies.

Keywords: Astronomical simulations, Astrophysical dust processes, Protoplanetary disks, Circumstellar dust, Planet formation
Simplified Model of the Solar Magnetic Field. This paper considers a structure consisting of two rings of magnetic dipoles symmetrical relative to the equatorial plane as a possible model for the source of the solar magnetic field. It shows that the magnetic field generated by this structure corresponds to Joy's law and Hale's polarity law. Approximate calculations show that the form and shape of the equatorial field of this structure are close to measured values, and the resulting distribution of sunspots is in agreement with Joy's law to Maunder's butterfly diagram. Based on this structure, it is possible to explain the appearance of two peaks (Gnevyshev gap) in the distribution of sunspots at the maximum of solar activity. Calculating the polar field based on the principles of magnetic hysteresis shows a good coincidence of the calculated and measured values and makes it possible to predict the behavior of the polar field in the interval to the nearest minimum of solar activity. Analyzing dipole nutation makes it possible to predict the intensity of the upcoming solar activity maxima, while a nutation period of approximately 8 months can be associated with 1.3 yr-period field oscillations. Despite the fact that the emergence and the functioning of the proposed configuration of magnetic dipoles is considered in a simplified manner and only from the point of view of gyromagnetic and thermal forces for speed and clarity, this does not limit the use of the proposed structure as a potential model in other, more global-scale general hydromagnetic theories of solar magnetism.

Keywords: Stellar magnetic fields, Sunspots, Solar magnetic fields
Laboratory Benchmark of n ≥ 4 Dielectronic Recombination Satellites of Fe XVII. We calculated cross sections for the dielectronic recombination (DR) satellite lines of Fe XVII and benchmarked our predictions with experimental cross sections of Fe XVII resonances that were monoenergetically excited in an electron-beam ion trap. We extend the benchmark to all resolved DR and direct electron-impact excitation (DE) channels in the experimental data set, specifically the n ≥ 4 DR resonances of Fe XVII, complementing earlier investigations of n = 3 channels. Our predictions for the DR and DE absolute cross sections for the higher n complexes disagree considerably with experimental results when using the same methods as in previous works. However, we achieve agreement within ∼10% of the experimental results by an approach whereby we doubly convolve the predicted cross sections with both the spread of the electron-beam energy and the photon energy resolution of our experiment. We then calculated rate coefficients from the experimental and theoretical cross sections, finding general agreement within 2σ with the rates found in the OPEN-ADAS atomic database.

Keywords: Laboratory astrophysics, Atomic data benchmarking, Atomic physics
Milky Way-est: Cosmological Zoom-in Simulations with Large Magellanic Cloud and Gaia–Sausage–Enceladus Analogs. We present Milky Way-est, a suite of 20 cosmological cold-dark-matter-only zoom-in simulations of Milky Way (MW)-like host halos. Milky Way-est hosts are selected such that they (i) are consistent with the MW's measured halo mass and concentration, (ii) accrete a Large Magellanic Cloud (LMC)-like (≈1011 M ⊙) subhalo within the last 2 Gyr on a realistic orbit, placing them near 50 kpc from the host center at z ≈ 0, and (iii) undergo a &gt;1:5 sub-to-host halo mass ratio merger with a Gaia–Sausage–Enceladus (GSE)-like system at early times (0.67 &lt; z &lt; 3). Hosts satisfying these LMC and GSE constraints constitute &lt;1% of all halos in the MW's mass range, and their total masses grow rapidly at late times due to LMC analog accretion. Compared to hosts of a similar final halo mass that are not selected to include LMC and GSE analogs, Milky Way-est hosts contain 22% more subhalos with present-day virial masses above 108 M ⊙ throughout the virial radius, on average. This enhancement reaches ≈80% in the inner 100 kpc and is largely, if not entirely, due to LMC-associated subhalos. These systems also induce spatial anisotropy in Milky Way-est subhalo populations, with ≈60% of the total subhalo population within 100 kpc found in the current direction of the LMC. Meanwhile, we find that GSE-associated subhalos do not significantly contribute to present-day Milky Way-est subhalo populations. These results provide context for our Galaxy's dark matter structure and subhalo population and will help interpret a range of measurements that are currently only possible in the MW.

Keywords: N-body simulations, Milky Way dark matter halo, Dark matter, Large Magellanic Cloud