Sazuna/UAT_keywords huggingface dataset:
EMPRESS. VII. Ionizing Spectrum Shapes of Extremely Metal-poor Galaxies: Uncovering the Origins of Strong He II and the Impact on Cosmic Reionization. Strong high-ionization lines such as He II of young galaxies are puzzling at high and low redshift. Although recent studies suggest the existence of nonthermal sources, whether their ionizing spectra can consistently explain multiple major emission lines remains a question. Here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (EMPGs) that show strong He II λ4686. We parameterize the ionizing spectra composed of a blackbody and power-law radiation mimicking various stellar and nonthermal sources. We use photoionization models for nebulae and determine seven parameters of the ionizing spectra and nebulae by Markov Chain Monte Carlo methods, carefully avoiding systematics of abundance ratios. We obtain the general shapes of ionizing spectra explaining ~10 major emission lines within observational errors with smooth connections from observed X-ray and optical continua. We find that an ionizing spectrum of one EMPG has a blackbody-dominated shape, while the others have convex downward shapes at &gt;13.6 eV, which indicate a diversity of the ionizing spectrum shapes. We confirm that the convex downward shapes are fundamentally different from ordinary stellar spectrum shapes, and that the spectrum shapes of these galaxies are generally explained by the combination of the stellar and ultraluminous X-ray sources. Comparisons with stellar synthesis models suggest that the diversity of the spectrum shapes arises from differences in the stellar age. If galaxies at z ≳ 6 are similar to the EMPGs, high-energy (&gt;54.4 eV) photons of the nonstellar sources negligibly contribute to cosmic reionization due to relatively weak radiation.

Keywords: Ultraluminous x-ray sources, Galaxy formation, Dwarf galaxies
Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud. We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ~20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm-3, and rotation measure (RM) of +456 rad m-2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523-7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ~1 mJy at 1400 MHz and ~25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ -3, where S  ν  ∝ ν  α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds.

Keywords: Neutron stars, Radio transient sources, Radio continuum emission, Pulsars
Identification and Spectroscopic Characterization of 128 New Herbig Stars. We present optical spectroscopy observations of 145 high-mass pre-main-sequence candidates from the catalog of Vioque et al. 2020 From these, we provide evidence for the Herbig nature of 128 sources. This increases the number of known objects of the class by ~50%. We determine the stellar parameters of these sources using the spectra and Gaia EDR3 data. The new sources are well distributed in mass and age, with 23 sources between 4 and 8 M ☉ and 32 sources above 8 M ☉. Accretion rates are inferred from Hα and Hβ luminosities for 104 of the new Herbigs. These accretion rates, combined with previous similar estimates, allow us to analyze the accretion properties of Herbig stars using the largest sample ever considered. We provide further support to the existence of a break in accretion properties at ~3-4 M ☉, which was already reported for the previously known Herbig stars. We re-estimate the potential break in accretion properties to be at ${3.87}_{-0.96}^{+0.38}$ M ☉. As observed for the previously known Herbig stars, the sample of new Herbig stars independently suggests intense inner-disk photoevaporation for sources with masses above ~7 M ☉. These observations provide robust observational support to the accuracy of the Vioque et al. 2020 catalog of Herbig candidates. *Based on observations collected at the European Southern Observatory (ESO) under ESO program 0104.C-0937(A) and 0104.C-0937(B), observations made in the Observatorios de Canarias del IAC, program 103-INT13/19B, and observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto from 2019-04-Sept to 2019-06-Sept.

Keywords: Herbig Ae/Be stars, Emission line stars, Massive stars, Young stellar objects, Pre-main sequence stars, Star formation, Stellar accretion, Hertzsprung Russell diagram
Observing Planet-driven Dust Spirals with ALMA. Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations of thermal emission from the dust component of protoplanetary disks have revealed an abundance of substructures that may be interpreted as evidence for embedded planets, but planet-driven spiral arms-perhaps one of the most compelling lines of evidence-have proven comparatively elusive. In this work, we test the capabilities of ALMA to detect the planet-driven spiral signal in continuum emission. Carrying out hydrodynamic simulations and radiative transfer calculations, we present synthetic Band 7 continuum images for a wide range of disk and observing conditions. We show that thermal mass planets at tens of astronomical units typically drive spirals detectable within a few hours of integration time, and the detectable planet mass may be as low as ~Neptune mass (0.3 M th). The grains probed by ALMA form spirals morphologically identical to the underlying gas spiral. The temperature of the dust spiral is crucial in determining its contrast, and spirals are easier to detect in disks with an adiabatic equation of state and longer cooling times. Resolving the spiral is not necessary for its detection; with the help of residual maps, the optimal beam size is a few times the spiral width at a constant noise level. Finally, we show how the presence of gaps and rings can impair our ability to recognize colocated spirals. Our work demonstrates the planet-finding potential of the current design specification of ALMA, and suggests that observing capability is not the bottleneck in searching for spirals induced by thermal mass planets.

Keywords: Planetary-disk interactions, Protoplanetary disks, Planet formation
Homologous Compact Major Blowout-eruption Solar Flares and their Production of Broad CMEs. We analyze the formation mechanism of three homologous broad coronal mass ejections (CMEs) resulting from a series of solar blowout-eruption flares with successively increasing intensities (M2.0, M2.6, and X1.0). The flares originated from NOAA Active Region 12017 during 2014 March 28-29 within an interval of ≍24 hr. Coronal magnetic field modeling based on nonlinear force-free field extrapolation helps to identify low-lying closed bipolar loops within the flaring region enclosing magnetic flux ropes. We obtain a double flux rope system under closed bipolar fields for all the events. The sequential eruption of the flux ropes led to homologous flares, each followed by a CME. Each of the three CMEs formed from the eruptions gradually attained a large angular width, after expanding from the compact eruption-source site. We find these eruptions and CMEs to be consistent with the "magnetic-arch-blowout" scenario: each compact-flare blowout eruption was seated in one foot of a far-reaching magnetic arch, exploded up the encasing leg of the arch, and blew out the arch to make a broad CME.

Keywords: Solar flares, Solar coronal mass ejections
Experiments on the Electrostatic Transport of Charged Anorthite Particles under Electron Beam Irradiation. To reveal the effect of secondary electron emission on the charging properties of a surface covered by micron-sized insulating dust particles and the migration characteristics of these particles, for the first time we used a laser Doppler method to measure the diameters and velocities of micron-sized anorthite particles under electron beam irradiation with an incident energy of 350 eV. Here, anorthite particles are being treated as a proxy for lunar regolith. We experimentally confirm that the vertical transport of anorthite particles is always dominant, although horizontal transport occurs. In our experiments, some anorthite particles were observed to have large vertical velocities up to 9.74 m s-1 at the measurement point. The upper boundary of the vertical velocities V z of these high-speed anorthite particles are well constrained by its diameter D, that is, ${V}_{{\rm{z}}}^{2}$ linearly depends on D -2. These velocity-diameter data provide strong constraints on the dust charging and transportation mechanisms. The shared charge model could not explain the observed velocity-diameter data. Both the isolated charge model and patched charge model appear to require a large dust charging potential of -350 to -78 V to reproduce the observed data. The microstructures of the dusty surface may play an important role in producing this charging potential and in understanding the pulse migration phenomenon observed in our experiment. The presented results and analysis in this paper are helpful for understanding the dust charging and electrostatic transport mechanisms in airless celestial bodies such as the Moon and asteroids in various plasma conditions.

Keywords: Astrophysical dust processes, Interstellar dust processes, Lunar atmosphere
Post-starburst Galaxies in the Centers of Intermediate-redshift Clusters. We present results from MUSE spatially resolved spectroscopy of 21 post-starburst galaxies in the centers of eight clusters from z ~ 0.3 to z ~ 0.4. We measure spatially resolved star formation histories (SFHs), the time since quenching (t  Q ), and the fraction of stellar mass assembled in the past 1.5 Gyr (μ 1.5). The SFHs display a clear enhancement of star formation prior to quenching for 16 out of 21 objects, with at least 10% (and up to &gt;50%) of the stellar mass being assembled in the past 1.5 Gyr and t  Q  ranging from less than 100 to ~800 Myr. By mapping t  Q  and μ 1.5, we analyze the quenching patterns of the galaxies. Most galaxies in our sample have quenched their star formation from the outside in or show a side-to-side/irregular pattern, both consistent with quenching by ram pressure stripping. Only three objects show an inside-out quenching pattern, all of which are at the high-mass end of our sample. At least two of them currently host an active galactic nucleus. In two post-starbursts, we identify tails of ionized gas indicating that these objects had their gas stripped by ram pressure very recently. Post-starburst features are also found in the stripped regions of galaxies undergoing ram pressure stripping in the same clusters, confirming the link between these classes of objects. Our results point to ram pressure stripping as the main driver of fast quenching in these environments, with active galactic nuclei playing a role at high stellar masses.

Keywords: Galaxy clusters, Galaxy environments, E+A galaxies, Galaxy evolution, Post-starburst galaxies
MiMO: Mixture Model for Open Clusters in Color-Magnitude Diagrams. We propose a mixture model of open clusters (OCs) in color-magnitude diagrams (CMDs) to measure the OC properties, including isochrone parameters (age, distance, metallicity, and dust extinction), stellar mass function (MF), and binary parameters (binary fraction and mass-ratio distribution), with high precision and reliability. The model treats an OC in the CMD as a mixture of single and binary member stars and field stars in the same region. The cluster members are modeled using a theoretical stellar model, mass function, and binary properties. The field component is modeled nonparametrically using a separate field-star sample in the vicinity of the cluster. Unlike conventional methods that rely on stringent member selection, ours allows us to use a sample of more complete cluster members and attendant field stars. The larger star sample reduces the statistical error and diminishes the potential bias by retaining more stars that are crucial for age estimation and MF measurement. After validating the method with 1000 mock clusters, we measured the parameters of 10 real OCs using Gaia EDR3 data. The best-fit isochrones are consistent with previous measurements in general but with more precise age estimates for several OCs. The inferred MF slope is -2.7 to -1.6 for clusters younger than 2 Gyr, while older clusters appear to have significantly flatter MFs. The binary fraction is 30%-50%. The photometric and astrometric distances agree well.

Keywords: Hertzsprung Russell diagram, Binary stars, Stellar ages, Bayesian statistics, Stellar mass functions, Mixture model, Open star clusters
Searches for Modulated γ-Ray Precursors to Compact Binary Mergers in Fermi-GBM Data. GW170817 is the only gravitational-wave event for which a confirmed γ-ray counterpart, GRB 170817A, has been detected. Here, we present a method to search for another type of γ-ray signal, a γ-ray burst precursor, associated with a compact binary merger. If emitted shortly before the coalescence, a high-energy electromagnetic (EM) flash travels through a highly dynamical and relativistic environment, created by the two compact objects orbiting each other. Thus, the EM signal arriving at an Earth observer could present a somewhat predictable time-dependent modulation. We describe a targeted search method for light curves exhibiting such a modulation, parameterized by the observer-frame component masses and binary merger time, using Fermi-GBM data. The sensitivity of the method is assessed based on simulated signals added to GBM data. The method is then applied to a selection of potentially interesting compact binary mergers detected during the second (O2) and third (O3) observing runs of Advanced LIGO and Advanced Virgo. We find no significant modulated γ-ray precursor signal associated with any of the considered events.

Keywords: Neutron stars, Compact binary stars, Black holes
Coevolution of Broad Emission Lines and X-Ray Spectrum in Changing-look AGNs. Changing-look active galactic nuclei (CLAGNs) show the disappearance and reappearance of broad emission lines in a few years, which challenges the orientation-based AGN unification model. We reduce the X-ray data for five well-studied CLAGNs that show a strong change in broad emission lines in the past several decades. We find that the X-ray photon index, Γ, and the Eddington-scaled X-ray luminosity, L 2-10 keV/L Edd, normally follow negative and positive correlations when the Eddington ratio is lower and higher than a critical value of ~10-3. We find that the CLAGNs observed with broad Hβ emission lines stay in the positive part of the Γ-L 2-10 keV/L Edd correlation, while the broad Hβ lines become weak or disappear in the anticorrelation part of the Γ-L 2-10 keV/L Edd correlation, which suggests that the evolution of the broad lines should be correlated with the evolution of the underlying accretion process. We further find that the CLAGNs are consistent with the other different types of AGNs in the L bol-L bol/L Edd correlation. These results support that the CLAGNs belong to a special stage of AGNs with a bolometric Eddington ratio ~1%, where the broad emission lines are easily affected by the strong variation in ionization luminosity that is caused by the transition of accretion modes.

Keywords: Accretion, Black hole physics, Active galactic nuclei
The GALAH Survey: A New Sample of Extremely Metal-poor Stars Using a Machine-learning Classification Algorithm. Extremely metal-poor (EMP) stars provide a valuable probe of early chemical enrichment in the Milky Way. Here we leverage a large sample of ~600,000 high-resolution stellar spectra from the GALAH survey plus a machine-learning algorithm to find 54 candidates with estimated [Fe/H] ≤-3.0, six of which have [Fe/H] ≤-3.5. Our sample includes ~20% main-sequence EMP candidates, unusually high for EMP star surveys. We find the magnitude-limited metallicity distribution function of our sample is consistent with previous work that used more complex selection criteria. The method we present has significant potential for application to the next generation of massive stellar spectroscopic surveys, which will expand the available spectroscopic data well into the millions of stars.

Keywords: High resolution spectroscopy, Population III stars, Classification, Stellar abundances, Galactic archaeology, Galaxy stellar content, Stellar classification, Population II stars, CEMP stars
Polarization from Aligned Dust Grains in the β Pic Debris Disk. We present 870 μm Atacama Large Millimeter/submillimeter Array polarization observations of thermal dust emission from the iconic, edge-on debris disk β Pic. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the ~3σ level when averaging the emission across the entire disk. The corresponding polarization fraction is P frac = 0.51% ± 0.19%. The polarization position angle χ is aligned with the minor axis of the disk, as expected from models of dust grains aligned via radiative alignment torques (RAT) with respect to a toroidal magnetic field (B-RAT) or with respect to the anisotropy in the radiation field (k-RAT). When averaging the polarized emission across the outer versus inner thirds of the disk, we find that the polarization arises primarily from the SW third. We perform synthetic observations assuming grain alignment via both k-RAT and B-RAT. Both models produce polarization fractions close to our observed value when the emission is averaged across the entire disk. When we average the models in the inner versus outer thirds of the disk, we find that k-RAT is the likely mechanism producing the polarized emission in β Pic. A comparison of timescales relevant to grain alignment also yields the same conclusion. For dust grains with realistic aspect ratios (i.e., s &gt; 1.1), our models imply low grain-alignment efficiencies.

Keywords: Theoretical models, A stars, Radiative transfer simulations, Polarimetry, Dust continuum emission, Interplanetary magnetic fields, Submillimeter astronomy, Interplanetary dust, Debris disks, Interferometry
A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings. Recent observations revealed that several extremely low-density exoplanets show featureless transmission spectra. While atmospheric aerosols are a promising explanation for both the low-density and featureless spectra, there is another attractive possibility: the presence of circumplanetary rings. Previous studies suggested that rings cause anomalously large transit radii. However, it remains poorly understood how rings affect the transmission spectrum. Here, we provide a framework to characterize the transmission spectra of ringed exoplanets. We develop an analytical prescription to include rings in the transmission spectra for arbitrarily viewing geometries. We also establish a simple postprocessing model that can include the ring's effects on precomputed ring-free spectra. The ring flattens the transmission spectrum for a wide range of viewing geometries, consistent with the featureless spectra of extremely low-density exoplanets. Near-future observations by the James Webb Space Telescope at longer wavelengths would be able to distinguish the aerosol and ring scenarios. We also find that rocky rings might cause a silicate feature at ~10 μm if the ring's optical depth is around unity. Thus, the ring's spectral features, if detected, would provide tight constrains on the physical properties of exoplanetary rings. We also discuss the ring's stability and suggest that thick rings are sustainable only at the equilibrium temperature of ≲300 K for the ring's age comparable to Kepler planets. This might indicate the intrinsic deficit of thick rings in the Kepler samples, unless rings are much younger than the planets as suggested for Saturn.

Keywords: Exoplanets, Exoplanet rings, Exoplanet atmospheres, Transmission spectroscopy
Estimating the Injection Duration of 20 MeV Protons in Large Western Solar Energetic Particle Events. An ad hoc analytical calculation is presented to infer the duration of injection of 20 MeV protons in 21 selected western solar energetic particle (SEP) events. We convolve the solution of diffusion equation with a "triangle" source to model the time-intensity profiles over the onset and the peaking phase. The effects of "corotating" flux tubes and of solar wind convection are neglected. To accommodate these simplifications, only western events whose associated flares erupted between W15 and W90 are selected. The time-intensity profiles of these events are reconstructed from the timescales presented in Kahler (2005) and Kahler (2013) using the modified Weibull function. From the linear relation between the logarithm of the peak intensity and the logarithm of the fluence of 27-37 MeV protons presented in Kahler &amp; Ling, we derive an optimal radial mean free path (λ mfp) of 0.08 au and adopt this value to fit all selected events. The inferred duration of injection for the selected events, which in general increases with the initial speed of the associated coronal mass ejection (CME) (V cme), is less than 1 hr for V cme &lt; 1000 km s-1 and varies from a few to ~10 hr for 1000 km s-1 &lt; V cme &lt; 2000 km s-1. We then estimate the distance that the associated CMEs have traveled over the duration of injection. Most CMEs in selected events have traveled to less than 60 solar radii by the time the majority of accelerated particles have been injected into the interplanetary space.

Keywords: Solar energetic particles, Interplanetary physics, Solar particle emission
The Lick AGN Monitoring Project 2016: Dynamical Modeling of Velocity-resolved Hβ Lags in Luminous Seyfert Galaxies. We have modeled the velocity-resolved reverberation response of the Hβ broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic Nucleus (AGN) Monitoring Project 2016 sample, drawing inferences on the geometry and structure of the low-ionization broad-line region (BLR) and the mass of the central supermassive black hole. Overall, we find that the Hβ BLR is generally a thick disk viewed at low to moderate inclination angles. We combine our sample with prior studies and investigate line-profile shape dependence, such as ${\mathrm{log}}_{10}(\mathrm{FWHM}/\sigma )$ , on BLR structure and kinematics and search for any BLR luminosity-dependent trends. We find marginal evidence for an anticorrelation between the profile shape of the broad Hβ emission line and the Eddington ratio, when using the rms spectrum. However, we do not find any luminosity-dependent trends, and conclude that AGNs have diverse BLR structure and kinematics, consistent with the hypothesis of transient AGN/BLR conditions rather than systematic trends.

Keywords: Seyfert galaxies, Active galaxies, Active galactic nuclei