Sazuna/UAT_keywords huggingface dataset:
Age-dating Red Giant Stars Associated with Galactic Disk and Halo Substructures. The vast majority of Milky Way stellar halo stars were likely accreted from a small number (≲3) of relatively large dwarf galaxy accretion events. However, the timing of these events is poorly constrained and predominantly relies on indirect dynamical mixing arguments or imprecise age measurements of stars associated with debris structures. Here, we aim to infer robust stellar ages for stars associated with galactic substructures to more directly constrain the merger history of the Galaxy. By combining kinematic, asteroseismic, and spectroscopic data where available, we infer stellar ages for a sample of 10 red giant stars that were kinematically selected to be within the stellar halo, a subset of which are associated with the Gaia-Enceladus-Sausage halo substructure, and compare their ages to 3 red giant stars in the Galactic disk. Despite systematic differences in both absolute and relative ages determined here, age rankings of stars in this sample are robust. Passing the same observable inputs to multiple stellar age determination packages, we measure a weighted average age for the Gaia-Enceladus-Sausage stars in our sample of 8 ± 3 (stat.) ± 1 (sys.) Gyr. We also determine hierarchical ages using isochrones for the populations of Gaia-Enceladus-Sausage, in situ halo and disk stars, finding a Gaia-Enceladus-Sausage population age of 8.0 ${}_{-2.3}^{+3.2}$ Gyr. Although we cannot distinguish hierarchical population ages of halo or disk structures with our limited data and sample of stars, this framework should allow a distinct characterization of Galactic substructures using larger stellar samples and additional data available in the near future.

Keywords: Stellar kinematics, Galactic archaeology, Spectroscopy, Asteroseismology, Hierarchical models
Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations. The discovery of GW170817 and GRB 170817A in tandem with AT 2017gfo cemented the connection between neutron star mergers, short gamma-ray bursts (GRBs), and kilonovae. To investigate short GRB observations in the context of diverse kilonova behavior, we present a comprehensive optical and near-IR catalog of 85 bursts discovered over 2005-2020 on timescales of ≲12 days. The sample includes previously unpublished observations of 23 bursts and encompasses both detections and deep upper limits. We identify 11.8% and 15.3% of short GRBs in our catalog with upper limits that probe luminosities lower than those of AT 2017gfo and a fiducial neutron star-black hole kilonova model (for pole-on orientations), respectively. We quantify the ejecta masses allowed by the deepest limits in our catalog, constraining blue and "extremely blue" kilonova components of 14.1% of bursts to Mej ≲ 0.01-0.1 M☉. The sample of short GRBs is not particularly constraining for red kilonova components. Motivated by the large catalog, as well as model predictions of diverse kilonova behavior, we investigate modified search strategies for future follow-up to short GRBs. We find that ground-based optical and near-IR observations on timescales of ≳2 days can play a significant role in constraining more diverse outcomes. We expect future short GRB follow-up efforts, such as from the James Webb Space Telescope, to expand the reach of kilonova detectability to redshifts of z ≍ 1.

Keywords: Neutron stars, Gamma-ray bursts
Properties of the Obscuring Torus in NGC 1052 from Multiepoch Broadband X-Ray Spectroscopy. Obscuration of the innermost parts of active galactic nuclei (AGN) is observed in the majority of the population both in the nearby universe and at high redshift. However, the nature of the structures causing obscuration, especially in low-luminosity AGN, is poorly understood at present. We present a novel approach to multiepoch broadband X-ray spectroscopy, anchored in the long-term average spectrum in the hard X-ray band, applied to the nearby, X-ray-bright AGN in the galaxy NGC 1052. From spectral features due to X-ray reprocessing in the circumnuclear material, based on a simple, uniform-density torus X-ray reprocessing model, we find a covering factor of 80%-100% and a globally averaged column density in the range (1-2) × 1023 cm-2. This closely matches the independently measured variable line-of-sight column density range, leading to a straightforward and self-consistent picture of the obscuring torus in NGC 1052, similar to several other AGN in recent literature. Comparing this X-ray-constrained torus model with measurements of spatially resolved subparsec absorption from radio observations, we find that it may be possible to account for both X-ray and radio data with a torus model featuring a steep density gradient along the axis of the relativistic jets. This provides a valuable direction for the development of improved physical models for the circumnuclear environment in NGC 1052 and potentially in a wider class of AGN.

Keywords: Radio active galactic nuclei, Low-luminosity active galactic nuclei, Active galactic nuclei, X-ray active galactic nuclei
Extracting the Main Trend in a Data Set: The Sequencer Algorithm. Scientists aim to extract simplicity from observations of the complex world. An important component of this process is the exploration of data in search of trends. In practice, however, this tends to be more of an art than a science. Among all trends existing in the natural world, one-dimensional trends, often called sequences, are of particular interest, as they provide insights into simple phenomena. However, some are challenging to detect, as they may be expressed in complex manners. We present the Sequencer, an algorithm designed to generically identify the main trend in a data set. It does so by constructing graphs describing the similarities between pairs of observations, computed with a set of metrics and scales. Using the fact that continuous trends lead to more elongated graphs, the algorithm can identify which aspects of the data are relevant in establishing a global sequence. Such an approach can be used beyond the proposed algorithm and can optimize the parameters of any dimensionality reduction technique. We demonstrate the power of the Sequencer using real-world data from astronomy, geology, and images from the natural world. We show that, in a number of cases, it outperforms the popular t-Distributed Stochastic Neighbor Embedding and Uniform Manifold Approximation and Projection dimensionality reduction techniques. This approach to exploratory data analysis, which does not rely on training or tuning any parameter, has the potential to enable discoveries in a wide range of scientific domains. The source code is available on GitHub, and we provide an online interface at http://sequencer.org.

Keywords: Astronomy data analysis
Detection of Flare-associated CME Candidates on Two M-dwarfs by GWAC and Fast, Time-resolved Spectroscopic Follow-ups. The flare-associated stellar coronal mass ejections (CMEs) of solar-like and late-type stars profoundly impact the habitability of any expolanets in the systems. In this paper, we report the detection of flare-associated CMEs for two M-dwarfs, thanks to a high-cadence survey carried out by the Ground Wide-angle Camera system and fast photometric and spectroscopic follow-ups. The flare energies in the R band are determined to be 1.6 × 1035 erg and 8.1 × 1033 erg based on modeling of their light curves. The time-resolved spectroscopic observations start at about 20 and 40 minutes after the trigger in both cases. The large projected maximum velocity of ~500-700 km s-1 suggests that the high-velocity wings of their Hα emission lines most likely result from CME events in both stars, after excluding the possibility of chromospheric evaporation and coronal rain. The masses of the CMEs are estimated to be 1.5-4.5 × 1019 g and 7.1 × 1018 g.

Keywords: Stellar coronal mass ejections, Time domain astronomy, Stellar flares, Optical flares, Spectroscopy, Late-type dwarf stars
Searching for TeV Candidates in 4LAC High-synchrotron- peaked Frequency BL Lac Objects. The next generation of TeV detectors is expected to have significantly enhanced performance. It is therefore constructive to search for new TeV candidates for observation. This paper focuses on TeV candidates among the high-synchrotron-peaked BL Lacertae objects (HBLs) reported in the fourth catalog of active galactic nuclei detected by Fermi's Large Area Telescope, i.e., 4LAC. By cross-matching the Fermi data with radio and optical observations, we collected the multiwavelength features of 180 HBLs with known redshifts. The data set contains 39 confirmed TeV sources and 141 objects whose TeV detection has not yet been reported (either not yet observed, or observed but not detected). Using two kinds of supervised machine-learning (SML) methods, we searched for new possible TeV candidates (PTCs) among the nondetected objects by assessing the similarity of their multi-wavelength properties to existing TeV-detected objects. The classification results of the two SML classifiers were combined and the 24 highest-confidence PTCs were proposed as the best candidates. We calculate, here, the 12 year averaged Fermi spectra of these PTCs and estimate their detectability by extrapolating the Fermi spectra and including the extragalactic background light attenuation. Four candidates are suggested to have a high likelihood of being detected by the Large High Altitude Air Shower Observatory, and 24 are candidates for Cherenkov Telescope Array observations.

Keywords: Blazars, Active galactic nuclei, BL Lacertae objects
First Simultaneous In Situ Measurements of a Coronal Mass Ejection by Parker Solar Probe and STEREO-A. We present the first Parker Solar Probe mission (PSP)-observed coronal mass ejection (CME) that hits a second spacecraft before the end of the PSP encounter, providing an excellent opportunity to study short-term CME evolution. The CME was launched from the Sun on 2019 October 10 and was measured in situ at PSP on 2019 October 13 and at STEREO-A on 2019 October 14. The small, but not insignificant, radial (~0.15 au) and longitudinal (~8°) separation between PSP and STEREO-A at this time allows for both observations of short-term radial evolution as well as investigation of the global CME structure in longitude. Although initially a slow CME, magnetic field and plasma observations indicate that the CME drove a shock at STEREO-A and also exhibited an increasing speed profile through the CME (i.e., evidence for compression). We find that the presence of the shock and other compression signatures at 1 au are due to the CME having been overtaken and accelerated by a high speed solar wind stream (HSS). We estimate the minimum interaction time between the CME and the HSS to be ~2.5 days, indicating the interaction started well before the CME arrival at PSP and STEREO-A. Despite alterations of the CME by the HSS, we find that the CME magnetic field structure is similar between the vantage points, with overall the same flux rope classification and the same field distortions present. These observations are consistent with the fact that coherence in the magnetic structure is needed for steady and continued acceleration of the CME.

Keywords: Solar coronal mass ejections, Heliosphere
Spatial Variations of Magnetic Field along Active Galactic Nuclei Jets on Sub-parsec to Megaparsec Scales. We report the systematic analysis of knots, hotspots, and lobes in 57 active galactic nuclei (AGNs) to investigate the variation of the magnetic field along the jet from the sub-parsec base to the terminus on kiloparsec-to-megaparsec scales. Expanding the number of radio/X-ray samples in the work of Kataoka &amp; Stawarz, we analyzed the data in 12 FR I and 30 FR II radio galaxies, 12 quasars, and three BL Lac objects, which contained 76 knots, 42 hotspots, and 29 radio lobes. We first derived the equipartition magnetic fields in the cores and then estimated those in various jet components by assuming Best ∝ d-1, where d is the distance from the jet base. On the other hand, the magnetic field in large-scale jets (knots, hotspots, and lobes), Beq, can be estimated from the observed flux and spatial extent under the equipartition hypothesis. We show that the magnetic field decreases as the distance along the jet increases, but generally in a more gentle way than ∝d-1. The increase in Beq/Best at large d may suggest the deceleration of the jet downstream, but there is no difference between FR I and FR II jets. Moreover, the magnetic fields in the hotspots are systematically larger than those in knots and lobes. Finally, we applied the same analysis to knots and lobes in Centaurus A to check whether the above discussion will hold even in a single jet source.

Keywords: Jets, Radio jets, Quasars, Fanaroff-Riley radio galaxies, Magnetic fields
One Year in the Life of Young Suns: Data-constrained Corona-wind Model of κ<SUP>1</SUP> Ceti. The young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of X-ray and extreme-UV (EUV) flux, stellar wind, and eruptive events. These outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. While X-ray fluxes and surface magnetic fields can be derived from observations, the EUV emission, and wind mass fluxes, coronal mass ejections and associated stellar energetic particle events cannot be directly observed. Here, we present the results of a three-dimensional magnetohydrodynamic (MHD) model with inputs constrained by spectropolarimetric data, Hubble Space Telescope/STIS far-UV and X-ray data, and stellar magnetic maps reconstructed at two epochs separated by 11 months. The simulations show that over the course of the year the global stellar corona had undergone a drastic transition from a simple dipole-like to a tilted dipole with multipole field components and thus provided favorable conditions for corotating interaction regions (CIRs) that drive strong shocks. The dynamic pressures exerted by CIRs are 1300 times larger than those observed from the Sun and can contribute to the atmospheric erosion of early Venus, Earth, Mars, and young Earth-like exoplanets. Our data-constrained MHD model provides the framework to model coronal environments of G-M planet-hosting dwarfs. The model outputs can serve as a realistic input for exoplanetary atmospheric models to evaluate the impact of stellar coronal emission, stellar winds, and CIRs on their atmospheric escape and chemistry that can be tested in the upcoming James Webb Space Telescope and ground-based observations.

Keywords: Magnetohydrodynamics, Exoplanets, G dwarf stars, Stellar winds, Planet hosting stars, Stellar coronae
No Impact of Core-scale Magnetic Field, Turbulence, or Velocity Gradient on Sizes of Protostellar Disks in Orion A. We compared the sizes and fluxes of a sample of protostellar disks in Orion A measured with the Atacama Large Millimeter/submillimeter Array 0.87 mm continuum data from the VLA/ALMA Nascent Disk and Multiplicity survey with the physical properties of their ambient environments on the core scale of 0.6 pc estimated with the Green Bank Ammonia Survey data and the legacy catalog datasets of the polarimeter for the Submillimeter Common-User Bolometer Array. We did not find any significant dependence of the disk radii and continuum fluxes on a single parameter on the core scale, such as nonthermal line width, magnetic field orientation and strength, or magnitude and orientation of the velocity gradient. Among these parameters, we only found a positive correlation between the magnitude of the velocity gradient and the nonthermal line width. Thus, the observed velocity gradients are more likely related to turbulent motion but not large-scale rotation. Our results of no clear dependence of the disk radii on these parameters are more consistent with the expectation from nonideal MHD simulations of disk formation in collapsing cores, where the disk size is self-regulated by magnetic braking and diffusion, compared to other simulations that only include turbulence and/or a magnetic field misaligned with the rotational axis. Therefore, our results could hint that the nonideal MHD effects play a more important role in the disk formation. Nevertheless, we cannot exclude the influences on the observed disk size distribution by dynamical interaction in a stellar cluster or amounts of angular momentum on the core scale, which cannot be probed with the current data.

Keywords: Star forming regions, Interstellar magnetic fields, Star formation, Circumstellar disks, Protostars
Detection of Galactic and Extragalactic Millimeter-wavelength Transient Sources with SPT-3G. High angular resolution cosmic microwave background experiments provide a unique opportunity to conduct a survey of time-variable sources at millimeter wavelengths, a population that has primarily been understood through follow-up measurements of detections in other bands. Here we report the first results of an astronomical transient survey with the South Pole Telescope (SPT) using the SPT-3G camera to observe 1500 deg2 of the southern sky. The observations took place from 2020 March to November in three bands centered at 95, 150, and 220 GHz. This survey yielded the detection of 15 transient events from sources not previously detected by the SPT. The majority are associated with variable stars of different types, expanding the number of such detected flares by more than a factor of two. The stellar flares are unpolarized and bright, in some cases exceeding 1 Jy, and have durations from a few minutes to several hours. Another population of detected events last for 2-3 weeks and appear to be extragalactic in origin. Though data availability at other wavelengths is limited, we find evidence for concurrent optical activity for two of the stellar flares. Future data from SPT-3G and forthcoming instruments will provide real-time detection of millimeter-wave transients on timescales of minutes to months.

Keywords: High energy astrophysics, Millimeter astronomy, Surveys, Transient sources, Active galactic nuclei, Transient detection, Stellar flares
Modeling Stellar Activity-rotation Relations in Unsaturated Cool Stars. We apply a surface flux transport model developed for the Sun to reconstruct the stellar activity-rotation relationship, LX/Lbol versus Ro, observed for unsaturated cool stars (Rossby numbers Ro ≳ 0.1). This empirical flux transport model incorporates modulations of magnetic flux strength consistent with observed solar activity cycles, as well as surface flux dynamics consistent with observed and modeled stellar relationships. We find that for stellar flux models corresponding to a range of 0.1 ≲ (Ro/RoSun) ≲ 1.2, the LX/Lbol versus Ro relation matches well the power-law behavior observed in the unsaturated regime of cool stars. Additionally, the magnetic activity cycles captured by the stellar simulations produce a spread about the power-law relation consistent with that observed in cool star populations, indicating that the observed spread may be caused by intrinsic variations resulting from cyclic stellar behavior. The success of our flux transport modeling in reproducing the observed activity relationship across a wide range of late-F, G, K, and M stars suggests that the photospheric magnetic fields of all unsaturated cool stars exhibit similar flux emergence and surface dynamic behavior, and may hint at possible similarities in stellar dynamo action across a broad range of stellar types.

Keywords: Solar magnetic flux emergence, Stellar magnetic fields, Exoplanet systems, Solar x-ray emission, Stellar physics, Solar magnetic fields, Stellar evolution
Analyzing the Galactic Pulsar Distribution with Machine Learning. We explore the possibility of inferring the properties of the Galactic population of neutron stars through machine learning. In particular, in this paper we focus on their dynamical characteristics and show that an artificial neural network is able to estimate with high accuracy the parameters that control the current positions of a mock population of pulsars. For this purpose, we implement a simplified population-synthesis framework (where selection biases are neglected at this stage) and concentrate on the natal kick-velocity distribution and the distribution of birth distances from the Galactic plane. By varying these and evolving the pulsar trajectories in time, we generate a series of simulations that are used to train and validate a suitably structured convolutional neural network. We demonstrate that our network is able to recover the parameters governing the distribution of kick velocity and Galactic height with a mean relative error of about 10-2. We discuss the limitations of our idealized approach and study a toy problem to introduce selection effects in a phenomenological way by incorporating the observed proper motions of 216 isolated pulsars. Our analysis highlights that by increasing the sample of pulsars with accurate proper-motion measurements by a factor of ~10, one of the future breakthroughs of the Square Kilometre Array, we might succeed in constraining the birth spatial and kick-velocity distribution of the neutron stars in the Milky Way with high precision through machine learning.

Keywords: Neutron stars, Neural networks, Convolutional neural networks, Pulsars, Proper motions
An Empirical Determination of the Dependence of the Circumgalactic Mass Cooling Rate and Feedback Mass Loading Factor on Galactic Stellar Mass. Using our measurements of the Hα emission line flux originating in the cool (T ~ 104 K) gas that populates the halos of galaxies, we build a joint model to describe the mass of the cool circumgalactic medium (CGM) as a function of galactic stellar mass ( ${10}^{9.5}\lt {M}_{\ast }/{M}_{\odot }\lt {10}^{11}$) and environment. Because the Hα emission correlates with the main cooling channel for this gas, we are able to estimate the rate at which the CGM cools and becomes fuel for star formation in the central galaxy. We describe this calculation, which uses our observations, previous measurements of some critical CGM properties, and modeling of the cooling mechanism using the CLOUDY modeling suite. We find that the mass cooling rate is larger than the star formation rates of the central galaxies by a factor of ~4-90, empirically confirming that there is sufficient fuel to resolve the gas consumption problem and that feedback is needed to avoid collecting too much cold gas in galaxies. We find excellent agreement between our estimates of both the mass cooling rates and mass loading factors and the predictions of independent theoretical studies. The convergence in results that we find from several completely different treatments of the problem, particularly at the lower end of the galactic mass range, is a strong indication that we have a relatively robust understanding of the quantitative effects of feedback across this mass range.

Keywords: Cooling flows, Cool intergalactic medium