Sazuna/UAT_keywords huggingface dataset:
The Far-UV Interstellar Radiation Field in Galactic Disks: Numerical and Analytic Models. The intensity of the far-ultraviolet (FUV; 6-13.6 eV) interstellar radiation field (ISRF) in galaxies determines the thermal and chemical evolution of the neutral interstellar gas and is key for interpreting extragalactic observations and for theories of star formation. We run a series of galactic disk models and derive the FUV ISRF intensity as a function of the dust-to-gas ratio, star formation rate density, gas density, scale radius, and observer position. We develop an analytic formula for the median FUV ISRF flux. We identify two-dimensionless parameters in the problem: (1) the dimensionless galactic radius, X, which measures the radial extent of FUV sources (OB stellar associations) in the disk; and (2) the opacity over the intersource distance, τ⋆, which measures the importance of dust absorption. These parameters encapsulate the dependence on all of the physical parameters. We find that there exists a critical τ⋆, or equivalently a critical dust-to-gas ratio, ${Z}_{d,\mathrm{crit}}^{{\prime} }\approx 0.01-0.1$ , the Milky Way value, at which the ISRF changes behavior. For ${Z}_{d}^{{\prime} }\gt {Z}_{d,\mathrm{crit}}^{{\prime} }$ the ISRF is limited by dust absorption. With decreasing ${Z}_{d}^{{\prime} }$ , the ISRF intensity increases as more sources contribute to the flux. For ${Z}_{d}^{{\prime} }\lt {Z}_{d,\mathrm{crit}}^{{\prime} }$ the ISRF saturates as the disk becomes optically thin. We find that the ISRF per star formation rate density in low-metallicity systems, such as dwarf and high-redshift galaxies, is higher by up to a factor of 3-6 compared to their Milky Way counterparts. We discuss the implications these findings have for the potential mechanisms that regulate star formation in low-metallicity galaxies.

Keywords: Interstellar phases, Stellar feedback, Interstellar radiation field, OB associations, Interstellar dust extinction, Photodissociation regions, OB stars, Ultraviolet extinction, Star formation, Interstellar medium
Subsecond Spikes in Fermi GBM X-Ray Flux as a Probe for Solar Flare Particle Acceleration. Solar flares are known to release a large amount of energy into accelerating electrons. Studying small timescale (≤2s) fluctuations in nonthermal X-ray flux offers the opportunity to probe the nature of those acceleration mechanisms. By comparing the durations, differences in timing between energy bands, and the periodicity of these spikes against the relevant timescales called for by various acceleration mechanisms, a test for each mechanism&amp;'s validity can be made. This work details the analysis of fast fluctuations in Fermi Gamma-ray Burst Monitor (Fermi GBM) data from two M9.3 class solar flares that occurred on SOL2011-07-30 and SOL2011-08-04. This study shows the usefulness of Fermi GBM data as a means of examining these small timescale spikes and presents a rigorous method of identifying, counting, and measuring the temporal properties of these subsecond X-ray spikes. In the two flares examined we found spikes to primarily occur in spans of 60-100 s in the impulsive phase. The relative spike intensity averaged between 6% and 28% when compared to the slowly varying component of the X-ray flux. The average spike durations were 0.49 and 0.38 s for the 2 flares. The spike duration distribution for the SOL2011-08-04 flare was found to follow a power law with a -1.2 ± 0.3 index. Of the three spiking intervals identified, only one was found to have a periodicity, showing significant power at the 1.7 ± 0.1 Hz frequency.

Keywords: Time domain astronomy, Particle physics, Solar x-ray flares
Spectroscopic Tomography: A First Weak-lensing Detection Using Spectroscopic Redshifts Only. We describe the first spectroscopic tomographic (spectrotomographic) weak-lensing measurement for a galaxy cluster based only on background galaxies with spectroscopically determined redshifts. We use the massive cluster A2029 to demonstrate the power of combining spectroscopy and lensing to obtain accurate masses and to overcome biases from contamination and photometric redshift errors. We detect the shear signal from the cluster at &gt; 3.9σ significance. The shear signal scales with source redshift in a way that is consistent with the angular diameter distance ratio variation in a ΛCDM universe. Furthermore, the amplitude of the measured signal is consistent with the X-ray mass. Upcoming spectroscopic instruments such as the Prime Focus Spectrograph on Subaru will permit spectrotomographic weak-lensing measurements with a signal-to-noise ratio comparable with current photometric-redshift-based weak-lensing measurements for hundreds of galaxy clusters. Thus, spectrotomography may enable sensitive cosmological constraints that complement and are independent of other measurement techniques.

Keywords: Weak gravitational lensing, Rich galaxy clusters, Redshift surveys
Compact Elliptical Galaxies in Different Local Environments: A Mixture of Galaxies with Different Origins?. We present the stellar populations of 138 compact elliptical galaxies (cEs) in the redshift range of z &lt; 0.05 using the Sloan Digital Sky Survey (SDSS) DR12. Our cEs are divided into those with [cE(w)] and without [cE(w/o)] a bright (Mr &lt; -21 mag) host galaxy. We investigated the stellar population properties of cEs based on the Lick line indices extracted from SDSS spectra. cE(w)s show [Z/H] and [α/Fe] distributions skewed toward higher values compared to those of the cE(w/o)s. No statistically significant difference in age distribution was found between the cE(w)s and cE(w/o)s. In the mass-metallicity distribution, cE(w)s deviate from the relation observed for early-type galaxies at a given stellar mass, whereas cE(w/o)s conform to the relation. Based on the different features in the stellar populations of cE(w)s and cE(w/o)s, we can propose two different cE formation channels tracing different original masses of the progenitors. cE(w)s would be the remnant cores of the massive progenitor galaxies whose outer parts are tidally stripped by a massive neighboring galaxy (i.e., a nurture origin). In contrast, cE(w/o)s are likely the faint end of early-type galaxies maintaining in situ evolution in an isolated environment with no massive galaxy nearby (i.e., a nature origin). Our results reinforce the propositions that cEs comprise a mixture of galaxies with two types of origins depending on their local environment.

Keywords: Galaxy formation, Compact galaxies, Stellar populations, Compact dwarf galaxies, Galaxy evolution, Compact objects, Tidal interaction, Elliptical galaxies
A Model for the Fast Blue Optical Transient AT2018cow: Circumstellar Interaction of a Pulsational Pair-instability Supernova. The fast blue optical transient (FBOT) ATLAS18qqn (AT2018cow) has a light curve as bright as that of superluminous supernovae (SLSNe) but rises and falls much faster. We model this light curve by circumstellar interaction of a pulsational pair-instability (PPI) supernova (SN) model based on our PPISN models studied in previous work. We focus on the 42 M☉ He star (core of a 80 M☉ star) which has circumstellar matter (CSM) of mass 0.50 M☉. With the parameterized mass cut and the kinetic energy of explosion E, we perform hydrodynamical calculations of nucleosynthesis and optical light curves of PPISN models. The optical light curve of the first ∼20 days of AT2018cow is well reproduced by the shock heating of CSM for the 42 M☉ He star with E = 5 × 1051 erg. After day 20, the light curve is reproduced by the radioactive decay of 0.6 ${M}_{\odot }^{56}$ Co, which is a decay product of 56Ni in the explosion. We also examine how the light-curve shape depends on the various model parameters, such as CSM structure and composition. We also discuss (1) other possible energy sources and their constraints, (2) the origin of the observed high-energy radiation, and (3) how our result depends on the radiative transfer codes. Based on our successful model for AT2018cow and the model for SLSN with CSM mass as large as $20\,{M}_{\odot }$ , we propose the working hypothesis that PPISN produces SLSNe if the CSM is massive enough and FBOTs if CSM is less than ∼1 M☉.

Keywords: Stellar pulsations, Light curves, Radiative transfer, Supernovae, Supernova dynamics
Black Hole Mergers from Hierarchical Triples in Dense Star Clusters. Hierarchical triples are expected to be produced by the frequent binary-mediated interactions in the cores of globular clusters. In some of these triples, the tertiary companion can drive the inner binary to merger following large eccentricity oscillations, as a result of the eccentric Kozai-Lidov mechanism. In this paper, we study the dynamics and merger rates of black hole (BH) hierarchical triples, formed via binary-binary encounters in the CMC Cluster Catalog, a suite of cluster simulations with present-day properties representative of the Milky Way&amp;'s globular clusters. We compare the properties of the mergers from triples to the other merger channels in dense star clusters, and show that triple systems do not produce significant differences in terms of mass and effective spin distribution. However, they represent an important pathway for forming eccentric mergers, which could be detected by LIGO-Virgo/Kamioka Gravitational-Wave Detector (LVK), and future missions such as LISA and the DECi-hertz Interferometer Gravitational wave Observatory. We derive a conservative lower limit for the merger rate from this channel of 0.35 Gpc-3 yr-1 in the local universe and up to $\sim 9 \% $ of these events may have a detectable eccentricity at LVK design sensitivity. Additionally, we find that triple systems could play an important role in retaining second-generation BHs, which can later merge again in the core of the host cluster.

Keywords: Globular star clusters, Gravitational wave detectors, Black holes, Stellar mass black holes, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Trinary stars, Astrophysical black holes, Star clusters
IRIS Observations of the Low-atmosphere Counterparts of Active Region Outflows. Active region (AR) outflows have been studied in detail since the launch of Hinode/EIS and are believed to provide a possible source of mass and energy to the slow solar wind. In this work, we investigate the lower atmospheric counterpart of AR outflows using observations from the Interface Region Imaging Spectrograph (IRIS). We find that the IRIS Si IV, C II&gt; and Mg II transition region (TR) and chromospheric lines exhibit different spectral features in the outflows as compared to neighboring regions at the footpoints ("moss") of hot AR loops. The average redshift of Si IV in the outflow region (≈5.5 km s-1) is smaller than typical moss (≈12-13 km s-1) and quiet Sun (≈7.5 km s-1) values, while the C II line is blueshifted (≈-1.1-1.5 km s-1), in contrast to the moss where it is observed to be redshifted by about ≈2.5 km s-1. Further, we observe that the low atmosphere underneath the coronal outflows is highly structured, with the presence of blueshifts in Si IV and positive Mg II k2 asymmetries (which can be interpreted as signatures of chromospheric upflows) which are mostly not observed in the moss. These observations show a clear correlation between the coronal outflows and the chromosphere and TR underneath, which has not been shown before. Our work strongly suggests that these regions are not separate environments and should be treated together, and that current leading theories of AR outflows, such as the interchange reconnection model, need to take into account the dynamics of the low atmosphere.

Keywords: Solar active regions, Solar chromosphere, Solar transition region
DAMPE Proton Spectrum Indicates a Slow-diffusion Zone in the nearby ISM. The hardening and softening features in the DAMPE proton spectrum are very likely to have originated from a nearby supernova remnant (SNR). The proton spectrum from the nearby SNR is required to be very hard below ≈10 TeV. To reproduce this feature, we illustrate that an anomalously slow-diffusion zone for cosmic rays (CRs) must exist in the local interstellar medium (ISM) after also taking the dipole anisotropy of CRs into account. Assuming that the diffusion coefficient is homogeneous in the nearby ISM, we show that the diffusion coefficient is constrained to the magnitude of 1026 cm2 s-1 when normalized to 1 GeV, which is about 100 times smaller than the average value in the Galaxy. We further discuss the spatial distribution of the slow diffusion and find two distinct possibilities. In one case, the SNR is several hundred parsecs away from the solar system, and both the SNR and the solar system must be included in a large slow-diffusion zone. In the other case, the SNR is very close with a distance of ∼50 pc and the slow-diffusion zone is only limited around the SNR, while the current multiwavelength observations do not indicate such a close source. This work provides a new way of studying the CR diffusion in the local ISM.

Keywords: Supernova remnants, Interstellar medium, Cosmic rays
Progenitors of Type IIb Supernovae. II. Observable Properties. Type IIb supernovae (SNe IIb) present a unique opportunity for investigating the evolutionary channels and mechanisms governing the evolution of stripped-envelope SN progenitors due to a variety of observational constraints. Comparison of these constraints with the full distribution of theoretical properties not only helps determine the prevalence of observed properties in nature, but can also reveal currently unobserved populations. In this follow-up paper, we use the large grid of models presented in Sravan et al. to derive distributions of single and binary SNe IIb progenitor properties and compare them to constraints from three independent observational probes: multiband SN light curves, direct progenitor detections, and X-ray/radio observations. Consistent with previous work, we find that while current observations exclude single stars as SN IIb progenitors, SN IIb progenitors in binaries can account for them. We also find that the distributions indicate the existence of an unobserved dominant population of binary SNe IIb at low metallicity that arise due to mass transfer initiated on the Hertzsprung Gap. In particular, our models indicate the existence of a group of highly stripped (envelope mass ∼0.1-0.2M⊙) progenitors that are compact (&lt;50R⊙) and blue (Teff ≲ 105 K) with ∼104.5-105.5 L⊙ and low-density circumstellar mediums. As discussed in Sravan et al., this group is necessary to account for SN IIb fractions and likely exist regardless of metallicity. The detection of the unobserved populations indicated by our models would support weak stellar winds and inefficient mass transfer in SN IIb progenitors.

Keywords: Stellar photometry, Binary stars, Core-collapse supernovae, Stellar mass loss, Companion stars
High-level Ab Initio Studies of the Spectroscopic Properties of Triatomic [Al, S, O]<SUP>x</SUP> (x = 0, +1) and Its Potential for Detection in Space. Highly reliable molecular properties have been computed for the [Al, S, O]x (x = 0, +1) molecular system. Spectroscopic parameters are predicted from analysis of each isomer&amp;'s 3D potential energy surface calculated using the explicitly correlated multireference configuration interaction method, including the Davidson correction (MRCI-F12+Q). These parameters provide an accurate prediction of spectroscopic data that can be used in laboratory and observational studies of these molecules. Linear-SAlO is expected to have a large permanent dipole moment suitable for detection in the circumstellar envelopes of large, evolved, oxygen-rich stars such as VY Canis Majoris, IK Tauri, and R Doradus. Frequencies are provided for rotational transitions originating from the most highly populated rotational state based on a Boltzmann distribution. Additionally, both linear isomers exhibit a flat potential along the bending angle and are predicted to have very low bending mode frequencies (&lt;200 cm-1), complicating the spectra of these molecules.

Keywords: Radio spectroscopy, Line positions, Red supergiant stars, Molecular spectroscopy, Astrochemistry
Fluctuation Amplitudes of Magnetic-field Directional Turnings and Magnetic-velocity Alignment Structures in the Solar Wind. Magnetic-field directional turning (MFDT) and magnetic-velocity alignment structure (MVAS) are two typical types of structures in the solar wind. However, their fluctuation amplitudes in different turbulence states have not been studied before. Here, we present the amplitude distributions of MFDTs and MVASs in the ${C}_{{vb}}^{{\prime} }-{\sigma }_{r}$ plane, where ${C}_{{vb}}^{{\prime} }$ is the correlation coefficient between magnetic-field and velocity fluctuations multiplied by the sign of the x component of the mean field in geocentric solar ecliptic coordinates, and σr is normalized residual energy. Measurements from the WIND spacecraft in the slow solar wind during 2005-2009 are used for the analysis. The data are cut into intervals with duration of 6 minutes, and the intervals that are nearly incompressible are selected for analysis. We find that for the fluctuations with $| {C}_{{vb}}^{{\prime} }| \lt 0.55$ and -1 &lt; σr &lt; -0.6, which are considered to be associated with MFDTs, the level contours of the pixel average amplitude of magnetic-field fluctuations in the plane show a horizontal-stripe feature with approximately $10| {\sigma }_{r}| $ km s-1 in Alfvén units. For the fluctuations with $| {C}_{{vb}}^{{\prime} }| \gt 0.85$ and -0.9 &lt; σr &lt; -0.2, which are considered to be associated with MVASs, the level contours of the pixel average amplitude of velocity fluctuations show a vertical stripe feature with approximately $58.6| {C}_{{vb}}^{{\prime} }| \,-47.5$ km s-1. Consequently, the level contours of the pixel average amplitudes of Elsässer variables ${{\boldsymbol{z}}}^{\pm }$ show "U" and "W" shapes, respectively. These results will help us to understand the nature of the fluctuations in the solar wind.

Keywords: Interplanetary turbulence, Solar wind
The MAVERIC Survey: Radio Catalogs and Source Counts from Deep Very Large Array Imaging of 25 Galactic Globular Clusters. The MAVERIC survey is the first deep radio continuum imaging survey of Milky Way globular clusters, with a central goal of finding and classifying accreting compact binaries, including stellar-mass black holes. Here we present radio source catalogs for 25 clusters with ultra-deep Karl G. Jansky Very Large Array observations. The median observing time was 10 hr per cluster, resulting in typical rms sensitivities of 2.3 and 2.1 μJy per beam at central frequencies of 5.0 and 7.2 GHz, respectively. We detect nearly 1300 sources in our survey at 5σ, and while many of these are likely to be background sources, we also find strong evidence for an excess of radio sources in some clusters. The radio spectral index distribution of sources in the cluster cores differs from the background, and shows a bimodal distribution. We tentatively classify the steep-spectrum sources (those much brighter at 5.0 GHz) as millisecond pulsars and the flat-spectrum sources as compact or other kinds of binaries. These provisional classifications will be solidified with the future addition of X-ray and optical data. The outer regions of our images represent a deep, relatively wide-field (∼0.4 deg2) and high-resolution C band background survey, and we present source counts calculated for this area. We also release radio continuum images for these 25 clusters to the community.

Keywords: Globular star clusters, X-ray binary stars, Surveys, Radio source counts, Radio sources, Radio pulsars
On the Correlation between L Dwarf Optical and Infrared Variability and Radio Aurorae. Photometric variability attributed to cloud phenomena is common in L/T transition brown dwarfs. Recent studies show that such variability may also trace aurorae, suggesting that localized magnetic heating may contribute to observed brown dwarf photometric variability. We assess this potential correlation with a survey of 17 photometrically variable brown dwarfs using the Karl G. Jansky Very Large Array at 4-8 GHz. We detect quiescent and highly circularly polarized flaring emission from one source, 2MASS J17502484-0016151, which we attribute to auroral electron cyclotron maser emission. The detected auroral emission extends throughout the frequency band at ∼5-25σ, and we do not detect evidence of a cutoff. Our detection confirms that 2MASS J17502484-0016151 hosts a magnetic field strength of ≥2.9 kG, similar to those of other radio-bright ultracool dwarfs. We show that Hα emission continues to be an accurate tracer of auroral activity in brown dwarfs. Supplementing our study with data from the literature, we calculate the occurrence rates of quiescent emission in L dwarfs with low- and high-amplitude variability and conclude that high-amplitude optical and infrared variability does not trace radio magnetic activity in L dwarfs.

Keywords: Brown dwarfs, L dwarfs, Earth's clouds, Radio observatories, Radio continuum emission, Radio astronomy, Radio sources
A DESGW Search for the Electromagnetic Counterpart to the LIGO/Virgo Gravitational-wave Binary Neutron Star Merger Candidate S190510g. We present the results from a search for the electromagnetic counterpart of the LIGO/Virgo event S190510g using the Dark Energy Camera (DECam). S190510g is a binary neutron star (BNS) merger candidate of moderate significance detected at a distance of 227 ± 92 Mpc and localized within an area of 31 (1166) square degrees at 50% (90%) confidence. While this event was later classified as likely nonastrophysical in nature within 30 hours of the event, our short latency search and discovery pipeline identified 11 counterpart candidates, all of which appear consistent with supernovae following offline analysis and spectroscopy by other instruments. Later reprocessing of the images enabled the recovery of six more candidates. Additionally, we implement our candidate selection procedure on simulated kilonovae and supernovae under DECam observing conditions (e.g., seeing and exposure time) with the intent of quantifying our search efficiency and making informed decisions on observing strategy for future similar events. This is the first BNS counterpart search to employ a comprehensive simulation-based efficiency study. We find that using the current follow-up strategy, there would need to be 19 events similar to S190510g for us to have a 99% chance of detecting an optical counterpart, assuming a GW170817-like kilonova. We further conclude that optimization of observing plans, which should include preference for deeper images over multiple color information, could result in up to a factor of 1.5 reduction in the total number of follow-ups needed for discovery.

Keywords: Gravitational wave astronomy
Small-scale Magnetic Flux Ropes in the First Two Parker Solar Probe Encounters. Small-scale magnetic flux ropes (SFRs) are a type of structure in the solar wind that possess helical magnetic field lines. In a recent report we presented the radial variations of the properties of SFRs from 0.29 to 8 au using in situ measurements from the Helios, Advanced Composition Explorer/WIND (ACE/Wind), Ulysses, and Voyager spacecrafts. With the launch of the Parker Solar Probe (PSP), we extend our previous investigation further into the inner heliosphere. We apply a Grad-Shafranov-based algorithm to identify SFRs during the first two PSP encounters. We find that the number of SFRs detected near the Sun is much less than at larger radial distances, where magnetohydrodynamic (MHD) turbulence may act as the local source to produce these structures. The prevalence of Alfvénic structures significantly suppresses the detection of SFRs at closer distances. We compare the SFR event list with other event identification methods, yielding a dozen well-matched events. The cross-section maps of two selected events confirm the cylindrical magnetic flux-rope configuration. The power-law relation between the SFR magnetic field and heliocentric distances seems to hold down to 0.16 au.

Keywords: Magnetohydrodynamics, Astronomy databases, Interplanetary turbulence, Solar wind, Astronomy data analysis