Sazuna/UAT_keywords huggingface dataset:
CLOVER: Convnet Line-fitting Of Velocities in Emission-line Regions. When multiple star-forming gas structures overlap along the line of sight and emit optically thin emission at significantly different radial velocities, the emission can become non-Gaussian and often exhibits two distinct peaks. Traditional line-fitting techniques can fail to account adequately for these double-peaked profiles, providing inaccurate measurements of cloud kinematics. We present a new method, called Convnet Line-fitting Of Velocities in Emission-line Regions (CLOVER), for distinguishing between one-component, two-component, and noise-only emission lines using 1D convolutional neural networks trained with synthetic spectral cubes. CLOVER utilizes spatial information in spectral cubes by predicting on 3 × 3 pixel subcubes, using both the central pixel’s spectrum and the average spectrum over the 3 × 3 grid as input. On an unseen set of 10,000 synthetic spectral cubes in each predicted class, CLOVER has classification accuracies of ∼99% for the one-component class and ∼97% for the two-component class. For the noise-only class, which is analogous to a signal-to-noise cutoff of four for traditional line-fitting methods, CLOVER has classification accuracy of 100%. CLOVER also has exceptional performance on real observations, correctly distinguishing between the three classes across a variety of star-forming regions. In addition, CLOVER quickly and accurately extracts kinematics directly from spectra identified as two-component class members. Moreover, we show that CLOVER is easily scalable to emission lines with hyperfine splitting, making it an attractive tool in the new era of large-scale NH3 and N2H+ mapping surveys.

Keywords: Convolutional neural networks, Star formation, Interstellar medium
Further Evidence for Looplike Fine Structure inside “Unipolar” Active Region Plages. Earlier studies using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory (SDO) have suggested that active region (AR) plages and strong network concentrations often have small, looplike features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Because of the unexpected nature of these findings, we have searched the SDO database for examples of inverted-Y structures rooted inside “unipolar” plages, with such jetlike structures being interpreted as evidence for magnetic reconnection between small bipoles and the dominant-polarity field. Several illustrative cases are presented from the period of 2013-2015, all of which are associated with transient outflows from AR “moss.” The triangular or dome-shaped bases have horizontal dimensions of ∼2-4 Mm, corresponding to ∼1-3 granular diameters. We also note that the spongy-textured Fe IX 17.1 nm moss is not confined to plages, but may extend into regions where the photospheric field is relatively weak or even has mixed polarity. We again find a tendency for bright coronal loops seen in the 17.1, 19.3, and 21.1 nm passbands to show looplike fine structure and compact brightenings at their footpoints. These observations provide further confirmation that present-day magnetograms are significantly underrepresenting the amount of minority-polarity flux inside AR plages and again suggest that footpoint reconnection and small-scale flux cancellation may play a major role in coronal heating, both inside and outside ARs.

Keywords: Solar extreme ultraviolet emission, Solar coronal loops, Solar coronal heating, Solar active regions, Solar magnetic fields, Solar corona
Ensemble Forecasting of Major Solar Flares with Short-, Mid-, and Long-term Active Region Properties. We apply an ensemble technique for major flare prediction by considering short-, mid-, and long-term active region (AR) properties and their relative contributions. For this, we consider magnetic parameters from Solar Dynamics Observatory/Helioseismic and Magnetic Imager and flare lists from Geostationary Operational Environmental Satellites. In this study, we simultaneously consider flaring rates during short- (1 day), mid- (several days), and long-term (several years) timeframes. In our model, the predicted rate is given by a weighted combination of the three rates such that the sum of their weights is 1. We calculate the Brier skill scores (BSSs) for investigating prediction performance and weights of these three terms to provide optimal results. The BSS (0.22) of the model with only long-term properties is higher than that with only short-term (0.07) or mid-term (0.08) properties. When short-/mid-term properties are additionally considered, the BSS is improved to 0.28/0.24. Our model has the best performance (BSS = 0.29) when all terms are considered, and their relative contributions to the short-, mid-, and long-term rates are 20%, 20%, and 60%, respectively. In addition, the model with three terms is more effective at predicting major flares in strong ARs. In view of the energy storage and release process, long-term magnetic properties may indicate the storage of magnetic free energy, while short- and mid-term flare history may reflect a recent trend of energy release process. Our results suggest that the performances of other existing flare models based on long-term properties should be improved by considering short- and/or mid-term flare history.

Keywords: Space weather, The Sun, Solar flares, Solar magnetic fields
The Equation of State and Some Key Parameters of Neutron Stars: Constraints from GW170817, the Nuclear Data, and the Low-mass X-Ray Binary Data. In this work we parameterize the equation of state of dense neutron star (NS) matter with four pressure parameters of \{{\hat{p}}1,{\hat{p}}2,{\hat{p}}3,{\hat{p}}4\} and then set the combined constraints with the data of GW170817 and the data of six low-mass X-ray binaries (LMXBs) with thermonuclear burst or alternatively the symmetry energy of the nuclear interaction. We find that the nuclear data effectively narrow down the possible range of {\hat{p}}1, the gravitational-wave data plays the leading role in bounding {\hat{p}}2, and the LMXB data as well as the lower bound on the maximal gravitational mass of non-rotating NSs govern the constraints on {\hat{p}}3 and {\hat{p}}4. Using posterior samples of pressure parameters and some universal relations, we further investigate how the current data sets can advance our understanding of tidal deformability (Λ), moment of inertia (I), and binding energy (BE) of NSs. For a canonical mass of 1.4 M ⊙, we have {I}1.4={1.43}-0.13+0.30 × {10}38 {kg} {{{m}}}2, {{{Λ }}}1.4={390}-210+280 , {R}1.4={11.8}-0.7+1.2 {km}, and {BE}}1.4={0.16}-0.02+0.01 {M}⊙  if the constraints from the nuclear data and the gravitational-wave data have been jointly applied. For the joint analysis of gravitational-wave data and the LMXB data, we have {I}1.4={1.28}-0.08+0.15× {10}38 {kg} {{{m}}}2, {{{Λ }}}1.4={220}-90+90, {R}1.4={11.1}-0.6+0.7 {km}, and {BE}}1.4={0.18}-0.01+0.01 {M}⊙ . These results suggest that the current constraints on Λ and R still suffer from significant systematic uncertainties, while I 1.4 and BE1.4 are better constrained.

Keywords: Low-mass x-ray binary stars, Neutron star cores, Gravitational waves, Relativistic binary stars
Understanding Lyα Nebulae at Low Redshift. I. The Sizes, Powering, and Kinematics of “Green Bean” Galaxies. A new but rare sample of spatially extended emission line nebulae, nicknamed “Green Beans,” was discovered at z ≈ 0.3 thanks to strong [O III] emission, and subsequently shown to be local cousins of the Lyα nebulae found at high redshift. Here we use follow-up APO/DIS spectroscopy to better understand how these low-redshift Lyα nebulae compare to other populations of strong emission line sources. Our spectroscopic data show that low-z Lyα nebulae have active galactic nucleus (AGN)-like emission line ratios, relatively narrow line widths (FWHM ≲ 1000 km s-1), and emission line kinematics resembling those of Type 2 AGN at the same redshift, confirming that they are powered by Type 2 AGN with typical ionizing continua. While low-z Lyα nebulae are larger and less concentrated than compact, star-forming Green Pea galaxies, we find that they resemble typical Type 2 AGN in terms of r-band concentration and size. Based on this pilot study, low-z Lyα nebulae appear to be a subset of Type 2 AGN with bluer optical continua and high [O III] equivalent widths but with comparable sizes and similar [O III] kinematics. These characteristics may simply reflect the fact that low-z Lyα nebulae are drawn from the high-luminosity end of the Type 2 AGN distribution, with higher nuclear activity driving higher [O III] equivalent widths and more central star formation leading to bluer optical continua. Deeper spectroscopic follow-up of the full sample will shed further light on these issues and on the relationship between these low-z Lyα nebulae and the Lyα nebula population at high redshift.

Keywords: Active galaxies, Emission line galaxies, Galaxy kinematics, Galaxy evolution, Lyman-alpha galaxies
SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries. We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN 2017gmr from hours after discovery through the first 180 days. SN 2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼500 R ☉ progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130 ± 0.026 M ☉ of 56Ni are present, if the light curve is solely powered by radioactive decay, although the 56Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of Hα and [O I] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.

Keywords: Type II supernovae, Massive stars, Core-collapse supernovae
The Sloan Digital Sky Survey Reverberation Mapping Project: Accretion and Broad Emission Line Physics from a Hypervariable Quasar. We analyze extensive spectroscopic and photometric data of the hypervariable quasar SDSS J141324+530527 (RMID 017) at z = 0.456, an optical “changing-look” quasar from the Sloan Digital Sky Survey Reverberation Mapping project that increased in optical luminosity by a factor ≃10 between 2014 and 2017. The observed broad emission lines all respond in luminosity and width to the changing optical continuum, as expected for photoionization in a stratified, virialized broad emission line region. The luminosity changes therefore result from intrinsic changes in accretion power rather than variable obscuration. The variability is continuous and apparently stochastic, disfavoring an origin as a discrete event such as a tidal disruption flare or microlensing event. It is coordinated on day timescales with blue leading red, consistent with reprocessing powering the entire optical spectral energy distribution. We show that this process cannot work in a standard thin disk geometry on energetic grounds, and would instead require a large covering factor reprocessor. Disk instability models could potentially also explain the data, provided that the instability sets in near the inner radius of a geometrically thick accretion disk.

Keywords: Accretion, Supermassive black holes, Quasars
KIC 4142768: An Evolved Gamma Doradus/Delta Scuti Hybrid Pulsating Eclipsing Binary with Tidally Excited Oscillations. We present the characterization of KIC 4142768, an eclipsing binary with two evolved A-type stars in an eccentric orbit with a period of 14 days. We measure the fundamental parameters of the two components ({M}1=2.05{M}⊙ ,{R}1=2.96{R}⊙  and {M}2=2.05{M}⊙ ,{R}2=2.51{R}⊙ ) by combining Kepler photometry and spectra from the Keck HIRES. The measured surface rotation rates are only one-fifth of the pseudo-synchronous rate of the eccentric orbit. The Fourier spectrum of the light curve reveals hybrid pulsations of δ Scuti and γ Doradus type, with pulsation frequencies at about 15-18 day-1 for p modes and about 0.2-1.2 day-1 for low-frequency g modes. Some of the g modes are exact orbital harmonics and are likely tidally excited. Their pulsation amplitudes and phases both agree with predictions from linear tidal theory for l = 2, m = 2 prograde modes. We examine the period spacing patterns in the self-driven g modes and identify them mostly as prograde sectoral dipole modes. The unstable frequency range and frequency spacing of the p modes and the inferred asymptotic g-mode period spacings both agree with the stellar model for the primary star evolved to a late stage of the main sequence. The inferred rotation rate of the convective core boundary is very slow, similar to the small surface rotation rate inferred from the spectroscopy. The measured surface and near-core rotation rates provide constraints for testing the mechanism of angular momentum transfer and tidal synchronization in evolved eccentric binary star systems.

Keywords: Eclipsing binary stars, Stellar oscillations, Asteroseismology, Binary stars
Cosmological Evolution of the Absorption of γ-Ray Burst X-Ray Afterglows. X-ray absorption of γ-ray burst (GRB) afterglows is prevalent yet poorly understood. X-ray-derived neutral hydrogen column densities (N H) of GRB X-ray afterglows show an increase with redshift, which might give a clue for the origin of this absorption. We use more than 350 X-ray afterglows with spectroscopic redshift (z) from the Swift X-ray Telescope repository as well as over 100 Lyα absorption measurements in z &gt; 1.6 sources. The observed trend of the average optical depth τ at 0.5 keV is consistent with both a sharp increase of host N H(z), and an absorbing diffuse intergalactic medium (IGM), along with decreasing host contribution to τ. We analyze a subsample of high-z GRBs with N H derived both from the X-ray afterglow and the Lyα line. The increase of X-ray-derived N H(z) is contrasted by no such increase in the Lyα-derived column density. We argue that this discrepancy implies a lack of association between the X-ray and Lyα absorbers at high z. This points toward the X-ray absorption at high z being dominated by an intervening absorber, which lends credibility to an absorbing IGM contribution.

Keywords: X-ray transient sources, Warm-hot intergalactic medium, Gamma-ray bursts
Characterizing the Magnetic Environment of Exoplanet Stellar Systems. We employ a flux transport model incorporating observed stellar activity relations to characterize stellar interplanetary fields on cycle timescales for a range of stellar activity defined by the Rossby number. This framework allows us to examine the asterospheric environments of exoplanetary systems and yields references against which exoplanetary observations can be compared. We examine several quantitative measures of star-exoplanet interaction: the ratio of open to total stellar magnetic flux, the location of the stellar Alfvén surface, and the strength of interplanetary magnetic field polarity inversions, all of which influence planetary magnetic environments. For simulations in the range of Rossby numbers considered (0.1-5 RoSun), we find that (1) the fraction of open magnetic flux available to interplanetary space increases with Rossby number, with a maximum of around 40% at stellar minimum for low-activity stars, while the open flux for very active stars (Ro ∼ 0.1-0.25 RoSun) is ∼1-5% (2) the mean Alfvén surface radius, R A, varies between 0.7 and 1.3 R A,Sun and is larger for lower stellar activity; and (3) at high activity, the asterospheric current sheet becomes more complex with stronger inversions, possibly resulting in more frequent reconnection events (e.g., magnetic storms) at the planetary magnetosphere. The simulations presented here serve to bound a range of asterospheric magnetic environments within which we can characterize the conditions impacting any exoplanets present. We relate these results to several known exoplanets and discuss how they might be affected by changes in asterospheric magnetic field topologies.

Keywords: Stellar magnetic fields, Exoplanet systems, Stellar activity, Stellar physics, Solar physics, Stellar winds
Unveiling Dust Aggregate Structure in Protoplanetary Disks by Millimeter-wave Scattering Polarization. Dust coagulation in a protoplanetary disk is the first step in planetesimal formation. However, the pathway from dust aggregates to planetesimals remains unclear. Both numerical simulations and laboratory experiments have suggested the importance of dust structure in planetesimal formation, but it is not well constrained by observations. We study how the dust structure and porosity alter polarimetric images at millimeter wavelengths by performing 3D radiative transfer simulations. Aggregates with different porosities and fractal dimensions are considered. As a result, we find that dust aggregates with lower porosity and/or higher fractal dimension are favored to explain the observed millimeter-wave scattering polarization of disks. Although we cannot rule out the presence of aggregates with extremely high porosity, a population of dust particles with relatively compact structure is at least necessary to explain polarized-scattered waves. In addition, we show that particles with moderate porosity show a weak wavelength dependence of the scattering polarization, indicating that multiwavelength polarimetry is useful to constrain dust porosity. Finally, we discuss implications for dust evolution and planetesimal formation in disks.

Keywords: Polarimetry, Protoplanetary disks, Planet formation
Signatures of Tidal Disruption in Ultra-faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V. The ultra-faint dwarf galaxy Leo V has shown both photometric overdensities and kinematic members at large radii, along with a tentative kinematic gradient, suggesting that it may have undergone a close encounter with the Milky Way. We investigate these signs of disruption through a combination of (i) high precision photometry obtained with the Hubble Space Telescope (HST), (ii) two epochs of stellar spectra obtained with the Hectochelle Spectrograph on the MMT, and (iii) measurements from the Gaia mission. Using the HST data, we examine one of the reported stream-like overdensities at large radii, and conclude that it is not a true stellar stream, but instead a clump of foreground stars and background galaxies. Our spectroscopic analysis shows that one known member star is likely a binary, and challenges the membership status of three others, including two distant candidates that had formerly provided evidence for overall stellar mass loss. We also find evidence that the proposed kinematic gradient across Leo V might be due to small number statistics. We update the systemic proper motion of Leo V, finding ({μ }α \cos δ ,{μ }δ )=(0.009+/- 0.560, -0.777 ± 0.314) mas yr-1, which is consistent with its reported orbit that did not put Leo V at risk of being disturbed by the Milky Way. These findings remove most of the observational clues that suggested Leo V was disrupting; however, we also find new plausible member stars, two of which are located &gt;5 half-light radii from the main body. These stars require further investigation. Therefore, the nature of Leo V still remains an open question.

Keywords: Stellar populations, Tidal disruption, Dwarf galaxies, HST photometry, Galactic and extragalactic astronomy, Spectroscopy
A Search for Short-term Hard X-Ray Bursts in the Direction of the Repeating FRB 121102. The nature of fast radio bursts (FRBs), which occur on millisecond timescales in the radio band, is well-understood. Among their unknown observational properties are their broadband spectra, and persistent and transient multiwavelength counterparts. Well-localized FRBs provide the opportunity to address these issues in archival observations. We performed searches for 15-150 keV hard X-ray bursts on timescales as short as 1 ms in the direction of the repeating FRB 121102 (with a spacial resolution of a few arcminutes) in the archival Swift/BAT data between 2016 October and 2017 September. We found no significant (5σ) hard X-ray bursts in the direction of the repeating FRB. We derived an upper limit of the hard X-ray (15-150 keV) flux of any X-ray bursts on a 1 ms timescale of around 1.01 × 10-7 erg cm-2 s-1, if assuming a photoindex of 2 for potential X-ray flares in the X-ray band. A plausible scenario for the repeating FRB as being associated with a magnetar giant flare is still far below the upper limit.

Keywords: Neutron stars, Radio bursts, X-ray transient sources, Non-thermal radiation sources, Magnetars, Radio transient sources
A New Technique for Finding Galaxies Leaking Lyman-continuum Radiation: [S II]-deficiency. The source responsible for the reionization of the universe is believed to be the population of star-forming galaxies at z ∼ 6 to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of “leaky” galaxies have been discovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program to test a new technique for finding leaky galaxies, using the weakness of the [S II] nebular emission lines relative to typical star-forming galaxies as evidence that the interstellar medium (ISM) is optically thin to the Lyman continuum. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to detect significant emerging flux below the Lyman edge in two out of three [S II]-weak star-forming galaxies at z ∼ 0.3. We show that these galaxies differ markedly in their properties from the class of leaky “Green-Pea” galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the ISM. Like the Green Peas, they have exceptionally high star formation rates per unit area. They also share some properties with the known leaky galaxies at z ∼ 3, but are significantly dustier. Our results validate a new method to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the universe.

Keywords: Galaxy formation, Star formation, Interstellar medium, Intergalactic medium, Extragalactic astronomy
Fast-to-Alfvén Mode Conversion and Ambipolar Heating in Structured Media. I. Simplified Cold Plasma Model. Linear fast magnetoacoustic waves are introduced into a cold stratified plasma model made up of a doubly periodic ensemble of straight diminished-Alfvén-speed tubes. Coupling between fast and Alfvén waves is produced by stratification and the tube structures, and scattering is strong for wavelengths comparable to the inter-tube separation. Ambipolar diffusion is found to be enhanced by the structuring and is potentially significant at high frequencies. The production of kink waves is discussed and modeled. It is found that the tube structure significantly alters the wave energy reaching the corona and the form that it takes, even for moderate fast-slow tube contrast, with Alfvén waves becoming prominent.

Keywords: Solar atmospheric motions, Solar chromosphere, Alfven waves