Sazuna/UAT_keywords huggingface dataset:
Galactic Interstellar Sulfur Isotopes: A Radial <SUP>32</SUP>S/<SUP>34</SUP>S Gradient?. We present observations of 12C32S, 12C34S, 13C32S, and 12C33S J = 2-1 lines toward a large sample of massive star-forming regions by using the Arizona Radio Observatory 12 m telescope and the IRAM 30 m. Taking new measurements of the carbon 12C/13C ratio, the 32S/34S isotope ratio was determined from the integrated 13C32S/12C34S line intensity ratios for our sample. Our analysis shows a 32S/34S gradient from the inner Galaxy out to a galactocentric distance of 12 kpc. An unweighted least-squares fit to our data yields 32S/34S = (1.56 ± 0.17)DGC + (6.75 ± 1.22) with a correlation coefficient of 0.77. Errors represent 1σ standard deviations. Testing this result by (a) excluding the Galactic center region, (b) excluding all sources with C34S opacities &gt;0.25, (c) combining our data and old data from previous study, and (d) using different sets of carbon isotope ratios leads to the conclusion that the observed 32S/34S gradient is not an artifact but persists irrespective of the choice of sample and carbon isotope data. A gradient with rising 32S/34S values as a function of galactocentric radius implies that the solar system ratio should be larger than that of the local interstellar medium. With the new carbon isotope ratios, we indeed obtain a local 32S/34S isotope ratio about 10% below the solar system one, as expected in the case of decreasing 32S/34S ratios with time and increased amounts of stellar processing. However, taking older carbon isotope ratios based on a lesser amount of data, such a decrease is not seen. No systematic variation of 34S/33S ratios along galactocentric distance was found. The average value is 5.9 ± 1.5, the error denoting the standard deviation of an individual measurement.

Keywords: Interstellar molecules, Abundance ratios, Galaxy chemical evolution, Stellar abundances, Interstellar medium, Stellar nucleosynthesis, Radio astronomy, Milky Way Galaxy
A Gravitational Redshift Measurement of the White Dwarf Mass-Radius Relation. The mass-radius relation of white dwarfs is largely determined by the equation of state of degenerate electrons, which causes the stellar radius to decrease as mass increases. Here we observationally measure this relation using the gravitational redshift effect, a prediction of general relativity that depends on the ratio between stellar mass and radius. Using observations of over 3000 white dwarfs from the Sloan Digital Sky Survey and the Gaia space observatory, we derive apparent radial velocities from absorption lines, stellar radii from photometry and parallaxes, and surface gravities by fitting atmospheric models to spectra. By averaging the apparent radial velocities of white dwarfs with similar radii and, independently, surface gravities, we cancel out random Doppler shifts and measure the underlying gravitational redshift. Using these results, we empirically measure the white dwarf mass-radius relation across a wide range of stellar masses. Our results are consistent with leading theoretical models, and our methods could be used with future observations to empirically constrain white dwarf core composition and evolution.

Keywords: White dwarf stars, General relativity, DA stars
Influence of C/O Ratio on Hot Jupiter Atmospheric Chemistry. We conducted laboratory experiments to study the chemistry in hot Jupiter atmospheres with a C/O ratio of 0.35. We compared our results with the ones obtained previously for atmospheres with a C/O ratio of 1 to investigate the influence of the C/O ratio on the chemistry and formation of photochemical organic aerosol. We found that the C/O ratio and the gas mixture compositions strongly influence the pathways responsible for the formation of CO2. Thermochemical reactions are primarily responsible for the formation of CO2 in low C/O ratio atmospheres, while photochemistry is the dominant process in high C/O ratio atmospheres even if the final CO2 concentration is the same in both cases. Our results show that low C/O atmospheres at the thermochemical equilibrium contain a higher water abundance, while high C/O atmospheres are significantly depleted in water. However, in low C/O atmospheres, the water abundance is not affected by UV photolysis, while our previous work demonstrated that a significant amount of water can be produced in high C/O ratio atmospheres. This contrast in water production suggests that photochemistry should be considered when interpreting exoplanet transit spectra. Finally, we did not observe the formation of a detectable amount of nonvolatile photochemical aerosols in low C/O atmospheres, in contrast to our previous study. We infer that for a C/O ratio &lt; 1, water likely inhibits organic growth and aerosol formation, suggesting that photochemical organic aerosols are likely to be observed in planets presenting a carbon enrichment compared to their host stars.

Keywords: Exoplanet atmospheric composition , Laboratory astrophysics, Planetary atmospheres, Exoplanet atmospheres
Information Theoretical Approach to Understanding Flare Waiting Times. There is not currently a consensus on the process responsible for producing the waiting time distribution of solar flares. This study presents an information theoretical approach to determining whether solar flare data are significantly distinguishable from a nonstationary Poisson process. A study of solar flares stronger than C1 class detected by the Geostationary Operational Environmental Satellite from 1975 to 2017 was performed. A sequence of waiting times (time elapsed between adjacent X-ray flare peaks) was constructed from the data. Surrogate waiting time sequences were produced using a time-varying Poisson firing rate from the Bayesian block procedure. Utilizing Shannon entropy, the mutual information of time-lagged waiting time distributions was computed for both the original data and the surrogates using a method of discretization by binning. When the entire period is considered, we see that when compared to carefully constructed surrogates, there is a significant elevation of mutual information on a timescale of approximately 30 hr, demonstrating that flares are confidently related to subsequent flares, contradicting the null hypothesis that flares are produced by a nonstationary Poisson process. When only 4 yr subsets of the data are considered, we see that at relatively small timescales (on the order of 10-30 hr), solar flare waiting times have a significant impact on subsequent flares. When corrected for the number of points in each considered time window, there is no correlation between the magnitude of significance and position in the solar cycle.

Keywords: Solar activity, Poisson distribution, Solar flares
Binary Intermediate-mass Black Hole Mergers in Globular Clusters. We consider the formation of binary intermediate black holes (BIMBHs) in globular clusters (GC), which could happen either in situ or due to the mergers between clusters. We simulate the evolution of the BIMBH orbit (and its subsequent merger) due to stellar ejections. We also take into account the evaporation of GCs due to the tidal field of the host galaxy and two-body relaxation. Our results show that if at least 10-3 of all GCs become BIMBH hosts and the BIMBH masses are ∼1% of the GC mass, at least one of the inspiraling (or merging) BIMBHs will be detected by LISA during its 4 yr mission lifetime. Most of the detected BIMBHs come (1) from heavy GCs (≳3 × 105 ${M}_{\odot }$), as lower-mass GCs end up being disrupted before their BIMBHs have time to merge, and (2) from redshifts 1 &lt; z &lt; 3, assuming that most GCs form around z ∼ 4 and given that the merger timescale for most BIMBHs is ∼1 Gyr. If the BIMBH to GC mass ratio is lower (∼10-3) but the fraction of BIMBH hosts among GCs is higher (≳10-2), some of their mergers will also be detected by LIGO, Virgo, and KAGRA and the proposed Einstein Telescope.

Keywords: Globular star clusters, Intermediate-mass black holes, Gravitational waves, Black holes
Reliable Probability Forecast of Solar Flares: Deep Flare Net-Reliable (DeFN-R). We developed a reliable probabilistic solar-flare forecasting model using a deep neural network, named Deep Flare Net-Reliable (DeFN-R). The model can predict the maximum classes of flares that occur in the following 24 hr after observing images, along with the event occurrence probability. We detected active regions from 3 × 105 solar images taken during 2010-2015 by Solar Dynamic Observatory and extracted 79 features for each region, which we annotated with flare occurrence labels of X-, M-, and C-classes. The extracted features are the same as used by Nishizuka et al.; for example, line-of-sight/vector magnetograms in the photosphere, brightening in the corona, and the X-ray emissivity 1 and 2 hr before an image. We adopted a chronological split of the database into two for training and testing in an operational setting: the data set in 2010-2014 for training and the one in 2015 for testing. DeFN-R is composed of multilayer perceptrons formed by batch normalizations and skip connections. By tuning optimization methods, DeFN-R was trained to optimize the Brier skill score (BSS). As a result, we achieved BSS = 0.41 for ≥C-class flare predictions and 0.30 for ≥M-class flare predictions by improving the reliability diagram while keeping the relative operating characteristic curve almost the same. Note that DeFN is optimized for deterministic prediction, which is determined with a normalized threshold of 50%. On the other hand, DeFN-R is optimized for a probability forecast based on the observation event rate, whose probability threshold can be selected according to users' purposes.

Keywords: Classification, Neural networks, Space weather, Astrostatistics techniques, Solar active regions, Solar magnetic fields, Solar x-ray flares, Solar activity, Magnetic fields, Time series analysis
Exploring the Acceleration Mechanisms for Particle Injection and Power-law Formation during Transrelativistic Magnetic Reconnection. Magnetic reconnection in the relativistic and transrelativistic regimes is able to accelerate particles to hard power-law energy spectra f ∝ γ-p (approaching p = 1). The underlying acceleration mechanism that determines the spectral shape is currently a topic of intense investigation. By means of fully kinetic plasma simulations, we carry out a study of particle acceleration during magnetic reconnection in the transrelativistic regime of a proton-electron plasma. While earlier work in this parameter regime has focused on the effects of electric field parallel to the local magnetic field on the particle injection (from thermal energy to the lower-energy bound of the power-law spectrum), here we examine the roles of both parallel and perpendicular electric fields to gain a more complete understanding on the injection process and further development of a power-law spectrum. We show that the parallel electric field does contribute significantly to particle injection, and is more important in the initial phase of magnetic reconnection. However, as the simulation proceeds, the acceleration by the perpendicular electric field becomes more important for particle injection and completely dominates the acceleration responsible for the high-energy power-law spectrum. This holds robustly, in particular for longer reconnection times and larger systems, i.e., in simulations that are more indicative of the processes in astrophysical sources.

Keywords: Non-thermal radiation sources, Magnetic fields
Mapping Circumstellar Magnetic Fields of Late-type Evolved Stars with the Goldreich-Kylafis Effect: CARMA Observations at λ1.3 mm of R Crt and R Leo. Mapping magnetic fields is the key to resolving the unclear physical picture of circumstellar magnetic fields in late-type evolved stars. Observations of linearly polarized emission from thermal molecular line transitions due to the Goldreich-Kylafis (G-K) effect provide valuable insights into the magnetic field geometry in these sources that are complementary to other key studies. In this paper, we present the detection of spectral-line polarization from both the thermal J = 2-1 CO line and the v = 1, J = 5-4 SiO maser line toward two thermal-pulsating asymptotic giant branch stars, R Crt and R Leo. The observed fractional linear polarization in the CO emission is measured as ml ∼ 3.1% and ml ∼ 9.7% for R Crt and R Leo, respectively. A circumstellar envelope (CSE) model profile and the associated parameters are estimated and used as input to a more detailed modeling of the predicted linear polarization expected from the G-K effect. The observed thermal line polarization level is consistent with the predicted results from the G-K model for R Crt; additional effects need to be considered for R Leo.

Keywords: Stellar magnetic fields, Asymptotic giant branch stars, Circumstellar masers, CO line emission, Polarimetry
Presupernova Neutrinos: Directional Sensitivity and Prospects for Progenitor Identification. We explore the potential of current and future liquid scintillator neutrino detectors of ${ \mathcal O }(10)$ kt mass to localize a presupernova neutrino signal in the sky. In the hours preceding the core collapse of a nearby star (at distance $D\lesssim 1$ kpc), tens to hundreds of inverse beta decay events will be recorded, and their reconstructed topology in the detector can be used to estimate the direction to the star. Although the directionality of inverse beta decay is weak (∼8% forward-backward asymmetry for currently available liquid scintillators), we find that for a fiducial signal of 200 events (which is realistic for Betelgeuse), a positional error of ∼60° can be achieved, resulting in the possibility to narrow the list of potential stellar candidates to less than 10, typically. For a configuration with improved forward-backward asymmetry (∼40%, as expected for a lithium-loaded liquid scintillator), the angular sensitivity improves to ∼15°, and—when a distance upper limit is obtained from the overall event rate—it is in principle possible to uniquely identify the progenitor star. Any localization information accompanying an early supernova alert will be useful to multimessenger observations and to particle physics tests using collapsing stars.

Keywords: Neutrino telescopes, Neutrino astronomy, Supernova neutrinos, High energy astrophysics
Dual Supermassive Black Holes at Close Separation Revealed by the Hyper Suprime-Cam Subaru Strategic Program. The unique combination of superb spatial resolution, wide-area coverage, and deep depth of the optical imaging from the Hyper Suprime-Cam (HSC) Subaru Strategic Program is utilized to search for dual quasar candidates. Using an automated image analysis routine on 34,476 known Sloan Digital Sky Survey quasars, we identify those with two (or more) distinct optical point sources in HSC images covering 796 deg2. We find 421 candidates out to a redshift of 4.5 of which one hundred or so are more likely after filtering out contaminating stars. Angular separations of 0"6-4"0 correspond to projected separations of 3-30 kpc, a range relatively unexplored for population studies of luminous dual quasars. Using Keck I/Low Resolution Imaging Spectrometer and Gemini-N/Near-Infrared Integral Field Spectrometer, we spectroscopically confirm three dual quasar systems at z &lt; 1, two of which are previously unknown out of eight observed, based on the presence of characteristic broad emission lines in each component, while highlighting that the continuum of one object in one of the pairs is reddened. In all cases, the [O III]λ5007 emission lines have mild velocity offsets, thus the joint [O III] line profile is not double-peaked. We find a dual quasar fraction of 0.26 ± 0.18% and no evidence for evolution. A comparison with the Horizon-AGN simulation seems to support the case of no evolution in the dual quasar fraction when broadly matching the quasar selection. These results may indicate a scenario in which the frequency of the simultaneous triggering of luminous quasars is not as sensitive as expected to the cosmic evolution of the merger rate or gas content of galaxies.

Keywords: Supermassive black holes, Galaxy mergers, Quasars
Probing the Line-locking Signatures within the C IV Broad Absorption Line in Quasar SDSS J092345+512710. Quasar SDSS J092345.19+512710.1 (hereafter J0923+5127) shows two broad absorption line (BAL) systems. The blue one at ∼14,000 km s-1, called BAL system A, has been reported to show a synchronized kinematic shift of its C IV and Si IV BALs. In this paper, we mainly concentrate on the red one at ∼4000 km s-1, called BAL system B, which can be resolved into multiple narrow absorption lines (NALs). We identify 11 NAL systems from BAL system B and find that these blended NALs show complex line-locking phenomena, which offers evidence for the idea that radiation pressure plays an important role in the dynamics of these clumpy outflow clouds.

Keywords: Quasar absorption line spectroscopy, Broad-absorption line quasar, Quasars
Nanoflare Diagnostics from Magnetohydrodynamic Heating Profiles. The nanoflare paradigm of coronal heating has proven extremely promising for explaining the presence of hot, multi-million degree loops in the solar corona. In this paradigm, localized heating events supply enough energy to heat the solar atmosphere to its observed temperatures. Rigorously modeling this process, however, has proven difficult because it requires an accurate treatment of both the magnetic field dynamics and reconnection as well as the plasma response to magnetic perturbations. In this paper, we combine fully 3D magnetohydrodynamic (MHD) simulations of coronal active region plasma driven by photospheric motions with spatially averaged, time-dependent hydrodynamic (HD) modeling of coronal loops to obtain physically motivated observables that can be quantitatively compared with observational measurements of active region cores. We take the behavior of reconnected field lines from the MHD simulation and use them to populate the HD model to obtain the thermodynamic evolution of the plasma and subsequently the emission measure distribution. We find that the photospheric driving of the MHD model produces only very low-frequency nanoflare heating that cannot account for the full range of active region core observations as measured by the low-temperature emission measure slope. Additionally, we calculate the spatial and temporal distributions of field lines exhibiting collective behavior, and argue that loops occur due to random energization occurring on clusters of adjacent field lines.

Keywords: Magnetohydrodynamics, Solar coronal heating, Magnetic fields, Solar magnetic reconnection
The Excitation Conditions of CN in TW Hya. We report observations of the cyanide anion, CN, in the disk around TW Hya covering the N = 1-0, N = 2-1, and N = 3-2 transitions. Using line-stacking techniques, 24 hyperfine transitions are detected out of the 30 within the observed frequency ranges. Exploiting the super-spectral resolution from the line-stacking method reveals the splitting of hyperfine components previously unresolved by laboratory spectroscopy. All transitions display a similar emission morphology, characterized by an azimuthally symmetric ring, peaking at ≍45 au (0"75), and a diffuse outer tail extending out to the disk edge at ≍200 au. Excitation analyses assuming local thermodynamic equilibrium (LTE) yield excitation temperatures in excess of the derived kinetic temperatures based on the local line widths for all fine-structure groups, suggesting assumptions of LTE are invalid. Using the 0D radiative transfer code RADEX, we demonstrate that such non-LTE effects may be present when the local H2 density drops to 107 cm-3 and below. Comparison with models of TW Hya find similar densities at elevated regions in the disk, typically z / r ≳ 0.2, consistent with model predictions where CN is formed via vibrationally excited H2 in the disk atmospheric layers where UV irradiation is less attenuated.

Keywords: Submillimeter astronomy, Protoplanetary disks, Radiative transfer, Astrochemistry
Properties of the Hot Ambient Medium of Early-type Galaxies Hosting Powerful Radio Sources. We present an archival analysis of Chandra X-ray observations for 12 nearby early-type galaxies hosting radio sources with radio power &gt;1023 W Hz-1 at 1.4 GHz, similar to the radio power of the radio source in NGC 4261. Previously, in a similar analysis of eight nearby X-ray and optically bright elliptical galaxies, Werner et al. found that NGC 4261 exhibited unusually low central gas entropy compared to the full sample. In the central 0.3 kpc of NGC 4261, the ratio of cooling time to freefall time (tcool/tff) is less than 10, indicating that cold clouds may be precipitating out of the hot ambient medium and providing fuel for accretion in the central region. NGC 4261 also hosts the most powerful radio source in the original sample. Because NGC 4261 may represent an important phase during which powerful feedback from a central active galactic nucleus (AGN) is fueled by multiphase condensation in the central kiloparsec, we searched the Chandra archive for analogs to NGC 4261. We present entropy profiles of those galaxies, as well as profiles of tcool/tff. We find that one of them, IC 4296, exhibits properties similar to NGC 4261, including the presence of only single-phase gas outside of r ∼ 2 kpc and a similar central velocity dispersion. We compare the properties of NGC 4261 and IC 4296 to hydrodynamic simulations of AGN feedback fueled by precipitation. Over the course of those simulations, the single-phase galaxy has an entropy gradient that remains similar to the entropy profiles inferred from our observations.

Keywords: AGN host galaxies, Radio galaxies, Early-type galaxies
Suzaku Measurements of Hot Halo Emission at Outskirts for Two Poor Galaxy Groups: NGC 3402 and NGC 5129. We present Suzaku off-center observations of two poor galaxy groups, NGC 3402 and NGC 5129, with temperatures below 1 keV. Through spectral decomposition, we measured their surface brightnesses and temperatures out to 530 and 1430 times the critical density of the universe for NGC 3402 and NGC 5129, respectively. These quantities are consistent with extrapolations from existing inner measurements of the two groups. With the refined bolometric X-ray luminosities, both groups prefer LX-T relations without a break in the group regime. Furthermore, we have determined the electron number densities and hydrostatic masses at these radii. We found that the surface brightness and electron number density profiles require two β model components, as well as the indication that a third β model may be needed for NGC 3402. Adding the gas mass measured from the X-ray data and stellar mass from group galaxy members, we computed baryon fractions of fb =0.0693 ± 0.0068 and fb = 0.095 ± 0.014 for NGC 3402 and NGC 5129, respectively. Combining other poor groups with well-measured X-ray emission to the outskirts, we found an average baryon fraction extrapolated to r500 of $\overline{\,{f}_{b,500}}$ = 0.0912 ± 0.0050 for X-ray-bright groups with temperatures between 0.8 and 1.3 keV, extending existing constraints to lower-mass systems and indicating that significant baryon losses exist below approximately r500.

Keywords: Galaxy clusters, X-ray astronomy, Galaxy groups, Scaling relations