Sazuna/UAT_keywords huggingface dataset:
Semi-empirical Models of Spicule from Inversion of Ca II 8542 Å Line. We study a solar spicule observed off-limb using high-resolution imaging spectroscopy in the Ca II 8542 Å line obtained with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. Using a new version of the non-LTE code NICOLE specifically developed for this problem we invert the spicule single- and double-peak line profiles. This new version considers off-limb geometry and computes atomic populations by solving the 1D radiative transfer assuming a vertical stratification. The inversion proceeds by fitting the observed spectral profiles at 14 different heights with synthetic profiles computed in the model by solving the radiative transfer problem along its length. Motivated by the appearance of double-peak Ca II 8542 Å spicule profiles, which exhibit two distinct emission features well separated in wavelength, we adopt a double-component scenario. We start from the ansatz that the spicule parameters are practically constant along the spicule axis for each component, except for a density drop. Our results support this ansatz by attaining very good fits to the entire set of 14 × 4 profiles (14 heights and 4 times). We show that the double-component model with uniform temperature of 9560 K, exponential decrease of density with a height scale of 1000-2000 km, and the counter-oriented line-of-sight velocities of components reproduce the double-peak line profiles at all spicule segments well. Analyses of the numerical response function reveals the necessity of the inversions of spectra at multiple height positions to obtain height-dependent, degeneracy-free reliable models with a limited number of free parameters.

Keywords: High resolution spectroscopy, Solar spicules, Radiative transfer, Ground-based astronomy, Solar chromosphere
Multiwavelength Selected Compton-thick AGNs in Chandra Deep Field-South Survey. Even in deep X-ray surveys, Compton-thick active galactic nuclei (CT AGNs, NH ≥ 1.5 × 1024 cm-2) are difficult to identify due to X-ray flux suppression and their complex spectral shapes. However, the study of CT AGNs is vital for understanding the rapid growth of black holes and the origin of the cosmic X-ray background. In the local universe, the fraction of CT AGNs accounts for 30% of the whole AGN population. We expect a higher fraction of CT AGNs in deep X-ray surveys; however, only 10% of AGNs have been identified as CT AGNs in the 7 Ms Chandra Deep Field-South survey. In this work, we select 51 AGNs with abundant multiwavelength data. Using the method of the mid-infrared (mid-IR) excess, we select hitherto unknown eight CT AGN candidates in our sample. Seven of these candidates can be confirmed as CT AGNs based on the multiwavelength identification approach, and a new CT AGN (XID 133) is identified through the mid-IR diagnostics. We also discuss the X-ray origin of these eight CT AGNs and the reason why their column densities were underestimated in previous studies. We find that the multiwavelength approaches of selecting CT AGNs are highly efficient, provided the high quality of observational data. We also find that CT AGNs have a higher Eddington ratio than non-CT AGNs, and that both CT AGNs and non-CT AGNs show similar properties of host galaxies.

Keywords: Active galaxies, Active galactic nuclei, X-ray active galactic nuclei
GHOST: Using Only Host Galaxy Information to Accurately Associate and Distinguish Supernovae. We present GHOST, a database of 16,175 spectroscopically classified supernovae (SNe) and the properties of their host galaxies. We have constructed GHOST using a novel host galaxy association method that employs deep postage stamps of the field surrounding a transient. Our gradient ascent method achieves fewer misassociations for low-z hosts and higher completeness for high-z hosts than previous methods. Using dimensionality reduction, we identify the host galaxy properties that distinguish SN classes. Our results suggest that the host galaxies of superluminous SNe, Type Ia SNe, and core-collapse SNe can be separated by brightness and derived extendedness measures. Next, we train a random forest model to predict SN class using only host galaxy information and the radial offset of the SN. We can distinguish Type Ia SNe and core-collapse SNe with ∼70% accuracy without any photometric or spectroscopic data from the event itself. Vera C. Rubin Observatory will usher in a new era of transient population studies, demanding improved photometric tools for rapid identification and classification of transient events. By identifying the host features with high discriminatory power, we will maintain SN sample purities and continue to identify scientifically relevant events as data volumes increase. The GHOST database and our corresponding software for associating transients with host galaxies are both publicly available through the astro_ghost package.

Keywords: Open source software, Astronomy databases, Classification, Support vector machine, Random Forests, Supernovae
High-resolution Mid-infrared Spectroscopy of GV Tau N: Surface Accretion and Detection of NH<SUB>3</SUB> in a Young Protoplanetary Disk. Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence that protoplanetary disks are engaged in accretion, the process(es) responsible remain unclear. Here we present evidence for redshifted molecular absorption in the spectrum of a Class I source that indicates rapid inflow at the disk surface. High-resolution mid-infrared spectroscopy of GV Tau N reveals a rich absorption spectrum of individual lines of C2H2, HCN, NH3, and H2O. From the properties of the molecular absorption, we can infer that it carries a significant accretion rate ${\dot{M}}_{\mathrm{abs}}$ ∼ 10-8-10-7 M☉ yr-1, comparable to the stellar accretion rates of active T Tauri stars. Thus, we may be observing disk accretion in action. The results may provide observational evidence for supersonic "surface accretion flows," which have been found in MHD simulations of magnetized disks. The observed spectra also represent the first detection of NH3 in the planet formation region of a protoplanetary disk. With NH3 only comparable in abundance to HCN, it cannot be a major missing reservoir of nitrogen. If, as expected, the dominant nitrogen reservoir in inner disks is instead N2, its high volatility would make it difficult to incorporate into forming planets, which may help to explain the low nitrogen content of the bulk Earth.

Keywords: Interstellar molecules, T Tauri stars, Protoplanetary disks, Circumstellar disks, Stellar accretion disks, Planet formation
Threaded-field-line Model for the Low Solar Corona Powered by the Alfvén Wave Turbulence. We present an updated global model of the solar corona, including the transition region. We simulate the realistic three-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfvén wave turbulence and its nonlinear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed-field regions, the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes, we account for a reflection of the outward-propagating waves, which is accompanied by the generation of weaker counterpropagating waves. The nonlinear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point of the lower boundary of the global corona model, chosen at some heliocentric distance, R = Rb ∼ 1.1R⊙, well above the transition region. One can readily solve the plasma parameters along the magnetic field line from 1D equations for the plasma motion and heat transport together with the Alfvén wave propagation, which adequately describe the physics within the heliocentric distance range R⊙ &lt; R &lt; Rb, in the low solar corona. By interfacing this threaded-field-line model with the full MHD global corona model at r = Rb, we find the global solution and achieve a faster-than-real-time performance of the model on ∼200 cores.

Keywords: Solar extreme ultraviolet emission, Solar coronal heating, Solar wind, Alfven waves, Solar corona, Solar transition region
White Dwarf Photospheric Abundances in Cataclysmic Variables. I. SS Aurigae and TU Mensae. Chemical abundance studies of cataclysmic variables have revealed high nitrogen to carbon ratios in a number of cataclysmic variable white dwarfs (based on ultraviolet emission and absorption lines), as well as possible carbon deficiency in many secondaries (based on the absence of infrared CO absorption lines). These indicate that the accreted material on the white dwarf surface and the donor itself might be contaminated with CNO processed material. To further understand the origin of this abundance anomaly, there is a need for further chemical abundance study. In the present work, we carry out a far-ultraviolet spectral analysis of the extreme SU UMa dwarf nova TU Men and the U Gem dwarf nova SS Aur using archival spectra. We derive the mass and temperature of the WD using the recently available DR2 Gaia parallaxes. The analysis of HST STIS spectra yields a WD mass ${M}_{\mathrm{wd}}={0.77}_{-0.13}^{+0.16}{M}_{\odot }$ with a temperature of 27,750 ± 1000 K for TU Men and a WD mass Mwd ∼ 0.80 ± 0.15 M⊙ with a temperature of ∼30,000 ± 1000 K for SS Aur. However, the analysis of a FUSE spectrum for SS Aur gives a higher temperature of ∼33,375 ± 1875 K, yielding a higher WD mass of ∼1 ± 0.25 M⊙, which could be due to the effect of a second hot emitting component present in the short wavelengths of FUSE. Most importantly, based on the white dwarf far-ultraviolet absorption lines, we find that both systems have subsolar carbon and silicon abundances. For TU Men, we also find suprasolar nitrogen abundance, evidence of CNO processing. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of University for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: White dwarf stars, U Geminorum stars, Dwarf novae, SU Ursae Majoris stars, Cataclysmic variable stars
Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles. The random walk of magnetic field lines is an important ingredient in understanding how the connectivity of the magnetic field affects the spatial transport and diffusion of charged particles. As solar energetic particles propagate away from near-solar sources, they interact with the fluctuating magnetic field, which modifies their distributions. We develop a formalism in which the differential equation describing the field line random walk contains both effects due to localized magnetic displacements and a non-stochastic contribution from the large-scale expansion. We use this formalism together with a global magnetohydrodynamic simulation of the inner-heliospheric solar wind, which includes a turbulence transport model, to estimate the diffusive spreading of magnetic field lines that originate in different regions of the solar atmosphere. We first use this model to quantify field line spreading at 1 au, starting from a localized solar source region, and find rms angular spreads of about 20°-60°. In the second instance, we use the model to estimate the size of the source regions from which field lines observed at 1 au may have originated, thus quantifying the uncertainty in calculations of magnetic connectivity; the angular uncertainty is estimated to be about 20°. Finally, we estimate the filamentation distance, i.e., the heliocentric distance up to which field lines originating in magnetic islands can remain strongly trapped in filamentary structures. We emphasize the key role of slab-like fluctuations in the transition from filamentary to more diffusive transport at greater heliocentric distances.

Keywords: Solar energetic particles, Solar wind, Interplanetary magnetic fields, Interplanetary turbulence
The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Spatiokinematics of Water Masers during a Contemporaneous Flare Event. Following an eruptive accretion event in NGC 6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly variable water masers associated with the massive star-forming region, NGC 6334I. High velocity H2O maser proper motions were detected in five maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1, and UCHII-W3. The overall average of the derived relative proper motion is 85 km s-1. This mean proper motion is in agreement with the previous results from VLA multiepoch observations. Our position as well as the velocity variance and covariance matrix analyses of the maser proper motions show its major axis to have a position angle of -79°4, cutting through the dust cavity around MM1B and being aligned in the northwest-southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast-southwest bipolar outflow, the CS(6-5) north-south collimated bipolar outflow, and the radio jet. The relative proper motions of the H2O masers in UCHII-W1 are likely not driven by the jets of the MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H2O masers trace shocks of jet motion.

Keywords: Stellar jets, Star forming regions, Long baseline interferometry, Astrophysical masers, Shocks
Alfvén Wave Mode Conversion in Pulsar Magnetospheres. The radio emission anomaly coincident with the 2016 glitch of the Vela pulsar may be caused by a starquake that launches Alfvén waves into the magnetosphere, disturbing the original radio emitting region. To quantify the lifetime of the Alfvén waves, we investigate a possible energy loss mechanism, the conversion of Alfvén waves into fast magnetosonic waves. Using axisymmetric force-free simulations, we follow the propagation of Alfvén waves launched from the stellar surface with small amplitude into the closed zone of a force-free dipolar pulsar magnetosphere. We observe mode conversion happening in the ideal force-free regime. The conversion efficiency during the first passage of the Alfvén wave through the equator can be large, for waves that reach large amplitudes as they travel away from the star, or propagate on the field lines passing close to the Y point. However, the conversion efficiency is reduced due to dephasing on subsequent passages and considerable Alfvén power on the closed field lines remains. Thus while some leakage into the fast mode happens, we need detailed understanding of the original quenching in order to say whether mode conversion alone can lead to reactivation of the pulsar on a short timescale.

Keywords: Magnetars, Alfven waves, Magnetic fields, Pulsars
Classifying Blazar Candidates from the 3FGL Unassociated Catalog into BL Lacertae Objects and Flat Spectrum Radio Quasars Using Swift and WISE Data. We utilize machine-learning methods to distinguish BL Lacertae (BL Lac) objects from flat spectrum radio quasars (FSRQs) within a sample of likely X-ray blazar counterparts to Fermi 3FGL unassociated gamma-ray sources. From our previous work, we have extracted 84 sources that were classified as ≥99% likely to be blazars. We then utilize Swift-XRT, Fermi, and The Wide-field Infrared Survey Explorer (WISE) data together to distinguish the specific type of blazar, FSRQs, or BL Lac objects. Various X-ray and gamma-ray parameters can be used to differentiate between these subclasses. These are also known to occupy different parameter space on the WISE color-color diagram. Using all these data together would provide more robust results for the classified sources. We utilized a random forest classifier to calculate the probability for each blazar to be associated with a BL Lac object or an FSRQ. Based on Pbll, which is the probability for each source to be a BL Lac object, we placed our sources into five different categories based on this value as follows: Pbll ≥ 99%: highly likely BL Lac object, Pbll ≥ 90%: likely BL Lac object, Pbll ≤ 1%: highly likely FSRQ, Pbll ≤ 10%: likely FSRQ, and 90% &lt; Pbll &lt; 10%: ambiguous. Our results categorize the 84 blazar candidates as 50 likely BL Lac objects and the other 34 as being ambiguous. A small subset of these sources have been listed as associated sources in the most recent Fermi catalog, 4FGL, and in these cases our results are in agreement on the classification.

Keywords: Blazars, BL Lacertae objects, High energy astrophysics
Double-peaked Lines, Dual VLBI Components, and Precessing Jets in J1328+2752. In this work, we report a radio galaxy with precessing jets, double-peaked emission lines and the presence of two compact radio components with a projected separation of ∼6 parsec in very long baseline interferometry (VLBI) observations. The emission-line peak separations could be suggesting the presence of a supermassive binary black hole (BBH) with a separation of 6.3 parsec, matching the VLBI results. The kinematic jet precession model applied to the jets of J1328+2752 indicates that if it is a BBH, the accretion disk of the primary black hole is not coplanar with the binary system orbit, making its jet precess under the effect of the torque produced by the secondary black hole. However, we find that the Bardeen-Petterson effect can also provide precession timescales compatible with the jet precession period inferred in this source. This source has previously been identified as a restarted double-double radio galaxy (DDRG). Our findings therefore have important ramifications for the nature of DDRGs in general.

Keywords: Radio cores, Radio jets, Very long baseline interferometry, Active galaxies, Radio galaxies, Radio continuum emission
Elliptical Accretion Disk as a Model for Tidal Disruption Events. Elliptical accretion disk models for tidal disruption events (TDEs) have been recently proposed and independently developed by two groups. Although these two models are characterized by a similar geometry, their physical properties differ considerably. In this paper, we further investigate the properties of the elliptical accretion disk of the nearly uniform distribution of eccentricity within the disk plane. Our results show that the elliptical accretion disks have distinctive hydrodynamic structures and spectral energy distributions, associated with TDEs. The soft X-ray photons generated at pericenter and nearby are trapped in the disk and advected around the ellipse because of large electron scattering opacity. They are absorbed and reprocessed into emission lines and low-frequency continuum via recombination and bremsstrahlung emission. Because of the rapid increase of bound-free and free-free opacities with radius, the low-frequency continuum photons become trapped in the disk at large radius and are advected through apocenter and back to the photon-trapping radius. Elliptical accretion disks predict sub-Eddington luminosities and emit mainly at the photon-trapping radius of thousands of Schwarzschild radii with a blackbody spectrum of nearly single temperature of typically about 3 × 104 K. Because of the self-regulation, the photon-trapping radius expands and contracts following the rise and fall of accretion rate. The radiation temperature is nearly independent of BH mass and accretion rate and varies weakly with the stellar mass and the viscosity parameter. Our results are well consistent with the observations of optical/UV TDEs.

Keywords: Accretion, Black hole physics, Supermassive black holes, Tidal disruption, Active galaxies, Galaxy accretion disks
Identifying Candidate Optical Variables Using Gaia Data Release 2. Gaia is undertaking a deep synoptic survey of the Galaxy, but photometry from individual epochs has, as of yet, only been released for a minimal number of sources. We show that it is possible to identify variable stars in Gaia Data Release 2 by selecting stars with unexpectedly large photometric uncertainties given their brightness and number of observations. By comparing our results to existing catalogs of variables, we show that information on the amplitude of variability is also implicitly present in the Gaia photometric uncertainties. We present a catalog of about 9.3 million candidate variable stars, and discuss its limitations and prospects for future tests and extensions.

Keywords: Catalogs, Sky surveys, Variable stars
Tracing Dark Energy History with Gamma-Ray Bursts. Observations of gamma-ray bursts up to z ∼ 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble's diagram and then we estimate the set (Ωm, ΩΛ) in the framework of flat and non-flat ΛCDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4σ, i.e., H0 = (67.4 ± 0.5) km s-1 Mpc-1 and H0 = (74.03 ± 1.42) km s-1 Mpc-1. We show our new sample provides tighter constraints on Ωm since at z ≤ 1.2 we see that w(z) agrees within 1σ with the standard value w = -1. The situation is the opposite at larger z, where gamma-ray bursts better fix w(z) that seems to deviate from w = -1 at 2σ and 4σ level, depending on the redshift bins. In particular, we investigate the w(z) evolution through a piecewise formulation over seven redshift intervals. From our fitting procedure we show that at z ≥ 1.2 the case w &lt; -1 cannot be fully excluded, indicating that dark energy's influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper.

Keywords: Gamma-ray bursts, Standard candles, Dark energy
A Possible Selection Rule for Flares Causing Sunquakes. Sunquakes are helioseismic power enhancements initiated by solar flares, but not all flares generate sunquakes. It is curious why some flares cause sunquakes while others do not. Here we propose a hypothesis to explain the disproportionate occurrence of sunquakes: during a flare's impulsive phase when the flare's impulse acts upon the photosphere, delivered by shock waves, energetic particles from higher atmosphere, or by downward Lorentz Force, a sunquake tends to occur if the background oscillation at the flare footpoint happens to oscillate downward in the same direction with the impulse from above. To verify this hypothesis, we select 60 strong flares in Solar Cycle 24, and examine the background oscillatory velocity at the sunquake sources during the flares' impulsive phases. Since the Doppler velocity observations at sunquake sources are usually corrupted during the flares, we reconstruct the oscillatory velocity in the flare sites using helioseismic holography method with an observation-based Green's function. A total of 24 flares are found to be sunquake active, giving a total of 41 sunquakes. It is also found that in 3-5 mHz frequency band, 25 out of 31 sunquakes show net downward oscillatory velocities during the flares' impulsive phases, and in the 5-7 mHz frequency band, 33 out of 38 sunquakes show net downward velocities. These results support the hypothesis that a sunquake more likely occurs when a flare impacts a photospheric area with a downward background oscillation.

Keywords: Helioseismology, Solar flares, Solar oscillations