Sazuna/UAT_keywords huggingface dataset:
The Evolution of the Supersoft X-Ray Source WX Cen Dominated by Magnetic Wind. WX Cen is most likely one of the Galactic counterparts of compact binary supersoft X-ray sources as a member of the V Sagittae class, in which mass is transferred from a donor secondary to a massive white dwarf primary via an accretion disk. Based on the photometric observations from the TESS space telescope and AAVSO database, 218 times of light minimum were determined. By collecting all available eclipse timings of WX Cen from the literature together with those newly determined, we constructed an O-C diagram and analyzed the variations in the orbital period of the eclipsing binary. It is confirmed that the orbital period is continuously decreasing and the rate of the change in the orbital period is revised to $\dot{P}=-4.4(4)\times {10}^{-7}\mathrm{day}\,{\mathrm{yr}}^{-1}=-0.038(3)\,{\rm{s}}\,{\mathrm{yr}}^{-1}$ . The mass of the donor secondary is estimated as M s ~ 0.6 M ⊙, when the white dwarf mass is M WD ~ 0.9 M ⊙. By considering a conservative mass transfer from the secondary to the primary, the orbital period of WX Cen should be increasing, which is opposite to the observed continuous decrease. Therefore, the decrease in the period can be plausibly explained as the result of angular momentum loss (AML) via magnetic wind from the secondary and/or from the accretion disk. The AML causes the donor secondary with a low mass to continually be filling its critical Roche lobe and transferring material to the white dwarf. In this way, the evolution of WX Cen is dominated by the magnetic wind and continuously radiating supersoft X-rays.

Keywords: Close binary stars, Eclipsing binary stars, Orbital evolution
Observations of Waves and Structures by Frequency-Wavenumber Spectrum in Solar Wind Turbulence. A well-known shortcoming of single-spacecraft spectral analysis is that only the 1D wavenumber spectrum can be observed, assuming the characteristic wave propagation speed is much smaller than the solar wind flow speed. This limitation has motivated an extended debate about whether fluctuations observed in the solar wind are waves or structures. Multispacecraft analysis techniques can be used to calculate the wavevector independent of the observed frequency, thus allowing one to study the frequency-wavenumber spectrum of turbulence directly. The dispersion relation for waves can be identified, which distinguishes them from nonpropagating structures. We use magnetic field data from the four Magnetospheric Multiscale (MMS) spacecraft to measure the frequency-wavenumber spectrum of solar wind turbulence based on the k-filtering and phase differencing techniques. Both techniques have been used successfully in the past for the Earth's magnetosphere, although applications to solar wind turbulence have been limited. We conclude that the solar wind turbulence intervals observed by MMS show features of nonpropagating structures that are associated with frequencies close to zero in the plasma rest frame. However, there is no clear evidence of propagating Alfvén waves that have a nonzero rest-frame frequency. The lack of waves may be due to instrument noise and spacecraft separation. Our results support the idea of turbulence dominated by quasi-2D structures.

Keywords: Interplanetary turbulence, Solar wind
Diagnosing Limb Asymmetries in Hot and Ultrahot Jupiters with High-resolution Transmission Spectroscopy. Due to their likely tidally synchronized nature, (ultra)hot Jupiter atmospheres should experience strongly spatially heterogeneous instellation. The large irradiation contrast and resulting atmospheric circulation induce temperature and chemical gradients that can produce asymmetries across the eastern and western limbs of these atmospheres during transit. By observing an (ultra)hot Jupiter's transmission spectrum at high spectral resolution, these asymmetries can be recovered-namely through net Doppler shifts originating from the exoplanet's atmosphere yielded by cross-correlation analysis. Given the range of mechanisms at play, identifying the underlying cause of observed asymmetry is nontrivial. In this work, we explore sources and diagnostics of asymmetries in high-resolution cross-correlation spectroscopy of hot and ultrahot Jupiters using both parameterized and self-consistent atmospheric models. If an asymmetry is observed, we find that it can be difficult to attribute it to equilibrium chemistry gradients because many other processes can produce asymmetries. Identifying a molecule that is chemically stable over the temperature range of a planetary atmosphere can help establish a baseline to disentangle the various potential causes of limb asymmetries observed in other species. We identify CO as an ideal molecule, given its stability over nearly the entirety of the ultrahot Jupiter temperature range. Furthermore, we find that if limb asymmetry is due to morning terminator clouds, blueshifts for a number of species should decrease during transit. Finally, by comparing our forward models to those of Kesseli et al., we demonstrate that binning high-resolution spectra into two phase bins provides a desirable trade-off between maintaining signal to noise and resolving asymmetries.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Radiative transfer simulations, Hot Jupiters
Inflationary and Phase-transitional Primordial Magnetic Fields in Galaxy Clusters. Primordial magnetic fields (PMFs) are possible candidates for explaining the observed magnetic fields in galaxy clusters. Two competing scenarios of primordial magnetogenesis have been discussed in the literature: inflationary and phase-transitional. We study the amplification of both large- and small-scale correlated magnetic fields, corresponding to inflation- and phase transition-generated PMFs, in a massive galaxy cluster. We employ high-resolution magnetohydrodynamic cosmological zoom-in simulations to resolve the turbulent motions in the intracluster medium. We find that the turbulent amplification is more efficient for the large-scale inflationary models, while the phase transition-generated seed fields show moderate growth. The differences between the models are imprinted on the spectral characteristics of the field (such as the amplitude and the shape of the magnetic power spectrum) and therefore also on the final correlation length. We find a one order of magnitude difference between the final strengths of the inflation- and phase transition-generated magnetic fields, and a factor of 1.5 difference between their final coherence scales. Thus, the final configuration of the magnetic field retains information about the PMF generation scenarios. Our findings have implications for future extragalactic Faraday rotation surveys with the possibility of distinguishing between different magnetogenesis scenarios.

Keywords: Galaxy clusters, Intracluster medium, Primordial magnetic fields, Magnetohydrodynamical simulations
The Bimodal Absorption System Imaging Campaign (BASIC). I. A Dual Population of Low-metallicity Absorbers at z &lt; 1. The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 H I-selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields at z ≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) at z &lt; 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲ z ≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with &lt;10% solar metallicities, we find no associated galaxies with $\mathrm{log}{M}_{\star }\gtrsim 9.0$ within ρ/R vir and ∣∆v∣/v esc ≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or H I column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ -1.4) systems have a probability of ${0.39}_{-0.15}^{+0.16}$ for having a host galaxy with $\mathrm{log}{M}_{\star }\geqslant 9.0$ within ρ/R vir ≤ 1.5, while the higher metallicity absorbers have a probability of ${0.78}_{-0.13}^{+0.10}$ . This implies metal-enriched pLLSs/LLSs at z &lt; 1 are typically associated with the CGM of galaxies with $\mathrm{log}{M}_{\star }\gt 9.0$ , whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ -2.1 at z &lt; 1, which is lower than previously estimated.

Keywords: Quasar absorption line spectroscopy, Lyman limit systems, Circumgalactic medium, Intergalactic medium, Galaxy spectroscopy, Metallicity
FEASTS: IGM Cooling Triggered by Tidal Interactions through the Diffuse H I Phase around NGC 4631. We use the single-dish radio telescope Five-hundred meter Aperture Spherical Telescope (FAST) to map the H I in the tidally interacting NGC 4631 group with a resolution of 3.'24 (7 kpc), reaching a 5σ column density limit of 1017.9 cm-2 assuming a line width of 20 km s-1. Taking the existing interferometric H I image from the Hydrogen Accretion in LOcal GAlaxieS project of Westerbork Synthesis Radio Telescope as a reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse H I in the group. This diffuse H I extends more than 120 kpc across, and accounts for more than one-fourth of the total H I detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse H I has a typical column density above 1019.5 cm-2, and is highly turbulent with a velocity dispersion of around 50 km s-1. It increases in column density with the dense H I, and tends to be associated with the kinematically hotter part of the dense H I. Through simple modeling, we find that the majority of the diffuse H I in the tail region is likely to induce cooling out of the hot intragalactic medium (IGM) instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse H I may represent a condensing phase of the IGM. Ongoing and past active tidal interactions may have produced the wide-spreading H I distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse H I.

Keywords: Galaxy evolution, Neutral hydrogen clouds, Galaxy accretion, Intergalactic medium
Gaussian Process Modeling Blazar Multiwavelength Variability: Indirectly Resolving Jet Structure. Blazar jet structure can be indirectly resolved by analyzing the multiwavelength variability. In this work, we analyze the long-term variability of blazars in radio, optical, and X-ray energies with the Gaussian process (GP) method. The multiwavelength variability can be successfully characterized by the damped-random walk model. The nonthermal optical characteristic timescales of 38 blazars are statistically consistent with the γ-ray characteristic timescales of 22 blazars. For three individual sources (3C 273, PKS 1510-089, and BL Lac), the nonthermal optical, X-ray, and γ-ray characteristic timescales are also consistent within the measured 95% errors, but the radio timescale of 3C 273 is too large to be constrained by the decade-long light curve. The synchrotron and inverse-Compton emissions have the same power spectral density, suggesting that the long-term jet variability is irrelevant to the emission mechanism. In the plot of the rest-frame timescale versus black hole mass, the optical-γ-ray timescales of the jet variability occupy almost the same space with the timescales of accretion disk emission from normal quasars, which may imply that the long-term variabilities of the jet and accretion disk are driven by the same physical process. It is suggested that the nonthermal optical-X-ray and γ-ray emissions are produced in the same region, while the radio core, which can be resolved by very long baseline interferometry, locates at a far more distant region from the black hole. Our study suggests a new methodology for comparing thermal and nonthermal emissions, which is achieved by using the standard GP method.

Keywords: Blazars, Light curves, Jets, Time series analysis
Solar Flare Ribbon Fronts. I. Constraining Flare Energy Deposition with IRIS Spectroscopy. Spectral lines formed at lower atmospheric layers show peculiar profiles at the "leading edge" of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He I λ10830 line, as well as broad and centrally reversed profiles in the spectra of the Mg II and C II lines observed by the IRIS satellite, has been reported. In this work, we aim to understand the physical origin of such peculiar IRIS profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the IRIS Mg II profiles at the ribbon leading edge during four large flares and perform a detailed comparison with a grid of radiative hydrodynamic models using the RADYN+FP code. We also studied their transition region (TR) counterparts, finding that these ribbon front locations are regions where TR emission and chromospheric evaporation are considerably weaker compared to other parts of the ribbons. Based on our comparison between the IRIS observations and modeling, our interpretation is that there are different heating regimes at play in the leading edge and the main bright part of the ribbons. More specifically, we suggest that bombardment of the chromosphere by more gradual and modest nonthermal electron energy fluxes can qualitatively explain the IRIS observations at the ribbon leading front, while stronger and more impulsive energy fluxes are required to drive chromospheric evaporation and more intense TR emission in the bright ribbon. Our results provide a possible physical origin for the peculiar behavior of the IRIS chromospheric lines in the ribbon leading edge and new constraints for the flare models.

Keywords: Solar activity, Solar atmosphere, Solar chromosphere, Solar flares
Inferring the Energy and Distance Distributions of Fast Radio Bursts Using the First CHIME/FRB Catalog. Fast radio bursts (FRBs) are brief, energetic, typically extragalactic flashes of radio emission whose progenitors are largely unknown. Although studying the FRB population is essential for understanding how these astrophysical phenomena occur, such studies have been difficult to conduct without large numbers of FRBs and characterizable observational biases. Using the recently released catalog of 536 FRBs published by the Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst (CHIME/FRB) collaboration, we present a study of the FRB population that also calibrates for selection effects. Assuming a Schechter function, we infer a characteristic energy cut-off of ${E}_{\mathrm{char}}={2.38}_{-1.64}^{+5.35}\times {10}^{41}$ erg and a differential power-law index of γ = $-{1.3}_{-0.4}^{+0.7}$ . Simultaneously, we infer a volumetric rate of [ ${7.3}_{-3.8}^{+8.8}$ (stat.) ${}_{-1.8}^{+2.0}(\mathrm{sys}.)]\times {10}^{4}$ Gpc-3 yr-1 above a pivot energy of 1039 erg and below a scattering timescale of 10 ms at 600 MHz, and find we cannot significantly constrain the cosmic evolution of the FRB population with star-formation rate. Modeling the host's dispersion measure (DM) contribution as a log-normal distribution and assuming a total Galactic contribution of 80 pc cm-3, we find a median value of ${\mathrm{DM}}_{\mathrm{host}}={84}_{-49}^{+69}$ pc cm-3, comparable with values typically used in the literature. Proposed models for FRB progenitors should be consistent with the energetics and abundances of the full FRB population predicted by our results. Finally, we infer the redshift distribution of FRBs detected with CHIME, which will be tested with the localizations and redshifts enabled by the upcoming CHIME/FRB Outriggers project.

Keywords: Radio bursts, Radio transient sources
Photometric Calibrations of M-dwarf Metallicity with Markov Chain Monte Carlo and Bayesian Inference. Knowledge of stellar atmospheric parameters (T eff, $\mathrm{log}g$ , [Fe/H]) of M dwarfs can be used to constrain both theoretical stellar models and Galactic chemical evolutionary models, and guide exoplanet searches, but their determination is difficult due to the complexity of the spectra of their cool atmospheres. In our ongoing effort to characterize M dwarfs, and in particular their chemical composition, we carried out multiband photometric calibrations of metallicity for early- and intermediate-type M dwarfs. The third Gaia data release provides high-precision astrometry and three-band photometry. This information, combined with the 2MASS and CatWISE2020 infrared photometric surveys and a sample of 4919 M dwarfs with metallicity values determined with high-resolution spectroscopy by The Cannon and APOGEE spectra, allowed us to study the effect of the metallicity in color-color and color-magnitude diagrams. We divided this sample into two subsamples: we used 1000 stars to train the calibrations with Bayesian statistics and Markov Chain Monte Carlo techniques, and the remaining 3919 stars to check the accuracy of the estimations. We derived several photometric calibrations of metallicity applicable to M dwarfs in the range of -0.45 ≤ [Fe/H] ≤ + 0.45 dex and spectral types down to M5.0 V that yield uncertainties down to the 0.10 dex level. Lastly, we compared our results with other photometric estimations published in the literature for an additional sample of 46 M dwarfs in wide binary systems with FGK-type primary stars and found a great predictive performance.

Keywords: Fundamental parameters of stars, Hertzsprung Russell diagram, Metallicity, Low mass stars
Target Selection and Validation of DESI Quasars. The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 &lt; z &lt; 2.1 and using Lyα forests in quasar spectra at z &gt; 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands (g, r, z) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 &lt; r &lt; 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ~1000 s. With a 310 deg-2 target density, the main selection allows DESI to select more than 200 deg-2 quasars (including 60 deg-2 quasars with z &gt; 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.

Keywords: Sky surveys, Redshift surveys, Quasars
The Fundamental Signature of Star Formation Quenching from AGN Feedback: A Critical Dependence of Quiescence on Supermassive Black Hole Mass, Not Accretion Rate. We identify the intrinsic dependence of star formation quenching on a variety of galactic and environmental parameters, utilizing a machine-learning approach with Random Forest classification. We have previously demonstrated the power of this technique to isolate causality, not mere correlation, in complex astronomical data. First, we analyze three cosmological hydrodynamical simulations (Eagle, Illustris, and IllustrisTNG), selecting snapshots spanning the bulk of cosmic history from comic noon (z ~ 2) to the present epoch, with stellar masses in the range $9\lt \mathrm{log}({M}_{* }/{M}_{\odot })\lt 12$ . In the simulations, black hole mass is unanimously found to be the most predictive parameter of central galaxy quenching at all epochs. Perhaps surprisingly, black hole accretion rate (and hence the bolometric luminosity of active galactic nuclei, AGN) is found to be of little predictive power over quenching. This theoretical result is important for observational studies of galaxy quenching, as it cautions against using the current AGN state of a galaxy as a useful proxy for the cumulative impact of AGN feedback on a galactic system. The latter is traced by black hole mass, not AGN luminosity. Additionally, we explore a subset of "observable" parameters, which can be readily measured in extant wide-field galaxy surveys targeting z = 0-2, at $9\lt \mathrm{log}({M}_{* }/{M}_{\odot })\lt 12$ . All three simulations predict that, in lieu of black hole mass, the stellar gravitational potential will outperform the other parameters in predicting quenching. We confirm this theoretical prediction observationally in the SDSS (at low redshifts) and in CANDELS (at intermediate and high redshifts).

Keywords: Galaxy evolution
Tracing the Evolution of SMBHs and Stellar Objects in Galaxy Mergers: A Multi-mass Direct N-body Model. By using direct N-body numerical simulations, we model the dynamical coevolution of two supermassive black holes (SMBHs) and the surrounding stars in merging galaxies. In order to investigate how different stellar components evolve during the merger, we generate evolved stellar distributions with an initial mass function. Special schemes have also been developed to deal with some rare but interesting events, such as the tidal disruption of main-sequence stars, plunging low-mass stars, white dwarfs, neutron stars and stellar-mass black holes, and the partial tidal disruption of red giants or asymptotic giant branch stars. Our results indicate that the formation of a bound SMBH binary will enhance the capture rates of stellar objects by SMBHs. Compared to the equal stellar mass model, the multi-mass model tends to result in a higher average mass of disrupted stars. Instead of being tidally disrupted by the SMBH, roughly half of the captured main-sequence stars will directly plunge into the SMBH because of their small stellar radii. Giant stars, on the other hand, can be stripped of their envelopes if they are close enough to the SMBH. Though most remnants of the giant stars can survive after the disruption, a small fraction still could plunge into the SMBH quickly or after many orbital periods. Our results also indicate significant mass segregation of compact stars at the beginning of the merger, and then this effect is destroyed as the two SMBHs form a bound binary.

Keywords: Computational astronomy, Galaxy dynamics, Gravitational wave sources, Galaxy nuclei, Galaxy mergers, Galaxy evolution