Sazuna/UAT_keywords huggingface dataset:
The TeV Diffuse Cosmic Neutrino Spectrum and the Nature of Astrophysical Neutrino Sources. The diffuse flux of cosmic neutrinos has been measured by the IceCube Observatory from TeV to PeV energies. We show that an improved characterization of this flux at lower energies, TeV and sub-TeV, reveals important information on the nature of the astrophysical neutrino sources in a model-independent way. Most significantly, it could confirm the present indications that neutrinos originate in cosmic environments that are optically thick to GeV-TeV γ-rays. This conclusion will become inevitable if an uninterrupted or even steeper neutrino power law is observed in the TeV region. In such γ-ray-obscured sources, the γ-rays that inevitably accompany cosmic neutrinos will cascade down to MeV-GeV energies. The requirement that the cascaded γ-ray flux accompanying cosmic neutrinos should not exceed the observed diffuse γ-ray background puts constraints on the peak energy and density of the radiation fields in the sources. Our calculations inspired by the existing data suggest that a fraction of the observed diffuse MeV-GeV γ-ray background may be contributed by neutrino sources with intense radiation fields that obscure the high-energy γ-ray emission accompanying the neutrinos.

Keywords: Neutrino astronomy, Gamma-rays
Dynamic Property and Magnetic Nonpotentiality of Two Types of Confined Solar Flares. We analyze 152 large confined flares (GOES class ≥ M1.0 and ≤ 45° from disk center) during 2010-2019, and classify them into two types according to the criterion taken from the work of Li et al. "Type I" flares are characterized by slipping motions of flare loops and ribbons and a stable filament underlying the flare loops. "Type II" flares are associated with the failed eruptions of the filaments, which can be explained by the classical 2D flare model. A total of 59 flares are "Type I" flares (about 40%) and 93 events are "Type II" flares (about 60%). There are significant differences in distributions of the total unsigned magnetic flux (ΦAR) of active regions (ARs) producing the two types of confined flares, with "Type I" confined flares from ARs with a larger ΦAR than "Type II." We calculate the mean shear angle ΨHFED within the core of an AR prior to the flare onset, and find that it is slightly smaller for "Type I" flares than that for "Type II" events. The relative nonpotentiality parameter ΨHFED/ΦAR has the best performance in distinguishing the two types of flares. About 73% of "Type I" confined flares have ΨHFED/ΦAR&lt;1.0 × 10-21 degree Mx-1, and about 66% of "Type II" confined events have ΨHFED/ΦAR ≥ 1.0 × 10-21 degree Mx-1. We suggest that "Type I" confined flares cannot be explained by the standard flare model in 2D/3D, and the occurrence of multiple slipping magnetic reconnections within the complex magnetic systems probably leads to the observed flare.

Keywords: Solar active region magnetic fields, Solar flares, Solar filaments, Solar coronal mass ejections, Solar activity
The Photoionization Dynamics, Electronic Spectroscopy, and Excited State Photochemistry of AlCO and AlOC. The high cosmic abundance of carbon monoxide (CO) and the ubiquitous nature of aluminum-coated dust grains sets the stage for the production of weakly bound triatomic molecules AlCO (X 2Π) and AlOC (X 2Π) in circumstellar envelopes of evolved stars. Following desorption of cold AlCO and AlOC from the dust grain surface, incoming stellar radiation in the 2-9 eV wavelength range (visible to vacuum ultraviolet) will drive various photochemical processes. Ionization to the singlet cation state will cause an immediate Al-X (X = C, O) bond dissociation to form Al+ (1S) and CO (X 1Σ+) coproducts, whereas ionization to the higher-lying triplet states will lead to stabilization of AlCO+ (X 3Π) and AlOC+(X 3Π) in deep potential wells. In competition with ionization is electronic excitation. Excitation to the spectroscopically bright 1 2Π and 2 2Σ+ states will lead to either highly Stokes-shifted fluorescence, or photodissociation to yield Al (2D) + CO (X 1Σ+) products via nonadiabatic pathways, making AlCO and AlOC good candidates for electronic experimental studies. These many photoinduced pathways spanning orders of magnitude of the electromagnetic spectrum will lead to the depletion of AlCO and AlOC in astronomical environments, potentially explaining the lack of observational detection of these molecules. Furthermore, these results indicate new catalytic pathways to the freeing of aluminum atoms trapped in solid aluminum dust grains. Additionally, the results herein implicate an ion-neutral reaction as a possible important pathway in [Al, C, O] cation formation.

Keywords: Computational methods, Photoionization, Molecular spectroscopy, Astrochemistry
A Long-period Pre-ELM System Discovered from the LAMOST Medium-resolution Survey. We present LAMOST J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated, extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189 days. The large-amplitude ellipsoidal variations and the evident Balmer and He I emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, ${T}_{\mathrm{eff}}={5793}_{-133}^{+124}\,{\rm{K}}$ , makes it cooler than the known ELMs, but hotter than most cataclysmic variable donors. Combining the mean density within the Roche lobe and the radius constrained from our spectral energy distribution fitting, we obtain the mass of the pre-ELM, M 1 = 0.176 ± 0.014 M ⊙. The joint fitting of light and radial velocity curves yields an inclination angle of $i={66.5}_{-1.7}^{+1.4}$ degrees, corresponding to a mass of the compact object of M 2 = 1.09 ± 0.05 M ⊙. The very bloated pre-ELM has a smaller surface gravity ( $\mathrm{log}g=3.9\pm 0.01$ , R 1 = 0.78 ± 0.02 R ⊙) than the known ELMs or pre-ELMs. The temperature and the luminosity ( ${L}_{\mathrm{bol}}={0.62}_{-0.10}^{+0.11}\,{L}_{\odot }$ ) of J0419 are close to those of the main sequence, which makes the selection of such systems through the H-R diagram inefficient. Based on the evolutionary model, the relatively long period and small $\mathrm{log}g$ indicate that J0419 could be close to the "bifurcation period" in the orbital evolution, which makes J0419 a unique source to connect ELM/pre-ELM WD systems, wide binaries, and cataclysmic variables.

Keywords: Close binary stars, White dwarf stars, Cataclysmic variable stars, Low mass stars
Type IIP Supernova IV. Shock Breakout from Progenitor Stars Modeled with Convective Overshoot and Mass Loss. Red supergiant stars lose a lot of mass in slow winds that forms a circumstellar medium (CSM) around the star. When the star retains a substantial hydrogen envelope at the time of explosion, it displays characteristic light curves and spectra of a Type II plateau supernova (SN), e.g., the nearby SN 2013ej. When the shock wave launched deep inside the star exits the surface, it probes the CSM and scripts the history of mass loss from the star. We simulate with the STELLA code the SN radiative display resulting from shock breakout (SBO) for a set of progenitor stars. We evolved these stars with the MESA code from their main-sequence to core-collapse phase using diverse evolutionary inputs. We explore the SN display for different internal convective overshoot and compositional mixing inside the progenitor stars and two sets of mass-loss schemes, one the standard "Dutch" scheme and the other an enhanced, episodic and late mass loss. The SBO from the star shows closely time-separated double-peaked bolometric light curves for the Dutch case, as well as high-velocity ejecta with minuscule mass accelerated during SBO. The earlier of the peaks, which we call the precursor peaks, are compared with analytical expressions for SBO of stars. We also contrast the breakout flash from an optically thick CSM with that of the rarefied medium established by Dutch wind. We describe how the multigroup photon spectra of the breakout flashes differ between these cases.

Keywords: Shocks, Stellar convective zones, Core-collapse supernovae, Stellar mass loss
On the Evolution of Rotational Modulation Amplitude in Solar-mass Main-sequence Stars. We investigate the relation between rotation periods P rot and photometric modulation amplitudes R per for ≈4000 Sun-like main-sequence stars observed by Kepler, using P rot and R per from McQuillan et al., effective temperature T eff from LAMOST DR6, and parallax data from Gaia EDR3. As has been suggested in previous works, we find that P rot scaled by the convective turnover time τ c, or the Rossby number Ro, serves as a good predictor of R per: R per plateaus at around 1% in relative flux for 0.2 ≲ Ro/Ro⊙ ≲ 0.4, and decays steeply with increasing Ro for 0.4 ≲ Ro/Ro⊙ ≲ 0.8, where Ro⊙ denotes Ro of the Sun. In the latter regime we find ${\rm{d}}\,\mathrm{ln}\,{R}_{\mathrm{per}}/{\rm{d}}\,\mathrm{ln}\,\mathrm{Ro}$ ~ -4.5 to -2.5, although the value is sensitive to detection bias against weak modulation and may depend on other parameters including T eff and surface metallicity. The existing X-ray and Ca II H and K flux data also show transitions at Ro/Ro⊙ ~ 0.4, suggesting that all these transitions share the same physical origin. We also find that the rapid decrease of R per with increasing Ro causes rotational modulation of fainter Kepler stars with Ro/Ro⊙ ≳ 0.6 to be buried under the photometric noise. This effect sets the longest P rot detected in the McQuillan et al. sample as a function of T eff and obscures the signature of stalled spin down that has been proposed to set in around Ro/Ro⊙ ~ 1.

Keywords: Starspots, Light curves, Stellar magnetic fields, Stellar activity, Stellar rotation
Investigating the Nature of the Luminous Ambiguous Nuclear Transient ASASSN-17jz. We present observations of the extremely luminous but ambiguous nuclear transient (ANT) ASASSN-17jz, spanning roughly 1200 days of the object's evolution. ASASSN-17jz was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in the galaxy SDSS J171955.84+414049.4 on UT 2017 July 27 at a redshift of z = 0.1641. The transient peaked at an absolute B-band magnitude of M  B,peak = -22.81, corresponding to a bolometric luminosity of L bol,peak = 8.3 × 1044 erg s-1, and exhibited late-time ultraviolet emission that was still ongoing in our latest observations. Integrating the full light curve gives a total emitted energy of E tot = (1.36 ±0.08) × 1052 erg, with (0.80 ± 0.02) × 1052 erg of this emitted within 200 days of peak light. This late-time ultraviolet emission is accompanied by increasing X-ray emission that becomes softer as it brightens. ASASSN-17jz exhibited a large number of spectral emission lines most commonly seen in active galactic nuclei (AGNs) with little evidence of evolution. It also showed transient Balmer features, which became fainter and broader over time, and are still being detected &gt;1000 days after peak brightness. We consider various physical scenarios for the origin of the transient, including supernovae (SNe), tidal disruption events, AGN outbursts, and ANTs. We find that the most likely explanation is that ASASSN-17jz was a SN IIn occurring in or near the disk of an existing AGN, and that the late-time emission is caused by the AGN transitioning to a more active state.

Keywords: Accretion, Tidal disruption, Galaxy accretion disks, Active galactic nuclei, Supernovae
On the Dwarf Irregular Galaxy NGC 6822. I. Young, Intermediate, and Old Stellar Populations. We present accurate and deep multiband (g, r, i) photometry of the Local Group dwarf irregular galaxy NGC 6822. The images were collected with wide-field cameras at 2 m/4 m (INT, CTIO, CFHT) and 8 m class telescopes (Subaru) covering a 2 deg2 field of view across the center of the galaxy. We performed point-spread function photometry of ≈7000 CCD images, and the final catalog includes more than 1 million objects. We developed a new approach to identify candidate field and galaxy stars and performed a new estimate of the galaxy center by using old stellar tracers, finding that it differs by 1.'15 (R.A.) and 1.'53 (decl.) from previous estimates. We also found that young (main sequence, red supergiants), intermediate (red clump, asymptotic giant branch (AGB)), and old (red giant branch) stars display different radial distributions. The old stellar population is spherically distributed and extends to radial distances larger than previously estimated (~1°). The young population shows a well-defined bar and a disk-like distribution, as suggested by radio measurements, that is off-center compared with the old population. We discuss pros and cons of the different diagnostics adopted to identify AGB stars and develop new ones based on optical-near-IR-mid-IR color-color diagrams to characterize oxygen- and carbon-rich stars. We found a mean population ratio between carbon and M-type (C/M) stars of 0.67 ± 0.08 (optical/near-IR/mid-IR), and we used the observed C/M ratio with empirical C/M-metallicity relations to estimate a mean iron abundance of [Fe/H] ~ -1.25 (σ = 0.04 dex), which agrees quite well with literature estimates.

Keywords: Stellar photometry, Dwarf irregular galaxies, Stellar populations, Asymptotic giant branch stars, Metallicity
Periodic Solar Wind Structures Observed in Measurements of Elemental and Ionic Composition in situ at L1. Mesoscale periodic structures observed in solar wind plasma serve as an important diagnostic tool for constraining the processes that govern the formation of the solar wind. These structures have been observed in situ and in remote data as fluctuations in proton and electron density. However, only two events of this type have been reported regarding the elemental and ionic composition. Composition measurements are especially important in gaining an understanding of the origin of the solar wind as the composition is frozen into the plasma at the Sun and does not evolve as it advects through the heliosphere. Here, we present the analysis of four events containing mesoscale periodic solar wind structure during which the Iron and Magnesium number density data, measured by the Solar Wind Ion Composition Spectrometer (SWICS) on board the Advanced Composition Explorer spacecraft, are validated at statistically significant count levels. We use a spectral analysis method specifically designed to extract periodic signals from astrophysical time series and apply it to the SWICS 12 minute native resolution data set. We find variations in the relative abundance of elements with low first ionization potential, mass dependencies, and charge state during time intervals in which mesoscale periodic structures are observed. These variations are linked to temporal or spatial variations in solar source regions and put constraints on the solar wind formation mechanisms that produce them. Techniques presented here are relevant for future, higher-resolution studies of data from new instruments such as Solar Orbiter's Heavy Ion Sensor.

Keywords: Solar wind, Solar corona, Plasma physics
Generation of Solar-like Differential Rotation. We analyze the simulation result shown in Hotta &amp; Kusano (2021) in which the solar-like differential rotation is reproduced. The Sun is rotating differentially with the fast equator and the slow pole. It is widely thought that the thermal convection maintains the differential rotation, but recent high-resolution simulations tend to fail to reproduce the fast equator. This fact is an aspect of one of the biggest problems in solar physics called the convective conundrum. Hotta &amp; Kusano succeed in reproducing the solar-like differential rotation without using any manipulation with an unprecedentedly high-resolution simulation. In this study, we analyze the simulation data to understand the maintenance mechanism of the fast equator. Our analyses lead to conclusions that are summarized as follows. (1) The superequipatition magnetic field is generated by the compression, which can indirectly convert the massive internal energy to magnetic energy. (2) The efficient small-scale energy transport suppresses large-scale convection energy. (3) Non-Taylor-Proudman differential rotation is maintained by the entropy gradient caused by the anisotropic latitudinal energy transport enhanced by the magnetic field. (4) The fast equator is maintained by the meridional flow mainly caused by the Maxwell stress. The Maxwell stress itself also has a role in the angular momentum transport for the fast near-surface equator (we call it the P unching ball effect). The fast equator in the simulation is reproduced not due to the low Rossby number regime but due to the strong magnetic field. This study newly finds the role of the magnetic field in the maintenance of differential rotation.

Keywords: Solar convective zone, Stellar convective zones
A Double-decker Filament Formation Driven by Sunspot Rotation and Magnetic Reconnection. In this paper, through analyzing data from the Solar Dynamics Observatory (SDO) and the Global Oscillation Network Group (GONG), we present a study on the formation of a double-decker filament in NOAA Active Region 12665 from 2017 July 8 to 14. We find that magnetic reconnection occurs between two smaller filaments to form a longer filament. According to the evolution of the leading sunspot, it is obvious that the sunspot experiences a continuous rotation around its umbra. During the period from 03:00 UT on July 11 to 10:00 UT on July 14, the average speed of sunspot rotation is about 3.°7 hr-1. The continuous rotation of sunspot stretches the filament and results in the formation of a reversed S-shaped filament. Due to the motion of the magnetic field and internal magnetic reconnection, the filament splits into two branches and forms a double-decker filament structure. In the process of filament separation, internal magnetic reconnection can also accelerate the filament separation. Nonlinear force-free field extrapolation indicates that there are two magnetic flux ropes, which are consistent with the observed results. Eventually, the upper filament erupts and produces an M-class flare and a halo coronal mass ejection.

Keywords: Solar filaments, Solar magnetic reconnection
The Astrophysical Distance Scale. V. A 2% Distance to the Local Group Spiral M33 via the JAGB Method, Tip of the Red Giant Branch, and Leavitt Law. The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic J-band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt law, and the TRGB. We find: μ 0(TRGB I ) = 24.72 ± 0.02 (stat) ± 0.07 (sys) mag, μ 0(TRGBNIR) = 24.72 ± 0.04 (stat) ± 0.10 (sys) mag, μ 0(JAGB) = 24.67 ± 0.03 (stat) ± 0.04 (sys) mag, and μ 0(Cepheid) = 24.71 ± 0.04 (stat) ± 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure μ 0(JAGBF110W) = 24.71 ± 0.06 (stat) ± 0.05 (sys) mag using the (F814W-F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from the James Webb Space Telescope.

Keywords: Red giant tip, Galaxy distances, Observational cosmology, Carbon stars, Distance indicators, Hubble constant, Asymptotic giant branch stars, Cepheid variable stars, Triangulum Galaxy, Cepheid distance, Population II stars
Tracing Lyα and LyC Escape in Galaxies with Mg II Emission. Star-forming galaxies are considered the likeliest source of the H I ionizing Lyman continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z ≳ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the epoch of reionization. Emission from the Mg II λλ2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for eight LyC emitter candidates, selected to have strong Mg II emission lines. We securely detect LyC emission in 50% (4/8) of the galaxies with 2σ significance. This high detection rate suggests that strong Mg II emitters might be more likely to leak LyC than similar galaxies without strong Mg II. Using photoionization models, we constrain the escape fraction of Mg II as ~15%-60%. We confirm that the escape fraction of Mg II correlates tightly with that of Lyα, which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg II emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg II emission can be adopted to estimate the escape fraction of Lyα and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the epoch of reionization.

Keywords: Interstellar dust, Starburst galaxies, Emission line galaxies, Ultraviolet astronomy, Reionization
Hydrodynamics of Collisions and Close Encounters between Stellar Black Holes and Main-sequence Stars. Recent analyses have shown that close encounters between stars and stellar black holes occur frequently in dense star clusters. Depending upon the distance at closest approach, these interactions can lead to dissipating encounters such as tidal captures and disruptions, or direct physical collisions, all of which may be accompanied by bright electromagnetic transients. In this study, we perform a wide range of hydrodynamic simulations of close encounters between black holes and main-sequence stars that collectively cover the parameter space of interest, and we identify and classify the various possible outcomes. In the case of nearly head-on collisions, the star is completely disrupted with roughly half of the stellar material becoming bound to the black hole. For more distant encounters near the classical tidal-disruption radius, the star is only partially disrupted on the first pericenter passage. Depending upon the interaction details, the partially disrupted stellar remnant may be tidally captured by the black hole or become unbound (in some cases, receiving a sufficiently large impulsive kick from asymmetric mass loss to be ejected from its host cluster). In the former case, the star will undergo additional pericenter passages before ultimately being disrupted fully. Based on the properties of the material bound to the black hole at the end of our simulations (in particular, the total bound mass and angular momentum), we comment upon the expected accretion process and associated electromagnetic signatures that are likely to result.

Keywords: Globular star clusters, Hydrodynamical simulations, Tidal disruption, Transient sources, Astrophysical black holes