Sazuna/UAT_keywords huggingface dataset:
A Study of Variations of Galactic Cosmic-Ray Intensity Based on a Hybrid Data-processing Method. The low-energy cosmic-ray (CR) fluxes measured by space-borne instruments are generally considered to consist of gradually changing galactic CRs (GCRs) and short-lived solar energetic particles (SEPs). The SEP events cause sharp and ephemeral increases in the time profile of CR observations, with a higher occurrence rate in solar maximum. It is necessary to eliminate such spikes and obtain the pure GCR component while studying the modulation of GCRs in both short and long timescales. A hybrid data-processing method based on spike detection and time series analysis techniques is developed to remove the spikes and decompose the GCR data observed by the Interplanetary Monitoring Platform 8 into the long-term variation trend and the 27 day variation components. With the hybrid data-processing method, the 11 yr and 27 day variations in the intensity of low-energy GCRs can be studied systematically. Using the fitted trend component, the time lag in the solar modulation of low-energy GCRs is studied, and the results show that the time lag is both epoch and energy dependent. The obtained 27 day variation component is anticorrelated with the changes in solar wind velocity even during solar maximum. Implementing the running Fourier series fit procedure, the 27 day variation amplitude of the proton flux is computed. It is found that the yearly averaged values clearly show 11 and 22 yr variation cycles. In addition, the energy spectrum of the 27 day variation amplitude is softer in the A &lt; 0 solar minimum than that in the A &gt; 0 solar minimum.

Keywords: Solar activity, Solar energetic particles, Cosmic rays
Potential Impact of Fast Flavor Oscillations on Neutrino-driven Winds and Their Nucleosynthesis. The wind driven by the intense neutrino emission from a protoneutron star (PNS) is an important site for producing nuclei heavier than the Fe group. Because of certain features in the neutrino angular distributions, the so-called fast flavor oscillations may occur very close to the PNS surface, effectively resetting the neutrino luminosities and energy spectra that drive the wind. Using the unoscillated neutrino emission characteristics from two core-collapse supernova simulations representative of relevant progenitors at the lower and higher mass end, we study the potential effects of fast flavor oscillations on neutrino-driven winds and their nucleosynthesis. We find that such oscillations can increase the total mass loss by factors up to ∼1.5-1.7 and lead to significantly more proton-rich conditions. The latter effect can greatly enhance the production of 64Zn and the so-called light p-nuclei 74Se, 78Kr, and 84Sr. Implications for abundances in metal-poor stars, Galactic chemical evolution in general, and isotopic anomalies in meteorites are discussed.

Keywords: Neutrino oscillations, Explosive nucleosynthesis, Supernovae, Nucleosynthesis
Particle-in-cell Simulations of Secondary Magnetic Islands: Ion-scale Flux Ropes and Plasmoids. Ion-scale flux ropes and plasmoids are secondary magnetic islands produced during magnetic reconnection in various heliospheric plasma environments. Here we study the structure of secondary islands and the particle dynamics within them using particle-in-cell simulations. Ion-scale flux ropes (secondary islands with a strong core field) are formed in a strong guide field regime, whereas ion-scale plasmoids (secondary islands with a weak core field) are formed in a weak guide field regime. Currents in both types of secondary islands are carried primarily by electrons. Both types of secondary islands have a magnetic tension force pointing radially inward toward their center. In the flux rope type, this inward tension force is balanced by an outward magnetic pressure gradient of the strong core field; in the plasmoid type, it is countered by an outward thermal pressure gradient caused by electron and ion energizations. The transition between these two types occurs when Bg/B0 = 0.1-0.2 (Bg is the guide field, and B0 is the asymptotic magnetic field).

Keywords: Space plasmas, Interplanetary particle acceleration, Solar magnetic reconnection, Heliosphere
Extratidal Stars and Chemical Abundance Properties of Two Metal-poor Globular Clusters M53 (NGC 5024) and NGC 5053. We search for extratidal stars around two metal-poor Galactic globular clusters, M53 and NGC 5053, using the near-infrared APOGEE spectra. Applying the t-distributed stochastic neighbor embedding (t-SNE) algorithm on the chemical abundances and radial velocities results in identification of two isolated stellar groups composed of cluster member stars in the t-SNE projection plane. With additional selection criteria of radial velocity, location in the color-magnitude diagram, and abundances from a manual chemical analysis, we find a total of 73 cluster member candidates; seven extratidal stars are found beyond the tidal radii of the two clusters. The extratidal stars around the clusters tend to be located along the leading direction of the cluster proper motion, and the individual proper motion of these stars also seems to be compatible to those of clusters. Interestingly, we find that one extratidal star of NGC 5053 is located on the southern outskirts of M53, which is part of common stellar envelope by the tidal interaction between two clusters. We discuss the nature of this star in the context of the tidal interaction between two clusters. We find apparent Mg-Al anticorrelations with a clear gap and spread (∼0.9 dex) in Al abundances for both clusters, and a light Si abundance spread (∼0.3 dex) for NGC 5053. Since all extratidal stars have Mg-enhanced and Al-depleted features, they could be first-generation stars of two globular clusters. Our results support that M53 and NGC 5053 originated in dwarf galaxies and are surrounded by extended stellar substructures of more numerous populations of clusters.

Keywords: Globular star clusters, Stellar abundances
Compaction of Porous H<SUB>2</SUB>O Ice via Energetic Electrons. Here we have investigated the degree to which energetic electrons cause structural changes in microporous H2O ice using infrared and ultraviolet-visible spectroscopy as analytical tools. In these studies, we found that energetic electrons destroy both the dangling bond (DB) absorption bands, indicative of internal surface area, and the internal porosity of our samples. In addition, we find it takes about a factor of 3 higher fluence to decrease the internal pore volume by 63.2% than it does the internal surface area, which is likely because the surface area decreases by both destruction of the internal pores and also by smaller pores coalescing into large ones. Extrapolating our results to the interstellar medium (ISM), we estimate that the time needed for these processes to occur is significantly shorter than the expected lifetime of a molecular cloud, leading us to speculate that future detections of the DB absorption bands or other indicators of porosity in the ISM will be relatively rare.

Keywords: Solid matter physics, Laboratory astrophysics, Astrochemistry, Surface ices, Interstellar medium, Spectroscopy, Cosmic rays
Chandra Observations of Candidate Subparsec Binary Supermassive Black Holes. We present analysis of Chandra X-ray observations of seven quasars that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on the apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs, including harder or softer X-ray spectra, ripple-like profiles in the Fe K-α line, and distinct peaks in the spectrum due to the separation of the accretion disk into a circumbinary disk and mini disks around each SMBH. We obtained Chandra observations to test these models and assess whether these quasars could contain binary SMBHs. We instead find that the quasar spectra are all well fit by simple absorbed power-law models, with the rest-frame 2-10 keV photon indices, Γ, and the X-ray-to-optical power slopes, αOX, indistinguishable from those of the larger quasar population. This may indicate that these seven quasars are not truly subparsec binary SMBH systems, or it may simply reflect that our sample size was too small to robustly detect any differences. Alternatively, the X-ray spectral changes might only be evident at energies higher than probed by Chandra. Given the available models and current data, no firm conclusions are drawn. These observations will help motivate and direct further work on theoretical models of binary SMBH systems, such as modeling systems with thinner accretion disks and larger binary separations.

Keywords: Supermassive black holes, Quasars, Active galaxies, Active galactic nuclei, X-ray active galactic nuclei
Searching for Balmer-dominated Type Ia Supernova Remnants in M33. We searched for Balmer-dominated Type Ia supernova remnants (SNRs) in M33 by selecting thermal X-ray sources with ${L}_{{\rm{X}}}\geqslant 5\times {10}^{35}$ erg s-1, identifying associated Hα emission features, and checking their [S II] and [O III] emission properties. Our search did not find any Balmer-dominated Type Ia SNRs in M33. This result is puzzling because M33 is 2-3 times more massive than the Large Magellanic Cloud (LMC), yet the LMC hosts five Balmer-dominated Type Ia SNRs and M33 has none. We have considered observational biases; interstellar densities and ionization conditions; the Type Ia SN rate expected from the star formation history and Type Ia SN delay time distribution function; and the metallicity effect. None of these can explain the absence of X-ray-bright Balmer-dominated Type Ia SNRs in M33. It is intriguing that the Galaxy has X-ray-bright and thermal Type Ia SNRs (Kepler and Tycho), as well as X-ray-faint and nonthermal Type Ia SNRs (G1.9+0.3, SN1006, and RCW86), while the LMC does not have the X-ray-faint and nonthermal ones and M33 does not have the X-ray-bright and thermal ones.

Keywords: Supernova remnants, Triangulum Galaxy, Type Ia supernovae, Interstellar medium
The Statistical Properties of Spiral Arms in Nearby Disk Galaxies. We analyze 4378 nearby bright disk (S0 and spiral) galaxies selected from the Sloan Digital Sky Survey to characterize their spiral structure and systematically investigate the relationships between spiral arm properties (strength, pitch angle, and number) and the global properties of the host galaxies. This is to date the largest sample of galaxies with comprehensive measurements of spiral properties based on Fourier decomposition. We find that spiral pitch angle decreases (arms become more tightly wound) toward galaxies of earlier Hubble type, higher stellar mass, redder color, and greater degree of central concentration. The dependence of pitch angle on stellar mass is mainly driven by color, and for a given concentration, spiral arms are more tightly wound in redder galaxies. Spiral pitch angles show a bimodal distribution, peaking at φ = 12° ± 3°4 and 23° ± 4°3. Spiral arms weaken in galaxies of earlier type, redder color, and higher concentration, but for a given concentration, spiral arms become more prominent in more massive and bluer galaxies. We confirm that spiral arm strength loosely correlates with pitch angle, although the scatter in this relation is considerable and depends systematically on mass and color; for a given pitch angle, more massive or bluer galaxies have stronger arms. Galaxies of earlier Hubble type, higher mass concentration, or redder color have fewer spiral arms. Lastly, galaxies with stronger bars have fewer but stronger arms. We discuss the possible origins of these various relationships, which provide useful empirical guidance to theories of spiral structure. Depending on the galaxy, both the density wave and swing amplification mechanisms operate.

Keywords: Galaxy formation, Spiral galaxies, Hubble classification scheme, Galaxy structure, Galaxy evolution, Spiral pitch angle
The Dynamical State of the Frontier Fields Galaxy Cluster Abell 370. We study the dynamics of Abell 370 (A370), a highly massive Hubble Frontier Fields galaxy cluster, using self-consistent three-dimensional N-body/hydrodynamical simulations. Our simulations are constrained by X-ray, optical spectroscopic and gravitational lensing, and Sunyaev-Zel'dovich (SZ) effect observations. Analyzing archival Chandra observations of A370 and comparing the X-ray morphology to the latest gravitational lensing mass reconstruction, we find offsets of ∼30 and ∼100 kpc between the two X-ray surface brightness peaks and their nearest mass surface density peaks, suggesting that it is a merging system, in agreement with previous studies. Based on our dedicated binary cluster merger simulations, we find that initial conditions of the two progenitors with virial masses of $1.7\times {10}^{15}$ and $1.6\times {10}^{15}\,{M}_{\odot }$ , an infall velocity of 3500 km s-1, and an impact parameter of 100 kpc can explain the positions and the offsets between the peaks of the X-ray emission and mass surface density, the amplitude of the integrated SZ signal, and the observed relative line-of-sight velocity. Moreover, our best model reproduces the observed velocity dispersion of cluster member galaxies, which supports the large total mass of A370 derived from weak lensing. Our simulations strongly suggest that A370 is a post major merger after the second core passage in the infalling phase, just before the third core passage. In this phase, the gas has not settled down in the gravitational potential well of the cluster, which explains why A370 does not follow closely the galaxy cluster scaling relations.

Keywords: Relativistic mechanics, Sunyaev-Zeldovich effect, N-body simulations
The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging: H I Gas, Star Formation, and Numerical Simulations. A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA H I emission line mapping, optical imaging, and numerical simulations of VCC 848 in order to examine the effect of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its H I gas concentrated within the central high-surface-brightness star-forming region, while the remaining H I is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N(H I) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central ∼1.5 kpc. VCC 848 is consistent with being a main-sequence star-forming galaxy for its current stellar mass and SFR. The H II region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest H II region is extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial noncoplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with a centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary and, in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger.

Keywords: Dwarf irregular galaxies, Blue compact dwarf galaxies, Hydrodynamical simulations, Disk galaxies, Irregular galaxies, Dwarf galaxies, Galaxy interactions, H I line emission, Galaxy mergers, Interstellar medium
Testing Comptonization as the Origin of the Continuum in Nonmagnetic Cataclysmic Variables: The Photon Index of X-Ray Emission. The X-ray spectra of nonmagnetic cataclysmic variables (nmCVs) in the ∼0.3-15 keV energy band have been described by either one or several optically thin thermal plasma components or by cooling flow models. We tested whether the spectral continuum in nmCVs could be successfully described by Comptonization of soft photons off hot electrons presented in a cloud surrounding the source (the transition layer (TL)). We used public XMM-Newton EPIC-pn, Chandra HETG/ACIS and LETG/HRC, and RXTE PCA and HEXTE observations of four dwarf novae (U Gem, SS Cyg, VW Hyi, and SS Aur) observed in the quiescent and outburst states. In total, we analyzed 18 observations, including a simultaneous 0.4-150 keV Chandra/RXTE spectrum of SS Cyg in quiescence. We fitted the spectral continuum with up to two thermal Comptonization components (the COMPTT or COMPTB models in XSPEC) using only one thermal plasma temperature and one optical depth. In this framework, the two seed photon components are presumably coming from the innermost and outer parts of the TL (or innermost part of the disk). We obtained that the thermal Comptonization can successfully describe the spectral continuum of these nmCVs in the ∼0.4-150 keV energy band. Moreover, we present the first principal radiative transfer model that explains the quasi-constancy of the spectral photon index observed around 1.8, which strongly supports the Comptonization framework in nmCVs.

Keywords: X-ray binary stars
The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa from Asteroseismology with TESS. Most previous efforts to calibrate how rotation and magnetic activity depend on stellar age and mass have relied on observations of clusters, where isochrones from stellar evolution models are used to determine the properties of the ensemble. Asteroseismology employs similar models to measure the properties of an individual star by matching its normal modes of oscillation, yielding the stellar age and mass with high precision. We use 27 days of photometry from the Transiting Exoplanet Survey Satellite to characterize solar-like oscillations in the G8 subgiant of the 94 Aqr triple system. The resulting stellar properties, when combined with a reanalysis of 35 yr of activity measurements from the Mount Wilson HK project, allow us to probe the evolution of rotation and magnetic activity in the system. The asteroseismic age of the subgiant agrees with a stellar isochrone fit, but the rotation period is much shorter than expected from standard models of angular momentum evolution. We conclude that weakened magnetic braking may be needed to reproduce the stellar properties, and that evolved subgiants in the hydrogen shell-burning phase can reinvigorate large-scale dynamo action and briefly sustain magnetic activity cycles before ascending the red giant branch.

Keywords: Stellar oscillations, Stellar rotation, Stellar evolution, Stellar activity
Molecular Clouds Surrounding Supernova Remnant G43.9+1.6: Associated and Nonassociated. Many supernova remnants (SNRs) are considered to evolve in molecular environments, but the associations between SNRs and molecular clouds (MCs) are often unclear. Being aware of such ambiguity, in our study, we report on the molecular environment toward SNR G43.9+1.6 through CO line observations. We investigated the correlations between the SNR and MCs at different velocities, and found two velocity components, i.e., ∼5 km s-1 and ∼50 km s-1, showing spatial correlations with the remnant. However, no kinematic evidence of a disturbance was found for the ∼5 km s-1 velocity component. Furthermore, at the distance of the ∼5 km s-1 velocity component, either near or far, the derived physical parameters are unreasonable. We conclude that the SNR is not associated with the ∼5 km s-1 velocity component, and their spatial correlation is just a chance correlation. For the ∼50 km s-1 velocity component, kinematic evidence of disturbances, as well as the spatial correlation, indicate that it is associated with the SNR. We found that all the CO spectra extracted from the molecular clumps distributed along the border of the remnant are with broadened components presented, which can be fitted by Gaussian functions. Through further analysis, we suggest that the SNR is at a near kinematic distance of about 3.1 kpc.

Keywords: Radio spectroscopy, Interstellar molecules, Interstellar line emission, Stellar-interstellar interactions, Interstellar dynamics, Millimeter astronomy, Molecular clouds, Supernova remnants, Interstellar medium
A 3D Framework to Explore the Propagation Effects in Stars Exhibiting Electron Cyclotron Maser Emission. Recently, coherent radio emission has been discovered from a number of hot magnetic stars, via the process of electron cyclotron maser emission (ECME). This emission, observed in the form of highly circularly polarized pulses, has interesting properties that contain information about the host star. One of the important properties of ECME is the frequency dependence of the pulse arrival time. This has been attributed to the propagation effect by Trigilio et al. and could explain the sequence observed for CU Vir qualitatively. However, no quantitative treatment exists for this phenomenon despite it being a promising tool to estimate the density in the stellar magnetosphere. Additionally, the effect of propagation through the magnetosphere on ECME has been thought to be limited to giving rise to a particular sequence of arrival of pulses, and in some cases producing the upper cutoff frequency for ECME. Here, we present a framework to deal with the propagation effect by considering continuous refraction in the inner magnetosphere of the star. This framework is capable of incorporating any type of density distribution, and in principle any type of magnetic field, though we limit ourselves to a dipolar magnetic field for this work. We show by simulation that for stars with high obliquity, the propagation effect can influence not only the sequence of arrival of pulses drastically, but also the pulse shapes, and the observability of a pulse from a particular magnetosphere.

Keywords: Early-type variable stars, Magnetic stars, Astrophysical masers, Astronomical simulations
Phase-modulated X-Ray Emission from Cepheids due to Pulsation-driven Shocks. Cepheids are pulsating variable stars with a periodic chromospheric response at UV wavelengths close to their minimum radius phase. Recently, an X-ray variable signature was captured in observations during the maximum radius phase. This X-ray emission came as a surprise and is not understood. In this work, we use the modern astrophysical code PLUTO to investigate the effects of pulsations on Cepheid X-ray emission. We run a number of hydrodynamic numerical simulations with a variety of initial and boundary conditions in order to explore the capability of shocks to produce the observed phase-dependent X-ray behavior. Finally, we use the Simulated Observations of X-ray Sources (SOXS) package to create synthetic spectra for each simulation case and link our simulations to observables. We show that, for certain conditions, we can reproduce observed X-ray fluxes at phases 0.4-0.8 when the Cepheid is at maximum radius. Our results span a wide range of mass-loss rates, 2 × 10-13 M⊙ yr-1 to 3 × 10-8 M⊙ yr-1, and peak X-ray luminosities, 5 × 10-17 erg cm-2 s-1 to 1.4 × 10-12 erg cm-2 s-1. We conclude that Cepheids exhibit two-component emission with (a) shock waves being responsible for the phase-dependent variable emission (phases 0.2-0.6) and (b) a separate quiescent mechanism being the dominant emission mechanism for the remaining phases.

Keywords: Late-type stars, High energy astrophysics, Pulsating variable stars, Plasma astrophysics, Stellar physics, Stellar flares, Delta Cepheid variable stars, Shocks, Stellar coronae, Stellar atmospheres, Magnetohydrodynamical simulations