Sazuna/UAT_keywords huggingface dataset:
Proton Energy Spectra of Energetic Storm Particle Events and Relation with Shock Parameters and Turbulence. The proton energy spectra of 23 energetic storm particle (ESP) events of various types, occurring either in association with (16 events) or in the absence of (7 events) solar energetic particles (SEPs), are investigated by using data from particle instruments aboard STEREO A in the energy range from 84.1 keV to 100 MeV. The obtained spectra were fitted with several known functions. Out of the 12 ESP events occurring in association with SEPs and quasi-perpendicular shocks, the Weibull distribution provides good fits to the spectra over the whole energy range in five cases. For the other seven events it fits the high energy tail, with lower energies explained by the power law predicted by the diffusive shock acceleration (DSA). Conversely, for the four SEP-associated ESPs at quasi-parallel shocks, a double power law better reproduces the observed spectra. Moreover, a significant correlation of the downstream turbulence level is found with the background subtracted Weibull parameters for quasi-perpendicular shocks, and with the proton peak value in the intermediate energy range of 4-6 MeV for all 16 considered shocks. Our results suggest that the downstream turbulence is a relevant factor in particle acceleration and that stochastic acceleration (SA) can be a plausible mechanism for reacceleration at interplanetary shocks. In the seven cases not associated with SEPs, an Ellison-Ramaty form fits the observed spectra, consistently with a DSA process, suggesting that a strong shock and/or a high energy particle background should be present for the SA to be at work.

Keywords: Interplanetary turbulence, Interplanetary particle acceleration, S-process, Interplanetary shocks
Element Abundance Analysis of the Metal-rich Stellar Halo and High-velocity Thick Disk in the Galaxy. Based on the second Gaia data release (DR2) and APOGEE (DR16) spectroscopic surveys, we define two kinds of star samples: high-velocity thick disk (HVTD) with vφ &gt; 90 km s-1 and metal-rich stellar halo (MRSH) with vφ &lt; 90 km s-1. Due to high-resolution spectra data from APOGEE (DR16), we can accurately analyze the element abundance distribution of HVTD and MRSH. These element abundances constitute a multidimensional data space, and we introduce an algorithm method for processing multidimensional data to give the result of dimensionality reduction clustering. According to chemical property analysis, we derive that some HVTD stars could originate from the thin disk and some MRSH stars could originate from dwarf galaxies, but those stars that have similar chemical abundance characteristics in both samples may form in situ.

Keywords: Galaxy structure, Galaxy disks, Galaxy stellar halos, Galaxy abundances, Galaxy kinematics
Accretion-Induced Collapse of Neutron Stars in the Disks of Active Galactic Nuclei. The disks of active galactic nuclei (AGNs) have emerged as a rich environment for the evolution of stars and their compact remnants. The very dense medium favors rapid accretion, while torques and migration traps enhance binary formation and mergers. Both long and short gamma-ray bursts are hence expected. We show that AGN disks constitute an ideal environment for another interesting phenomenon: the accretion-induced collapse (AIC) of neutron stars (NSs) to black holes (BHs). Rapid accretion in the dense disks can cause NSs to grow to the point of exceeding the maximum mass allowed by their equation of state. General relativistic magnetohydrodynamical simulations have shown that electromagnetic signatures are expected if the NS is surrounded by a minidisk prior to collapse, which then rapidly accretes onto the BH, and/or if the NS is highly magnetized, from reconnection of the magnetosphere during collapse. Here we compute the rates of AICs and their locations within the disks for both isolated NSs and for (initially stable) NSs formed from NS-NS mergers. We find that the global AIC rates are ~0.07-20 Gpc-3 yr-1, and we discuss their observable prospects and signatures as they emerge from the dense disk environments.

Keywords: Neutron stars, Gamma-ray bursts, Active galactic nuclei
"Super GZK" Particles in a Classic Kramers' Diffusion-over-a-barrier Model. I. The Case of Protons. In interactions of ultra-high-energy cosmic ray (UHECR) protons with cosmic microwave background photons, we focus in this work on photopion production reactions and the effects of the measured, broad, energy-loss distributions in these reactions on the evolution of the protons' density functions in energy space. We rely on a Fokker-Planck transport equation in energy space whose transport coefficients are calculated using laboratory measurements. We also derive a Fokker-Planck potential that accounts for both systematic (drift) and stochastic (dispersive) energy losses due to photopion production reactions. Our results show that dispersive energy losses have significant effects on estimating the protons' horizon distance and their energy spectrum, as well as to elucidate a broadness in the GZK cutoff. We use the derived Fokker-Planck potential to assign a characteristic probability for a proton to clear the potential barrier as a function of energy. This estimate of probability can be used to assist observations in distinguishing between protons and heavy ions as charged particles. Our model is able to account for the so-called super GZK particles as a classic diffusion-over-a-barrier manifestation of the transport of UHECR protons in energy space in quantifying the extent and broadness of the GZK cutoff.

Keywords: Ultra-high-energy cosmic radiation
Multiple Sources of Solar High-energy Protons. During the 24th solar cycle, the Fermi Large Area Telescope (LAT) has observed a total of 27 solar flares possessing delayed γ-ray emission, including the exceptionally well-observed flare and coronal mass ejection (CME) on 2017 September 10. Based on the Fermi/LAT data, we plot, for the first time, maps of possible sources of the delayed &gt;100 MeV γ-ray emission of the 2017 September 10 event. The long-lasting γ-ray emission is localized under the CME core. The γ-ray spectrum exhibits intermittent changes in time, implying that more than one source of high-energy protons was formed during the flare-CME eruption. We find a good statistical correlation between the γ-ray fluences of the Fermi/LAT-observed delayed events and the products of corresponding CME speed and the square root of the soft X-ray flare magnitude. Data support the idea that both flares and CMEs jointly contribute to the production of subrelativistic and relativistic protons near the Sun.

Keywords: Solar energetic particles, Solar gamma-ray emission, Solar flares
Automated Photometry of γ Cassiopeiae: The Last Roundup. γ Cassiopeiae (B0.5IVe) is the noted prototype of a subgroup of classical Be stars exhibiting hard thermal X-ray emission. This paper reports results from a 23 yr optical campaign on this star with an automated photometric telescope (APT). A series of unstable long cycles of length 56-91 days has nearly ceased over the last decade. Also, we revise the frequency of the dominant coherent signal at 0.82238 days-1. This signal's amplitude has nearly disappeared in the last 15 yr but has somewhat recovered its former strength. We confirm the presence of secondary nonradial pulsation signals found by other authors at frequencies 1.24, 2.48, and 5.03 days-1. The APT data from intensively monitored nights reveal rapidly variable amplitudes among these frequencies. We show that peculiarities in the 0.82 days-1 waveform exist that can vary even over several days. Although the 0.82 days-1 frequency is near the star's presumed rotational frequency, because of its phase slippage with respect to a dip pattern in its far-UV light curve, it is preferable to consider the UV pattern, not the 0.82 days-1 signal, as associated with rotational modulation. We also find hints of the UV dip pattern in periodograms of seasonal data early in our program.

Keywords: B stars
The Atacama Cosmology Telescope: Detection of Millimeter-wave Transient Sources. We report on the serendipitous discovery of three transient millimeter-wave sources using data from the Atacama Cosmology Telescope. The first, detected at R.A. = 273.8138, decl. = -49.4628 at ~50σ total, brightened from less than 5 mJy to at least 1100 mJy at 150 GHz with an unknown rise time shorter than 13 days, during which the increase from 250 mJy to 1100 mJy took only 8 minutes. Maximum flux was observed on 2019 November 8. The source's spectral index in flux between 90-150 GHz was positive, α = 1.5 ± 0.2. The second, detected at R.A. = 105.1584, decl. = -11.2434 at ~20σ total, brightened from less than 20 mJy to at least 300 mJy at 150 GHz with an unknown rise time shorter than 8 days. Maximum flux was observed on 2019 December 15. Its spectral index was also positive, α = 1.8 ± 0.2. The third, detected at R.A. = 301.9952, decl. = 16.1652 at ~40σ total, brightened from less than 8 mJy to at least 300 mJy at 150 GHz over a day or less but decayed over a few days. Maximum flux was observed on 2018 September 11. Its spectrum was approximately flat, with a spectral index of α = -0.2 ± 0.1. None of the sources were polarized to the limits of these measurements. The two rising-spectrum sources are coincident in position with M and K stars, while the third is coincident with a G star.

Keywords: Millimeter astronomy, Transient sources, Stellar flares, Time domain astronomy, Ground-based astronomy
Evaluating Low-frequency Pulsar Observations to Monitor Dispersion with the Giant Metrewave Radio Telescope. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project has the primary goal of detecting and characterizing low-frequency gravitational waves through high-precision pulsar timing. The mitigation of interstellar effects is crucial to achieve the necessary precision for gravitational wave detection. Effects like dispersion and scattering are stronger at lower observing frequencies, with the variation of these quantities over week-month timescales requiring high-cadence multifrequency observations for pulsar timing projects. In this work, we utilize the dual-frequency observing capability of the Giant Metrewave Radio Telescope (GMRT) and evaluate the potential decrease in dispersion measure (DM) uncertainties when combined with existing pulsar timing array data. We present the timing analysis for four millisecond pulsars observed with the GMRT simultaneously at 322 and 607 MHz, and compare the DM measurements with those obtained through NANOGrav observations with the Green Bank Telescope and Arecibo Observatory at 1400-2300 MHz frequencies. Measured DM values with the GMRT and NANOGrav program show significant offsets for some pulsars, which could be caused by pulse profile evolution between the two frequency bands. In comparison to the predicted DM uncertainties when incorporating these low-frequency data into the NANOGrav data set, we find that higher-precision GMRT data is necessary to provide improved DM measurements. Through the detection and analysis of pulse profile baseline ripple in data on test pulsar B1929+10, we find that, while not important for these data, it may be relevant for other timing data sets. We discuss the possible advantages and challenges of incorporating GMRT data into NANOGrav and International Pulsar Timing Array data sets.

Keywords: Radio interferometers, Millisecond pulsars
Flare-induced Photospheric Velocity Diagnostics. We present radiative-hydrodynamic simulations of solar flares generated by the RADYN and RH codes to study the perturbations induced in photospheric Fe I lines by electron beam heating. We investigate how variations in the beam parameters result in discernible differences in the induced photospheric velocities. Line synthesis revealed a significant chromospheric contribution to the line profiles resulting in an apparent red asymmetry by as much as 40 m s-1 close to the time of maximum beam heating, which was not reflective of the upflow velocities that arose from the radiative-hydrodynamic simulations at those times. The apparent redshift to the overall line profile was produced by significant chromospheric emission that was blueshifted by as much as 400 m s-1 and fills in the blue side of the near-stationary photospheric absorption profile. The velocity information that can be retrieved from photospheric line profiles during flares must therefore be treated with care to mitigate the effects of higher parts of the atmosphere providing an erroneous velocity signal.

Keywords: Solar activity, Radiative transfer simulations, Solar flares, Solar photosphere
Observations of Magnetic Reconnection with Large Separatrix Angles and Separatrix Jets above the Solar Surface. We analyze six cases of magnetic reconnection with large separatrix angles and separatrix jets observed on the solar disk. The separatrix angle is defined as the angle between the two separatrices on the two sides of the outflow region. The plasma jets are observed immediately downstream of the separatrices. The morphological characteristics and magnetic field configurations of all magnetic reconnections are displayed. At the same time, we calculate several physical parameters of each case, which include the inflow velocity (from 2.3 to 24 km s-1), the outflow velocity (from 1.9 to 43 km s-1), the separatrix jet velocity (from 13 to 82 km s-1), the width (from 0.42 × 103 to 1.2 × 103 km) and length (from 1.4 × 103 to 4.3 × 103 km) of the current sheet, and the separatrix angle θsep (from 72° to 128°). We find that the outflow velocity, the separatrix jet velocity, and the width and length of the current sheet are positively related to the inflow velocity, but the separatrix angle does not depend on the inflow velocity and it is related to the initial magnetic field configuration before magnetic reconnection. Meanwhile, the velocities of the outflow and the separatrix jet decrease with increasing $\left|{\theta }_{{\rm{sep}}}-90^\circ \right|$ , indicating that when the separatrix angle is close to 90°, the jet and the outflow reach their maximum velocities. These observations are compared with the results of the theoretical model and the numerical simulation.

Keywords: Solar activity, Solar magnetic fields, Solar magnetic reconnection
Effects of Multiscale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks. Radio relics associated with merging galaxy clusters indicate the acceleration of relativistic electrons in merger-driven shocks with low sonic Mach numbers (Ms ≲ 3) in the intracluster medium (ICM). Recent studies have suggested that electron injection to diffusive shock acceleration (DSA) could take place through the so-called Fermi-like acceleration in the shock foot of β = Pgas/PB ≈ 20-100 shocks and the stochastic shock drift acceleration (SSDA) in the shock transition of β ≈ 1-5 shocks. Here, we explore how the SSDA can facilitate electron preacceleration in weak quasi-perpendicular (Q⊥) shocks in β ≈ 20-100 plasmas by performing particle-in-cell simulations in a two-dimensional domain large enough to properly encompass ion-scale waves. We find that in supercritical shocks with ${M}_{{\rm{s}}}\gtrsim {M}_{\mathrm{AIC}}^{* }\sim 2.3$ , multiscale waves are excited by the ion and electron temperature anisotropies in the downstream of the shock ramp, and that through stochastic pitch-angle scattering off the induced waves, electrons are confined in the shock transition for an extended period. Gaining energy through the gradient-drift along the motional electric field, electrons could be preaccelerated all the way to injection to DSA at such ICM shocks. Our findings imply that the electron DSA process at weak ICM shocks could explain the origin of radio relics. However, a further investigation of electron acceleration at subcritical shocks with Ms &lt; 2.3 is called for, since the Mach numbers of some observed radio relic shocks derived from radio or X-ray observations are as low as Ms ~ 1.5.

Keywords: Galaxy clusters, Shocks, Cosmic rays
Testing the Limits of Precise Subgiant Characterization with APOGEE and Gaia: Opening a Window to Unprecedented Astrophysical Studies. Given their location on the Hertzsprung-Russell (H-R) diagram, thoroughly characterized subgiant stars can place stringent constraints on a wide range of astrophysical problems. Accordingly, they are prime asteroseismic targets for the Transiting Exoplanet Survey Satellite (TESS) mission. In this work, we infer stellar properties for a sample of 347 subgiants located in the TESS Continuous Viewing Zones, which we select based on their likelihood of showing asteroseismic oscillations. We investigate how well they can be characterized using classical constraints (photometry, astrometry) and validate our results using spectroscopic values. We derive luminosities, effective temperatures, and radii with mean 1σ random (systematic) uncertainties of 4.5% (2%), 33 K (60 K), and 2.2% (2%), as well as more model-dependent quantities such as surface gravities, masses, and ages. We use our sample to demonstrate that subgiants are ideal targets for mass and age determination based on H-R diagram location alone, discuss the advantages of stellar parameters derived from a detailed characterization over widely available catalogs, show that the generally used 3D extinction maps tend to overestimate the extinction for nearby stars (distance ≲500 pc), and find a correlation that supports the rotation-activity connection in post-main-sequence stars. The complementary roles played by classical and asteroseismic data sets will open a window to unprecedented astrophysical studies using subgiant stars.

Keywords: Subgiant stars
Searching for Surviving Companion in the Young SMC Supernova Remnant 1E 0102.2-7219. 1E 0102.2-7219 (hereafter E0102) is a young supernova remnant (SNR) in the Small Magellanic Cloud. It contains oxygen-rich SN ejecta, a possible neutron star (NS), and a small amount of fast-moving H-rich ejecta material. These properties are also seen in Cas A; it has thus been suggested that E0102 is also a Type IIb SNR, whose SN progenitor's hydrogen envelope was stripped off possibly via interactions with a companion star. To search for a surviving companion of E0102's SN progenitor, we have used archival Hubble Space Telescope (HST) continuum images to make photometric measurements of stars projected in the SNR to construct color-magnitude diagrams and compare the stars with those expected from surviving companions of Type IIb SNe. We have also used the Multi-Unit Spectroscopic Explorer observations taken with the Very Large Telescope to perform spectroscopic analyses of stars and search for peculiar radial velocities as diagnostics of surviving companions. We further use the HST and Gaia data to inspect proper motions of stars for complementary kinetic studies. No plausible companion candidates are found if the SN explosion site was near the NS, while the B3 V star 34a may be a plausible companion candidate if the SN explosion site is near the SN ejecta's expansion center. If the NS is real and associated with E0102, it needs a ~1000 km s-1 runaway velocity, which has been observed in other SNRs and can be acquired from an asymmetric SN explosion or a kick by the SN explosion of a massive companion.

Keywords: Type II supernovae, Massive stars, Small Magellanic Cloud, Supernova remnants, Companion stars, Magellanic Clouds
CHAOS. VI. Direct Abundances in NGC 2403. We report the direct abundances for the galaxy NGC 2403 as observed by the CHemical Abundances Of Spirals (CHAOS) project. Using the Multi-Object Double Spectrograph on the Large Binocular Telescope, we observe two fields with H II regions that cover an Rg/Re range of 0.18-2.31. Thirty-two H II regions contain at least one auroral line detection, and we detect a total of 122 temperature-sensitive auroral lines. Here, for the first time, we use the intrinsic scatter in the Te-Te diagrams, added in quadrature to the uncertainty on the measured temperature, to determine the uncertainty on an electron temperature inferred for one ionization zone from a measurement in a different ionization zone. We then use all available temperature data within a H II region to obtain a weighted-average temperature within each ionization zone. We rederive the oxygen abundances of all CHAOS galaxies using this new temperature prioritization method, and we find that the gradients are consistent with the results of a recent study of Berg et al. For NGC 2403, we measure a direct oxygen abundance gradient of -0.09(±0.03) dex/Re, with an intrinsic dispersion of 0.037(±0.017) dex and a N/O abundance gradient of -0.17(±0.03) dex/Re with an intrinsic dispersion of 0.060(±0.018) dex. For direct comparison, we use the line intensities from an earlier study of NGC 2403 by Berg et al. and find their recomputed values for the O/H and N/O gradients are consistent with ours.

Keywords: Spiral galaxies, Chemical abundances, Galaxy evolution, Interstellar medium, H II regions
Collisional Growth and Fragmentation of Dust Aggregates with Low Mass Ratios. I. Critical Collision Velocity for Water Ice. We investigated fundamental processes of collisional sticking and fragmentation of dust aggregates by carrying out N-body simulations of submicron-sized icy dust monomers. We examined the conditions for collisional growth of two colliding dust aggregates in a wide range of the mass ratio 1-64. We found that the mass transfer from a larger dust aggregate to a smaller one is a dominant process in collisions with a mass ratio of 2-30 and an impact velocity of ≈30-170 m s-1. As a result, the critical velocity, vfra, for fragmentation of the largest body is considerably reduced for such unequal-mass collisions; vfra of collisions with a mass ratio of 3 is about half of that obtained from equal-mass collisions. The impact velocity is generally higher for collisions between dust aggregates with higher mass ratios because of the difference between the radial drift velocities in the typical condition of protoplanetary disks (PPDs). Therefore, the reduced vfra for unequal-mass collisions would delay growth of dust grains in the inner region of PPDs.

Keywords: Interstellar dust, Protoplanetary disks, N-body simulations
The Coupling of Galactic Dark Matter Halos with Stellar Bars. Resonant torques couple stellar bars to dark matter halos. Here we use high-resolution numerical simulations to demonstrate long-term angular momentum transfer between stellar bars and dark matter orbits of varying orientation. We show that bar-driven reversals of dark matter orbit orientations can play a surprisingly large role in the evolution of the bar pattern speed. In predominantly prograde (corotating) halos, dark matter orbits become trapped in the stellar bar, forming a parallel dark matter bar. This dark matter bar reaches more than double the vertical height of the stellar bar. In halos dominated by retrograde orbits, a dark matter wake forms oriented perpendicular to the stellar bar. These dark matter overdensities provide a novel space to look for dark matter annihilation or decay signals. We predict that the Milky Way hosts a dark matter bar aligned with the stellar bar as well as a dark matter wake, the near side of which should extend from the Galactic center to a galactic longitude of l ≈ 323°.

Keywords: Galaxy dark matter halos, Computational astronomy, Barred spiral galaxies