Sazuna/UAT_keywords huggingface dataset:
Statistical and Observational Research on Solar Flare EUV Spectra and Geometrical Features. We performed statistical analysis on the flare emission data to examine parameters related to the flare extreme-ultraviolet (EUV) spectra. This study used the data from the Geostationary Operational Environmental Satellite X-ray Sensors to determine the fundamental flare parameters. The relationship between soft X-ray data and EUV emission data observed by the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory (SDO) MEGS-A was investigated for 50 events. The results showed the hotter Fe line emissions have strong correlation with soft X-ray data in many cases. However, our statistical study revealed that EUV flare peak flux of Fe XV, Fe XVI and He II lines have weak correlation with soft X-ray peak flux. In EUV line light curves, there was time difference in peak time, however the tendency to reach the peak in order from the hotter line to cooler line was not so clear. These results indicate that the temporal evolution of EUV emission can be roughly explained by soft X-ray data. However, the time changes of temperature and density distributions in the flare loop must be needed for accurate reproduction. Moreover, we compared the geometrical features of solar flares observed by the Atmospheric Imaging Assembly on board the SDO with the fundamental flare parameters for 32 events. The ribbon distance strongly correlated with both soft X-ray flare rise and decay times. This results indicate that the geometrical feature is essential parameter for predicting flare emission duration.

Keywords: Solar flares, Solar flare spectra
The Nonstandard Properties of a "Standard" PWN: Unveiling the Mysteries of PWN G21.5-0.9 Using Its IR and X-Ray Emission. The evolution of a pulsar wind nebula (PWN) depends on properties of the progenitor star, supernova, and surrounding environment. As some of these quantities are difficult to measure, reproducing the observed dynamical properties and spectral energy distribution (SED) with an evolutionary model is often the best approach to estimating their values. G21.5-0.9, powered by the pulsar J1833-1034, is a well observed PWN for which previous modeling efforts have struggled to reproduce the observed SED. In this study, we reanalyze archival infrared (IR; Herschel, Spitzer) and X-ray (Chandra, NuSTAR, Hitomi) observations. The similar morphology observed between IR line and continuum images of this source indicates that a significant portion of this emission is generated by surrounding dust and gas, and not synchrotron radiation from the PWN. Furthermore, we find that the broadband X-ray spectrum of this source is best described by a series of power laws fit over distinct energy bands. For all X-ray detectors, we find significant softening and decreasing unabsorbed flux in higher energy bands. Our model for the evolution of a PWN is able to reproduce the properties of this source when the supernova ejecta has a low initial kinetic energy Esn ≍ 1.2 × 1050 erg and the spectrum of particles injected into the PWN at the termination shock is softer at low energies. Lastly, our hydrodynamical modeling of the supernova remnant can reproduce its morphology if there is a significant increase in the density of the ambient medium ∼1.8 pc north of the explosion center.

Keywords: Supernova remnants, Infrared astronomy, X-ray astronomy, Pulsars
How Well Can We Measure the Stellar Mass of a Galaxy: The Impact of the Assumed Star Formation History Model in SED Fitting. The primary method for inferring the stellar mass (M*) of a galaxy is through spectral energy distribution (SED) modeling. However, the technique rests on assumptions such as the galaxy star formation history (SFH) and dust attenuation law that can severely impact the accuracy of derived physical properties from SED modeling. Here we examine the effect that the assumed SFH has on the stellar properties inferred from SED fitting by ground-truthing them against mock observations of high-resolution cosmological hydrodynamic galaxy formation simulations. Classically, SFHs are modeled with simplified parameterized functional forms, but these forms are unlikely to capture the true diversity of galaxy SFHs and may impose systematic biases with underreported uncertainties on results. We demonstrate that flexible nonparametric SFHs outperform traditional parametric forms in capturing variations in galaxy SFHs and, as a result, lead to significantly improved stellar masses in SED fitting. We find a decrease in the average bias of 0.4 dex with a delayed-τ model to a bias under 0.1 dex for the nonparametric model, though this is heavily dependent on the choice of prior for the nonparametric model. Similarly, using nonparametric SFHs in SED fitting results in increased accuracy in recovered galaxy star formation rates and stellar ages.

Keywords: Hydrodynamical simulations, Astronomy data modeling, Galaxy properties, Spectral energy distribution, Stellar masses, Radiative transfer simulations
The Spatially Resolved Bipolar Nebula of Sakurai's Object. II. Mapping the Planetary Nebula Expansion. Observations of the ejecta from the final flash (FF) of helium shell burning in Sakurai's Object (V4334 Sgr) are presented for 2015-2019, a period ∼20-24 yr after discovery. Adaptive optics images at Ks trace the expanding debris. While most of the ejecta mass is in ∼200 K dust, a small fraction, ∼0.4%, of the dust mass is at ∼760 K. The 760 K continuum dominates the near-IR images. Spatial-spectral images in He I 10830 Å show an ∼1"6 diameter bipolar planetary nebula at position angle 21° ± 5° with the SW moving toward us and the NE moving away. Seen in integrated light, the nebula is nearly circular. Near-IR continuum images show ejecta moving radially away from a bright central point source. High-resolution mid-IR spectra reveal molecular hydrocarbon lines with an expansion velocity of 270 ± 5 km s-1 seen in absorption against the dust continuum. The hydrocarbons originate in material produced in the FF. The bipolar nebula and debris clouds are discussed in the context of a highly inclined disk model. The proper motion has been measured placing V4334 Sgr in the thick disk population. There is no evidence that a hot white dwarf Wolf-Rayet ([WR]) wind has emerged; no [WR] spectral features were detected. The possibility of a binary companion involved in the evolution is discussed.

Keywords: Protoplanetary nebulae
The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics. We present a public catalog of transients from the Zwicky Transient Facility (ZTF) Bright Transient Survey, a magnitude-limited (m &lt; 19 mag in either the g or r filter) survey for extragalactic transients in the ZTF public stream. We introduce cuts on survey coverage, sky visibility around peak light, and other properties unconnected to the nature of the transient, and show that the resulting statistical sample is spectroscopically 97% complete at &lt;18 mag, 93% complete at &lt;18.5 mag, and 75% complete at &lt;19 mag. We summarize the fundamental properties of this population, identifying distinct duration-luminosity correlations in a variety of supernova (SN) classes and associating the majority of fast optical transients with well-established spectroscopic SN types (primarily SN Ibn and II/IIb). We measure the Type Ia SN and core-collapse (CC) SN rates and luminosity functions, which show good consistency with recent work. About 7% of CC SNe explode in very low-luminosity galaxies (Mi &gt; -16 mag), 10% in red-sequence galaxies, and 1% in massive ellipticals. We find no significant difference in the luminosity or color distributions between the host galaxies of SNe Type II and SNe Type Ib/c, suggesting that line-driven wind stripping does not play a major role in the loss of the hydrogen envelope from their progenitors. Future large-scale classification efforts with ZTF and other wide-area surveys will provide high-quality measurements of the rates, properties, and environments of all known types of optical transients and limits on the existence of theoretically predicted but as yet unobserved explosions. * An interactive catalog with all data used in this paper is available at https://sites.astro.caltech.edu/ztf/bts and is updated in real time.

Keywords: Surveys, Transient sources, Time domain astronomy, Supernovae, Catalogs
On the Reliability of Photometric and Spectroscopic Tracers of Halo Relaxation. We characterize the relaxation state of galaxy systems by providing an assessment of the reliability of the photometric and spectroscopic probe via the semianalytic galaxy evolution model. We quantify the correlations between the dynamical age of simuglated galaxy groups and popular proxies of halo relaxation in observation, which are mainly either spectroscopic or photometric. We find the photometric indicators demonstrate a stronger correlation with the dynamical relaxation of galaxy groups compared to the spectroscopic probes. We take advantage of the Anderson Darling statistic (A2) and the velocity segregation ( $\overline{{\rm{\Delta }}V}$ ) as our spectroscopic indicators, and use the luminosity gap (∆m12) and the luminosity decentering (Doffset) as photometric ones. First, we find that a combination of ∆m12 and Doffset evaluated by a bivariant relation ( ${\rm{B}}=0.04\times {\rm{\Delta }}{m}_{12}-0.11\times \mathrm{Log}({D}_{\mathrm{off}-\mathrm{set}})+0.28$ ) shows a good correlation with the dynamical age compared to all other indicators. Second, by using the observational X-ray surface brightness map, we show that the bivariant relation brings about some acceptable correlations with X-ray proxies. These correlations are as well as the correlations between A2 and X-ray proxies, offering a reliable yet fast and economical method of quantifying the relaxation of galaxy systems. This study demonstrates that using photometric data to determine the relaxation status of a group will lead to some promising results that are comparable with the more expensive spectroscopic counterpart.

Keywords: Galaxy clusters, Galactic and extragalactic astronomy, Galaxy groups, Sloan photometry, N-body simulations
ALMA and VLA Observations of EX Lupi in Its Quiescent State. Extreme outbursts in young stars may be a common stage of pre-main-sequence stellar evolution. These outbursts, caused by enhanced accretion and accompanied by increased luminosity, can also strongly impact the evolution of the circumstellar environment. We present Atacama Large Millimeter Array (ALMA) and Very Large Array observations of EX Lupi, a prototypical outburst system, at 100, 45, and 15 GHz. We use these data, along with archival ALMA 232 GHz data, to fit radiative transfer models to EX Lupi's circumstellar disk in its quiescent state following the extreme outburst in 2008. The best-fit models show a compact disk with a characteristic dust radius of 45 au and a total mass of 0.01 M☉. Our modeling suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred by the recent outburst, and an ice line that has migrated inward to 0.2-0.3 au post-outburst. At 15 GHz, we detected significant emission over the expected thermal disk emission which we attribute primarily to stellar (gyro)synchrotron and free-free disk emission. Altogether, these results highlight what may be a common impact of outbursts on the circumstellar dust.

Keywords: FU Orionis stars, Millimeter astronomy, Radio continuum emission, Pre-main sequence stars, Protoplanetary disks, Stellar accretion disks, Radio interferometry
Implications of Grain Size Distribution and Composition for the Correlation between Dust Extinction and Emissivity. We study the effect of variations in dust size distribution and composition on the correlation between the spectral shape of extinction (parameterized by RV) and far-infrared dust emissivity (parameterized by the power-law index β). Starting from the size distribution models proposed by Weingartner &amp; Draine, using the dust absorption and emission properties derived by Laor &amp; Draine for carbonaceous and silicate grains, and by Li &amp; Draine for polycyclic aromatic hydrocarbon grains, we calculate the extinction and compare it with the reddening vector derived by Schlafly et al. An optimizer and an Markov chain Monte Carlo method are used to explore the space of available parameters for the size distributions. We find that larger grains are correlated with high RV. However, this trend is not enough to explain the emission-extinction correlation observed by Schlafly et al. For the RV - β correlation to arise, we need to impose explicit priors for the carbonaceous and silicate volume priors as functions of RV. The results show that a composition with higher ratio of carbonaceous to silicate grains leads to higher RV and lower β. A relation between E(B - V)/τ353 and RV is apparent, with possible consequences for the recalibration of emission-based dust maps as a function of RV.

Keywords: Silicate grains, Polycyclic aromatic hydrocarbons, Interstellar dust extinction, Interstellar absorption, Carbonaceous grains, Interstellar medium, Interstellar dust processes, Interstellar scattering
The Possibility of the Secondary Object in GW190814 as a Neutron Star. A compact object was observed with a mass of $2.50\mbox{--}2.67\,{M}_{\odot }$ by LIGO Scientific and Virgo collaborations (LVC) in GW190814, which provides a great challenge to investigations of supranuclear matter. To study this object, the properties of the neutron star are systematically calculated within the latest density-dependent relativistic mean-field (DDRMF) parameterizations, which are determined by the ground-state properties of spherical nuclei. The maximum masses of the neutron star calculated by DD-MEX and DD-LZ1 sets can be around $2.55\,{M}_{\odot }$ with quite stiff equations of state generated by their strong repulsive contributions from vector potentials at high densities. Their maximum speeds of sound cs/c are smaller than $\sqrt{0.8}$ at the center of the neutron star, and the dimensionless tidal deformabilities at $1.4\,{M}_{\odot }$ are less than 800. Furthermore, the radii of $1.4\,{M}_{\odot }$ also satisfy the constraint from the observation of simultaneous mass-radius measurements (Neutron star Interior Composition Explorer). Therefore, we conclude that one cannot exclude the possibility of the secondary object in GW190814 as a neutron star composed of hadron matter from DDRMF models.

Keywords: Neutron stars, Nuclear astrophysics, Gravitational wave astronomy, Compact objects
Canonical X-Ray Fluorescence Line Intensities as Column Density Indicators. X-ray line fluorescence is ubiquitous around powerful accretion sources, namely, active galactic nuclei and X-ray binaries. The brightest and best-studied line is the Fe Kα line at λ = 1.937 Å(6.4 keV). This paper presents a survey of all well-measured Chandra/HETG grating spectra featuring several Kα fluorescence lines from elements between Mg and Ni. Despite the variety of sources and physical conditions, we identify a common trend that dictates the Kα line intensity ratios between elements. For the most part, the line intensities are well described by a simple, plane-parallel approximation of a near-neutral, solar-abundance, high column density (NH &gt; 1024 cm-2) medium. This approximation gives canonical photon-intensity line ratios for the Kα fluorescence of all elements, e.g., 0.104:0.069:1.0:0.043 for Si:S:Fe:Ni, respectively. Deviations from these ratios are shown to be primarily due to excess column density along the line of sight beyond the Galactic column. Therefore, measured fluorescence line ratios provide an independent estimate of NH and insight into the environment of accretion sources. Residual discrepancies with the canonical ratios could be due to a variety of effects such as a fluorescing medium with NH &lt; 1024 cm-2, a non-neutral medium, variations in the illuminating spectrum, nonsolar abundances, or an irregular source geometry. However, evidently and perhaps surprisingly, these are uncommon, and their effect remains minor.

Keywords: X-ray active galactic nuclei, High mass x-ray binary stars
The Lyα Emission in Solar Flares. I. A Statistical Study on Its Relationship with the 1-8 ŠSoft X-Ray Emission. We statistically study the relationship between the Lyα and 1-8 Å soft X-ray (SXR) emissions from 658 M- and X-class solar flares observed by the Geostationary Operational Environmental Satellite during 2006-2016. Based on the peak times of the two wave band emissions, we divide the flares into three types. Type I (III) has an earlier (a later) peak time in the Lyα emission than that in the SXR emission, while type II has nearly the same peak time (within the time resolution of 10 s) between the Lyα and SXR emissions. In these 658 flares, we find that there are 505 (76.8%) type I flares, 10 (1.5%) type II flares, and 143 (21.7%) type III flares, and that the three types appear to have no dependence on the flare duration, flare location, or solar cycle. Besides the main peak, the Lyα emission of the three type flares also shows sub-peaks which can appear in the impulsive or gradual phase of the flare. It is found that the main-peak (for type I) and subpeak (for type III) emissions of Lyα that appear in the impulsive phase follow the Neupert effect in general. This indicates that such Lyα emissions are related to the nonthermal electron beam heating. While the main-peak (for type III) and subpeak (for type I) emissions of Lyα that appear in the gradual phase are supposed to be primarily contributed by the thermal plasma that cools down.

Keywords: Solar flares, Solar ultraviolet emission, Solar x-ray emission, Solar corona, Solar activity, Solar chromosphere
Hard X-Ray Excess from the Magnificent Seven Neutron Stars. We report significant hard X-ray excesses in the energy range 2-8 keV for two nearby isolated neutron stars: RX J1856.6-3754 and RX J0420.0-5022. These neutron stars have previously been observed in soft X-rays to have nearly thermal spectra at temperatures ∼100 eV, which are thought to arise from the warm neutron star surfaces. We find nontrivial hard X-ray spectra well above the thermal surface predictions with archival data from the XMM-Newton and Chandra X-ray telescopes. We analyze possible systematic effects that could generate such spurious signals, such as nearby X-ray point sources and pileup of soft X-rays, but we find that the hard X-ray excesses are robust to these systematics to the extent that is possible to test. We also investigate possible sources of hard X-ray emission from the neutron stars and find no satisfactory explanation with known mechanisms, suggesting that a novel source of X-ray emission is at play. We do not find high-significance hard X-ray excesses from the other five Magnificent Seven isolated neutron stars.

Keywords: Neutron stars, X-ray astronomy, Neutron star cores, X-ray point sources, X-ray stars
The Lifetimes of Star Clusters Born with a Top-heavy IMF. Several observational and theoretical indications suggest that the initial mass function (IMF) becomes increasingly top-heavy (i.e., overabundant in high-mass stars with mass $m\gt 1{M}_{\odot }$ ) with decreasing metallicity and increasing gas density of the forming object. This affects the evolution of globular clusters (GCs) owing to the different mass-loss rates and the number of black holes formed. Previous numerical modeling of GCs usually assumed an invariant canonical IMF. Using the state-of-the-art NBODY6 code, we perform a comprehensive series of direct N-body simulations to study the evolution of star clusters, starting with a top-heavy IMF and undergoing early gas expulsion. Utilizing the embedded cluster mass-radius relation of Marks &amp; Kroupa for initializing the models, and by varying the degree of top-heaviness, we calculate the minimum cluster mass needed for the cluster to survive longer than 12 Gyr. We document how the evolution of different characteristics of star clusters such as the total mass, the final size, the density, the mass-to-light ratio, the population of stellar remnants, and the survival of GCs is influenced by the degree of top-heaviness. We find that the lifetimes of clusters with different IMFs moving on the same orbit are proportional to the relaxation time to a power of x that is in the range of 0.8-1. The observed correlation between concentration and the mass function slope in Galactic GCs can be accounted for excellently in models starting with a top-heavy IMF and undergoing an early phase of rapid gas expulsion.

Keywords: Globular star clusters, Stellar mass functions, N-body simulations, Dynamical evolution
Evolution of C IV Absorbers. I. The Cosmic Incidence. We present a large high-resolution study of the distribution and evolution of C IV absorbers, including the weakest population with equivalent widths ${W}_{r}\lt 0.3\,\mathring{\rm A} $ . By searching 369 high-resolution, high signal-to-noise ratio spectra of quasars at $1.1\leqslant {z}_{\mathrm{em}}\leqslant 5.3$ from Keck/HIRES and VLT/UVES, we find 1268 C IV absorbers with ${W}_{r}\geqslant 0.05$ Å (our ∼50% completeness limit) at redshifts $1.0\leqslant z\leqslant 4.75$ . A Schechter function describes the observed equivalent width distribution with a transition from power-law to exponential decline at ${W}_{r}\gtrsim 0.5\,\mathring{\rm A} $ . The power-law slope α rises by ∼7%, and the transition equivalent width W⋆ falls by ∼20% from $\langle z\rangle =1.7$ to 3.6. We find that the comoving redshift path density, ${dN}/{dX}$ , of ${W}_{r}\geqslant 0.05$ Å absorbers rises by ∼1.8 times from z ≃ 4.0 to 1.3, while the ${W}_{r}\geqslant 0.6$ Å ${dN}/{dX}$ rises by a factor of ∼8.5. We quantify the observed evolution by a model in which ${dN}/{dX}$ decreases linearly with increasing redshift. The model suggests that populations with larger ${W}_{r}$ thresholds evolve faster with redshift and appear later in the universe. The cosmological TECHNICOLOR DAWN simulations at z = 3-5 overproduce the observed abundance of absorbers with ${W}_{r}\leqslant 0.3\,\mathring{\rm A} $ while yielding better agreement at higher ${W}_{r}$ . Our empirical linear model successfully describes C IV evolution in the simulations and the observed evolution of ${W}_{r}\geqslant 0.6$ Å C IV for the past $\sim 12\,\mathrm{Gyr}$ . Combining our measurements with the literature gives us a picture of C IV absorbing structures becoming more numerous and/or larger in physical size over the last $\approx 13\,\mathrm{Gyr}$ of cosmic time (z ∼ 6-0).

Keywords: High resolution spectroscopy, Quasar absorption line spectroscopy, Circumgalactic medium, Galaxy evolution, Intergalactic medium