Sazuna/UAT_keywords huggingface dataset:
On the Origin of Metal-poor Stars in the Solar Neighborhood. We determined the ages, kinematic parameters, and Galactic orbital parameters of six metal-poor (-2.4 &lt; [Fe/H] &lt; -1.0 dex), F-type, high-proper-motion (HPM) stars to investigate their HPM nature and origin. For the kinematical procedure, the astrometric data from the Gaia DR2 were used. High-resolution ELODIE spectra of the six dwarfs were also used to obtain accurate [Fe/H] abundances and up-to-date [α/Fe] abundances. The calculations for stellar ages were based on Bayesian statistics, with the computed ages falling in the range 9.5-10.1 Gyr. On the basis of the metallicities and ages, six HMP stars are either members of the halo (HD 6755, HD 84937, BD +42 3607) or members of the low-metallicity tail of the thick disk (HD 3567, HD 194598, HD 201891). However, Galactic orbital parameters suggest thin disk (HD 84937, HD 194598), thick disk (HD 3567, HD 201891), and halo (HD 6755, BD +42 3607) populations. The dynamical analysis was also performed for the escape scenario from the candidate GCs. The tidal disruption of a dwarf galaxy was also considered as an alternative origin. HD 6755, HD 194598, and HD 3567, with their retrograde orbital motions, are likely candidate stars for a tidally disrupted dwarf galaxy origin. However, the relationship of HD 194598 with NGC 6284 presents an interesting case. Its encounter velocity is low (16 ± 28 km s-1), and their ages and metallicities are very nearly consistent with each other at the 1σ level. The rest of the HPM sample stars have a 4%-18% probability of encountering with selected GCs for 1.5 tidal radii. This indicates that a globular cluster origin for the program stars is unlikely.

Keywords: Stellar kinematics, Stellar abundances, Chemical abundances, Solar neighborhood, High-velocity stars, Halo stars, Stellar associations
'Oumuamua's Rotation with the Mechanical Torque Produced by Interstellar Medium. The first interstellar object 'Oumuamua was discovered in 2017. When 'Oumuamua travels in interstellar space, it keeps colliding with the interstellar medium (ISM). Given a sufficiently long interaction time, its rotation state may change significantly because of the angular momentum transfer with the interstellar medium. Using generated Gaussian random spheres with dimension ratios 6:1:1 and 5:5:1, this paper explores the ISM torque curve and proposes that ISM collision may account for 'Oumuamua's tumbling with the simple constant-torque analytical method. The statistic results show that the asymptotic obliquities distribute mostly at 0° and 180° and most cases spin down at the asymptotic obliquity, indicating that the ISM collision effect is similar to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect with zero heat conductivity assumed. Given a long time of deceleration of the spin rate, an initial major-axis rotation may evolve into tumbling motion under ISM torque. Using a constant-torque analytical model, the timescales of evolving into tumbling for the sample of 200 shapes are found to range from several gigayears to tens of gigayears, highly dependent on the chosen shape. The mean value is about 8.5 ± 0.5 Gyr for prolate shapes and 7.3 ± 0.4 Gyr for oblate shapes. Rotation of asteroids in the Oort cloud might also be dominated by the ISM collision effect since the YORP effect is quite weak at such a long distance from the Sun. Although this paper assumes an ideal mirror reflection and a constant relative velocity of 'Oumuamua, the results still show the importance of the ISM collision effect.

Keywords: Asteroids, Oort cloud objects, Diffuse interstellar clouds
Effects of Superthermal Plasmas on the Linear Growth of Multiband EMIC Waves. Observations show that particle velocity distributions in space plasmas generally exhibit a non-Maxwellian high-energy tail that can be well fitted with kappa distributions. To better understand the correlation between realistic particle velocity distributions and plasma wave excitation, we investigate the linear cyclotron instability of multiband electromagnetic ion cyclotron (EMIC) waves in a kappa plasma containing hot anisotropic protons, which provides the free energy for the wave growth. We find that the effects of superthermal plasmas on EMIC wave instability have a strong dependence on the emission band, temperature anisotropy Ahp, and parallel beta βhp of hot protons. For H+ and He+ band EMIC waves, the maximum growth rates exhibit distinct behaviors with the variation of the spectral index κ of kappa distributions for different Ahp values. The maximum growth rates decrease with increasing κ-value for low Ahp and increase with increasing κ-value for high Ahp. For O+ band waves, the effects of superthermal plasmas on the maximum growth rate are strongly controlled by βhp. For low βhp, the growth rate decreases monotonically with increasing κ-value for all Ahp. For high βhp, increase of κ-value tends to enhance the wave growth for intermediate Ahp and to suppress the wave growth otherwise. Our results also indicate that the presence of a high-energy tail tends to decrease the real frequency corresponding to the maximum growth rate for all three bands. While the minimum electron resonant energy for O+ band EMIC waves decreases as the κ-value increases, the minimum electron resonant energies for H+ and He+ band waves remain unaffected.

Keywords: Van Allen radiation belts, Planetary magnetospheres, Space plasmas
Relativistic Reflection and Reverberation in GX 339-4 with NICER and NuSTAR. We analyze seven Neutron Star Interior Composition Interior Explorer (NICER) and Nuclear Spectroscopic Telescope Array epochs of the black hole X-ray binary GX 339-4 in the hard state during its two most recent hard-only outbursts in 2017 and 2019. These observations cover the 1-100 keV unabsorbed luminosities between 0.3% and 2.1% of the Eddington limit. With NICER's negligible pileup, high count rate, and unprecedented time resolution, we perform a spectral-timing analysis and spectral modeling using relativistic and distant reflection models. Our spectral fitting shows that as the inner disk radius moves inward, the thermal disk emission increases in flux and temperature, the disk becomes more highly ionized, and the reflection fraction increases. This coincides with the inner disk increasing its radiative efficiency around ∼1% Eddington. We see a hint of the hysteresis effect at ∼0.3% of Eddington; the inner radius is significantly truncated during the rise (&gt;49Rg), while only a mild truncation (∼5Rg) is found during the decay. At higher frequencies (2-7 Hz) in the highest-luminosity epoch, a soft lag is present whose energy dependence reveals a thermal reverberation lag with an amplitude similar to previous findings for this source. We also discuss the plausibility of the hysteresis effect and the debate of the disk truncation problem in the hard state.

Keywords: X-ray astronomy, Black holes, High energy astrophysics, Stellar mass black holes, Low-mass x-ray binary stars, Astrophysical black holes
Detailed Calculations of the Efficiency of Planetesimal Accretion in the Core-accretion Model. We present the results of a study of the accretion rate of planetesimals by a growing proto-Jupiter in the core-accretion model. The purpose of our study is to test the assumptions of Pollack et al. regarding the flux of planetesimals and their encounter velocities with the protoplanet. Using a newly developed code, we have accurately calculated planetesimals trajectories during their passage in the envelope by combining detailed three-body integrations with gas drag. To be consistent with Pollack et al., our calculations do not include the effect of nebular gas. The results point to several new findings. For instance, we find that only 4-5 M⊕ is accreted in the first 1.5 Myr before the onset of rapid gas accretion and ∼10 M⊕ is accreted simultaneously during this phase. We also find that mass accretion remains small (0.3-0.4 M⊕) for ∼1 Myr after this time. This late accretion, together with a rapid infall of gas, could lead to a mixing of accreted material throughout the outer regions, which may explain the enhancement of high-Z material in Jupiter's envelope. Results demonstrate that planetesimal encounters with the protoplanetary envelope become so fast that in most cases, ram pressure breaks them up. As a result, the accretion rate is largely independent of the planetesimals' size and composition. We also carried out some calculations considering nebular gas drag. As expected, the accreted mass of planetesimals depended strongly on their size and composition. In general, nebular gas lowered the amount of accreted planetesimals, although the majority of planetesimals were still accreted during the rapid gas accretion phase.

Keywords: Planet formation, Jupiter, Planetesimals
New Conductive Opacities for White Dwarf Envelopes. Thanks to their continuous cooling and relative simplicity, white dwarf stars are routinely used to measure the ages of stellar populations. The usefulness of white dwarfs as cosmochronometers depends on the availability of accurate cooling models. A key ingredient of those models is conductive opacities, which largely govern the cooling rate. In this work, we present improved conductive opacities for the regime of moderate coupling and moderate degeneracy that characterizes an important portion of the envelopes of DA and DB white dwarfs. We find differences of up to a factor of 3 between our calculations and the commonly used opacities of Cassisi et al., which we attribute to an improved account of electron-electron scattering. The cooling models are strongly affected by those changes in the conductive opacities: the age of a 4000 K white dwarf can be reduced by as much as 2 Gyr. We provide analytical fits to our new opacities to facilitate the implementation of this important effect in white dwarf evolution codes.

Keywords: Stellar interiors, White dwarf stars, Stellar evolution
Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and the Implications for CME-CME Interactions. We study the clustering properties of fast coronal mass ejections (CMEs) that occurred during solar cycles 23 and 24. We apply two methods: the Max Spectrum method can detect the predominant clusters, and the declustering threshold time method provides details on the typical clustering properties and timescales. Our analysis shows that during the different phases of solar cycles 23 and 24, CMEs with speeds ≥1000 km s-1 preferentially occur as isolated events and in clusters with, on average, two members. However, clusters with more members appear, particularly during the maximum phases of the solar cycles. Over the total period and in the maximum phases of solar cycles 23 and 24, about 50% are isolated events, 18% (12%) occur in clusters with two (three) members, and another 20% in larger clusters ≥4, whereas in a solar minimum, fast CMEs tend to occur more frequently as isolated events (62%). During different solar cycle phases, the typical declustering timescales of fast CMEs are τc = 28-32 hr, irrespective of the very different occurrence frequencies of CMEs during a solar minimum and maximum. These findings suggest that τc for extreme events may reflect the characteristic energy build-up time for large flare and CME-prolific active regions. Statistically associating the clustering properties of fast CMEs with the disturbance storm time index at Earth suggests that fast CMEs occurring in clusters tend to produce larger geomagnetic storms than isolated fast CMEs. This may be related to CME-CME interaction producing a more complex and stronger interaction with Earth's magnetosphere.

Keywords: Solar corona, Solar coronal mass ejections
Inferring Contributions from Unresolved Point Sources to Diffuse Emissions Measured in UV Sky Surveys: General Method and SOHO/SWAN Case Study. In observations of diffuse emissions like, e.g., the Lyα heliospheric glow, contributions to the observed signal from point sources (e.g., stars) are considered to be a contamination. There are relatively few bright point sources that are usually properly resolved and can be subtracted or masked. We present results of an analysis of the distribution of point sources using UV sky-survey maps from the Solar and Heliospheric Observatory (SOHO)/Solar Wind ANisotropy (SWAN) instrument and spectrophotometry data from the International Ultraviolet Explorer satellite. The estimated distribution suggests that the number of these sources increases with decreasing intensity. Below a certain threshold, these sources cannot be resolved against the diffuse signal from the backscatter glow, that results in a certain physical background from unresolved point sources. Detection, understanding, and subtraction of the point-source background has implications for proper characterization of diffuse emissions and accurate comparison with models. Stars are also often used as standard candles for in-flight calibration of satellite UV observations, thus proper understanding of signal contributions from the point sources is important for the calibration process. We present a general approach to quantify the background radiation level from unresolved point sources in UV sky-survey maps. In the proposed method, a distribution of point sources as a function of their intensity is properly integrated to compute the background signal level. These general considerations are applied to estimate the unresolved-point-source background in the SOHO/SWAN observations that on average amounts to 28.9 R. We also discuss the background radiation anisotropies and general questions related to modeling the point-source contributions to diffuse UV-emission observations.

Keywords: Solar ultraviolet emission, Galaxy properties, Heliosphere, Ultraviolet surveys, Interstellar medium
Near-infrared [ {Fe} {II} ] and H<SUB>2</SUB> Line Mapping of the Supernova Remnant IC 443 with the IRSF/SIRIUS. We investigate properties of the interstellar medium (ISM) interacting with shocks around the Galactic supernova remnant IC 443, using the results of near-infrared [Fe II] and H2 line mapping with the InfraRed Survey Facility/Simultaneous Infrared Imager for Unbiased Survey. In the present study, we newly performed H2 1-0 S(1) and 2-1 S(1) line mapping with the narrowband filters tuned for these lines, covering the entire remnant ( $30^{\prime} \times \ 35^{\prime} $ ). Combined with an [Fe II] line map, our result shows that the H2 line emission is significantly detected in the southern region, while the [Fe II] line emission is detected all over the remnant, suggesting that slow and fast shocks propagate through the southern region and the entire remnant, respectively. In particular, the H2 line emission is relatively strong compared to the [Fe II] line emission in the southwestern region, where TeV γ-ray emission is detected. As the strong H2 line emission indicates the dominance of the dense ISM, this result supports the scenario that the γ-ray emission is likely to be produced through a heavy interaction between cosmic-ray protons and the dense ISM in the southwestern shell. We also find that the H2 and [Fe II] line emissions show an anti-correlated spatial distribution in the same region, suggesting the presence of the clumpy ISM. Such a clumpy morphology of the ISM around IC 443 may assist cosmic-ray protons to efficiently interact with large amounts of the ISM protons.

Keywords: Supernova remnants, Cosmic rays, Infrared astronomy
S62 and S4711: Indications of a Population of Faint Fast-moving Stars inside the S2 Orbit—S4711 on a 7.6 yr Orbit around Sgr A*. We present high-pass filtered NACO and SINFONI images of the newly discovered stars S4711-S4715 between 2004 and 2016. Our deep H+K-band (SINFONI) and K-band (NACO) data show the S-cluster star S4711 on a highly eccentric trajectory around Sgr A* with an orbital period of 7.6 yr and a periapse distance of 144 au to the supermassive black hole (SMBH). S4711 is hereby the star with the shortest orbital period and the smallest mean distance to the SMBH during its orbit to date. The used high-pass filtered images are based on coadded data sets to improve the signal to noise. The spectroscopic SINFONI data let us determine detailed stellar properties of S4711 like the mass and the rotational velocity. The faint S-cluster star candidates, S4712-S4715, can be observed in a projected distance to Sgr A* of at least temporarily ≤120 mas. From these stars, S4714 is the most prominent, with an orbital period of 12 yr and an eccentricity of 0.985. The stars S4712-S4715 show similar properties, with magnitudes and stellar masses comparable to those of S4711. The MCMC simulations determine confidently precise uncertainties for the orbital elements of S62 and S4711-S4715. The presence of S4711 in addition to S55, S62, and the also newly found star S4714 implies a population of faint stars that can be found at distances to Sgr A* that are comparable to the size of our solar system. These short orbital time period stars in the dense cluster around the SMBH in the center of our Galaxy are perfect candidates to observe gravitational effects such as the periapse shift.

Keywords: Relativistic stars, B stars, Galactic center, Black holes, Milky Way Galaxy
Early Ultraviolet Observations of Type IIn Supernovae Constrain the Asphericity of Their Circumstellar Material. We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. We use this survey to constrain the geometry of the circumstellar material (CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical CSM, we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher-luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% for the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common—consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modeling of these events.

Keywords: Supernovae
Kinetic Simulations of Radiative Magnetic Reconnection in the Coronae of Accreting Black Holes. We perform 2D and 3D particle-in-cell simulations of reconnection in magnetically dominated e± plasmas subject to strong Compton cooling. Magnetic reconnection under such conditions can operate in accretion disk coronae around black holes, which produce hard X-rays through Comptonization. Our simulations show that most of the plasma in the reconnection layer is kept cold by Compton losses and locked in magnetically dominated plasmoids with a small thermal pressure. Compton drag clears cavities inside plasmoids and also affects their bulk motions. These effects, however, weakly change the reconnection rate and the plasmoid size distribution from those in nonradiative reconnection. This demonstrates that the reconnection dynamics is governed by similar magnetic stresses in both cases and weakly affected by thermal pressure. We examine the energy distribution of particles energized by radiative reconnection and observe two distinct components: (1) A mildly relativistic peak, which results from bulk motions of cooled plasmoids. This component receives most of the dissipated reconnection power and dominates the output X-ray emission. The peak has a quasi-Maxwellian shape with an effective temperature of ∼100 keV. Thus, it mimics thermal Comptonization used previously to fit hard-state spectra of accreting black holes. (2) A high-energy tail, which receives ∼20% of the dissipated reconnection power. It is populated by particles accelerated impulsively at X-points or "picked up" by fast outflows from X-points. The high-energy particles immediately cool, and their inverse Compton emission explains the MeV spectral tail detected in the hard state of Cyg X-1. Our first-principle simulations support magnetic reconnection as a mechanism powering hard X-ray emission from magnetically dominated regions of accreting black holes.

Keywords: Accretion, Solar magnetic reconnection, Relativistic jets, Stellar accretion disks, Astrophysical black holes, Relativistic disks
The Role of Clouds on the Depletion of Methane and Water Dominance in the Transmission Spectra of Irradiated Exoplanets. Observations suggest an abundance of water and a paucity of methane in the majority of observed exoplanetary atmospheres. We isolate the effect of atmospheric processes to investigate possible causes. Previously, we studied the effect of effective temperature, surface gravity, metallicity, carbon-to-oxygen ratio, and stellar type assuming cloud-free thermochemical equilibrium and disequilibrium chemistry. However, under these assumptions, methane remains a persisting spectral feature in the transmission spectra of exoplanets over a certain parameter space, the Methane Valley. In this work, we investigate the role of clouds on this domain and we find that clouds change the spectral appearance of methane in two direct ways: (1) by heating up the photosphere of colder planets and (2) by obscuring molecular features. The presence of clouds also affects methane features indirectly: (1) cloud heating results in more evaporation of condensates and hence releases additional oxygen, causing water-dominated spectra of colder carbon-poor exoplanets, and (2) HCN/CO production results in a suppression of depleted methane features by these molecules. The presence of HCN/CO and a lack of methane could be an indication of cloud formation on hot exoplanets. Cloud heating can also deplete ammonia. Therefore, a simultaneous depletion of methane and ammonia is not unique to photochemical processes. We propose that the best targets for methane detection are likely to be massive but smaller planets with a temperature around 1450 K orbiting colder stars. We also construct Spitzer synthetic color maps and find that clouds can explain some of the high-contrast observations by IRAC's channel 1 and 2.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheres
The Dynamic Proto-atmospheres around Low-mass Planets with Eccentric Orbits. Protoplanets are able to accrete primordial atmospheres when embedded in the gaseous protoplanetary disk. The formation and structure of the proto-atmosphere are subject to the planet-disk environment and orbital effects. In particular, when planets are on eccentric orbits, their velocities relative to the gas can exceed the sound speed. The planets generate atmosphere-stripping bow shocks. We investigate the proto-atmospheres on low-mass planets with eccentric orbits with radiation-hydrodynamics simulations. A 2D radiative model of the proto-atmosphere is established with tabulated opacities for the gas and dust. The solutions reveal large-scale gas recycling inside a bow shock structure. The atmospheres on eccentric planets are typically three to four orders of magnitude less massive than those on planets with circular orbits. Overall, however, a supersonic environment is favorable for planets to keep an early stable atmosphere, rather than harmful, due to the steady gas supply through the recycling flow. We also quantitatively explore how such atmospheres are affected by the planet's velocity relative to the gas, the planet mass, and the background gas density. Our time-dependent simulations track the orbital evolution of the proto-atmosphere with the planet-disk parameters changing throughout the orbit. Atmospheric properties show oscillatory patterns as the planet travels on an eccentric orbit, with a lag in phase. To sum up, low-mass eccentric planets can retain small proto-atmospheres despite the stripping effects of bow shocks. The atmospheres are always connected to and interacting with the disk gas. These findings provide important insights into the impacts of migration and scattering on planetary proto-atmospheres.

Keywords: Planet formation, Elliptical orbits, Planetary atmospheres, Hydrodynamics