Sazuna/UAT_keywords huggingface dataset:
Formation of Solar Quiescent Coronal Loops through Magnetic Reconnection in an Emerging Active Region. Coronal loops are the building blocks of solar active regions. However, their formation mechanism remains poorly understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge into the solar atmosphere. Extreme-ultraviolet observations by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) clearly show the newly formed loops following magnetic reconnection within a plasma sheet. Formation of the loops is also seen in the Hα line-core images taken by the New Vacuum Solar Telescope. Observations from the Helioseismic and Magnetic Imager on board SDO show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.4 km s-1 before the formation of coronal loops. During the loop formation process, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. The three-dimensional magnetic field structure reconstructed through a magnetohydrostatic model shows field lines consistent with the loops in AIA images. Numerous bright blobs with an average width of 1.37 Mm appear intermittently in the plasma sheet and move upward with a projected velocity of ~114 km s-1. The temperature, emission measure, and density of these blobs are about 3 MK, 2.0 × 1028 cm-5, and 1.2 × 1010 cm-3, respectively. A power spectral analysis of these blobs indicates that the observed reconnection is likely not dominated by a turbulent process. We have also identified flows with a velocity of 20-50 km s-1 toward the footpoints of the newly formed coronal loops.

Keywords: Solar magnetic flux emergence, Solar magnetic reconnection, Solar coronal loops, Solar physics, Solar active regions
Probing Microporous ASW with Near-infrared Spectroscopy: Implications for JWST's NIRSpec. The presence of porous amorphous solid water (ASW) in interstellar ice mantles has long been suspected but, to date, has not been identified. With the upcoming launch of the James Webb Space Telescope (JWST), future detections of porous ASW seem promising. To this end, we investigated the near-infrared spectra of ASW to confirm that two features that have been seen sporadically in literature and have either not been identified or only tentatively identified were indeed due to dangling bond (DB) absorption bands. These bands may provide an additional way to identify porous ASW with remote sensing spectroscopy. Our systematic study tested the thermal stability of these features and their spectral shifts during gas adsorption. We correlated these changes to what we observed in the well-studied fundamental DB absorptions at 3720 and 3696 cm-1. We find excellent agreement between the behavior of the fundamental DB absorption bands with those centered at 5326 and 7235 cm-1, as well as a shoulder located at 7285 cm-1, confirming that all these features are due to DBs present in porous ASW. We estimate that these weaker DB absorptions should be identifiable after 4-5 hr of observation time with JWST's NIRSpec instrument. These new features may not only prove useful in future observational campaigns in search of porous ASW but also may serve as a powerful way to indirectly detect weakly absorbing species that challenge the ability of remote sensing spectroscopy.

Keywords: Solid matter physics, Laboratory astrophysics, Astrochemistry, Surface ices, Interstellar medium, Spectroscopy
Variable Irradiation on 1D Cloudless Eccentric Exoplanet Atmospheres. Exoplanets on eccentric orbits experience an incident stellar flux that can be markedly larger at periastron versus apoastron. This variation in instellation can lead to dramatic changes in atmospheric structure in regions of the atmosphere where the radiative and advective heating/cooling timescales are shorter than the orbital timescale. To explore this phenomenon, we develop a sophisticated one-dimensional (vertical) time-stepping atmospheric structure code, EGP+, capable of simulating the dynamic response of atmospheric thermal and chemical structure to time-dependent perturbations. Critically, EGP+ can efficiently simulate multiple orbits of a planet, thereby providing new opportunities for exoplanet modeling without the need for more computationally expensive models. We make the simplifying assumption of cloud-free atmospheres, and apply our model to HAT-P-2b, HD 17156b, and HD 80606b, which are known to be on higher-eccentricity orbits. We find that for those planets that have Spitzer observations, our planet-to-star ratio predictions are roughly consistent with observations. However, we are unable to reproduce the observed peak offsets from periastron passage. Finally, we discuss promising pathways forward for adding new model complexity that would enable more detailed studies of clear and cloudy eccentric planets as well as worlds orbiting active host stars.

Keywords: Exoplanet dynamics, Exoplanet atmospheres, Exoplanet atmospheric variability, Star-planet interactions, Eccentricity
Spatially Resolved RGS Analysis of Kepler's Supernova Remnant. The distribution and kinematics of the circumstellar medium (CSM) around a supernova remnant (SNR) tell us useful information about the explosion of its natal supernova (SN). Kepler's SNR, the remnant of SN 1604, is widely regarded to be of Type Ia origin. Its shock is moving through a dense, asymmetric CSM. The presence of this dense gas suggests that its parent progenitor system consisted of a white dwarf and an asymptotic giant branch (AGB) star. In this paper, we analyze a new and long observation with the reflection grating spectrometers on board the XMM-Newton satellite, spatially resolving the remnant emission in the cross-dispersion direction. We find that the CSM component is blueshifted with velocities in the general range 0-500 km s-1. We also derive information on the central bar structure and find that the northwest half is blueshifted, while the southeast half is redshifted. Our result is consistent with a picture proposed by previous studies, in which a "runaway" AGB star moved to the north-northwest and toward us in the line of sight, although it is acceptable for both single- and core-degenerate scenarios for the progenitor system.

Keywords: X-ray astronomy
Transport of Protostellar Cosmic Rays in Turbulent Dense Cores. Recent studies have suggested that low-energy cosmic rays (CRs) may be accelerated inside molecular clouds by the shocks associated with star formation. We use a Monte Carlo transport code to model the propagation of CRs accelerated by protostellar accretion shocks through protostellar cores. We calculate the CR attenuation and energy losses and compute the resulting flux and ionization rate as a function of both radial distance from the protostar and angular position. We show that protostellar cores have nonuniform CR fluxes that produce a broad range of CR ionization rates, with the maximum value being up to two orders of magnitude higher than the radial average at a given distance. In particular, the CR flux is focused in the direction of the outflow cavity, creating a "flashlight" effect and allowing CRs to leak out of the core. The radially averaged ionization rates are less than the measured value for the Milky Way of ζ ≈ 10-16 s-1; however, within r ≈ 0.03 pc from the protostar, the maximum ionization rates exceed this value. We show that variation in the protostellar parameters, particularly in the accretion rate, may produce ionization rates that are a couple of orders of magnitude higher or lower than our fiducial values. Finally, we use a statistical method to model unresolved subgrid magnetic turbulence in the core. We show that turbulence modifies the CR spectrum and increases the uniformity of the CR distribution but does not significantly affect the resulting ionization rates.

Keywords: High energy astrophysics, Astrochemistry, Star formation, Ionization, Protostars, Magnetic fields, Cosmic rays
Variations in Finite-difference Potential Fields. The potential field (PF) solution of the solar corona is a vital modeling tool for a wide range of applications, including minimum energy estimates, coronal magnetic field modeling, and empirical solar wind solutions. Given its popularity, it is important to understand how choices made in computing a PF may influence key properties of the solution. Here we study PF solutions for the global coronal magnetic field on 2012 June 13, computed with our high-performance finite-difference code POT3D. Solutions are analyzed for their global properties and locally around NOAA AR 11504, using the net open flux, open-field boundaries, total magnetic energy, and magnetic structure as metrics. We explore how PF solutions depend on (1) the data source, type, and processing of the inner boundary conditions; (2) the choice of the outer boundary condition height and type; and (3) the numerical resolution and spatial scale of information at the lower boundary. We discuss the various qualitative and quantitative differences that naturally arise by using different maps as input, and we illustrate how coronal morphology and open flux depend most strongly on the outer boundary condition. We also show how large-scale morphologies and the open magnetic flux are remarkably insensitive to model resolution, while the surface mapping and embedded magnetic complexity vary considerably. This establishes important context for past, current, and future applications of the PF for coronal and solar wind modeling.

Keywords: Astronomy software, Astronomy data analysis, Solar surface, Solar corona, Solar coronal holes
Longitudinally Resolved Spectral Retrieval (ReSpect) of WASP-43b. Thermal phase variations of short-period planets indicate that they are not spherical cows: day-to-night temperature contrasts range from hundreds to thousands of degrees, rivaling their vertical temperature contrasts. Nonetheless, the emergent spectra of short-period planets have typically been fit using one-dimensional (1D) spectral retrieval codes that only account for vertical temperature gradients. The popularity of 1D spectral retrieval codes is easy to understand: they are robust and have a rich legacy in solar system atmospheric studies. Exoplanet researchers have recently introduced multidimensional retrieval schemes to interpret the spectra of short-period planets, but these codes are necessarily more complex and computationally expensive than their 1D counterparts. In this paper we present an alternative: phase-dependent spectral observations are inverted to produce longitudinally resolved spectra that can then be fit using standard 1D spectral retrieval codes. We test this scheme on the iconic phase-resolved spectra of WASP-43b and on simulated observations for the James Webb Space Telescope (JWST) using the open-source PYRAT BAY 1D spectral retrieval framework. Notably, we take the model complexity of the simulations one step further from previous studies by allowing for longitudinal variations in composition in addition to temperature. We show that performing 1D spectral retrieval on longitudinally resolved spectra is more accurate than applying 1D spectral retrieval codes to disk-integrated emission spectra, even though this is identical in terms of computational load. We find that for the extant Hubble and Spitzer observations of WASP-43b, the difference between the two approaches is negligible, but JWST phase measurements should be treated with longitudinally resolved spectral retrieval (ReSpect).

Keywords: Bayesian statistics, Radiative transfer, Exoplanet atmospheres, Spectroscopy
ALMA Host Galaxy Observation of the Off-axis Gamma-Ray Burst XRF 020903. We investigated the radio properties of the host galaxy of X-ray flash, XRF 020903, which is the best example for investigating the off-axis origin of gamma-ray bursts (GRBs). Dust continuum at 233 GHz and CO are observed using the Atacama Large millimeter/submillimeter array. The molecular gas mass derived by applying the metallicity-dependent CO-to-H2 conversion factor matches the global trend along the redshift and stellar mass of the GRB host galaxies. The estimated gas depletion timescale (pertaining to the potential critical characteristics of GRB host galaxies) is equivalent to those of GRBs and super-luminous supernova hosts in the same redshift range. These properties of the XRF 020903 host galaxy observed in radio resemble those of GRB host galaxies, thereby supporting the identical origin of XRF 020903 and GRBs.

Keywords: Gamma-ray bursts
Star Formation Rate Function at z   4.5: An Analysis from Rest UV to Optical. We present a star formation rate function (SFRF) at z ~ 4.5 based on photometric data from the rest UV to optical of galaxies in the CANDELS GOODS-South field using spectral energy distribution (SED) fitting. We evaluate the incompleteness of our sample and correct for it to properly compare the SFRF in this study with those estimated based on other probes. The SFRF is obtained down to ~10 M⊙ yr-1, and it shows a significant excess compared to that estimated from the UV luminosity function and dust correction based on the UV spectral slope. As compared with the UV-based SFRF, the number density is larger by ~1 dex at a fixed SFR, or the best-fit Schechter parameter of the characteristic SFR, SFR*, is larger by ~1 dex. We extensively examine several assumptions on SED fitting to see the robustness of our result and find that the excess still exists even if the assumptions change such as star formation histories, dust extinction laws, and a one- or two-component model. By integrating our SFRF to 0.22 M⊙ yr-1, the cosmic star formation rate density (CSFRD) at this epoch is calculated to be ${4.53}_{-0.87}^{+0.94}\times {10}^{-2}\ {M}_{\odot }\,{\mathrm{yr}}^{-1}\ {\mathrm{Mpc}}^{-3}$ , which is ~0.25 dex larger than the previous measurement based on UV observations. We also find that galaxies with intensive star formation (&gt;10 M⊙ yr-1) occupy most of the CSFRD (~80%), suggesting that star formation activity at this epoch is dominated by intensively star-forming galaxies.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution
Searching for Dwarf Galaxies in Gaia DR2 Phase-space Data Using Wavelet Transforms. We present a wavelet-based algorithm to identify dwarf galaxies in the Milky Way in Gaia DR2 data. Our algorithm detects overdensities in 4D position-proper-motion space, making it the first search to explicitly use velocity information to search for dwarf galaxy candidates. We optimize our algorithm and quantify its performance by searching for mock dwarfs injected into Gaia DR2 data and for known Milky Way satellite galaxies. Comparing our results with previous photometric searches, we find that our search is sensitive to undiscovered systems at Galactic latitudes ∣b∣ &gt; 20° and with half-light radii larger than the 50% detection efficiency threshold for Pan-STARRS1 (PS1) at (i) absolute magnitudes of -7 &lt; MV &lt; -3 and distances of 32 kpc &lt; D &lt; 64 kpc, and (ii) MV &lt; -4 and 64 kpc &lt; D &lt; 128 kpc. Based on these results, we predict that our search is expected to discover 5 ± 2 new satellite galaxies: four in the PS1 footprint and one outside the Dark Energy Survey and PS1 footprints. We apply our algorithm to the Gaia DR2 data set and recover ~830 high-significance candidates, out of which we identify a "gold standard" list of ~200 candidates based on cross-matching with potential candidates identified in a preliminary search using Gaia EDR3 data. All of our candidate lists are publicly distributed for future follow-up studies. We show that improvements in astrometric measurements provided by Gaia EDR3 increase the sensitivity of this technique; we plan to continue to refine our candidate list using future data releases.

Keywords: Computational methods, Dwarf galaxies, Astrometry, Proper motions
RR Lyrae Stars in Stellar Streams with Gaia: The Escapers. We attempt to identify RR Lyrae (RRL) stars in stellar streams that might have escaped from seven globular clusters (GCs) based on proper motions, distances, color-magnitude diagrams, and other properties extracted from the Gaia Early Data Release 3 (EDR3) database. Specifically, we cross-match two large RRL stars catalogs (from Gaia DR2 and Catalina Sky Survey) with each other and with the EDR3 database, and we end up with a sample of ~150,000 unique RRL stars. We calculate distances to RRL stars using the MG-[Fe/H] and MV-[Fe/H] absolute magnitude-metallicity relations and adopt [Fe/H] values for the GCs from different spectroscopic studies. We also constrain our search to areas where stellar streams associated with GCs were previously suggested or identified in other studies. We identify 24 RRL stars that might have escaped from the following seven GCs: Palomar 13 (Pal 13), NGC 6341 (M92), NGC 5904 (M5), NGC 5466, NGC 1261, NGC 288, and NGC 1851. We list our findings in Table 2.

Keywords: Globular star clusters, Milky Way formation, Galaxy structure, Galaxy tides, Milky Way dynamics, Galaxy tails, RR Lyrae variable stars, Galaxy evolution, Galaxy accretion, Beta Lyrae stars, Milky Way evolution, Milky Way Galaxy
Studies of RR Lyrae Variables in Binary Systems. I. Evidence of a Trimodal Companion Mass Distribution. We present 87 candidates for RR Lyrae variable stars in binary systems, based on our new search using the light-travel time effect (LTTE) and observed - calculated (O - C) diagrams in the Galactic bulge time-series photometry of the Optical Gravitational Lensing Experiment. Out of these, 61 are new candidates, while 26 have been announced previously. Furthermore, 12 stars considered as binary candidates in earlier works are discarded from the list, either because they were found to have O - C diagrams incompatible with the LTTE or because their long-term periodicity is definitely caused by the Blazhko effect. This sample of RR Lyrae binary candidates allows us to draw the first firm conclusions about the population of such objects: no candidate has an orbital period below 1000 days, while their occurrence rate steadily increases with increasing period, and peaks between 3000 and 4000 days; however, the decrease in the number of stars toward even longer periods is probably the result of observational biases. The eccentricities show a very significant concentration between 0.25 and 0.3, with a quarter of candidates found in this single bin, overlaid on an otherwise flat distribution between 0.05 and 0.6. Only six stars have inferred eccentricities above 0.6. Lastly, the distribution of the mass functions is highly peculiar, exhibiting strong trimodality. We interpret these modes as the presence of three distinct groups of companions, with typical inferred masses of ~0.6, ~0.2, and ~0.067 M⊙, which can be associated with populations of white dwarf and main sequence, red dwarf, and brown dwarf companions, respectively.

Keywords: Binary stars, Astronomy data analysis, Stellar astronomy, RR Lyrae variable stars, Stellar masses, Time series analysis
Investigating Cold Dust Properties of 12 Nearby Dwarf Irregular Galaxies by Hierarchical Bayesian Spectral Energy Distribution Fitting. Combining infrared and submillimeter observations and applying a two-temperature modified blackbody (TMBB) model with a hierarchical Bayesian technique, we model the spectral energy distribution of 12 nearby dwarf irregular (dIrr) galaxies. We aim to probe potential submillimeter excess emission at 350, 500, and 850 μm and investigate the properties of cold dust parameters. Based on the TMBB model with cold dust emissivity index (βc) fixed to 2, one galaxy shows 500 μm excess emission and nine galaxies show excess at 850 μm (five of them still show 850 μm excess in the case of free βc). We find that the 850 μm excess emission is easily detected in the dIrr galaxies with low star formation activity. The 850 μm excess is more frequent and more prominent in dIrr galaxies with low molecular hydrogen gas mass fraction or low ratios between cold dust mass and gas mass. As galaxies evolve, the ratios between atomic hydrogen gas mass and stellar mass decrease and the 850 μm excess emission tends to decrease or even disappear. Our results suggest that the cold dust temperature may increase, as the dIrr galaxies have more intense star formation or richer metallicity. There is a weak anticorrelation between the cold dust-to-stellar mass ratio and the specific star formation rate for our galaxies.

Keywords: Interstellar dust, Dwarf irregular galaxies, Submillimeter astronomy, Interstellar medium
Turbulent Generation of Magnetic Switchbacks in the Alfvénic Solar Wind. One of the most important early results from the Parker Solar Probe (PSP) is the ubiquitous presence of magnetic switchbacks, whose origin is under debate. Using a three-dimensional direct numerical simulation of the equations of compressible magnetohydrodynamics from the corona to 40 solar radii, we investigate whether magnetic switchbacks emerge from granulation-driven Alfvén waves and turbulence in the solar wind. The simulated solar wind is an Alfvénic slow-solar-wind stream with a radial profile consistent with various observations, including observations from PSP. As a natural consequence of Alfvén-wave turbulence, the simulation reproduced magnetic switchbacks with many of the same properties as observed switchbacks, including Alfvénic v-b correlation, spherical polarization (low magnetic compressibility), and a volume filling fraction that increases with radial distance. The analysis of propagation speed and scale length shows that the magnetic switchbacks are large-amplitude (nonlinear) Alfvén waves with discontinuities in the magnetic-field direction. We directly compare our simulation with observations using a virtual flyby of PSP in our simulation domain. We conclude that at least some of the switchbacks observed by PSP are a natural consequence of the growth in amplitude of spherically polarized Alfvén waves as they propagate away from the Sun.

Keywords: Space plasmas, Interplanetary turbulence, Solar wind, Alfven waves, Magnetohydrodynamical simulations
IQ Collaboratory. II. The Quiescent Fraction of Isolated, Low-mass Galaxies across Simulations and Observations. We compare three major large-scale hydrodynamical galaxy simulations (EAGLE, Illustris-TNG, and SIMBA) by forward modeling simulated galaxies into observational space and computing the fraction of isolated and quiescent low-mass galaxies as a function of stellar mass. Using SDSS as our observational template, we create mock surveys and synthetic spectroscopic and photometric observations of each simulation, adding realistic noise and observational limits. All three simulations show a decrease in the number of quiescent, isolated galaxies in the mass range M* = 109-10 M⊙, in broad agreement with observations. However, even after accounting for observational and selection biases, none of the simulations reproduce the observed absence of quiescent field galaxies below M* = 109 M⊙. We find that the low-mass quiescent populations selected via synthetic observations have consistent quenching timescales, despite an apparent variation in the late-time star formation histories. The effect of increased numerical resolution is not uniform across simulations and cannot fully mitigate the differences between the simulations and the observations. The framework presented here demonstrates a path toward more robust and accurate comparisons between theoretical simulations and galaxy survey observations, while the quenching threshold serves as a sensitive probe of feedback implementations.

Keywords: Galaxy quenching, Dwarf galaxies, Galaxy evolution, Astronomical simulations