Sazuna/UAT_keywords huggingface dataset:
WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?. We present the discoveries of WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5, two low-temperature (1200-1400 K), high proper motion T-type subdwarfs. Both objects were discovered via their high proper motion (&gt;0"5 yr-1); WISEA J181006.18-101000.5 as part of the NEOWISE proper motion survey and WISEA J041451.67-585456.7 as part of the citizen science project Backyard Worlds; Planet 9. We have confirmed both as brown dwarfs with follow-up near-infrared spectroscopy. Their spectra and near-infrared colors are unique among known brown dwarfs, with some colors consistent with L-type brown dwarfs and other colors resembling those of the latest-type T dwarfs. While no forward model consistently reproduces the features seen in their near-infrared spectra, the closest matches suggest very low metallicities ([Fe/H] $\leqslant $ -1), making these objects likely the first examples of extreme subdwarfs of the T spectral class (esdT). WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5 are found to be part of a small population of objects that occupy the "substellar transition zone," and have the lowest masses and effective temperatures of all objects in this group.

Keywords: T dwarfs, Brown dwarfs, Subdwarf stars, T subdwarfs
On the Relationship between Magnetic Expansion Factor and Observed Speed of the Solar Wind from Coronal Pseudostreamers. For the past 30+ yr, the magnetic expansion factor (fs) has been used in empirical relationships to predict solar wind speed (vobs) at 1 au based on an inverse relationship between these two quantities. Coronal unipolar streamers (i.e., pseudostreamers) undergo limited field line expansion, resulting in fs-dependent relationships to predict the fast wind associated with these structures. However, case studies have shown that the in situ observed pseudostreamer solar wind was much slower than that derived with fs. To investigate this further, we conduct a statistical analysis to determine if fs and vobs are inversely correlated for a large sample of periods when pseudostreamer wind was observed at multiple 1 au spacecraft (i.e., ACE, STEREO-A/B). We use the Wang-Sheeley-Arge model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) photospheric field maps to identify 38 periods when spacecraft observe pseudostreamer wind. We compare the expansion factor of the last open field lines on either side of a pseudostreamer cusp with the corresponding in situ measured solar wind speed. We find that only slow wind (vobs &lt; 500 km s-1) is associated with pseudostreamers and that there is not a significant correlation between fs and vobs for these field lines. This suggests that field lines near the open-closed boundary of pseudostreamers are not subject to the steady-state acceleration along continuously open flux tubes assumed in the fs-vobs relationship. In general, dynamics at the boundary between open and closed field lines such as interchange reconnection will invalidate the steady-state assumptions of this relationship.

Keywords: Solar wind, Solar coronal streamers, Solar corona
Aluminum-26 Enrichment in the Surface of Protostellar Disks Due to Protostellar Cosmic Rays. The radioactive decay of aluminum-26 (26Al) is an important heating source in early planet formation. Since its discovery, there have been several mechanisms proposed to introduce 26Al into protoplanetary disks, primarily through contamination by external sources. We propose a local mechanism to enrich protostellar disks with 26Al through irradiation of the protostellar disk surface by cosmic rays accelerated in the protostellar accretion shock. We calculate the 26Al enrichment, [26Al/27Al ], at the surface of the protostellar disk in the inner au throughout the evolution of low-mass stars, from M-dwarfs to proto-Suns. Assuming constant mass accretion rates, $\dot{m}$ , we find that irradiation by MeV cosmic rays can provide significant enrichment on the disk surface if the cosmic rays are not completely coupled to the gas in the accretion flow. Importantly, we find that low accretion rates, $\dot{m}\lt {10}^{-7}$ M⊙ yr-1, are able to produce canonical amounts of 26Al, ${[}^{26}\mathrm{Al}{/}^{27}\mathrm{Al}]\approx 5\times {10}^{-5}$ . These accretion rates are experienced at the transition from Class I- to Class II-type protostars, when it is assumed that calcium-aluminum-rich inclusions condense in the inner disk. We conclude that irradiation of the inner disk surface by cosmic-ray protons accelerated in accretion shocks at the protostellar surface may be an important mechanism to produce 26Al. Our models show protostellar cosmic rays may be a viable model to explain the enrichment of 26Al found in the solar system.

Keywords: Meteorite composition, Chondrites, Cosmic ray nucleosynthesis, Nuclear abundances, Star formation, Protoplanetary disks, Interstellar medium, Protostars, Cosmic rays
Distances and Statistics of Local Molecular Clouds in the First Galactic Quadrant. We present an analysis of local molecular clouds ( $-6\lt {V}_{\mathrm{LSR}}\lt 30$ km s-1, i.e., &lt;1.5 kpc) in the first Galactic quadrant ( $25\buildrel{\circ}\over{.} 8\lt l\lt 49\buildrel{\circ}\over{.} 7$ and $| b| \lt 5^\circ $ ), a pilot region of the Milky Way Imaging Scroll Painting (MWISP) CO survey. Using the Spectral Clustering for Interstellar Molecular Emission Segmentation algorithm to divide large molecular clouds into moderate-size ones, we determined distances to 28 molecular clouds with the background-eliminated extinction-parallax method using the Gaia DR2 parallax measurements aided by AG and AV; the distance ranges from 250 to about 1.5 kpc. These incomplete distance samples indicate a linear relationship between the distance and the radial velocity (VLSR) with a scatter of 0.16 kpc, and kinematic distances may be systematically larger for local molecular clouds. In order to investigate fundamental properties of molecular clouds, such as the total sample number, the line width, the brightness temperature, the physical area, and the mass, we decompose the spectral cube using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. Post-selection criteria are imposed on DBSCAN clusters to remove the noise contamination, and we found that the separation of molecular cloud individuals is reliable based on a definition of independent consecutive structures in l-b-V space. The completeness of the local molecular cloud flux collected by the MWISP CO survey is about 80%. The physical area, A, shows a power-law distribution, dN/d $A\propto {A}^{-2.20\pm 0.18}$ , while the molecular cloud mass also follows a power-law distribution but is slightly flatter, dN/dM ∝ M-1.96 ± 0.11.

Keywords: Interstellar molecules, Molecular clouds, Interstellar dust extinction, Astrostatistics, Interstellar clouds
Geometric Support for Dark Matter by an Unaligned Einstein Ring in A3827. The nondetection of dark matter (DM) particles in increasingly stringent laboratory searches has encouraged alternative gravity theories where gravity is sourced only from visible matter. Here, we consider whether such theories can pass a two-dimensional test posed by gravitational lensing—to reproduce a particularly detailed Einstein ring in the core of the galaxy cluster A3827. We find that when we require the lensing mass distribution to strictly follow the shape (ellipticity and position angle) of the light distribution of cluster member galaxies, intracluster stars, and the X-ray emitting intracluster medium, we cannot reproduce the Einstein ring, despite allowing the mass-to-light ratios of these visible components to freely vary with radius to mimic alternative gravity theories. Alternatively, we show that the detailed features of the Einstein ring are accurately reproduced by allowing a smooth, freely oriented DM halo in the lens model, with relatively small contributions from the visible components at a level consistent with their observed brightnesses. This dominant DM component is constrained to have the same orientation as the light from the intracluster stars, indicating that the intracluster stars trace the gravitational potential of this component. The Einstein ring of A3827 therefore presents a new challenge for alternative gravity theories: not only must such theories find agreement between the total lensing mass and visible mass, but they must also find agreement between the projected sky distribution of the lensing mass and that of the visible matter, a more stringent test than has hitherto been posed by lensing data.

Keywords: Galaxy clusters, Strong gravitational lensing, Dark matter distribution
Setting the Stage for Cosmic Chronometers. II. Impact of Stellar Population Synthesis Models Systematics and Full Covariance Matrix. The evolution of differential ages of passive galaxies at different redshifts (cosmic chronometers) has been proved to be a method potentially able to constrain the Hubble parameter in a cosmology-independent way, but the systematic uncertainties must be carefully evaluated. In this paper, we compute the contribution to the full covariance matrix of systematic uncertainties due to the choice of initial mass function, stellar library, and metallicity, exploring a variety of stellar population synthesis models. Through simulations in the redshift range 0 &lt; z &lt; 1.5, we find that the choice of the stellar population synthesis model dominates the total error budget on H(z), with contributions at a level of ∼4.5%, discarding the most discordant model. The contribution due to the choice of initial mass function is &lt;0.5%, while that due to the stellar library is ∼6.6%, on average. We also assess the impact of an uncertainty in the stellar metallicity determination, finding that an error of ∼10% (5%) on the stellar metallicity propagates to a 9% (4%) error on H(z). These results are used to provide the combined contribution of these systematic effects on the error budget. For current H(z) measurements, where the uncertainties due to metallicity and star formation history were already included, we show that, using the more modern stellar libraries, the additional systematic uncertainty is between 5.4% (at z = 0.2) and 2.3% (at z = 1.5). To reach the goal of keeping the systematic error budget below the 1% level, we discuss the efforts needed to obtain higher resolution and signal-to-noise spectra and improvements in the modeling of stellar population synthesis.

Keywords: Galaxy stellar content, Observational cosmology, Galaxy evolution, Cosmological parameters
The Black Hole Mass-Color Relations for Early- and Late-type Galaxies: Red and Blue Sequences. The tight correlations between supermassive black hole (SMBH) mass (MBH) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and of the evolution of galaxies. Here, we present newly observed correlations between MBH and the host galaxy total UV-[3.6] color ( ${{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ , Pearson's r = 0.6-0.7) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured MBH in the Galaxy Evolution Explorer/S4G survey. The colors are carefully measured in a homogeneous manner using the far-UV, near-UV, and 3.6 μm magnitudes of the galaxies and their multicomponent structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ relations for the two morphological types have slopes that differ at ∼2σ level. Early-type galaxies define a red sequence in the ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by LUV/L3.6, it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ and MBH - L3.6,tot relations for the sample galaxies reveal a comparable level of vertical scatter in the log MBH direction, approximately 5%-27% more than the vertical scatter of the MBH - σ relation. Our ${M}_{\mathrm{BH}}-{{ \mathcal C }}_{\mathrm{UV},\mathrm{tot}}$ relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios. These new relations offer the prospect of estimating SMBH masses reliably using the galaxy color alone. Furthermore, we show that they are capable of estimating intermediate black hole masses in low-mass early- and late-type galaxies.

Keywords: Lenticular galaxies, Supermassive black holes, cD galaxies, Spiral galaxies, Galaxy colors, Galaxy structure, Galaxy nuclei, Galaxy photometry, Elliptical galaxies
The 100 pc White Dwarf Sample in the SDSS Footprint. We present follow-up spectroscopy of 711 white dwarfs within 100 pc, and we present a detailed model atmosphere analysis of the 100 pc white dwarf sample in the Sloan Digital Sky Survey footprint. Our spectroscopic follow-up is complete for 83% of the white dwarfs hotter than 6000 K, where the atmospheric composition can be constrained reliably. We identify 1508 DA white dwarfs with pure hydrogen atmospheres. The DA mass distribution has an extremely narrow peak at 0.59 M☉ and reveals a shoulder from relatively massive white dwarfs with M = 0.7-0.9 M☉. Comparing this distribution with binary population synthesis models, we find that the contribution from single stars that form through mergers cannot explain the overabundance of massive white dwarfs. In addition, the mass distribution of cool DAs shows a near absence of M &gt; 1 M☉ white dwarfs. The pile-up of 0.7-0.9 M☉ and the disappearance of M &gt; 1 M☉ white dwarfs is consistent with the effects of core crystallization. Even though the evolutionary models predict the location of the pile-up correctly, the delay from the latent heat of crystallization by itself is insufficient to create a significant pile-up, and additional cooling delays from related effects like phase separation are necessary. We also discuss the population of infrared-faint (ultracool) white dwarfs and demonstrate for the first time the existence of a well-defined sequence in color and magnitude. Curiously, this sequence is connected to a region in the color-magnitude diagrams where the number of white dwarfs with a helium-dominated atmosphere is low. This suggests that the infrared-faint white dwarfs likely have mixed H/He atmospheres.

Keywords: Stellar properties, Fundamental parameters of stars, White dwarf stars, Galaxy stellar content, Stellar mass functions, Spectrophotometry
A Survey for C II Emission-line Stars in the Large Magellanic Cloud. We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the C II λλ7231, 7236 emission lines in objects as faint as mλ7400 ∼ 18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged ∼50 deg2 using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population.

Keywords: Planetary nebulae nuclei, WC stars
Revisiting the Formation of HeH<SUP>+</SUP> in the Planetary Nebula NGC 7027. From four independent calculations using three different theoretical approaches, rate coefficients for the formation of HeH+ via the radiative association of He+ and H were computed. Good agreement is found between our new calculations and prior results obtained two decades ago for kinetic temperatures between ∼800 and 20,000 K. This finding is inconsistent with a recent claim in the literature of a wide variation in published values and establishes the robustness of our knowledge of this process for the formation of HeH+. The implications of the current results to the first detection of HeH+ and its modeled abundance in the planetary nebula NGC 7027 are discussed.

Keywords: Molecular physics
On the Accuracy of Time-delay Cosmography in the Frontier Fields Cluster MACS J1149.5+2223 with Supernova Refsdal. We study possible systematic effects on the values of the cosmological parameters measured through strong lensing analyses of the Hubble Frontier Field galaxy cluster MACS J1149.5+2223. We use the observed positions of a large set of spectroscopically selected multiple images, including those of supernova "Refsdal" with their published time delays. Starting from our reference model in a flat ΛCDM cosmology, published in Grillo et al. (2018), we confirm the relevance of the longest measurable time delay, between SX and S1, and an approximately linear relation between its value and that of H0. We perform true blind tests by considering a range of time delays around its original estimate of 345 ± 10 days, as an accurate measurement of this time delay is still not known at the time of analysis and writing. We investigate separately the impact of a constant sheet of mass at the cluster redshift, of a power-law profile for the mass density of the cluster main halo and of some scatter in the cluster member scaling relations. Remarkably, we find that these systematic effects do not introduce a significant bias on the inferred values of H0 and Ωm and that the statistical uncertainties dominate the total error budget: a 3% uncertainty on the time delay of image SX translates into approximately 6% and 40% (including both statistical and systematic 1σ) uncertainties for H0 and Ωm, respectively. Furthermore, our model accurately reproduces the extended surface brightness distribution of the supernova host. We also present the interesting possibility of measuring the value of the equation-of-state parameter w of the dark energy density, currently with a 30% uncertainty.

Keywords: Galaxy clusters, Cosmological parameters, Strong gravitational lensing, Hubble constant, Dark matter, Dark energy
Thermodynamical Evolution of Supra-arcade Downflows. Supra-arcade downflows (SADs) are dark, teardrop-shaped features descending upon flare arcades. They are thought to be the results of magnetic reconnection, but the detailed formation mechanism of SADs and their relationship to flare energy release are still unclear. In this work, we explore the thermodynamical properties of SADs in the 2011 October 22 limb flare using the observations of the Solar Dynamics Observatory/Atmospheric Imaging Assembly and an improved Differential Emission Measure (DEM) technique. Different heating events around SADs are identified and the propagation speeds of plasma heating are calculated. The first heating event starts with the increase of the emission measure at temperatures higher than 5 MK, about 2.8 minutes before the arrival of the first studied SAD. Its propagation speed is about 140 km s-1, a little faster than the speed of the SAD. However, the other two events have fast propagation speeds more than 700 km s-1. We suspect that the first heating event can be explained by adiabatic compression, but the others may have different causes. Besides, we observed that SADs can push away their surrounding spikes. The formation of SADs is further explained on the basis of patchy and bursty magnetic reconnection that reconnection outflows may push away surrounding plasma and leave dark lanes behind them. The reliability of the DEM results, heating and cooling mechanisms, and other SAD explanations are discussed.

Keywords: Solar coronal heating, Solar flares, Solar flare spectra, Solar magnetic reconnection
Effects of Thermal Emission on the Transmission Spectra of Hot Jupiters. The atmosphere on the dayside of a highly irradiated close-in gas giant (also known as a hot Jupiter) absorbs a significant part of the incident stellar radiation, which again gets re-emitted in the infrared wavelengths both from the day and the night sides of the planet. The re-emitted thermal radiation from the nightside facing the observers during the transit event of such a planet contributes to the transmitted stellar radiation. We demonstrate that the transit spectra at the infrared region get altered significantly when such re-emitted thermal radiation of the planet is included. We assess the effects of the thermal emission of the hot Jupiters on the transit spectra by simulating observational spectroscopic data with corresponding errors from the different channels of the upcoming James Webb Space Telescope. We find that the effect is statistically significant with respect to the noise levels of those simulated data. Hence, we convey the important message that the planetary thermal re-emission must be taken into consideration in the retrieval models of transit spectra for hot Jupiters for a more accurate interpretation of the observed transit spectra.

Keywords: Atmospheric effects, Radiative transfer, Exoplanet atmospheres, Transmission spectroscopy
Mesoscale Phenomena during a Macroscopic Solar Eruption. Our previous magnetohydrodynamic simulation of a macroscopic solar eruption discussed in Zhao et al. (2019) showed that the current sheet (CS) evolution during eruption went through four stages: the CS growth stage, the dynamic growth stage, the hot CS stage, and the dynamic hot CS stage. We now focus on various mesoscale phenomena associated with the ongoing reconnection. In the dynamic growth stage, the remnant chromospheric matter in the CS is quasi-periodically pushed into the prominence, inducing fast shocks propagating at a speed of 210 km s-1. In the hot CS phase, various shock features relevant for particle acceleration are identified throughout the flare loop. Finally, during both dynamic stages, we quantify the properties of magnetic islands. A typical island is accelerated to Alfvénic speed by the Lorentz force and cools down by radiative cooling and thermal conduction. It also tends to expand in size before colliding with another island, with the FR or with the flare arcade. Islands in the dynamic growth stage have a higher density and lower temperature, and vice versa in the dynamic hot CS stage. Islands tend to move upward in the dynamic growth stage, while almost equal fractions of downward-moving and upward-moving islands in the dynamic hot CS stage. Translating the island trajectories to phase space, we find that the function $\dot{y}=({{ay}}^{2}+{by}+c)\exp (\lambda y)$ fits the trajectory well, and its two fixed points represent the creation and the annihilation of the island.

Keywords: Solar flares, Solar magnetic reconnection, Solar prominences, Termination shock, Magnetohydrodynamical simulations