Sazuna/UAT_keywords huggingface dataset:
On the Synthesis of the Astronomically Elusive 1-Ethynyl-3-Silacyclopropenylidene (c-SiC<SUB>4</SUB>H<SUB>2</SUB>) Molecule in Circumstellar Envelopes of Carbon-rich Asymptotic Giant Branch Stars and Its Potential Role in the Formation of the Silicon Tetracarbide Chain (SiC<SUB>4</SUB>). Organosilicon molecules such as silicon carbide (SiC), silicon dicarbide (c-SiC2), silicon tricarbide (c-SiC3), and silicon tetracarbide (SiC4) represent basic molecular building blocks connected to the growth of silicon-carbide dust grains in the outflow of circumstellar envelopes of carbon-rich asymptotic giant branch (AGB) stars. Yet, the fundamental mechanisms of the formation of silicon carbides and of the early processes that initiate the coupling of silicon-carbon bonds in circumstellar envelopes have remained obscure. Here, we reveal in a crossed molecular beam experiment contemplated with ab initio electronic calculations that the astronomically elusive 1-ethynyl-3-silacyclopropenylidene molecule (c-SiC4H2, Cs, X1A') can be synthesized via a single-collision event through the barrierless reaction of the silylidyne radical (SiH) with diacetylene (C4H2). This system represents a benchmark of a previously overlooked class of reactions, in which the silicon-carbon bond coupling can be initiated by a barrierless and overall exoergic reaction between the simplest silicon-bearing radical (silylidyne) and a highly hydrogen-deficient hydrocarbon (diacetylene) in the inner circumstellar envelopes of evolved carbon-rich stars such as IRC+10216. Considering that organosilicon molecules like 1-ethynyl-3-silacyclopropenylidene might be ultimately photolyzed to bare carbon-silicon clusters like the linear silicon tetracarbide (SiC4), hydrogenated silicon-carbon clusters might represent the missing link eventually connecting simple molecular precursors such as silane (SiH4) to the population of silicon-carbide based interstellar grains ejected from carbon-rich AGB stars into the interstellar medium.

Keywords: Interstellar dust, Circumstellar envelopes, Laboratory astrophysics, Astrochemistry
Determination of Solar Wind Angular Momentum and Alfvén Radius from Parker Solar Probe Observations. As fundamental parameters of the Sun, the Alfvén radius and angular momentum loss determine how the solar wind changes from sub-Alfvénic to super-Alfvénic and how the Sun spins down. We present an approach to determining the solar wind angular momentum flux based on observations from Parker Solar Probe (PSP). A flux of about 0.15 × 1030 dyn cm sr-1 near the ecliptic plane and 0.7:1 partition of that flux between the particles and magnetic field are obtained by averaging data from the first four encounters within 0.3 au from the Sun. The angular momentum flux and its particle component decrease with the solar wind speed, while the flux in the field is remarkably constant. A speed dependence in the Alfvén radius is also observed, which suggests a "rugged" Alfvén surface around the Sun. Substantial diving below the Alfvén surface seems plausible only for relatively slow solar wind given the orbital design of PSP. Uncertainties are evaluated based on the acceleration profiles of the same solar wind streams observed at PSP and a radially aligned spacecraft near 1 au. We illustrate that the "angular momentum paradox" raised by Réville et al. can be removed by taking into account the contribution of the alpha particles. The large proton transverse velocity observed by PSP is perhaps inherent in the solar wind acceleration process, where an opposite transverse velocity is produced for the alphas with the angular momentum conserved. Preliminary analysis of some recovered alpha parameters tends to agree with the results.

Keywords: Fundamental parameters of stars, Solar wind, Solar rotation
VVV CL001: Likely the Most Metal-poor Surviving Globular Cluster in the Inner Galaxy. We present the first high-resolution abundance analysis of the globular cluster VVV CL001, which resides in a region dominated by high interstellar reddening toward the Galactic bulge. Using H-band spectra acquired by the Apache Point Observatory Galactic Evolution Experiment, we identified two potential members of the cluster, and estimated from their Fe I lines that the cluster has an average metallicity of [Fe/H] = -2.45 with an uncertainty due to systematics of 0.24 dex. We find that the light-(N), α-(O, Mg, Si), and Odd-Z (Al) elemental abundances of the stars in VVV CL001 follo w the same trend as other Galactic metal-poor globular clusters. This makes VVV CL001 possibly the most metal-poor globular cluster identified so far within the Sun's galactocentric distance and likely one of the most metal-deficient clusters in the Galaxy after ESO280-SC06. Applying statistical isochrone fitting, we derive self-consistent age, distance, and reddening values, yielding an estimated age of ${11.9}_{-4.05}^{+3.12}$ Gyr at a distance of ${8.22}_{-1.93}^{+1.84}$ kpc, revealing that VVV CL001 is also an old GC in the inner Galaxy. The Galactic orbit of VVV CL001 indicates that this cluster lies on a halo-like orbit that appears to be highly eccentric. Both chemistry and dynamics support the hypothesis that VVV CL001 could be an ancient fossil relic left behind by a massive merger event during the early evolution of the Galaxy, likely associated with either the Sequoia or the Gaia-Enceladus-Sausage structures.

Keywords: Globular star clusters, Red giant branch, Chemical abundances
ALMA Reveals a Cloud-Cloud Collision that Triggers Star Formation in the Small Magellanic Cloud. We present the results of Atacama Large Millimeter/submillimeter Array observations in 12CO(1-0) emission at 0.58 × 0.52 pc2 resolution toward the brightest H II region N66 of the Small Magellanic Cloud (SMC). The 12CO(1-0) emission toward the north of N66 reveals clumpy filaments with multiple velocity components. Our analysis shows that a blueshifted filament at a velocity range of 154.4-158.6 km s-1 interacts with a redshifted filament at a velocity of 158.0-161.8 km s-1. A third velocity component at a velocity range of 161-165.0 km s-1 constitutes hub-filaments. An intermediate-mass young stellar object (YSO) and a young pre-main-sequence star cluster have hitherto been reported in the intersection of these filaments. We find a V-shape distribution in the position-velocity diagram at the intersection of two filaments. This indicates the physical association of those filaments due to a cloud-cloud collision. We determine the collision timescale ∼0.2 Myr using the relative velocity (∼5.1 km s-1) and displacement (∼1.1 pc) of those interacting filaments. These results suggest that the event occurred about 0.2 Myr ago and triggered the star formation, possibly an intermediate-mass YSO. We report the first observational evidence for a cloud-cloud collision that triggers star formation in N66N of the low metallicity ∼0.2 Z☉ galaxy, the SMC, with similar kinematics as in N159W-South and N159E of the Large Magellanic Cloud.

Keywords: Small Magellanic Cloud, Star formation, H II regions, Interstellar medium
Claimed Detection of PH<SUB>3</SUB> in the Clouds of Venus Is Consistent with Mesospheric SO<SUB>2</SUB>. The observation of a 266.94 GHz feature in the Venus spectrum has been attributed to phosphine (PH3) in the Venus clouds, suggesting unexpected geological, chemical, or even biological processes. Since both PH3 and sulfur dioxide (SO2) are spectrally active near 266.94 GHz, the contribution to this line from SO2 must be determined before it can be attributed, in whole or part, to PH3. An undetected SO2 reference line, interpreted as an unexpectedly low SO2 abundance, suggested that the 266.94 GHz feature could be attributed primarily to PH3. However, the low SO2 and the inference that PH3 was in the cloud deck posed an apparent contradiction. Here we use a radiative transfer model to analyze the PH3 discovery, and explore the detectability of different vertical distributions of PH3 and SO2. We find that the 266.94 GHz line does not originate in the clouds, but above 80 km in the Venus mesosphere. This level of line formation is inconsistent with chemical modeling that assumes generation of PH3 in the Venus clouds. Given the extremely short chemical lifetime of PH3 in the Venus mesosphere, an implausibly high source flux would be needed to maintain the observed value of 20 ± 10 ppb. We find that typical Venus SO2 vertical distributions and abundances fit the JCMT 266.94 GHz feature, and the resulting SO2 reference line at 267.54 GHz would have remained undetectable in the ALMA data due to line dilution. We conclude that nominal mesospheric SO2 is a more plausible explanation for the JCMT and ALMA data than PH3.

Keywords: Biosignatures, Venus, Radiative transfer
Indication of a Pulsar Wind Nebula in the Hard X-Ray Emission from SN 1987A. Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. To date, the detection in the Atacama Large Millimeter/submillimeter Array data of a feature that is somehow compatible with the emission arising from a proto-pulsar wind nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33 yr old issue by analyzing archived observations of SN87A performed by Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the 10-20 kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magnetohydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is that of PWN emission.

Keywords: Neutron stars, X-ray astronomy, X-ray point sources, Plasma astrophysics, Supernova remnants, X-ray sources, Compact objects, X-ray observatories, Shocks, Interstellar synchrotron emission
PSR J1810+1744: Companion Darkening and a Precise High Neutron Star Mass. Keck-telescope spectrophotometry of the companion of PSR J1810+1744 shows a flat, but asymmetric light-curve maximum and a deep, narrow minimum. The maximum indicates strong gravity darkening (GD) near the L1 point, along with a heated pole and surface winds. The minimum indicates a low underlying temperature and substantial limb darkening. The GD is a consequence of extreme pulsar heating and the near-filling of the Roche lobe. Light-curve modeling gives a binary inclination i = 65°7 ± 0°4. With the Keck-measured radial-velocity amplitude Kc = 462.3 ± 2.2 km s-1, this gives an accurate neutron star mass MNS = 2.13 ± 0.04 M⊙, with important implications for the dense-matter equation of state. A classic direct-heating model, ignoring the L1 gravitational darkening, would predict an unphysical MNS &gt; 3 M⊙. A few other "spider" pulsar binaries have similar large heating and fill factor; thus, they should be checked for such effects.

Keywords: Binary stars
Eccentric Early Migration of Neptune. The dynamical structure of the Kuiper Belt can be used as a clue to the formation and evolution of the solar system, planetary systems in general, and Neptune's early orbital history in particular. The problem is best addressed by forward modeling where different initial conditions and Neptune's orbital evolutions are tested, and the model predictions are compared to orbits of known Kuiper Belt objects (KBOs). It has previously been established that Neptune radially migrated, by gravitationally interacting with an outer disk of planetesimals, from the original radial distance r ≲ 25 au to its current orbit at 30 au. Here we show that the migration models with a very low orbital eccentricity of Neptune (eN ≲ 0.03) do not explain KBOs with semimajor axes 50 &lt; a &lt; 60 au, perihelion distances q &gt; 35 au, and inclinations i &lt; 10°. If eN ≲ 0.03 at all times, the Kozai cycles control the implantation process and the orbits with q &gt; 35 au end up having, due to the angular momentum's z-component conservation, i &gt; 10°. Better results are obtained when Neptune's eccentricity is excited to eN ≃ 0.1 and subsequently damped by dynamical friction. The low-e and low-i orbits at 50-60 au are produced in this model when KBOs are lifted from the scattered disk by secular cycles—mainly the apsidal resonance ν8—near various mean motion resonances. These results give support to a (mild) dynamical instability that presumably excited the orbits of giant planets during Neptune's early migration.

Keywords: Neptune, Kuiper belt, Dynamical evolution
Hemispheric Tectonics on LHS 3844b. The tectonic regime of rocky planets fundamentally influences their long-term evolution and cycling of volatiles between interior and atmosphere. Earth is the only known planet with active plate tectonics, but observations of exoplanets may deliver insights into the diversity of tectonic regimes beyond the solar system. Observations of the thermal phase curve of super-Earth LHS 3844b reveal a solid surface and lack of a substantial atmosphere, with a temperature contrast between the substellar and antistellar point of around 1000 K. Here, we use these constraints on the planet's surface to constrain the interior dynamics and tectonic regimes of LHS 3844b using numerical models of interior flow. We investigate the style of interior convection by assessing how upwellings and downwellings are organized and how tectonic regimes manifest. We discover three viable convective regimes with a mobile surface: (1) spatially uniform distribution of upwellings and downwellings, (2) prominent downwelling on the dayside and upwellings on the nightside, and (3) prominent downwelling on the nightside and upwellings on the dayside. Hemispheric tectonics is observed for regimes (2) and (3) as a direct consequence of the day-to-night temperature contrast. Such a tectonic mode is absent in the present-day solar system and has never been inferred from astrophysical observations of exoplanets. Our models offer distinct predictions for volcanism and outgassing linked to the tectonic regime, which may explain secondary features in phase curves and allow future observations to constrain the diversity of super-Earth interiors.

Keywords: Exoplanet plate tectonics, Super Earths, Planetary interior, Exoplanets
Ultra-high Energy Inverse Compton Emission from Galactic Electron Accelerators. It is generally held that &gt;100 TeV emission from astrophysical objects unambiguously demonstrates the presence of PeV protons or nuclei, due to the unavoidable Klein-Nishina suppression of inverse Compton emission from electrons. However, in the presence of inverse Compton dominated cooling, hard high-energy electron spectra are possible. We show that the environmental requirements for such spectra can naturally be met in spiral arms, and in particular in regions of enhanced star formation activity, the natural locations for the most promising electron accelerators: powerful young pulsars. Our scenario suggests a population of hard ultra-high energy sources is likely to be revealed in future searches, and may also provide a natural explanation for the 100 TeV sources recently reported by the High-Altitude Water Cherenkov Observatory.

Keywords: Gamma-rays, High energy astrophysics, Pulsars
Evolution of Subsurface Zonal and Meridional Flows in Solar Cycle 24 from Helioseismological Data. The results of determinations of the azimuthal and meridional velocities by time-distance helioseismology from Helioseismic and Magnetic Imager on board Solar Dynamics Observatory from 2010 May to 2020 September at latitudes and Stonyhurst longitudes from - 60° to + 60° and depths to about 19 Mm below the photosphere are used to analyze spatiotemporal variations of the solar differential rotation and meridional circulation. The pattern of torsional oscillations, or latitudinal belts of alternating "fast" and "slow" zonal flows migrating from high latitudes toward the equator, is found to extend in the time-latitude diagrams over the whole time interval. The oscillation period is comparable with a doubled solar-activity-cycle and can be described as an extended solar cycle. The zonal-velocity variations are related to the solar-activity level, the local-velocity increases corresponding to the sunspot-number increases and being localized at latitudes where the strongest magnetic fields are recorded. The dramatic growth of the zonal velocities in 2018 appears to be a precursor of the beginning of Solar Cycle 25. The strong symmetrization of the zonal-velocity field by 2020 can be considered another precursor. The general pattern of poleward meridional flows is modulated by latitudinal variations similar to the extended-solar-cycle behavior of the zonal flows. During the activity maximum, these variations are superposed with a higher harmonic corresponding to meridional flows converging to the spot-formation latitudes. Our results indicate that variations of both the zonal and meridional flows exhibit the extended-solar-cycle behavior, which is an intrinsic feature of the solar dynamo.

Keywords: Helioseismology, Solar differential rotation, Solar meridional circulation, Solar cycle
A Test of the Cosmological Principle with Quasars. We study the large-scale anisotropy of the universe by measuring the dipole in the angular distribution of a flux-limited, all-sky sample of 1.36 million quasars observed by the Wide-field Infrared Survey Explorer (WISE). This sample is derived from the new CatWISE2020 catalog, which contains deep photometric measurements at 3.4 and 4.6 μm from the cryogenic, post-cryogenic, and reactivation phases of the WISE mission. While the direction of the dipole in the quasar sky is similar to that of the cosmic microwave background (CMB), its amplitude is over twice as large as expected, rejecting the canonical, exclusively kinematic interpretation of the CMB dipole with a p-value of 5 × 10-7 (4.9σ for a normal distribution, one-sided), the highest significance achieved to date in such studies. Our results are in conflict with the cosmological principle, a foundational assumption of the concordance ΛCDM model.

Keywords: Cosmology, Quasars, Large-scale structure of the universe, Observational cosmology, Cosmic microwave background radiation, Infrared astronomy, Active galactic nuclei
Kinetic Simulations of Electron Pre-energization by Magnetized Collisionless Shocks in Expanding Laboratory Plasmas. Collisionless shocks are common features in space and astrophysical systems where supersonic plasma flows interact, such as in the solar wind, the heliopause, and supernova remnants. Recent experimental capabilities and diagnostics allow detailed laboratory investigations of high-Mach-number shocks, which therefore can become a valuable way to understand shock dynamics in various astrophysical environments. Using 2D particle-in-cell simulations with a Coulomb binary collision operator, we demonstrate the mechanism for generation of energetic electrons and experimental requirements for detecting this process in the laboratory high-Mach-number collisionless shocks. We show through a parameter study that electron acceleration by magnetized collisionless shocks is feasible in laboratory experiments with laser-driven expanding plasmas.

Keywords: Shocks, Laboratory astrophysics, Planetary bow shocks, Plasma physics
The Contribution of Electrons to the Sputter-produced O<SUB>2</SUB> Exosphere on Europa. Electrons contribute a strong radiation component to the surface bombardment of Europa. However, they are not typically considered to contribute to erosion of the surface H2O-ice or produce exospheres of radiolytic O2, as laboratory studies on sputtering induced by electrons are sparse. Here we have measured the sputtering yield of H2O-ice induced by 0.5 keV electrons between 14 and 125 K, estimating the composition of the stable products ejected during irradiation. Combining these measurements with updated electron flux measurements, we estimate for the first time that the global surface production rate of O2 from electron-induced sputtering is larger than the production rate previously estimated for all of the ionic components combined. Our results emphasize the importance of electrons in producing exospheres on icy satellites and suggest that these exospheres need not be tied to environments where the surface is being bombarded with heavy ions.

Keywords: Exosphere, Cosmic rays, Solid matter physics, Laboratory astrophysics, Astrochemistry, Surface ices, Spectroscopy, Galilean satellites, Jovian satellites
On the Contribution of the X-Ray Source to the Extended Nebular He II Emission in IZW18. Nebular He II emission implies the presence of energetic photons (E ≥ 54 eV). Despite the great deal of effort dedicated to understanding He II ionization, its origin has remained mysterious, particularly in metal-deficient star-forming (SF) galaxies. Unfolding He II-emitting, metal-poor starbursts at z ∼ 0 can yield insight into the powerful ionization processes occurring in the primordial universe. Here we present a new study on the effects that X-ray sources have on the He II ionization in the extremely metal-poor galaxy IZw18 (Z ∼ 3% Z☉), whose X-ray emission is dominated by a single high-mass X-ray binary (HMXB). This study uses optical integral field spectroscopy, archival Hubble Space Telescope observations, and all of the X-ray data sets publicly available for IZw18. We investigate the time-variability of the IZw18 HMXB for the first time; its emission shows small variations on timescales from days to decades. The best-fit models for the HMXB X-ray spectra cannot reproduce the observed He II ionization budget of IZw18, nor can recent photoionization models that combine the spectra of both very low metallicity massive stars and the emission from HMXB. We also find that the IZw18 HMXB and the He II-emission peak are spatially displaced at a projected distance of ≃200 pc. These results reduce the relevance of X-ray photons as the dominant He II ionizing mode in IZw18, which leaves uncertain what process is responsible for the bulk of its He II ionization. This is in line with recent work discarding X-ray binaries as the main source responsible for He II ionization in SF galaxies.

Keywords: Blue compact dwarf galaxies, Dwarf galaxies, High mass x-ray binary stars, Emission line galaxies