Sazuna/UAT_keywords huggingface dataset:
Study of Plasma Heating Processes in a Coronal Mass Ejection–driven Shock Sheath Region Observed with the Metis Coronagraph. On 2021 September 28, a C1.6 class flare occurred in active region NOAA 12871, located approximately at 27°S and 51°W on the solar disk with respect to Earth's point of view. This event was followed by a partial halo coronal mass ejection (CME) that caused the deflection of preexisting coronal streamer structures, as observed in visible-light coronagraphic images. An associated type II radio burst was also detected by both space- and ground-based instruments, indicating the presence of a coronal shock propagating into interplanetary space. By using H I Lyα (121.6 nm) observations from the Metis coronagraph on board the Solar Orbiter mission, we demonstrate for the first time the capability of UV imaging to provide, via a Doppler dimming technique, an upper limit estimate of the evolution of the 2D proton kinetic temperature in the CME-driven shock sheath as it passes through the field of view of the instrument. Our results suggest that over the 22 minutes of observations, the shock propagated with a speed decreasing from about 740 ± 110 km s‑1 to 400 ± 60 km s‑1. At the same time, the postshock proton temperatures peaked at latitudes around the shock nose and decreased with time from about 6.8 ± 1.01 MK to 3.1 ± 0.47 MK. The application of the Rankine–Hugoniot jump conditions demonstrates that these temperatures are higher by a factor of about 2–5 than those expected from simple adiabatic compression, implying that significant shock heating is still going on at these distances.

Keywords: Interplanetary shocks, Solar wind, Plasma astrophysics, Active sun, Solar coronal mass ejection shocks, Solar physics, Radio bursts, Shocks
The Evolution of Photospheric Magnetic Fields at the Footpoints of Reconnected Structures in the Solar Atmosphere. Magnetic reconnection is believed to play an important role in the release and conversion of energy among magnetized plasma systems. So far, we have been unable to understand under what conditions magnetic reconnection can take place. Based on observations from the New Vacuum Solar Telescope and the Solar Dynamics Observatory (SDO), we study 16 magnetic reconnection events, and each event has a clear X-type configuration consisting of two sets of atmospheric structures. We focus on 38 footpoints that are relevant to these structures and can be clearly determined. By using SDO/Helioseismic and Magnetic Imager line-of-sight magnetograms, we track the field evolution of these footpoints. Prior to the occurrence of magnetic reconnection, the associated fields at the footpoints underwent convergence and shear motions, and thus became enhanced and complex. During the converging period, the rates of increase of the mean magnetic flux densities (MFDs) at these footpoints are 0.03–0.25 hr‑1. While the unsigned mean MFDs are 70–300 G, magnetic reconnection in the solar atmosphere takes place. Subsequently, the photospheric fields of these footpoints diffuse and weaken, with rates of decrease of the MFDs from 0.03 to 0.18 hr‑1. These results suggest that, due to the photospheric dynamical evolution at the footpoints, the footpoint MFDs increase from a small value to a large one, and the corresponding atmospheric magnetic fields become complicated and nonpotential; then reconnection happens and it releases the accumulated magnetic field energy. Our study supports the conjecture that magnetic reconnection releases free magnetic energy stored in the nonpotential fields.

Keywords: Solar activity, Solar magnetic fields, Solar magnetic reconnection
The 230 GHz Variability of Numerical Models of Sagittarius A*. I. Parameter Surveys on Varying the Ion-to-electron Temperature Ratio Under Strongly Magnetized Conditions. The 230 GHz lightcurves of Sagittarius A* (Sgr A*) predicted by general relativistic magnetohydrodynamics and general relativistic ray-tracing (GRRT) models by the Event Horizon Telescope Collaboration have higher variability M ΔT  compared to observations. In this series of papers, we explore the origin of such large brightness variability. In this first paper, we performed large GRRT parameter surveys that span from the optically thin to the optically thick regimes, covering the ion-to-electron temperature ratio under strongly magnetized conditions, R Low, from 1 to 60. We find that increasing R Low can lead to either an increase or a reduction in M ΔT  depending on the other model parameters, making it consistent with the observed variability of Sgr A* in some cases. Our analysis of GRRT image snapshots finds that the major contribution to the large M ΔT  for the R Low = 1 models comes from the photon ring. However, secondary contributions from the accretion flow are also visible depending on the spin parameter. Our work demonstrates the importance of the electron temperature used for modeling radiatively inefficient accretion flows and places new constraints on the ion-to-electron temperature ratio. A more in-depth analysis for understanding the dependencies of M ΔT  on R Low will be performed in subsequent papers.

Keywords: Black hole physics, Galactic center, Black holes, High energy astrophysics, Plasma astrophysics, Radiative transfer, Radio astronomy
Resolved Measurements of the CO-to-H<SUB>2</SUB> Conversion Factor in 37 Nearby Galaxies. We measure the CO-to-H2 conversion factor (α CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements of α CO for CO (2─1) and (1─0), respectively. The mean values for α CO (2─1) and α CO (1─0) are ${9.3}_{-5.4}^{+4.6}$ and ${4.2}_{-2.0}^{+1.9}\,{M}_{\odot }\,{\mathrm{pc}}^{-2}\,{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1})}^{-1}$ , respectively. The CO-intensity-weighted mean is 5.69 for α CO (2─1) and 3.33 for α CO (1─0). We examine how α CO scales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( $\overline{U}$ ). Among them, $\overline{U}$ , ΣSFR, and the integrated CO intensity (W CO) have the strongest anticorrelation with spatially resolved α CO. We provide linear regression results to α CO for all quantities tested. At galaxy-integrated scales, we observe significant correlations between α CO and W CO, metallicity, $\overline{U}$ , and ΣSFR. We also find that α CO in each galaxy decreases with the stellar mass surface density (Σ⋆) in high-surface-density regions (Σ⋆ ≥ 100 M ☉ pc−2), following the power-law relations ${\alpha }_{\mathrm{CO}\,(2\mbox{--}1)}\propto {{\rm{\Sigma }}}_{\star }^{-0.5}$ and ${\alpha }_{\mathrm{CO}\,(1\mbox{--}0)}\propto {{\rm{\Sigma }}}_{\star }^{-0.2}$ . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease in α CO with increasing Σ⋆ as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction in α CO. The decrease in α CO at high Σ⋆ is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge "Milky Way─like" to "starburst-like" conversion factors.

Keywords: Interstellar dust, Interstellar molecules, Interstellar line emission, Far infrared astronomy, H I line emission, Dust continuum emission, Interstellar medium, CO line emission
Zone of Preferential Heating for Minor Ions in the Solar Wind. The properties of minor ions in the solar wind are important indicators of the state of the solar corona and the heating processes it undergoes as it expands. Evidence of preferential heating of minor ions has been observed in the solar wind, and is believed to be active up to a certain radial boundary, beyond which thermalization due to Coulomb collisions predominates. Building on previous works that calculated the location of this boundary for alpha particles, this work calculates the outer radial boundary of the zone of preferential heating for selected heavy ions in the solar wind. This analysis uses ion data from the Solar Wind Ion Composition Spectrometer and proton data from the Solar Wind Electron, Proton, and Alpha Monitor aboard the Advance Composition Explorer spanning the years from 1998 through to 2011. Observations of proton and ion temperatures, velocities, and densities, and fixed parameters derived from temperature, density, and velocity scaling laws are used in a model function to predict the radial boundary and excess temperature at the boundary via reduction of the χ 2/degrees of freedom statistic. In this study, the values of the radial boundary of the preferential heating zone were quite high when compared to what was previously found for alpha particles, but a clear scaling relationship between excess temperature and ion properties was observed.

Keywords: Solar coronal heating, Solar wind
The Dynamics of Magnetic Rossby Waves in the Quasigeostrophic Shallow Water Magnetohydrodynamic Theory. The dynamics of magnetic Rossby waves are investigated by applying a quasigeostrophic shallow water magnetohydrodynamic system, which is linearized with respect to both uniform background flow and uniform magnetic field. Due to the influence of the free surface divergence, the phase speed for magnetic Rossby waves can be either a monotonically increasing or a monotonically decreasing function, and the resulting difference between the group velocity and the phase speed can be either positive or negative. This is determined by whether the corresponding Alfvén wave speed is the upper limit or not. Differently, the phase speed is always a monotonically increasing function and the difference between the group velocity and the phase speed is always positive for incompressible magnetic Rossby waves. Multiplying a factor, the wavenumber vector shares the same endpoint with the group velocity vector. The endpoint moves on a cycle that has a center at the k-axis and is tangent to the l-axis in the wavenumber space. The circle is quite similar to the Longuet-Higgins circle for Rossby waves on Earth's atmosphere and ocean. The fundamental dynamics is the theoretical basis for deeply understanding the meridional energy transport by waves and the interaction between waves and the background states.

Keywords: Alfven waves, Magnetohydrodynamics, Astrophysical fluid dynamics
Probing the Global 21 cm Background by Velocity-induced Dipole and Quadrupole Anisotropies. The motion of an observer in the rest frame of the cosmic 21 cm background induces an anisotropy in the observed background, even when the background is isotropic. The induced anisotropy includes a dipole and a quadrupole, in the order decreasing in amplitude. If observed, these multipole anisotropies can be used as additional probes of the spectral shape of the global 21 cm background for mitigating the ambiguity in the monopole spectrum probed by single-element radio telescopes such as EDGES and SARAS. This could also help with understanding the astrophysical and cosmological processes that occurred during the cosmic dawn and the epoch of reionization, and even improve the estimation of the solar velocity and the foreground spectra. Here, we study the feasibility of such observations and present science drivers for the measurement of the 21 cm dipole and quadrupole. We find that future 21 cm experiments can in principle detect the 21 cm dipole to high significance, potentially improving measurement accuracy of Earth velocity with respect to the Milky Way, galactic, and extragalactic foreground monopole spectra by an order of magnitude, as well as improving 21 cm astrophysical parameters by 2%–5%.

Keywords: Cosmology, Reionization, Cosmic background radiation
A New Route to Massive Hot Subdwarfs: Common Envelope Ejection from Asymptotic Giant Branch Stars. The hot subdwarf O/B stars (sdO/Bs) are known as extreme horizontal branch stars, which is of great importance in stellar evolution theory. The sdO/Bs are generally thought to have a helium-burning core and a thin hydrogen envelope (M env &lt; 0.02 M ⊙). In the canonical binary evolution scenario, sdO/Bs are considered to be the stripped cores of red giants. However, such a scenario cannot explain the recently discovered sdO/B binary SMSS J1920, where the strong Ca H and K lines in the spectrum are found. It suggests that this binary likely originated from the recent ejection of the common envelope (CE). In this work, we propose a new formation channel of massive sdO/Bs, namely, sdO/Bs produced from a CE ejection process with an asymptotic giant branch (AGB) star (hereafter the AGB CE channel). We constructed the evolutionary model of sdO/Bs and successfully explained most of the important observed parameters of the sdO/B star in SMSS J1920, including the evolutionary age, sdO/B mass, effective temperature, surface gravity, and surface helium abundance. The minimum sdO/B mass produced from the AGB CE channel is about 0.48 M ⊙. The evolutionary tracks in the $\mathrm{log}{T}_{\mathrm{eff}}\mbox{--}\mathrm{log}g$ plane may explain a fraction of the observational samples with high $\mathrm{log}{T}_{\mathrm{eff}}$ and low $\mathrm{log}g$ . Considering the wind mass loss of sdO/Bs, the model could produce helium-rich hot subdwarfs with $\mathrm{log}({n}_{\mathrm{He}}/{n}_{{\rm{H}}})\gtrsim -1$ .

Keywords: Binary stars, Common envelope evolution, Subdwarf stars, Asymptotic giant branch
The Influence of Stellar Rotation in Binary Systems on Core-collapse Supernova Progenitors and Multimessenger Signals. The detailed structure of core-collapse supernova progenitors is crucial for studying supernova explosion engines and the corresponding multimessenger signals. In this paper, we investigate the influence of stellar rotation on binary systems consisting of a 30M ⊙ donor star and a 20M ⊙ accretor using the MESA stellar evolution code. We find that through mass transfer in binary systems, fast-rotating red- and blue-supergiant progenitors can be formed within a certain range of the initial orbital periods, although the correlation is not linear. We also find that even with the same initial mass ratio of the binary system, the resulting final masses of the collapsars, the iron core masses, the compactness parameters, and the final rotational rates can vary widely and are sensitive to the initial orbital periods. For instance, the progenitors with strong convection form a thinner Si shell and a wider O shell compared to those in single-star systems. In addition, we conduct 2D self-consistent core-collapse supernova simulations with neutrino transport for these rotating progenitors derived from binary stellar evolution. We find that the neutrino and gravitational-wave signatures of these binary progenitors could exhibit significant variations. Progenitors with larger compactness parameters produce more massive proto-neutron stars, have higher mass accretion rates, and emit brighter neutrino luminosity and louder gravitational emissions. Finally, we observe stellar-mass black hole formation in some of our failed exploding models.

Keywords: Neutron stars, Hydrodynamical simulations, Black holes, Core-collapse supernovae, Gravitational wave astronomy
Early Planet Formation in Embedded Disks (eDisk). XIV. Flared Dust Distribution and Viscous Accretion Heating of the Disk around R CrA IRS 7B-a. We performed radiative transfer calculations and observing simulations to reproduce the 1.3 mm dust-continuum and C18O (2─1) images in the Class I protostar R CrA IRS7B-a, observed with the ALMA Large Program "Early Planet Formation in Embedded Disks (eDisk)." We found that a dust disk model passively heated by the central protostar cannot reproduce the observed peak brightness temperature of the 1.3 mm continuum emission (∼195 K), regardless of the assumptions about the dust opacity. Our calculation suggests that viscous accretion heating in the disk is required to reproduce the observed high brightness temperature. The observed intensity profile of the 1.3 mm dust-continuum emission along the disk minor axis is skewed toward the far side of the disk. Our modeling reveals that this asymmetric intensity distribution requires flaring of the dust along the disk vertical direction with the scale height following h/r ∼ r 0.3 as a function of radius. These results are in sharp contrast to those of Class II disks, which show geometrically flat dust distributions and lower dust temperatures. From our modeling of the C18O (2─1) emission, the outermost radius of the gas disk is estimated to be ∼80 au, which is larger than that of the dust disk (∼62 au), to reproduce the observed distribution of the C18O (2─1) emission in IRS 7B-a. Our modeling unveils a hot and thick dust disk plus a larger gas disk around one of the eDisk targets, which could be applicable to other protostellar sources in contrast to more evolved sources.

Keywords: Planet formation, Star formation, Radiative transfer, Interstellar medium
Aperture and Resolution Effects on Ultraviolet Star-forming Properties: Insights from Local Galaxies and Implications for High-redshift Observations. We present an analysis of the effects of spectral resolution and aperture scale on derived galaxy properties using far-ultraviolet (FUV) spectra of local star-forming galaxies from the International Ultraviolet Explorer (R ∼ 250, field of view (FOV) ∼ 10″ × 20″) and Cosmic Origins Spectrograph on the Hubble Space Telescope (R ∼ 15,000, FOV ∼ 2.″5). Using these spectra, we measured FUV luminosities, spectral slopes, dust attenuation, and equivalent widths. We find that galaxies with one dominant stellar cluster have FUV properties that are independent of aperture size, while galaxies with multiple bright clusters are sensitive to the total light fraction captured by the aperture. Additionally, we find significant correlations between the strength of stellar and interstellar absorption lines and metallicity, indicating metallicity-dependent line-driven stellar winds and interstellar macroscopic gas flows shape stellar and interstellar spectral lines, respectively. The observed line strength versus metallicity relation of stellar-wind lines agrees with the prediction of population synthesis models for young starbursts. In particular, measurements of the strong stellar C IV λλ1548, 1550 line provide an opportunity to determine stellar abundances as a complement to gas-phase abundances. We provide a relation between the equivalent width of the C IV line and the oxygen abundance of the galaxy. We discuss this relation in terms of the stellar-wind properties of massive stars. As the driving lines in stellar winds are mostly ionized iron species, the C IV line may eventually offer a method to probe α-element-to-iron ratios in star-forming galaxies once consistent models with nonsolar abundance ratios are available. These results have important implications for the galaxy-scale, low-resolution observations of high-redshift galaxies from JWST (R ∼ 100–3500). *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: Ultraviolet astronomy, Galaxy abundances, Galaxy evolution
Vacuum Ultraviolet Single Photon Ionization and Decomposition of 2-Aminopropionitrile in Astrophysical Objects. The molecule 2-aminopropionitrile (2-APN; H3CCH(NH2)CN) is a chiral precursor of the amino acid alanine and could play an important role in the emergence of the homochirality of life. To date, 2-APN has not yet been detected in the interstellar medium. To address the question of its absence, possibly through destruction by vacuum ultraviolet radiation in astrophysical media, we studied its photoionization and dissociative photoionization in the 9–14 eV (89–137 nm) energy range using photoelectron–photoion coincidence spectroscopy with velocity map imaging. Density functional theory calculations were performed at the PBE0/aug-cc-pVTZ level to determine structures for the various cationic fragments identified experimentally. Their appearance energies were calculated. The adiabatic ionization energy (AIE) of 2-APN is AIE = (9.85±0.01) eV and the appearance energy (AE) of the major fragment ion N≡CC(H)NH2 + is AE = (10.57±0.01) eV. Both ions, 2-APN+ and N≡CC(H)NH2 +, make up more than 90% of the formed ions. N≡CC(H)NH2 +, an isomer of the protonated HCN dimer, is also formed with high yield in the dissociative photoionization of aminoacetonitrile (NH2CH2CN), another α-aminonitrile observed in Sgr B2(N). Photoion yield spectra have been calibrated to absolute ionization cross sections. From these, we derive photoionization rates in several typical radiation fields relevant to different astrophysical objects. The rates show that, under almost all explored radiation fields, dissociative ionization is the dominant pathway for photoionization, leading to the loss of a methyl group (CH3) to form the planar thermodynamically stable amino cyano methylidynium ion N≡CC(H)NH2 +. The observed absence of 2-APN in Sgr B2 could thus be due to dominant dissociative photoionization.

Keywords: Photoionization, Photodissociation regions, Astrobiology, Quantum-chemical calculations, H II regions, Pre-biotic astrochemistry
The Plasma β in Quiet Sun Regions: Multi-instrument View. A joint campaign of several spaceborne and ground-based observatories, such as the GREGOR solar telescope, the Extreme-ultraviolet Imaging Spectrometer (EIS), and the Interface Region Imaging Spectrograph (Hinode Observing Plan 381, 2019 October 11–22) was conducted to investigate the plasma β in quiet Sun regions. In this work, we focus on 2019 October 13, 17, and 19 to obtain the plasma β at different heights through the solar atmosphere based on multiheight observational data. We obtained temperature, density, and magnetic field estimates from the GREGOR High-resolution Fast Imager, Infrared Spectrograph, Interface Region Imaging Spectrograph, and EIS and complementary data from the Solar Dynamics Observatory Atmospheric Imaging Assembly (AIA). Using observational data and models (e.g., FALC and PFSS), we determined the plasma β in the photosphere, chromosphere, transition region, and corona. The obtained plasma β values lie inside the expected ranges through the solar atmosphere. However, at EIS and AIA coronal heights (from 1.03 to 1.20 R ⊙), plasma β values appear in the limit defined by Gary; such behavior was previously reported by Rodríguez Gómez et al. Additionally, we obtained the plasma β in the solar photosphere at different optical depths from $\mathrm{log}\tau =-1.0$ to –2.0. These values decrease with optical depth. This work provides a complete picture of plasma β in quiet Sun regions through the solar atmosphere, which is a prerequisite of a better understanding of the plasma dynamics at the base of the solar corona.

Keywords: Quiet sun, Solar chromosphere, Solar photosphere, Solar transition region