Sazuna/UAT_keywords huggingface dataset:
Methanol Formation through Reaction of Low-energy CH<SUB>3</SUB> <SUP>+</SUP> Ions with an Amorphous Solid Water Surface at Low Temperature. We have performed experimental investigations of methanol formation via the reactions of low-energy CH3 + ions with an amorphous solid water (ASW) surface at ~10 K. A newly developed experimental apparatus enabled irradiation of the ASW surface by several eV ions and detection of trace amounts of reaction products on the surface. It was found that methanol molecules were produced by low-energy CH3 + irradiation of the ASW surface and that hydroxy groups in the produced methanol originated from water molecules in the ASW, as predicted in a previous theoretical study. Little temperature dependence of the observed methanol intensity is apparent in the temperature range 12-60 K. Ab initio molecular dynamics simulations under constant-temperature conditions of 10 K suggested that this reaction spontaneously produced a methanol molecule and an H3O+ ion, regardless of the contact point of CH3 + on the ASW surface. We have performed a simulation with an astrochemical model under molecular-cloud conditions, where the reaction between CH3 + and H2O ice, leading to methanol formation, was included. We found that the impact of the reaction on methanol abundance was limited only at the edge of the molecular cloud (&lt;1 mag) because of the low abundance of CH3 + in the gas phase, whereas the reaction between the abundant molecular ion (HCO+) and H2O ice, which has not yet been confirmed experimentally, can considerably affect the abundance of a complex organic molecule. This work sheds light on a new type of reaction between molecular ions and ice surfaces that should be included in astrochemical models.

Keywords: Astrochemistry, Ion-neutral reactions, Molecular physics, Interstellar dust processes, Molecular reactions
Sample Variance in Cosmological Observations with a Narrow Field of View. Surveys with a narrow field of view can play an important role in probing cosmology, but inferences from these surveys suffer from large sample variance, arising from random fluctuations around the cosmic mean. The standard method for computing the sample variance is based on two key approximations: treating perturbations linearly and the survey geometry as a box. We demonstrate that it can lead to a significant underestimate of the sample variance in narrow surveys. We present a new method for accurately computing the sample variance and apply our method to the recent observations of the warm-hot intergalactic medium (WHIM) based on spectroscopic measurements of blazars. We find that the sample variances in these surveys are significantly larger than the quoted measurement errors; for example, the cosmic mean baryon density contained in the WHIM could be lower by 54% at 1σ fluctuation than estimated in one observation. Accurately quantifying the sample variance is essential in deriving correct interpretations of the measurements in surveys with a small field of view.

Keywords: Cosmology, Observational cosmology
ACA CO(J = 2-1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds. We present the results of ALMA-ACA 7 m array observations in 12CO(J = 2-1), 13CO(J = 2-1), and C18O(J = 2-1) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7.″31 × 6.″50 (30 × 26 pc). We combined the ACA 7 m array 12CO(J = 2-1) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined 12CO(J = 2-1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM 12CO(J = 2-1) cube data, we cataloged 848 molecular clouds with a mass range from 103-106 M ☉. We found that high-mass clouds (≥105 M ☉) tend to associate with the 8 μm bright sources in the spiral arm region, while low-mass clouds (&lt;105 M ☉) tend to be apart from such 8 μm bright sources and to exist in the inter-arm region. We compared the cataloged clouds with GMCs observed by the IRAM 30 m telescope at 49 pc resolution (IRAM GMC), and found that a small IRAM GMC is likely to be identified as a single molecular cloud even in ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly dominated by the line-of-sight velocity difference between small clouds inside the GMC rather than the internal cloud velocity broadening.

Keywords: Local Group, Triangulum Galaxy, Molecular clouds, Interstellar medium
Neutrinos and Asteroseismology of Stars over the Helium Flash. The helium flash, occurring in stars of 0.6-2.0 M ⊙ at the end of the red giant branch, is not observable via optical means due to the energy of the process being used to lift the core out of degeneracy. Neutrinos, which are linked to the ignition of reactions triggered during the flash and serve as the only cooling process in the inert core, can help characterize changes in internal structure. In this work, we create 18 stellar models across three mass and six metallicity values, chosen in the context of the stellar abundance problem, to compare the evolutionary path up to and probe the helium flash by conducting a detailed study of neutrino emission throughout this crucial phase of stellar evolution. We demonstrate how thermal neutrino emissions could have an imprint on global asteroseismic parameters and use them as an additional tool to infer the impact of compositional changes. We find that a precision of 0.3 μHz in the determination of Δν is enough to distinguish between between the two most prominent solar composition models and confirm that asteroseismic observation can be enough to classify a star as undergoing the process of helium subflashes. We also predict nuclear neutrino emission fluxes and their evolution for all relevant sources.

Keywords: Red giant tip, Neutrino astronomy, Asteroseismology, Stellar abundances
The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b. The absorption signals of metastable He in HD 209458b and several other exoplanets can be explained via an escaping atmosphere model with a subsolar He/H ratio. The low abundance of helium can be a result of planet formation if there is a small amount of helium in their primordial atmosphere. However, another possibility is that the low He/H ratio is caused by the process of mass fractionation of helium in the atmosphere. In order to investigate the effect of fractionation in the hydrogen-helium atmosphere, we developed a self-consistent multi-fluid 1D hydrodynamic model based on the well-known open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be produced spontaneously in the multi-fluid model. We further modeled the transmission spectra of He 10830 lines for HD 209458b in a broad parameter space. The transmission spectrum of the observation can be fitted in the condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen, F He/F H, is 0.039. Our results indicate that the mass fractionation of helium to hydrogen can naturally interpret the low He/H ratio required by the observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the abundance of helium in the atmosphere is not needed even if its He abundance is similar to that of the Sun. The simulation presented in this work hints that in the escaping atmosphere, mass fractionation can also occur on other exoplanets, which needs to be explored further. *Revised Manuscript on 2022 June 7

Keywords: Hydrodynamical simulations, Radiative transfer simulations, Exoplanet atmospheres
On the Proposed Interstellar Origin of the USG 20140108 Fireball. A critical review of the evidence for the interstellar origin of the USG 20140108 fireball is presented. Examining United States Government (USG) fireball velocities where independent data are available shows the former to have significant (10-15 km s-1) uncertainties at large speeds and highly variable radiant accuracy, with average errors in excess of 10°. The ablation model fits to the observed lightcurve are possible for normal chondritic impactors only assuming low speeds. To match the high speed and low fragmentation height of the USG 20140108 fireball would require a high-density/strength object with low drag and a highly aerodynamic shape not made of iron. We suggest the simplest explanation for the unusual characteristics of USG 20140108 is that the speed, in particular, is substantially overestimated.

Keywords: Interstellar objects, Meteoroids
The Runaway Greenhouse Effect on Hycean Worlds. Hycean worlds are a proposed subset of sub-Neptune exoplanets with substantial water inventories, liquid surface oceans, and extended hydrogen-dominated atmospheres favorable for habitability. We aim to quantitatively define the inner edge of the Hycean habitable zone (HZ) using a 1D radiative-convective model. As a limiting case, we model a dry hydrogen-helium envelope above a surface ocean. For a 1 bar (10,100 bar) atmosphere, the hydrogen greenhouse effect alone sets the inner edge of the HZ at 0.216 au (0.58, 3.71 au) for a Sun-like G star and at 0.0364 au (0.110, 0.774 au) for an 3500 K M star. Introducing water vapor into the atmosphere, the runaway greenhouse instellation limit is greatly reduced due to the presence of superadiabatic layers where convection is inhibited. This moves the inner edge of the HZ from ≈1 au for a G star to 1.6 au (3.85 au) for a Hycean world with a H2-He inventory of 1 bar (10 bar). For an M star, the inner edge is equivalently moved from 0.17-0.28 au (0.54 au). Our results suggest that most of the current Hycean world observational targets are not likely to sustain a liquid water ocean. We present an analytical framework for interpreting our results, finding that the maximum possible outgoing longwave radiation scales approximately inversely with the dry mass inventory of the atmosphere. We discuss the possible limitations of our 1D modeling and recommend the use of 3D convection-resolving models to explore the robustness of superadiabatic layers.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheric dynamics, Habitable zone, Habitable planets, Exoplanet atmospheres, Exoplanet atmospheric structure
Testing the Collisionless Nature of Dark Matter with the Radial Acceleration Relation in Galaxy Clusters. The radial acceleration relation (RAR) represents a tight empirical relation between the inferred total and baryonic centripetal accelerations, g tot = GM tot(&lt; r)/r 2 and g bar = GM bar(&lt; r)/r 2, observed in galaxies and galaxy clusters. The tight correlation between these two quantities can provide insight into the nature of dark matter. Here we use BAHAMAS, a state-of-the-art suite of cosmological hydrodynamical simulations, to characterize the RAR in cluster-scale halos for both cold and collisionless dark matter (CDM) and self-interacting dark matter (SIDM) models. SIDM halos generally have reduced central dark matter densities, which reduces the total acceleration in the central region when compared with CDM. We compare the RARs in galaxy clusters simulated with different dark matter models to the RAR inferred from CLASH observations. Our comparison shows that the cluster-scale RAR in the CDM model provides an excellent match to the CLASH RAR obtained by Tian et al. including the high-acceleration regime probed by the brightest cluster galaxies (BCGs). By contrast, models with a larger SIDM cross section yield increasingly poorer matches to the CLASH RAR. Excluding the BCG regions results in a weaker but still competitive constraint on the SIDM cross section. Using the RAR data outside the central r &lt; 100 kpc region, an SIDM model with σ/m = 0.3 cm2 g-1 is disfavored at the 3.8σ level with respect to the CDM model. This study demonstrates the power of the cluster-scale RAR for testing the collisionless nature of dark matter.

Keywords: Galaxy clusters, Cosmology, Gravitational lensing, Intracluster medium, Dark matter
Brown Dwarf Retrievals on FIRE!: Atmospheric Constraints and Lessons Learned from High Signal-to-noise Medium-resolution Spectroscopy of a T9 Dwarf. Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been successfully applied to low-resolution (R ~ 100) spectra of L, T, and Y dwarfs, yielding constraints on the chemical abundances and temperature structures of these atmospheres. Medium-resolution (R ~ 103) spectra of brown dwarfs offer additional insight, as molecular features are more easily disentangled and the thermal structure of the upper atmosphere is better probed. We present results from a GPU-based retrieval analysis of a high signal-to-noise, medium-resolution (R ~ 6000) FIRE spectrum from 0.85 to 2.5 μm of the T9 dwarf UGPS J072227.51-054031.2. At 60× higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise. We examine the effect of different opacity sources, in particular for CH4. Furthermore, we find that flaws in the data like errors from order stitching can bias our constraints. We compare these retrieval results to those for an R ~ 100 spectrum of the same object, revealing how constraints on atmospheric abundances and temperatures improve by an order of magnitude or more with increased spectral resolution. In particular, we can constrain the abundance of H2S, which is undetectable at lower spectral resolution. While these medium-resolution retrievals offer the potential of precise, stellar-like constraints on atmospheric abundances (~0.02 dex), our retrieved radius is unphysically small ( $R={0.50}_{-0.01}^{+0.01}$ R Jup), indicating shortcomings with our modeling framework. This work is an initial investigation into brown dwarf retrievals at medium spectral resolution, offering guidance for future ground-based studies and JWST observations.

Keywords: Atmospheric composition, Brown dwarfs, Bayesian statistics, T dwarfs
A Type II Radio Burst Driven by a Blowout Jet on the Sun. Type II radio bursts are often associated with coronal shocks that are typically driven by coronal mass ejections (CMEs) from the Sun. Here we conduct a case study of a type II radio burst that is associated with a C4.5-class flare and a blowout jet, but without the presence of a CME. The blowout jet is observed near the solar disk center in the extreme-ultraviolet (EUV) passbands with different characteristic temperatures. Its evolution involves an initial phase and an ejection phase with a velocity of 560 ± 87 km s-1. Ahead of the jet front, an EUV wave propagates at a projected velocity of ~403 ± 84 km s-1 in the initial stage. The velocity of the type II radio burst is estimated to be ~641 km s-1, which corresponds to the shock velocity against the coronal density gradient. The EUV wave and the type II radio burst are closely related to the ejection of the blowout jet, suggesting that both are likely the manifestation of a coronal shock driven by the ejection of the blowout jet. The type II radio burst likely starts lower than those associated with CMEs. The combination of the velocities of the radio burst and the EUV wave yields a modified shock velocity at ~757 km s-1. The Alfvén Mach number is in the range of 1.09-1.18, implying that the shock velocity is 10%-20% larger than the local Alfvén velocity.

Keywords: Solar coronal radio emission, Solar coronal waves, Solar filament eruptions, Solar activity, Shocks
Sequential Remote Brightenings and Co-spatial Fast Downflows during Two Successive Flares. Remote brightenings often appear at the outskirts of the active regions of solar eruptive events. Nevertheless, their origin remains to be ascertained. In this study, we report imaging and spectroscopic observations of sequential remote brightenings with a combination of observations from the Hα Imaging Spectrograph on board the Chinese Hα Solar Explorer, which is the first space-based solar telescope of China, and from the Solar Dynamics Observatory. It is found that during two successive M-class flares occurring on 2022 August 17 multiple ribbon-like brightenings appeared in sequence away from the flaring active region. Meanwhile, abundant cool filament materials moved downward to the sequential remote brightenings, which were visible at the Hα red wing with a line-of-sight speed of up to 70 km s‑1. The extrapolated three-dimensional magnetic field configuration shows that the sequential remote brightenings correspond to the footpoints of closed ambient field lines whose conjugate footpoints are rooted in the main flare site. We suggest that the sequential remote brightenings are most likely to be caused by the heating of the interchange reconnection between the erupting flux rope and the closed ambient field, during which the rope-hosting filament materials are transferred to the periphery of the flaring active region along the closed ambient field rather than to the interplanetary space, such as in the scenario of slow solar wind formation.

Keywords: Active solar corona, Solar flares, Solar magnetic reconnection, Solar magnetic fields
Stellar Bars in Isolated Gas-rich Spiral Galaxies Do Not Slow Down. Elongated bar-like features are ubiquitous in galaxies, occurring at the centers of approximately two-thirds of spiral disks in the nearby Universe. Due to gravitational interactions between the bar and the other components of galaxies, it is expected that angular momentum and matter will redistribute over long (Gyr) timescales in barred galaxies. Previous work ignoring the gas phase of galaxies has conclusively demonstrated that bars should slow their rotation over time due to their interaction with dark matter halos. We have performed a simulation of a Milky Way-like galactic disk hosting a strong bar, including a state-of-the-art model of the interstellar medium and a live dark matter halo. In this simulation, the bar pattern does not slow down over time, and instead it remains at a stable, constant rate of rotation. This behavior has been observed in previous simulations using more simplified models for the interstellar gas, but the apparent lack of secular evolution has remained unexplained. We find that the presence of the gas phase arrests the process by which the dark matter halo slows down a bar, a phenomenon we term bar locking. This locking is responsible for stabilizing the bar pattern speed. We find that, in a Milky Way-like disk, a gas fraction of only about 5% is necessary for this mechanism to operate. Our result naturally explains why nearly all observed bars rotate rapidly and is especially relevant for our understanding of how the Milky Way arrived at its present state.

Keywords: Hydrodynamical simulations, Galaxy dynamics, Milky Way dynamics, Milky Way evolution, Barred spiral galaxies, Milky Way Galaxy
Data-constrained 3D Modeling of a Solar Flare Evolution: Acceleration, Transport, Heating, and Energy Budget. Solar flares are driven by the release of free magnetic energy and its conversion to other forms of energy-kinetic, thermal, and nonthermal. Quantification of partitions between these energy components and their evolution is needed to understand the solar flare phenomenon including nonthermal particle acceleration, transport, and escape as well as the thermal plasma heating and cooling. The challenge of remote-sensing diagnostics is that the data are taken with finite spatial resolution and suffer from line-of-sight (LOS) ambiguity including cases when different flaring loops overlap and project one over the other. Here, we address this challenge by devising a data-constrained evolving 3D model of a multiloop SOL2014-02-16T064620 solar flare of GOES class C1.5. Specifically, we employed a 3D magnetic model validated earlier for a single time frame and extended it to cover the entire flare evolution. For each time frame we adjusted the distributions of the thermal plasma and nonthermal electrons in the model so that the observables synthesized from the model matched the observations. Once the evolving model had been validated in this way, we computed and investigated the evolving energy components and other relevant parameters by integrating over the model volume. This approach removes the LOS ambiguity and permits us to disentangle contributions from the overlapping loops. It reveals new facets of electron acceleration and transport as well as of the heating and cooling of the flare plasma in 3D. We find signatures of substantial direct heating of the flare plasma not associated with the energy loss of nonthermal electrons.

Keywords: Solar flares, Solar extreme ultraviolet emission, Solar x-ray emission, Solar radio emission, Non-thermal radiation sources, Solar activity
Deficit of Hot Dust in Low-redshift Active Galactic Nuclei. We assemble a broadband spectral energy distribution (SED) ranging from the optical to the mid-infrared of nearby active galactic nuclei (AGNs) at z &lt; 0.4. The SED fitting analysis is performed using semiempirical templates derived from Palomar-Green quasars to classify the sample into normal, warm-dust-deficient (WDD), and hot-dust-deficient (HDD) AGNs. Kolmogorov-Smirnov tests reveal that HDD AGNs exhibit higher AGN luminosity on average than normal and WDD AGNs. The HDD fraction, on the other hand, is only weakly correlated with the black hole mass and inversely correlated with the Eddington ratio. By fixing the other parameters, we conclude that the HDD fraction is primarily connected with the AGN luminosity. This implies that there is a causal connection between the covering factor of the hot dust component and AGN luminosity, possibly due to the sublimation of the innermost dust or the thickening of the intervening gas in the broad-line region. Analysis of the outflow properties traced by the wing of [O III]λ5007 suggests that outflows may be related to the formation and maintenance of the hot dust component. Finally, we demonstrate through comparison with previous studies that the classification of HDD AGNs requires careful subtraction of the host galaxy light.

Keywords: Quasars
Comparing Energetic Storm Particle Heavy-ion Properties in Solar Cycles 23 and 24. We examine variations in energetic storm particle (ESP) heavy-ion average intensities and energy spectra between ~0.1 and 75 MeV nucleon-1 at coronal mass ejection (CME)-driven interplanetary shocks for events observed at the ACE spacecraft. We compare ESP events observed during the weaker solar cycle (SC) 24 and the relatively stronger SC 23 to investigate any effects on the strength of an SC, including the associated transient events, on ESP properties at 1 au. We find that the number of clearly defined heavy-ion ESP events at ACE during SC 23 is about twice that observed during SC 24 (76 versus 41). The average transit speed of the driving interplanetary CMEs (ICMEs) at 1 au is 20% higher during SC 23 than during SC 24 (859.4 km s-1 versus 729.1 km s-1). The correlation of ESP average intensities with ICME speeds shows that lower-speed ICMEs in SC 24 can be as efficient as the higher-speed events in SC 23 at producing ESPs below 2 MeV nucleon-1. The distribution and magnitude of the average intensities for energies below ~1 MeV nucleon-1 are consistent between both SCs. However, events with intensity enhancements at higher energies (&gt;~10 MeV nucleon-1) are more frequent and their intensity distributions are harder for SC 23, resulting in an increase in the rollover energy (E 0) for their spectra profiles. This suggests more efficient ESP acceleration at &gt;10 MeV nucleon-1 during SC 23.

Keywords: Solar cycle, Solar energetic particles, Interplanetary particle acceleration, Solar coronal mass ejections, Sunspot cycle