adsabs/SciX_UAT_keywords huggingface dataset:
The Behavior of HgMn Stars in the Far-UV-Paper 19: HD 149121

The analysis of three spectra of the Mn Hg Sr star HD 149121 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux of this star over two sets of observations separated by about 6 yr. The synthesis of the Sr II resonance line at 4215.52 Å in a high resolution high signal-to-noise SOPHIE spectrum of HD 149121 yields a large overabundance of about 200 times the solar abundance of strontium and confirms that HD 149121 is a strontium-rich HgMn star.

Keywords: chemically peculiar stars; mercury-manganese stars
Deep DECam Y-band Follow-up of WISEA J153429.75-104303.3 (a.k.a. "The Accident")

WISEA J153429.75-104303.3 (a.k.a. "The Accident") is a brown dwarf with unique observational properties unlike those of any other known (sub)stellar object. It is thought to be a very cold, metal-poor brown dwarf, and potentially the first identified Y-type subdwarf. Although WISEA J153429.75-104303.3 is extremely faint at λ ~ 1.25 μm, low-temperature atmosphere models suggest that Y-band flux could increase dramatically relative to J-band as metallicity decreases from solar. We therefore obtained deep Y-band follow-up imaging of WISEA J153429.75-104303.3 with the Dark Energy Camera, and report a resulting Y-band limit of Y > 21.79 mag (Vega, 5σ).

Keywords: t dwarfs; y dwarfs; metallicity
A Parameter Space Exploration of High-resolution Numerically Evolved Early Type Galaxies Including AGN Feedback and Accurate Dynamical Treatment of Stellar Orbits

An extensive exploration of the model parameter space of axisymmetric early type galaxies (ETGs) hosting a central supermassive black hole (SMBH) is conducted by means of high-resolution hydrodynamical simulations performed with our code MACER. Global properties such as (1) total SMBH accreted mass, (2) final X-ray luminosity and temperature of the X-ray emitting halos, (3) total amount of new stars formed from the cooling gas, and (4) total ejected mass in the form of supernovae and active galactic nuclei (AGN) feedback induced galactic winds, are obtained as a function of galaxy structure and internal dynamics. In addition to the galactic dark matter halo, the model galaxies are also embedded in a group/cluster dark matter halo; finally, cosmological accretion is also included, with the amount and time dependence derived from cosmological simulations. Angular momentum conservation leads to the formation of cold H I disks; these disks further evolve under the action of star formation induced by disk instabilities, of the associated mass discharge onto the central SMBH, and of the consequent AGN feedback. At the end of the simulations, the hot (metal-enriched) gas mass is roughly 10% the mass in the old stars, with twice as much having been ejected into the intergalactic medium. The cold gas disks are approximately kiloparsec in size, and the metal-rich new stars are in 0.1 kpc disks. The masses of cold gas and new stars are roughly 0.1% of the mass of the old stars. Overall, the final systems appear to reproduce quite successfully the main global properties of real ETGs.

Keywords: early-type galaxies; active galactic nuclei; stellar dynamics; interstellar medium; x-ray astronomy; cooling flows
A Lyα Transit Left Undetected: the Environment and Atmospheric Behavior of K2-25b

K2-25b is a Neptune-sized exoplanet (3.45R⊕) that orbits its M4.5 host with a period of 3.48 days. Due to its membership in the Hyades Cluster, the system has a known age (727 ± 75 Myr). K2-25b's youth and its similarities with Gl 436b suggested that K2-25b could be undergoing strong atmospheric escape. We observed two transits of K2-25b at Lyα using HST/STIS in order to search for escaping neutral hydrogen. We were unable to detect an exospheric signature, but placed an upper limit of (Rp/R⋆)∣Lyα < 0.56 at 95% confidence by fitting the light curve of the Lyα red wing, or < 1.20 in the blue wing. We reconstructed the intrinsic Lyα profile of K2-25 to determine its Lyα flux, and analyzed XMM-Newton observations to determined its X-ray flux. Based on the total X-ray and extreme ultraviolet irradiation of the planet (8763 ± 1049 erg s-1 cm-2), we estimated the maximum energy-limited mass-loss rate of K2-25b to be ${10.6}_{-6.13}^{+15.2}\times {10}^{10}$ g s-1 (0.56M⊕ per 1 Gyr), five times larger than the similarly estimated mass-loss rate of Gl 436b (2.2 × 1010 g s-1). The photoionization time is about 3 hr, significantly shorter than Gl 436b's 14 hr. A nondetection of a Lyα transit could suggest K2-25b is not significantly losing its atmosphere, or factors of the system are resulting in the mass loss being unobservable (e.g., atmosphere composition or the system's large high-energy flux). Further observations could provide more stringent constraints.

Keywords: exoplanets; hot neptunes
The Lorentz Force at Work: Multiphase Magnetohydrodynamics throughout a Flare Lifespan

The hour-long, gradual phase of solar flares is well observed across the electromagnetic spectrum, demonstrating many multiphase aspects, where cold condensations form within the heated post-flare system, but a complete 3D model is lacking. Using a state-of-the-art 3D magnetohydrodynamic simulation, we identify the key role played by the Lorentz force through the entire flare lifespan, and show that slow variations in the post-flare magnetic field achieve the bulk of the energy release. Synthetic images in multiple passbands closely match flare observations, and we quantify the role of conductive, radiative, and Lorentz force work contributions from flare onset to decay. This highlights how the non-force-free nature of the magnetic topology is crucial to trigger Rayleigh–Taylor dynamics, observed as waving coronal rays in extreme ultraviolet observations. Our C-class solar flare reproduces multiphase aspects such as post-flare coronal rain. In agreement with observations, we find strands of cooler plasma forming spontaneously by catastrophic cooling, leading to cool plasma draining down the post-flare loops. As there is force balance between magnetic pressure and tension and the plasma pressure in gradual-phase flare loops, this has potential for coronal seismology to decipher the magnetic field strength variation from observations.

Keywords: solar physics; solar flares; magnetohydrodynamics
GRASS. II. Simulations of Potential Granulation Noise Mitigation Methods

We present an updated version of the GRanulation And Spectrum Simulator (GRASS) which now uses an expanded library of 22 solar lines to empirically model time-resolved spectral variations arising from solar granulation. We show that our synthesis model accurately reproduces disk-integrated solar line profiles and bisectors, and we quantify the intrinsic granulation-driven radial-velocity (RV) variability for each of the 22 lines studied. We show that summary statistics of bisector shape (e.g., bisector inverse slope) are strongly correlated with the measured anomalous, variability-driven RV at high pixel signal-to-noise ratio SNR and spectral resolution. Further, the strength of the correlations varies both line by line and with the summary statistic used. These correlations disappear for individual lines at the typical spectral resolutions and SNRs achieved by current extremely precise radial velocity spectrographs; so we use simulations from GRASS to demonstrate that they can, in principle, be recovered by selectively binning lines that are similarly affected by granulation. In the best-case scenario (high SNR and large number of binned lines), we find that a ≲30% reduction in the granulation-induced root mean square RV can be achieved, but that the achievable reduction in variability is most strongly limited by the spectral resolution of the observing instrument. Based on our simulations, we predict that existing ultra-high-resolution spectrographs, namely, ESPRESSO and PEPSI, should be able to resolve convective variability in other, bright stars.

Keywords: astronomy software; exoplanet detection methods; high resolution spectroscopy; solar granulation; stellar granulation
Inelastic Processes in Low-energy Sulfur-Hydrogen Collisions

The cross sections and rate coefficients for inelastic processes in low-energy collisions of sulfur atoms and positive ions with hydrogen atoms and negative ions are calculated for the collisional energy range ${10}^{-4}\mbox{--}100\,\mathrm{eV}$ and for the temperature range 1000-10,000 K. Fifty-five covalent states and two ionic ones are considered. The ground ionic state ${{\rm{S}}}^{+}(3{p}^{3}{}^{4}S^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ provides only ${}^{4}{{\rm{\Sigma }}}^{-}$ molecular symmetry, while the first-excited ionic state ${{\rm{S}}}^{+}(3{p}^{3}{}^{2}D^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ provides three molecular symmetries: ${}^{2}{{\rm{\Sigma }}}^{-}$ , ${}^{2}{\rm{\Pi }}$ , and ${}^{2}{\rm{\Delta }}$ . The study of sulfur-hydrogen collisions is performed by the quantum model methods within the Born-Oppenheimer formalism. The electronic structure of the collisional quasimolecule is calculated by the semiempirical asymptotic method for each considered molecular symmetry. For nuclear dynamic calculations, the multichannel formula in combination with the Landau-Zener model is used. Nuclear dynamics within each considered symmetry is treated separately, and the total rate coefficients for each inelastic process have been summed over all symmetries. The largest values of the rate coefficients (exceeding ${10}^{-8}\,{\mathrm{cm}}^{3}\ {{\rm{s}}}^{-1}$ ) correspond to the mutual neutralization processes in ${{\rm{S}}}^{+}(3{s}^{2}3{p}^{3}{}^{4}S^\circ )\,+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ (the ground ionic state being the initial state), as well as in ${{\rm{S}}}^{+}(3{p}^{3}{}^{2}D^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ (the first-excited ionic state being the initial state) collisions. At the temperature 6000 K, the rate coefficients with large magnitudes have the values from the ranges $(1.08\mbox{--}4.48)\times {10}^{-8}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$ and $(1.19\mbox{--}5.05)\times {10}^{-8}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$ , respectively. The calculated rate coefficients with large and moderate values are important for NLTE stellar atmosphere modeling.

Keywords: atomic data benchmarking; atomic physics; stellar abundances
ASKAP-EMU Radio Emission from Type Ic Supernova SN1996aq in NGC 5584

We report the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe survey detection of radio continuum emission from SN1996aq, a Type Ic supernova within the nearby face-on spiral galaxy NGC 5584. Analysis at multiple radio frequencies reveals radio emission coincident with SN1996aq. We find a flatter radio spectral index compared to the 2009 observations, indicating rapid evolution of SN1996aq. Conversely, no radio emission is observed from NGC 5584's other known supernova, SN2007af. Furthermore, we identified two other significant radio continuum regions with properties consistent with H II regions.

Keywords: supernova remnants; supernovae; radio continuum emission; h ii regions; spectral index
A Low-mass Pre-main-sequence Eclipsing Binary in Lower Centaurus Crux Discovered with TESS

We report the discovery of 2M1222-57 as a low-mass, pre-main-sequence (PMS) eclipsing binary (EB) in the Lower Centaurus Crux (LCC) association for which, using Gaia parallaxes and proper motions with a neural net age estimator, we determine an age of 16.2 ± 2.2 Myr. The broadband spectral energy distribution (SED) shows clear excess at ≳10 μm indicative of a circumbinary disk, and new speckle imaging observations reveal a faint, tertiary companion separated by ~100 au. Hα emission is modulated on the orbital period, consistent with theoretical models of orbitally pulsed accretion streams reaching from the inner disk edge to the central stars. From a joint analysis of spectroscopically determined radial velocities and TESS light curves, together with additional tight constraints provided by the SED and the Gaia parallax, we measure masses for the eclipsing stars of 0.74 M ⊙ and 0.67 M ⊙; radii of 0.98 R ⊙ and 0.94 R ⊙; and effective temperatures of 3750 K and 3645 K. The masses and radii of both stars are measured to an accuracy of ~1%. The measured radii are inflated, and the temperatures suppressed, relative to predictions of standard PMS evolutionary models at the age of LCC; also, the Li abundances are ~2 dex less depleted than predicted by those models. However, models that account for the global and internal effects of surface magnetic fields are able to simultaneously reproduce the measured radii, temperatures, and Li abundances at an age of 17.0 ± 0.5 Myr. Altogether, the 2M1222-57 system presents very strong evidence that magnetic activity in young stars alters both their global properties and the physics of their interiors.

Keywords: pre-main sequence stars; eclipsing binary stars; fundamental parameters of stars; stellar ages; stellar accretion; stellar magnetic fields; stellar masses; stellar radii; stellar effective temperatures; stellar activity; low mass stars
Dust Coagulation Reconciles Protoplanetary Disk Observations with the Vertical Shear Instability. I. Dust Coagulation and the VSI Dead Zone

Protoplanetary disks exhibit a vertical gradient in angular momentum, rendering them susceptible to the vertical shear instability (VSI). The most important condition for the onset of this mechanism is a short timescale of thermal relaxation (≲0.1 orbital timescales). Simulations of fully VSI active disks are characterized by turbulent, vertically extended dust layers. This is in contradiction with recent observations of the outer regions of some protoplanetary disks, which appear highly settled. In this work, we demonstrate that the process of dust coagulation can diminish the cooling rate of the gas in the outer disk and extinct the VSI activity. Our findings indicate that the turbulence strength is especially susceptible to variations in the fragmentation velocity of the grains. A small fragmentation velocity of ≈100 cm s-1 results in a fully turbulent simulation, whereas a value of ≈400 cm s-1 results in a laminar outer disk, being consistent with observations. We show that VSI turbulence remains relatively unaffected by variations in the maximum particle size in the inner disk regions. However, we find that dust coagulation can significantly suppress the occurrence of VSI turbulence at larger distances from the central star.

Keywords: protoplanetary disks; hydrodynamical simulations; relaxation time; astrophysical dust processes
Formation of Interstellar Complex Organic Molecules on Water-rich Ices Triggered by Atomic Carbon Freezing

The reactivity of interstellar carbon atoms (C) on water-dominated ices is one of the possible ways to form interstellar complex organic molecules (iCOMs). In this work, we report a quantum chemical study of the coupling reaction of C (3P) with an icy water molecule, alongside possible subsequent reactions with the most abundant closed-shell frozen species (NH3, CO, CO2, and H2), atoms (H, N, and O), and molecular radicals (OH, NH2, and CH3). We found that C reacts spontaneously with the water molecule, resulting in the formation of 3C-OH2, a highly reactive species due to its triplet electronic state. While reactions with the closed-shell species do not show any reactivity, reactions with N and O form CN and CO, respectively, the latter ending up in methanol upon subsequent hydrogenation. The reactions with OH, CH3, and NH2 form methanediol, ethanol, and methanimine, respectively, upon subsequent hydrogenation. We also propose an explanation for methane formation observed in experiments through additions of H to C in the presence of ices. The astrochemical implications of this work are: (i) atomic C on water ice is locked into 3C-OH2, making difficult the reactivity of bare C atoms on icy surfaces, contrary to what is assumed in current astrochemical models; and (ii) the extraordinary reactivity of 3C-OH2 provides new routes toward the formation of iCOMs in a nonenergetic way, in particular ethanol, the mother of other iCOMs once it is in the gas phase.

Keywords: astrochemistry; interstellar medium; interstellar molecules; interstellar dust; surface ices; complex organic molecules; reaction rates; computational methods
The Discovery of Blue-cored Dwarf Early-type Galaxies in Isolated Environments

The presence of blue-cored dwarf early-type galaxies (dE(bc)s) in high-density environments supports the scenario of the transformation of infalling late-type galaxies into quiescent dwarf early-type galaxies by environmental effects. While low-density environments lacking environmental processes could not be relevant to the formation of dE(bc)s, we discovered a large sample of rare dE(bc)s in isolated environments at z < 0.01 using the NASA-Sloan Atlas catalog. Thirty-two isolated dE(bc)s were identified by visual inspection of the Sloan Digital Sky Survey images and g - r color profiles. We found that (1) isolated dE(bc)s exhibit similar structural parameters to dE(bc)s in the Virgo cluster; (2) based on the color-magnitude relation, color gradients, and optical emission lines of dE(bc)s, isolated dE(bc)s show more vigorous, centrally concentrated star formation (SF) compared to their counterparts in the Virgo cluster; (3) at a given stellar mass, isolated dE(bc)s tend to have a larger fraction of gas mass than their Virgo counterparts. We discuss a scenario of episodic SF sustained by gas accretion, suggested by Sánchez Almeida et al., in which the star-bursting blue compact dwarf galaxy (BCD)-quiescent BCD (QBCD) cycle can be repeated during the Hubble time. We suggest that, in this cadence, isolated dE(bc)s might be QBCDs at pre- or post-BCD stages. Our results imply that dE(bc)s comprise a mixture of objects with two types of origins, nature or nurture, depending on their environment.

Keywords: dwarf galaxies; blue compact dwarf galaxies; dwarf elliptical galaxies; field galaxies; star formation; galaxy environments; galaxy evolution
Properties of Suprathermal-through-energetic He Ions Associated with Stream Interaction Regions Observed over the Parker Solar Probe's First Two Orbits

The Integrated Science Investigation of the Sun (IS⊙IS) suite on board NASA's Parker Solar Probe (PSP) observed six distinct enhancements in the intensities of suprathermal-through-energetic (∼0.03-3 MeV nucleon-1) He ions associated with corotating or stream interaction regions (CIR or SIR) during its first two orbits. Our results from a survey of the time histories of the He intensities, spectral slopes, and anisotropies and the event-averaged energy spectra during these events show the following: (1) In the two strongest enhancements, seen at 0.35 and 0.85 au, the higher-energy ions arrive and maximize later than those at lower energies. In the event seen at 0.35 au, the He ions arrive when PSP was away from the SIR trailing edge and entered the rarefaction region in the high-speed stream. (2) The He intensities either are isotropic or show sunward anisotropies in the spacecraft frame. (3) In all events, the energy spectra between ∼0.2 and 1 MeV nucleon-1 are power laws of the form ∝E-2. In the two strongest events, the energy spectra are well represented by flat power laws between ∼0.03 and 0.4 MeV nucleon-1 modulated by exponential rollovers between ∼0.4 and 3 MeV nucleon-1. We conclude that the SIR-associated He ions originate from sources or shocks beyond PSP's location rather than from acceleration processes occurring at nearby portions of local compression regions. Our results also suggest that rarefaction regions that typically follow the SIRs facilitate easier particle transport throughout the inner heliosphere such that low-energy ions do not undergo significant energy loss due to adiabatic deceleration, contrary to predictions of existing models.

Keywords: solar wind; corotating streams; interplanetary particle acceleration
Finding Signs of Life on Transiting Earthlike Planets: High-resolution Transmission Spectra of Earth through Time around FGKM Host Stars

The search for life in the universe mainly uses modern Earth as a template. However, we know that Earth's atmospheric composition changed significantly through its geological evolution. Recent discoveries show that transiting, potentially Earthlike, exoplanets orbit a wide range of host stars, which strongly influence their atmospheric composition and remotely detectable spectra. Thus, a database for transiting terrestrial exoplanets around different host stars at different geological times is a crucial missing ingredient to support observational searches for signs of life in exoplanet atmospheres. Here, we present the first high-resolution transmission spectra database for Earthlike planets, orbiting a wide range of host stars, throughout four representative stages of Earth's history. These correspond to a prebiotic high-CO2 world—about 3.9 billion years ago in Earth's history—and three epochs through the increase in oxygen from 0.2% to modern atmospheric levels of 21%. We demonstrate that the spectral biosignature pairs O2+CH4 and O3+CH4 in the atmosphere of a transiting Earthlike planet would show a remote observer that a biosphere exists for oxygen concentrations of about 1% of modern Earth's—corresponding to about 1-2 billion years ago in Earth's history—for all host stars. The full model and high-resolution transmission spectra database, covering 0.4-20 μm, for transiting exoplanets—from young prebiotic worlds to modern Earth analogs orbiting a wide range of host stars—is available online. It is a tool to plan and optimize our observation strategy, train retrieval methods, and interpret upcoming observations with ground- and space-based telescopes.

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanet atmospheric composition; transmission spectroscopy; biosignatures; exoplanet atmospheric variability
Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

We performed a numerical study for interpreting observations of plasma blobs occurring in the solar corona. Considering all of the previous studies and the presence of magnetic null points together with propagating magnetohydrodynamic waves in the solar corona, we guessed that the interaction of fast magnetoacoustic waves with null points could give rise to blobs under coronal conditions. The outcome of these interactions contributes to coronal jets and flares that directly affects us on Earth. The propagation of magnetoacoustic waves in the vicinity of a magnetic null point contributes to the high current density accumulation at the small scale around the magnetic null point, which has significant magnetic gradients. When nonlinearity becomes dominant, the variation of current density could result in instabilities and thus anomalous resistivity. Moreover, it is demonstrated that plasmoids with eruption events take place in the solar corona without considering the transition region. In our numerical simulation results, it is interesting that plasma blobs manifest themselves in many parameters, including current density, temperature, plasma density, flows, and magnetic fields, simultaneously and consistent with the generation of plasmoids. In this work, it is found that plasmoid instability is the reason for the plasma blobs and tiny blobs are produced by the tearing instability occurring in thin current sheets.

Keywords: magnetohydrodynamics; magnetohydrodynamical simulations; the sun; solar corona