adsabs/SciX_UAT_keywords huggingface dataset:
The Infrared Evolution of Dust in V838 Monocerotis

Luminous Red Variables are most likely eruptions that are the outcome of stellar mergers. V838 Mon is one of the best-studied members of this class, representing an archetype for stellar mergers resulting from B-type stars. As result of the merger event, "nova-like" eruptions occur driving mass loss from the system. As the gas cools considerable circumstellar dust is formed. V838 Mon erupted in 2002 and is undergoing very dynamic changes in its dust composition, geometry, and infrared luminosity providing a real-time laboratory to validate mineralogical condensation sequences in stellar mergers and evolutionary scenarios. We discuss recent NASA Stratospheric Observatory for Infrared Astronomy 5-38 μm observations combined with archival NASA Spitzer spectra that document the temporal evolution of the freshly formed (within the last ≲20 yr) circumstellar material in the environs of V838 Mon. Changes in the 10 μm spectral region are strong evidence that we are witnessing a classical dust condensation sequence expected to occur in oxygen-rich environments where alumina formation is followed by that of silicates at the temperature cools.

Keywords: asymptotic giant branch stars; circumstellar dust; astrochemistry
Coronal Heating Rate in the Slow Solar Wind

This Letter reports the first observational estimate of the heating rate in the slowly expanding solar corona. The analysis exploits the simultaneous remote and local observations of the same coronal plasma volume, with the Solar Orbiter/Metis and the Parker Solar Probe instruments, respectively, and relies on the basic solar wind magnetohydrodynamic equations. As expected, energy losses are a minor fraction of the solar wind energy flux, since most of the energy dissipation that feeds the heating and acceleration of the coronal flow occurs much closer to the Sun than the heights probed in the present study, which range from 6.3 to 13.3 R ⊙. The energy deposited to the supersonic wind is then used to explain the observed slight residual wind acceleration and to maintain the plasma in a nonadiabatic state. As derived in the Wentzel-Kramers-Brillouin limit, the present energy transfer rate estimates provide a lower limit, which can be very useful in refining the turbulence-based modeling of coronal heating and subsequent solar wind acceleration.

Keywords: magnetohydrodynamics; magnetohydrodynamical simulations; interplanetary turbulence; solar corona; solar coronal heating; solar wind; solar physics; the sun
Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-selected Highly Reddened Active Galactic Nuclei

Cold, substellar objects such as brown dwarfs have long been recognized as contaminants in color-selected samples of active galactic nuclei (AGNs). In particular, their near- to mid-infrared colors (1-5 μm) can closely resemble the V-shaped (f λ ) spectra of highly reddened accreting supermassive black holes ("little red dots"), especially at 6 < z < 7. Recently, a NIRCam-selected sample of little red dots over 45 arcmin2 has been followed up with deep NIRSpec multiobject prism spectroscopy through the UNCOVER program. By investigating the acquired spectra, we identify 3 of the 14 followed-up objects as T/Y dwarfs with temperatures between 650 and 1300 K and distances between 0.8 and 4.8 kpc. At ${4.8}_{-0.1}^{+0.6}$ kpc, A2744-BD1 is the most distant brown dwarf discovered to date. We identify the remaining 11 objects as extragalactic sources at z spec ≳ 5. Given that three of these sources are strongly lensed images of the same AGN (A2744-QSO1), we derive a brown dwarf contamination fraction of 25% in this NIRCam selection of little red dots. We find that in the near-infrared filters, brown dwarfs appear much bluer than the highly reddened AGN, providing an avenue for distinguishing the two and compiling cleaner samples of photometrically selected highly reddened AGN.

Keywords: brown dwarfs; t dwarfs; y dwarfs; active galactic nuclei
Spectroscopic Confirmation of CEERS NIRCam-selected Galaxies at z ≃ 8-10

We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts z phot > 8. We measure emission line redshifts of z = 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure $z={9.77}_{-0.29}^{+0.37}$ and ${10.01}_{-0.19}^{+0.14}$ by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Lyα opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts z > 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two z ~ 10 sources observed are relatively luminous (M UV < -20), with blue continua (-2.3 ≲ β ≲ -1.9) and low dust attenuation ( ${A}_{V}\simeq {0.15}_{-0.1}^{+0.3}$ ); and at least one of them has a high stellar mass for a galaxy at that redshift ( $\mathrm{log}({M}_{\star }/{M}_{\odot })\simeq {9.3}_{-0.3}^{+0.2}$ ). Considered together with spectroscopic observations of other CEERS NIRCam-selected high-z galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35 z > 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z > 9.6. We find that z > 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (<Δz> = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-z sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at z > 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at z > 8.

Keywords: early universe; galaxy evolution; galaxy formation; high-redshift galaxies
Chemical Properties of the Local Galactic Disk and Halo. I. Fundamental Properties of 1544 Nearby, High Proper-motion M Dwarfs and Subdwarfs

Due to their ubiquity and very long main-sequence lifetimes, M dwarfs provide an excellent tool to study the formation and chemical enrichment history of our Galaxy. However, owing to their intrinsic faintness, the acquisition of high-resolution, high signal-to-noise spectra of low-mass stars has been limited to small numbers of very nearby stars, mostly from the Galactic disk population. On the other hand, large numbers of low- to medium-resolution spectra of M-type dwarf stars from both the local Galactic disk and halo are available from various surveys. In order to fully exploit these data, we develop a template-fit method using a set of empirically assembled M dwarf/subdwarf classification templates, based on the measurements of the TiO and CaH molecular bands near 7000 Å, which are used to classify M dwarfs/subdwarfs by spectral type and metallicity class. We further present a pipeline to automatically determine the effective temperature T eff, metallicity [M/H], α-element to iron abundance ratio [α/Fe], and surface gravity log g of M dwarfs/subdwarfs using the latest version of BT-Settl model atmospheres. We apply these methods to a set of low- to medium-resolution spectra of 1544 high proper-motion (μ ≥ 0.″4 yr-1) M dwarfs/subdwarfs, collected at the MDM observatory, Lick Observatory, Kitt-Peak National Observatory, and Cerro-Tololo Interamerican Observatory. Our metallicity estimates appear to be consistent with the expected color-magnitude variation of stars relative to the atmospheric composition, as our sample shows a clear stratification with respect to metallicity in the Hertzsprung-Russel diagram constructed from their Gaia DR2 parallaxes and optical magnitudes. Furthermore, the measured chemical parameters of the two components in 48 binary systems are in good agreement with each other, which suggest a precision of ±0.22 dex in [M/H], ±0.08 dex in [α/Fe], and ±0.16 dex in the combined index [α/Fe] + [M/H]. We find that the relationship between color and spectral subtype depends on metallicity class, as the color G BP - G RP is more sensitive to subtype for metal-rich M dwarfs in comparison to metal-poor M subdwarfs. We also demonstrate that effective temperature as a function of spectral subtype has a steeper slope for metal-rich M dwarfs than metal-poor M subdwarfs. There is also a good consistency between “metallicity class,” obtained from the empirical classification templates, and the index [α/Fe] + [M/H] (∼[α/H]), obtained from BT-Settl model fitting, which means that the more easily measured “metallicity class” can be used as a relatively reliable indicator of absolute α-element abundance, [α/H], in low-mass stars. Finally, we examine the distribution of our stars in the [α/Fe] versus [M/H] diagram, which shows evidence of clustering in chemical abundance makeup, suggestive of discrete populations among the local disk and halo stars. We predict that analyses of larger samples of spectra of nearby M-type stars will uncover a complex structure of our Galaxy.

Keywords: m dwarf stars
Toward a Live Homogeneous Database of Solar Active Regions Based on SOHO/MDI and SDO/HMI Synoptic Magnetograms. I. Automatic Detection and Calibration

Recent studies indicate that a small number of rogue solar active regions (ARs) may have a significant impact on the end-of-cycle polar field and the long-term behavior of solar activity. The impact of individual ARs can be qualified based on their magnetic field distribution. This motivates us to build a live homogeneous AR database in a series of papers. As the first of the series, we develop a method to automatically detect ARs from 1996 onward based on SOHO/MDI and SDO/HMI synoptic magnetograms. The method shows its advantages in excluding decayed ARs and unipolar regions and being compatible with any available synoptic magnetograms. The identified AR flux and area are calibrated based on the cotemporal SDO/HMI and SOHO/MDI data. The homogeneity and reliability of the database are further verified by comparing it with other relevant databases. We find that ARs with weaker flux have a weaker cycle dependence. Stronger ARs show a weaker cycle 24 compared with cycle 23. Several basic parameters, namely, the location, area, and flux of negative and positive polarities of the identified ARs, are provided in the paper. This paves the way for ARs' new parameters quantifying the impact on the long-term behavior of solar activity to be presented in the subsequent paper of the series. The constantly updated database covering more than two full solar cycles will be beneficial for the understanding and prediction of the solar cycle. The database and the detection codes are accessible online.

Keywords: solar cycle; solar active regions; astronomy databases; astronomy image processing
High-resolution Laboratory Measurements of K-shell X-Ray Line Polarization and Excitation Cross Sections in Helium-like S XV Ions

We report measurements of electron-impact excitation cross sections for the strong K-shell n = 2 → 1 transitions in S XV, using the LLNL EBIT-I electron beam ion trap, two crystal spectrometers, and the EBIT Calorimeter Spectrometer. The cross sections are determined by direct normalization to the well-known cross sections of radiative electron capture, measured simultaneously. Using contemporaneous polarization measurements with the two crystal spectrometers, whose dispersion planes are oriented parallel and perpendicular to the electron beam direction, the polarization of the direct excitation line emission is determined, and in turn the isotropic total cross sections are extracted. We further experimentally investigate various line-formation mechanisms, finding that radiative cascades and collisional inner-shell ionization dominate the degree of linear polarization and total line-emission cross sections of the forbidden line, z.

Keywords: laboratory astrophysics; atomic physics; atomic data benchmarking; experimental techniques; plasma physics; x-ray astronomy; theoretical models
Why the Laplace Resonant Angle is So Special

We analyze adjacent local pairs of mean-motion resonances (MMRs) between three orbiting bodies designed to produce a Laplace resonant phase angle φ L or one of its multiples N φ L, where integer N ≥ 2. This assumption yields a concrete pattern of Laplace resonances, very few of which (with angles φ L and 2φ L) have been observed in actual (extra)solar subsystems. All other MMRs face issues of proximity or remoteness of the orbits (they are too close or too far apart). We highlight one as yet unobservable MMR in each N-sequence for which these issues appear to be less acute.

Keywords: exoplanet dynamics; exoplanets; orbital resonances
The Transition Region between Brightest Cluster Galaxies and Intracluster Light in Galaxy Groups and Clusters

We take advantage of a state-of-art semianalytic model of galaxy formation, and the model presented by Contini & Gu, to investigate the mass distribution of brightest cluster galaxies (BCGs) and intracluster light (ICL) by addressing two points: (1) the region of transition between a BCG-dominated distribution and an ICL-dominated one, and (2) the relation between the total BCG+ICL mass and the ICL mass alone. We find the transition radius to be independent of both BCG+ICL and halo masses, with an average of 60 ± 40 kpc, in good agreement with previous observational measurements, but given the large scatter it can be considered as a sort of physical separation between the two components only on a cluster scale. From the analysis of the M ICL-M BCG+ICL relation, we construct a method able to extract the ICL mass directly from knowledge of the BCG+ICL mass. Given the large scatter in low-mass systems, such a method under/overpredicts the true value of the ICL in a significant way, up to a factor of three in the worst cases. On the other hand, for $\mathrm{log}{M}_{\mathrm{BCG}+\mathrm{ICL}}\gt 12$ or $\mathrm{log}{M}_{\mathrm{Halo}}\gt 14$ (where masses are in units of M ⊙), the difference between the true value and the one extracted from the M ICL-M BCG+ICL relation ranges between ±30%. We therefore suggest this relation as a reliable test for observational works aiming to isolate the ICL from the BCG, for systems hosted by haloes on a cluster scale.

Keywords: galaxy evolution; galaxy formation
Long Dark Gaps in the Lyβ Forest at z < 6: Evidence of Ultra-late Reionization from XQR-30 Spectra

We present a new investigation of the intergalactic medium near reionization using dark gaps in the Lyβ forest. With its lower optical depth, Lyβ offers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Lyα line. We identify dark gaps in the Lyβ forest using spectra of 42 QSOs at z em > 5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10 h -1 Mpc at z ≃ 5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Lyα forest are caused solely by ionizing ultraviolet background fluctuations and with models that include large neutral hydrogen patches at z < 6 due to a late end to reionization. Of particular interest is a very long (L = 28 h -1 Mpc) and dark (τ eff ≳ 6) gap persisting down to z ≃ 5.5 in the Lyβ forest of the z = 5.85 QSO PSO J025-11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of <x H I> ≳ 5% by z = 5.6. Finally, we infer constraints on <x H I> over 5.5 ≲ z ≲ 6.0 based on the observed Lyβ dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find <x H I> ≤ 0.05, 0.17, and 0.29 at z ≃ 5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than z = 6.

Keywords: reionization; intergalactic medium; quasar absorption line spectroscopy; high-redshift galaxies
The Sensitivity of NEO Surveyor to Low-perihelion Asteroids

Asteroids with low orbital perihelion distances experience extreme heating from the Sun that can modify their surfaces and trigger nontypical activity mechanisms. These objects are generally difficult to observe from ground-based telescopes due to their frequent proximity to the Sun. The Near-Earth Object (NEO) Surveyor mission, however, will regularly survey down to solar elongations of 45° and is well suited for the detection and characterization of low-perihelion asteroids. Here, we use the survey simulation software tools developed for mission verification to explore the expected sensitivity of NEO Surveyor to these objects. We find that NEO Surveyor is expected to be >90% complete for near-Sun objects larger than D ∼ 300 m. Additionally, if the asteroid (3200) Phaethon underwent a disruption event in the past to form the Geminid meteor stream, Surveyor will be >90% complete to any fragments larger than D ∼ 200 m. For probable disruption models, NEO Surveyor would be expected to detect dozens of objects on Phaethon-like orbits, compared to a predicted background population of only a handful of asteroids, setting strong constraints on the likelihood of this scenario.

Keywords: near-earth objects; asteroids
Between the Cosmic-Ray "Knee" and the "Ankle": Contribution from Star Clusters

We show that massive, young star clusters may be possible candidates that can accelerate Galactic cosmic rays (CRs) in the range of 107–109 GeV (between the "knee" and "ankle"). Various plausible scenarios, such as acceleration at the wind termination shock and supernova shocks inside these young star clusters, have been proposed, since it is difficult to accelerate particles up to the 107–109 GeV range in the standard paradigm of CR acceleration in supernova remnants. We consider a model for the production of different nuclei in CRs from massive stellar winds using the observed distribution of young star clusters in the Galactic plane. We present a detailed calculation of CR transport in the Galaxy, taking into account the effect of diffusion, interaction losses during propagation, and particle reacceleration by old supernova remnants to determine the all-particle CR spectrum. Using the maximum energy estimate from the Hillas criterion, we argue that a young, massive star cluster can accelerate protons up to a few tens of PeV. Upon comparison with the observed data, our model requires a CR source spectrum with an exponential cutoff of 5 × 107 Z GeV (50 Z PeV) from these clusters, together with a CR injection fraction of ∼5% of the wind kinetic energy. We discuss the possibility of achieving these requirements in star clusters, as well as the associated uncertainties, in the context of considering star clusters as the natural accelerator of the "second component" of Galactic CRs.

Keywords: cosmic rays; particle astrophysics; high energy astrophysics; galactic cosmic rays; young star clusters
New Recurrently Active Main-belt Comet 2010 LH15

We announce the discovery of a main-belt comet (MBC), 2010 LH15 (alternately designated 2010 TJ175). MBCs are a rare type of main-belt asteroid that display comet-like activity, such as tails or comae, caused by sublimation. Consequently, MBCs help us map the location of solar system volatiles, providing insight into the origins of material prerequisite for life as we know it. However, MBCs have proven elusive, with fewer than 20 found among the 1.1 million known main-belt asteroids. This finding derives from Active Asteroids, a NASA Partner Citizen Science program we designed to identify more of these important objects. After volunteers classified an image of 2010 LH15 as showing activity, we carried out a follow-up investigation which revealed evidence of activity from two epochs spanning nearly a decade. This discovery is timely, with 2010 LH15 inbound toward its 2024 March perihelion passage, with potential activity onset as early as late 2023.

Keywords: asteroid belt; asteroids; comae; comet tails
A Deep uGMRT View of the Ultra-steep Spectrum Radio Halo in A521

We present the first detailed analysis of the ultra-steep spectrum radio halo in the merging galaxy cluster A521, based on upgraded Giant Metrewave Radio telescope observations. The combination of radio observations (300–850 MHz) and archival X-ray data provides a new window into the complex physics occurring in this system. When compared to all previous analyses, our sensitive radio images detected the centrally located radio halo emission to a greater extent of ∼1.3 Mpc. A faint extension of the southeastern radio relic has been discovered. We detected another relic, recently discovered by MeerKAT, and coincident with a possible shock front in the X-rays, at the northwest position of the center. We find that the integrated spectrum of the radio halo is well-fitted with a spectral index of ‑1.86 ± 0.12. A spatially resolved spectral index map revealed the spectral index fluctuations, as well as an outward radial steepening of the average spectral index. The radio and X-ray surface brightness is well correlated for the entire and different subparts of the halo, with sublinear correlation slopes (0.50–0.65). We also found a mild anticorrelation between the spectral index and X-ray surface brightness. Newly detected extensions of the SE relic and the counter relic are consistent with the merger in the plane of the sky.

Keywords: galaxy clusters; radio continuum emission; extragalactic radio sources; intracluster medium; non-thermal radiation sources
A Strong Shock During a Nova Outburst: An Origin of Multiple Velocity Systems in Optical Spectra and of High-energy Emissions

We propose a theoretical explanation of absorption/emission line systems in classical novae based on a fully self-consistent nova explosion model. We found that a reverse shock is formed far outside the photosphere (≳1013 cm) because later-ejected mass with a faster velocity collides with earlier-ejected matter. Optically thick winds blow continuously at a rate of ~10-4 M ⊙ yr-1 near the optical maximum, but its velocity decreases toward the optical maximum and increases afterward, so that the shock arises only after the optical maximum. The nova ejecta is divided by the shock into three parts, the outermost expanding gas (earliest wind before maximum), shocked shell, and inner fast wind, which respectively contribute to pre-maximum, principal, and diffuse-enhanced absorption/emission line systems. A large part of nova ejecta is eventually confined to the shocked shell. The appearance of the principal system is consistent with the emergence of a shock. This shock is strong enough to explain thermal hard X-ray emissions. The shocked layer has a high temperature of kT sh ~ 1 keV $\,\times \,{({({v}_{\mathrm{wind}}-{v}_{\mathrm{shock}})/1000\,\mathrm{km}\,{{\rm{s}}}^{-1})}^{2}=1\ \mathrm{keV}\times (({v}_{{\rm{d}}}-{v}_{{\rm{p}}})/1000\,\mathrm{km}\,{{\rm{s}}}^{-1})}^{2}$ , where v d - v p is the velocity difference between the diffuse-enhanced (v d) and principal (v p) systems. We compare a 1.3 M ⊙ white dwarf model with the observational properties of the GeV gamma-ray detected classical nova V5856 Sgr (ASASSN-16ma) and discuss what kind of novae can produce GeV gamma-ray emissions.

Keywords: classical novae; high energy astrophysics; cataclysmic variable stars; shocks; x-ray astronomy; gamma-ray astronomy; white dwarf stars