adsabs/SciX_UAT_keywords huggingface dataset:
Prospects of Detecting Nonthermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect

Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as nonthermal particles. While the role that nonthermal electrons play in transporting flare energy is well studied, the properties and importance of nonthermal protons are rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of nonthermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by Orrall & Zirker. In the Orrall-Zirker effect, nonthermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross sections, and numerical models capable of self-consistently simulating the flaring nonequilibrium ionization stratification, and the nonthermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and nonthermal emission from Ly α and Ly β, the most promising lines that may exhibit a detectable signal. These new predictions are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the Ly β emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of nonthermal protons in flares observed by SPICE.

Keywords: solar flares; solar flare spectra; solar chromosphere; radiative transfer; radiative processes; charge transfer; non-thermal radiation sources; radiative transfer simulations; hydrodynamical simulations; solar ultraviolet emission
The Influence of Thermonuclear Bursts on Polar Caps of the Accreting X-Ray Millisecond Pulsar MAXI J1816-195

We report accretion-powered pulsations for the first time during thermonuclear bursts in hard X-rays, which were observed with Insight-HXMT in 2022 during the outburst of the accreting X-ray millisecond pulsar MAXI J1816-195. By stacking 73 bursts, we detected pulse profiles in 8–30 and 30–100 keV during bursts, which are identical to those obtained from the persistent (nonburst) emission. On average, no significant phase lag was observed between burst and persistent pulse profiles. In addition, we suggest that the interaction with burst photons can be used as a direct diagnostic to distinguish contributions from the hot plasma near polar caps and the corona around the accretion disk, which are highly degenerate in their spectral shapes.

Keywords: x-ray bursts; neutron stars; low-mass x-ray binary stars; millisecond pulsars
Unusually High HCO+/CO Ratios in and outside Supernova Remnant W49B

Galactic supernova remnants (SNRs) and their environments provide the nearest laboratories to study SN feedback. We performed molecular observations toward SNR W49B, the most luminous Galactic SNR in the X-ray band, aiming to explore signs of multiple feedback channels of SNRs on nearby molecular clouds (MCs). We found very broad HCO+ lines with widths of dv ~ 48-75 km s-1 in the SNR southwest, providing strong evidence that W49B is perturbing MCs at a systemic velocity of V LSR = 61-65 km s-1, and placing the W49B at a distance of 7.9 ± 0.6 kpc. We observed unusually high-intensity ratios of HCO+ J=1-0/CO J=1-0 not only at shocked regions (1.1 ± 0.4 and 0.70 ± 0.16) but also in quiescent clouds over 1 pc away from the SNR's eastern boundary (≥0.2). By comparing with the magnetohydrodynamics shock models, we interpret that the high ratio in the broad-line regions can result from a cosmic-ray (CR) induced chemistry in shocked MCs, where the CR ionization rate is enhanced to around 10-102 times of the Galactic level. The high HCO+/CO ratio outside the SNR is probably caused by the radiation precursor, while the luminous X-ray emission of W49B can explain a few properties in this region. The above results provide observational evidence that SNRs can strongly influence the molecular chemistry in and outside the shock boundary via their shocks, CRs, and radiation. We propose that the HCO+/CO ratio is a potentially useful tool to probe an SNR's multichannel influence on MCs.

Keywords: supernova remnants; molecular clouds; cosmic rays; x-ray sources; shocks
A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176

We present a detailed analysis of the disk and circumstellar environment of the forming O-type star AFGL 4176 mm1, placing results from the Atacama Large Millimeter/submillimeter Array (ALMA) into context with multiwavelength data. With ALMA, we detect seventeen 1.2 mm continuum sources within 5″ (21,000 au) of AFGL 4176 mm1. We find that mm1 has a spectral index of 3.4 ± 0.2 across the ALMA band, with >87% of its 1.2 mm continuum emission from dust. The source mm2, projected 4200 au from mm1, may be a companion or a blueshifted knot in a jet. We also explore the morphological differences between the molecular lines detected with ALMA, finding 203 lines from 25 molecules, which we categorize into several morphological types. Our results show that AFGL 4176 mm1 provides an example of a forming O-star with a large and chemically complex disk, which is mainly traced by nitrogen-bearing molecules. Lines that show strong emission on the blueshifted side of the disk are predominantly oxygen-bearing, which we suggest are tracing a disk accretion shock. The molecules C34S, H2CS, and CH3CCN trace a slow wide-angle wind or dense structures in the outflow cavity walls. With the Australia Telescope Compact Array (ATCA), we detect a compact continuum source (<2000 × 760 au) at 1.2 cm, associated with mm1, of which >96% is from ionized gas. The ATCA NH3(1, 1) and (2, 2) emission traces a large-scale (r ∼ 0.5 pc) rotating toroid with the disk source mm1 in the blueshifted part of this structure offset to the northwest.

Keywords: radio interferometry; circumstellar matter; circumstellar disks; star formation; massive stars; millimeter astronomy
The Blue Straggler Population of the Open Clusters Trumpler 5, Trumpler 20, and NGC 2477

We present a study based on Gaia DR2 of the population of blue straggler stars in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their position in the color-magnitude diagram, their proper motion components, and their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large blue straggler star population, which allowed us to analyze their radial distribution as a probe of the cluster's dynamical status. The blue straggler star distribution was compared with that of red giant branch stars to evaluate mass segregation. Our results indicate that blue straggler stars are not more centrally concentrated than red giant branch stars stars in any of the clusters. The radial distribution of blue straggler stars in Trumpler 5 is flat. Additionally, using a multi-epoch radial velocity survey conducted with the high-resolution spectrograph FLAMES/GIRAFFE at the Very Large Telescope, we measured the radial velocities of a sample of stragglers to compare with the mean radial velocity and velocity dispersion of the clusters. Based on the radial velocity variations for different epochs, we roughly classified these stars as possible close or long-period binaries.

Keywords: open star clusters; blue straggler stars; radial velocity; binary stars
The LSST Era of Supermassive Black Hole Accretion Disk Reverberation Mapping

The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will detect an unprecedentedly large sample of actively accreting supermassive black holes with typical accretion disk (AD) sizes of a few light days. This brings us to face challenges in the reverberation mapping (RM) measurement of AD sizes in active galactic nuclei using interband continuum delays. We examine the effect of LSST cadence strategies on AD RM using our metric AGN_TimeLagMetric. It accounts for redshift, cadence, the magnitude limit, and magnitude corrections for dust extinction. Running our metric on different LSST cadence strategies, we produce an atlas of the performance estimations for LSST photometric RM measurements. We provide an upper limit on the estimated number of quasars for which the AD time lag can be computed within 0 < z < 7 using the features of our metric. We forecast that the total counts of such objects will increase as the mean sampling rate of the survey decreases. The AD time lag measurements are expected for >1000 sources in each deep drilling field (DDF; (10 deg2)) in any filter, with the redshift distribution of these sources peaking at z ≈ 1. We find the LSST observation strategies with a good cadence (≲5 days) and a long cumulative season (~9 yr), as proposed for LSST DDF, are favored for the AD size measurement. We create synthetic LSST light curves for the most suitable DDF cadences and determine RM time lags to demonstrate the impact of the best cadences based on the proposed metric.

Keywords: quasars; accretion; time domain astronomy; reverberation mapping
The COS Legacy Archive Spectroscopy Survey (CLASSY) Treasury Atlas

Far-ultraviolet (FUV; ~1200-2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N1500 Å ≳ 5/resel), high-resolution (R ~ 15,000) FUV spectral database of 45 nearby (0.002 < z < 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < log M ⋆(M ⊙) < 10.1), star formation rate (-2.0 < log SFR (M ⊙ yr-1) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O32 < 38.0), reddening (0.02 < E(B - V) < 0.67), and nebular density (10 < n e (cm-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with the z ~ 0 mass-metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to z ≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time. ∗ 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: galaxies; ultraviolet surveys; emission line galaxies; interstellar line absorption; lyman-alpha galaxies; high-redshift galaxies
Backstreaming Pickup Ions

Ions that are reflected at the shock front and escape back into the upstream region can play the role of ions that start to be accelerated by a diffusive shock acceleration mechanism. Backstreaming ions have been shown to be generated from a superthermal tail of the solar wind at sufficiently high upstream temperatures. The number of such ions was found to be low and they were not found at shock angles exceeding 50°. The mechanism of production is multiple reflection when an ion changes the direction of motion inside the ramp for the first time, due to the cross-shock potential. Since pickup ions (PUIs) constitute a strongly superthermal population of protons a substantially stronger production of backstreaming PUIs can be expected. We study the reflection of PUIs in a planar stationary shock front using test particle analysis. The used model is inspired by the observed profile of the termination shock. The influence of magnetic compression, the shock angle, and the overshoot are analyzed. It is found that generation of backstreaming PUIs in this shock is substantially more efficient than the generation of backstreaming protons from thermal solar wind. The fraction of backstreaming PUIs rapidly increases with the increase of magnetic compression and the decrease of the shock angle. Overshoot enhances production of backstreaming PUIs and allows it for larger shock angles. No backstreaming ions have been found for shock angles larger than 60°. The results of the test particle analysis are supported by full-particle simulations.

Keywords: shocks; termination shock; interplanetary particle acceleration
Hidden Giants in JWST's PEARLS: An Ultramassive z = 4.26 Submillimeter Galaxy that Is Invisible to HST

We present a multiwavelength analysis using the Submillimeter Array (SMA), James Clerk Maxwell Telescope, NOEMA, JWST, the Hubble Space Telescope (HST), and the Spitzer Space Telescope of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A 1489. These SMA-located sources both lie at z = 4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at ≲ 2 μm, even with deep JWST/NIRCam observations. We investigate their stellar, interstellar medium, and dynamical properties, including a pixel-level spectral energy distribution analysis to derive subkiloparsec-resolution stellar-mass and A V maps. We find that 850.1 is one of the most massive and highly obscured, A V ~ 5, galaxies known at z > 4 with M * ~1011.8 M ⊙ (likely forming at z > 6), and 850.2 is one of the least massive and least obscured, A V ~ 1, members of the z > 4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z ≳ 3-4 based on imaging at ≲ 2 μm, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar-mass distribution, ${R}_{{\rm{e}}}^{\mathrm{mass}}$ ~1 kpc, but its expected evolution means that it matches both the properties of massive, quiescent galaxies at z ~ 1.5 and ultramassive early-type galaxies at z ~ 0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature that we link to the active dynamical environment it resides within.

Keywords: submillimeter astronomy; galaxy evolution; ultraluminous infrared galaxies; lyman-break galaxies; high-redshift galaxies
Company for the Ultra-high Density, Ultra-short Period Sub-Earth GJ 367 b: Discovery of Two Additional Low-mass Planets at 11.5 and 34 Days

GJ 367 is a bright (V ≈ 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrograph-collecting 371 high-precision measurements over a baseline of nearly 3 yr-and combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of M b = 0.633 ± 0.050 M ⊕ and a radius of R b = 0.699 ± 0.024 R ⊕, corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of ρ b = 10.2 ± 1.3 g cm-3, i.e., 85% higher than Earth's density. We revealed the presence of two additional non-transiting low-mass companions with orbital periods of ~11.5 and 34 days and minimum masses of ${M}_{{\rm{c}}}\sin {i}_{{\rm{c}}}$ = 4.13 ± 0.36 M ⊕ and ${M}_{{\rm{d}}}\sin {i}_{{\rm{d}}}$ = 6.03 ± 0.49 M ⊕, respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of ${0.91}_{-0.23}^{+0.07}$ . How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet. *Based on observations made with the ESO-3.6 m telescope at La Silla Observatory under programs 1102.C-0923 and 106.21TJ.001.

Keywords: exoplanet detection methods; exoplanet systems; exoplanets; extrasolar rocky planets
The Secular Dynamical Evolution of Binary Asteroid System (65803) Didymos Post-DART

The successful impact of NASA's DART mission with Dimorphos, the secondary body of binary asteroid system (65803) Didymos, altered the attitude, shape, and orbit of Dimorphos. In addition to perturbing the immediate short-term dynamics of the system, these changes have major implications for the binary Yarkovsky–O'Keefe–Radzievskii–Paddack (BYORP) effect and resulting long-term secular evolution. In this study, we assess the range of possible reshaping-induced changes in BYORP. We produce high-fidelity numerical simulations of the orbit-attitude coupled tidal-BYORP dynamical evolution of the Didymos system to constrain how the secular evolution changed from its preimpact behavior. We find that the nature of the dynamics is highly dependent on a variety of initial conditions and assumptions, and it is difficult to fully predict how the system will secularly evolve following the impact. Rather, we provide a range of feasible possibilities within the bounds of observations and current best estimates of the Didymos system parameters. ESA's Hera mission will help reduce uncertainties surrounding the postimpact state and shape of Dimorphos in 2027, allowing our predictions of the secular evolutionary effects and long-term fate of the Didymos system to be better refined.

Keywords: asteroid dynamics; asteroid rotation; asteroid satellites; asteroid surfaces; asteroids; near-earth objects; small solar system bodies
A Long Stream of Metal-poor Cool Gas around a Massive Starburst Galaxy at z = 2.67

We present the first detailed dissection of the circumgalactic medium (CGM) of massive starburst galaxies at z > 2. Our target is a submillimeter galaxy (SMG) at z = 2.674 that has a star formation rate of 1200 M⊙ yr-1 and a molecular gas reservoir of 1.3 × 1011 M⊙. We characterize its CGM with two background QSOs at impact parameters of 93 kpc and 176 kpc. We detect strong H I and metal-line absorption near the redshift of the SMG toward both QSOs, each consisting of three main subsystems spanning over 1500 km s-1. The absorbers show remarkable kinematic and metallicity coherence across a separation of ∼86 kpc. In particular, the cool gas in the CGM of the SMG exhibits high H I column densities ( ${\rm{log}}({N}_{{\rm{H}}{\rm\small{I}}}/{{\rm{cm}}}^{-2})=20.2,18.6$ ), a low metallicity ([M/H] ≈ -2.0), and nearly the same radial velocity (δv ∼ -300 km s-1). While the H I column densities match previous results on the massive halos hosting QSOs, the metallicity is lower by more than an order of magnitude, making it an outlier in the line width-metallicity relation of damped Lyα absorbers. The large physical extent, the velocity coherence, the high surface densities, and the low metallicity are all consistent with the cool, inflowing, and near-pristine gas streams predicted to penetrate hot massive halos at z > 1.5. We estimate a total gas accretion rate of ∼100 M⊙ yr-1 from three such streams. At this rate, it takes only a gigayear to acquire the molecular gas reservoir of the central starburst.

Keywords: starburst galaxies; circumgalactic medium
Vibrational Spectroscopy of a Potential Interstellar Ion: Protonated Methyl Formate

The abundance of methyl formate (MF, HCOOCH3) in star-forming regions of the interstellar medium (ISM) suggests the presence of protonated MF (H+MF). However, no spectroscopic data exist for isolated H+MF. Here, we address the vibrational properties of H+MF and its H+MF-Ln≤2 clusters (L = Ar/N2) by infrared photodissociation (IRPD) spectroscopy and density functional theory calculations. Protonation of MF occurs at the CO oxygen, resulting in four different isomers arising from the syn/anti (s/a) and cis/trans (c/t) orientation between OCH3 and the excess proton. H+MF photofragments into protonated methanol by CO elimination. The IRPD spectrum exhibits redshifted OH stretch bands of the most stable H+MF(t/s) and H+MF(c/a) conformers because of the high internal energy required for dissociation. Tagging of H+MF with inert ligands drastically reduces both the internal energy and the dissociation threshold. The resulting higher-resolution IRPD spectra allow determination of the most stable H+MF rotamers as (t/s) and (c/a). In the cold H+MF-L dimers, the ligand forms an OH...L hydrogen bond, while bonding to the positively charged 2pz orbital of the carbonyl C atom is less favorable. The latter allows estimation of the free OH stretch fundamental of the most stable H+MF(t/s) rotamer as 3545 ± 5 cm-1. While for neutral MF the more stable syn rotamer MF(s) dominates the population in both the laboratory and the ISM (>99%), the anti conformer is substantially populated for H+MF (∼30%), which is rationalized by protonation-induced isomerization. This mechanism may lead to an enhanced abundance of MF(a) in certain regions of the ISM.

Keywords: astrochemistry; laboratory astrophysics; interstellar medium; molecular spectroscopy; chemical abundances; electron impact ionization; molecule destruction