adsabs/SciX_UAT_keywords huggingface dataset:
The Mercury Lines in the Mean Far Ultraviolet Spectrum of HD 209459

The analysis of the coadded high resolution SWP spectrum of the Hg star HD 209459 recorded by the International Ultraviolet Explorer reveals the presence of two resonance lines of Hg II at 1649.92 and 1942.28 Å. The line synthesis of the least blended resonance line at 1942.28 Å, yields a mercury abundance of about 1000 times the solar mercury abundance. The abundances of other element are found to agree fairly well with previous determinations. These results suggest that HD 209459 might be a mild HgMn star. However more abundance determinations from high resolution high signal-to-noise optical spectra are necessary to clarify the status of this interesting object.

Keywords: chemically peculiar stars; mercury-manganese stars
Nonaxisymmetric Precession of Magnetars and Fast Radio Bursts

The repeating fast radio bursts (FRBs) 180916.J0158 and 121102 are visible during periodically occurring windows in time. We consider the constraints on internal magnetic fields and geometries if the cyclical behavior observed for FRB 180916.J0158 and FRB 121102 is due to the precession of magnetars. In order to frustrate vortex line pinning we argue that internal magnetic fields must be stronger than about 1016 G, which is large enough to prevent superconductivity in the core and destroy the crustal lattice structure. We conjecture that the magnetic field inside precessing magnetars has three components: (1) a dipole component with characteristic strength ~ 1014 G; (2) a toroidal component with characteristic strength ~ 1015-1016 G that only occupies a modest fraction of the stellar volume; and (3) a disordered field with characteristic strength ~ 1016 G. The disordered field is primarily responsible for permitting precession, which stops once this field component decays away, which we conjecture happens after ~1000 yr. Conceivably, as the disordered component damps bursting activity diminishes and eventually ceases. We model the quadrupolar magnetic distortion of the star, which is due to its ordered components primarily, as triaxial and very likely prolate. We address the question of whether the spin frequency ought to be detectable for precessing, bursting magnetars by constructing a specific model in which bursts happen randomly in time with random directions distributed in or between cones relative to a single symmetry axis. Within the context of these specific models, we find that there are precession geometries for which detecting the spin frequency is very unlikely.

Keywords: high energy astrophysics; transient sources
The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Formaldehyde (H2CO) is an important precursor to organics like methanol (CH3OH). It is important to understand the conditions that produce H2CO and prebiotic molecules during star and planet formation. H2CO possesses both gas-phase and solid-state formation pathways, involving either UV-produced radical precursors or CO ice and cold (≲20 K) dust grains. To understand which pathway dominates, gaseous H2CO's ortho-to-para ratio (OPR) has been used as a probe, with a value of 3 indicating "warm" conditions and <3 linked to cold formation in the solid state. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of multiple ortho- and para-H2CO transitions in the TW Hya protoplanetary disk to test H2CO formation theories during planet formation. We find disk-averaged rotational temperatures and column densities of 33 ± 2 K, (1.1 ± 0.1) × 1012 cm-2 and 25 ± 2 K, (4.4 ± 0.3) × 1011 cm-2 for ortho- and para-H2CO, respectively, and an OPR of 2.49 ± 0.23. A radially resolved analysis shows that the observed H2CO emits mostly at rotational temperatures of 30-40 K, corresponding to a layer with z/R ≥ 0.25. The OPR is consistent with 3 within 60 au, the extent of the pebble disk, and decreases beyond 60 au to 2.0 ± 0.5. The latter corresponds to a spin temperature of 12 K, well below the rotational temperature. The combination of relatively uniform emitting conditions, a radial gradient in the OPR, and recent laboratory experiments and theory on OPR ratios after sublimation, led us to speculate that gas-phase formation is responsible for the observed H2CO across the TW Hya disk.

Keywords: astrochemistry; protoplanetary disks; interstellar molecules; interstellar abundances
The HSC-SSP Transient Survey: Implications from Early Photometry and Rise Time of Normal Type Ia Supernovae

With a booming number of Type Ia supernovae (SNe Ia) discovered within a few days of their explosions, a fraction of SNe Ia that show luminosity excess in the early phase (early-excess SNe Ia) have been confirmed. In this article, we report early-phase observations of seven photometrically normal SNe Ia (six early detections and one deep non detection limit) at the COSMOS field through a half-year transient survey as a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In particular, a blue light-curve excess was discovered for HSC17bmhk, a normal SN Ia with rise time longer than 18.8 days, during the first four days after the discovery. The blue early excess in optical wavelength can be explained not only by interactions with a nondegenerate companion or surrounding dense circumstellar matter but also radiation powered by radioactive decays of 56Ni at the surface of the SN ejecta. Given the growing evidence of the early-excess discoveries in normal SNe Ia that have longer rise times than the average, and a similarity in the nature of the blue excess to a luminous SN Ia subclass, we infer that early excess discovered in HSC17bmhk and other normal SNe Ia are most likely attributed to radioactive 56Ni decay at the surface of the SN ejecta. In order to successfully identify normal SNe Ia with early excess similar to that of HSC17bmhk, early UV photometries or high-cadence blue-band surveys are necessary.

Keywords: type ia supernovae; supernovae
Sublimation of Laboratory Ices Millimeter/Submillimeter Experiment (SubLIME): Structure-specific Identifications of Products from UV-photolyzed Methanol Ice

Submillimeter/far-IR spectroscopy was used to detect and quantify organic molecules sublimated after the ultraviolet photolysis (at 12 K) and warm-up (up to 300 K) of a methanol (CH3OH) ice sample. Eleven sublimated photoproducts were uniquely identified: carbon monoxide (CO), formaldehyde (H2CO), ketene (C2H2O), acetaldehyde (CH3CHO), ethylene oxide (CH2OCH2), vinyl alcohol (CH2CHOH), ethanol (CH3CH2OH), dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), glycolaldehyde (HOCH2CHO), and acetone ((CH3)2CO). Two additional products were detected in the photolyzed ice by Fourier-transform infrared (FTIR) spectroscopy: carbon dioxide (CO2) and methane (CH4). The rotational temperatures and gas densities were calculated for the organics containing two or more C atoms via a rotation diagram analysis, and the gas-phase submillimeter/far-IR technique was used in tandem with mass spectrometry and FTIR spectroscopy of the ice during photolysis. The abundance ratios of the sublimated species (normalized to methanol) were compared to those observed in hot cores (Orion-KL, Sagittarius B2(N), and IRAS 16293-2422(B)) and in comets C/2014 Q2 (Lovejoy) and 67P/Churyumov-Gerasimenko.

Keywords: astrochemistry; molecular spectroscopy; experimental techniques; molecule formation
A Candidate Supermassive Black Hole in a Gravitationally Lensed Galaxy at Z ≈ 10

While supermassive black holes (SMBHs) are widely observed in the nearby and distant Universe, their origin remains debated with two viable formation scenarios with light and heavy seeds. In the light seeding model, the seed of the first SMBHs form from the collapse of massive stars with masses of 10–100 M ⊙, while the heavy seeding model posits the formation of 104–5 M ⊙ seeds from direct collapse. The detection of SMBHs at redshifts z ≳ 10, edging closer to their formation epoch, provides critical observational discrimination between these scenarios. Here, we focus on the JWST-detected galaxy, GHZ 9, at z ≈ 10 that is lensed by the foreground cluster, A2744. Based on 2.1 Ms deep Chandra observations, we detect a candidate X-ray active galactic nucleus (AGN), which is spatially coincident with the high-redshift galaxy, GHZ 9. The SMBH candidate is inferred to have a bolometric luminosity of $({1.0}_{-0.4}^{+0.5})\times {10}^{46}\ \mathrm{erg}\,{{\rm{s}}}^{-1}$ , which corresponds to a black hole (BH) mass of $({8.0}_{-3.2}^{+3.7})\times {10}^{7}\ {M}_{\odot }$ assuming Eddington-limited accretion. This extreme mass at such an early cosmic epoch suggests the heavy seed origin for this BH candidate. Based on the Chandra and JWST discoveries of extremely high-redshift quasars, we have constructed the first simple AGN luminosity function extending to z ≈ 10. Comparison of this luminosity function with theoretical models indicates an overabundant z ≈ 10 SMBH population, consistent with a higher-than-expected seed formation efficiency.

Keywords: high-redshift galaxies; x-ray active galactic nuclei; gravitational lensing; supermassive black holes; galaxy clusters
Typical X-Ray Outburst Light Curves of Aql X-1

We show that the typical X-ray outburst light curve of Aql X-1 can be reproduced by accretion onto a neutron star in the frame of the disk instability model without invoking partial accretion or the propeller effect. The knee and the subsequent sharp decay in the X-ray light curve can be generated naturally by taking into account the weak dependence of the disk aspect ratio, h/r, on the disk mass-flow rate, ${\dot{M}}_{\mathrm{in}}$ , in the X-ray irradiation flux calculation. This ${\dot{M}}_{\mathrm{in}}$ dependence of h/r only slightly modifies the irradiation temperature profile along the hot disk in comparison to that obtained with a constant h/r. Nevertheless, this small difference has a significant cumulative effect on the hot disk radius, leading to a much faster decrease in the size of the hot disk and thereby to a sharper decay in the X-ray outburst light curve. The same model also produces the long-term evolution of Aql X-1, consistent with its observed outburst recurrence time and typical light curve. Our results imply that the source accretes matter from the disk in the quiescent state as well. We also estimate that the dipole moment of the source μ ≲ 4 × 1026 G cm3 (B ≲ 4 × 108 G at the surface).

Keywords: accretion; neutron stars; low-mass x-ray binary stars; x-ray bursts; x-ray transient sources
Ultra-diffuse Galaxies as Extreme Star-forming Environments. I. Mapping Star Formation in H I-rich UDGs

Ultra-diffuse galaxies (UDGs) are both extreme products of galaxy evolution and extreme environments in which to test our understanding of star formation. In this work, we contrast the spatially resolved star formation activity of a sample of 22 H I-selected UDGs and 35 low-mass galaxies from the NASA Sloan Atlas (NSA) catalog within 120 Mpc. We employ a new joint spectral energy distribution fitting method to compute star formation rate and stellar mass surface density maps that leverage the high spatial resolution optical imaging data of the Hyper Suprime-Cam Subaru Strategic Program and the UV coverage of the Galaxy Evolution Explorer, along with H I radial profiles estimated from a subset of galaxies that have spatially resolved H I maps. We find that UDGs have low star formation efficiencies as a function of their atomic gas down to scales of 500 pc. We additionally find that the stellar mass-weighted sizes of our UDG sample are unremarkable when considered as a function of their H I mass-their stellar sizes are comparable to NSA dwarfs at fixed H I mass. This is a natural result in the picture where UDGs are forming stars normally, but at low efficiencies. We compare our results to predictions from contemporary models of galaxy formation, and find in particular that our observations are difficult to reproduce in models where UDGs undergo stellar expansion due to vigorous star formation feedback should bursty star formation be required down to z = 0.

Keywords: dwarf galaxies; low surface brightness galaxies; star formation; extragalactic astronomy
The Nuclear Reaction Network WinNet

We present the state-of-the-art single-zone nuclear reaction network WINNET, which is capable of calculating the nucleosynthetic yields of a large variety of astrophysical environments and conditions. This ranges from the calculation of the primordial nucleosynthesis, where only a few nuclei are considered, to the ejecta of neutron star mergers with several thousands of involved nuclei. Here we describe the underlying physics and implementation details of the reaction network. We additionally present the numerical implementation of two different integration methods, the implicit Euler method and Gears method, along with their advantages and disadvantages. We furthermore describe basic example cases of thermodynamic conditions that we provide together with the network and demonstrate the reliability of the code by using simple test cases. With this publication, WINNET will be publicly available and open source at GitHub and Zenodo.

Keywords: nucleosynthesis; nuclear astrophysics; computational methods; nuclear reaction cross sections
Optical Observations of the Type Ia Supernova 2022hrs

We present optical photometry and spectra of supernova (SN) 2022hrs (distance ~ 19 Mpc). It was classified as a Type Ia SN (SN Ia) based on its optical spectra, which exhibited high velocities in both Si II and Ca II absorption lines. The light curve of SN 2022hrs was typical of an SN Ia, with a peak magnitude of 13.01 ± 0.30 in B and a time interval of 14.5 days between detection and peak; its optical spectra are also normal. It is a standard SN Ia with no evidence of circumstellar material.

Keywords: photometry; type ia supernovae; spectroscopy; astronomical techniques; astrometry; supernovae; ejecta
GeV Gamma-Ray Emission from Pulsar Wind Nebula HESS J1356-645 with Fermi-Large Area Telescope

HESS J1356-645 is considered to be a pulsar wind nebula (PWN) associated with the pulsar PSR J1357-6429. We reanalyze the GeV gamma-ray emission in the direction of HESS J1356-645 with more than 13 yr of Fermi-Large Area Telescope data. The extended gamma-ray emission above 5 GeV is found to be spatially coincident with HESS J1356-645. The spectrum in the energy range of 1 GeV-1 TeV can be described by a power law with an index of Γ = 1.51 ± 0.10. The broadband spectrum of HESS J1356-645 can be reproduced by a leptonic model with a broken power-law electronic spectrum. In addition, we found evidence that the morphology of the GeV emission from HESS J1356-645 varies with energy; a behavior that is similar to that of the PWN Vela-X. More broadband observations will be helpful to study the energy-dependent characteristics of HESS J1356-645.

Keywords: pulsar wind nebulae
Revisiting the Formation of HeH+ in the Planetary Nebula NGC 7027

From four independent calculations using three different theoretical approaches, rate coefficients for the formation of HeH+ via the radiative association of He+ and H were computed. Good agreement is found between our new calculations and prior results obtained two decades ago for kinetic temperatures between ∼800 and 20,000 K. This finding is inconsistent with a recent claim in the literature of a wide variation in published values and establishes the robustness of our knowledge of this process for the formation of HeH+. The implications of the current results to the first detection of HeH+ and its modeled abundance in the planetary nebula NGC 7027 are discussed.

Keywords: molecular physics; molecule formation
Observational Characterization of Main-belt Comet and Candidate Main-belt Comet Nuclei

We report observations of nine main-belt comets (MBCs) or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of p V = 0.05 ± 0.02) of r n = (0.24 ± 0.05) km for 238P/Read, r n = (0.9 ± 0.2) km for 313P/Gibbs, r n = (0.6 ± 0.1) km for 324P/La Sagra, r n = (1.0 ± 0.2) km for 426P/PANSTARRS, r n = (0.5 ± 0.1) km for 427P/ATLAS, r n < (0.3 ± 0.1) km for P/2016 J1-A (PANSTARRS), r n < (0.17 ± 0.04) km for P/2016 J1-B (PANSTARRS), r n ≤ (0.5 ± 0.2) km for P/2017 S9 (PANSTARRS), recently redesignated 455P/PANSTARRS, and r n = (0.4 ± 0.1) km for P/2019 A3 (PANSTARRS). We identify evidence of activity in observations of 238P in 2021, and find similar inferred activity onset times and net initial mass-loss rates for 238P during perihelion approaches in 2010, 2016, and 2021. P/2016 J1-A and P/2016 J1-B are also found to be active in 2021 and 2022, making them collectively the tenth MBC confirmed to be recurrently active near perihelion and therefore likely to be exhibiting sublimation-driven activity. The nucleus of 313P is found to have colors of $g^{\prime} -r^{\prime} =0.52\pm 0.05$ and $r^{\prime} -i^{\prime} =0.22\pm 0.07$ , consistent with 313P being a Lixiaohua family member. We also report nondetections of P/2015 X6 (PANSTARRS), where we conclude that its current nucleus size is likely below our detection limits (r n ≲ 0.3 km). Lastly, we find that of 17 MBCs or candidate MBCs for which nucleus sizes (or inferred parent body sizes) have been estimated, >80% have r n ≤ 1.0 km, pointing to an apparent physical preference toward small MBCs, where we suggest that Yarkovsky-O'Keefe-Radzievskii-Paddack spin-up may play a significant role in triggering and/or facilitating MBC activity.

Keywords: main-belt comets; comet nuclei; comets; small solar system bodies
Characterizing the Advective Hot Flows of Nova-like Cataclysmic Variables in the X-Rays: The Case of BZ Cam and V592 Cas

We present a joint spectral analysis of ROSAT PSPC, Swift X-ray Telescope, and Nuclear Spectroscopic Telescope Array Focal Plane Module A/B (FPMA/B) data of the nova-like (NL) cataclysmic variables (CVs) BZ Cam and V592 Cas in the 0.1-78.0 keV band. Plasma models of collisional equilibrium fail to model the 6.0-7.0 iron line complex and continuum with ${\chi }_{\nu }^{2}$ larger than 2.0. Our results show nonequilibrium ionization (NEI) conditions in the X-ray plasma with temperatures of 8.2-9.4 keV and 10.0-12.9 keV for BZ Cam and V592 Cas, respectively. The centroids of He-like and H-like iron ionization lines are not at their equilibrium values as expected from NEI conditions. We find power-law spectral components that reveal the existence of scattering and Comptonization with a photon index of 1.50-1.87. We detect a P Cygni profile in the H-like iron line of BZ Cam translating to outflows of 4500-8700 km s-1 consistent with the fast winds in the optical and UV. This is the first time such a fast collimated outflow is detected in the X-rays from an accreting CV. An iron Kα line around 6.2-6.5 keV is found revealing the existence of reflection effects in both sources. We study the broadband noise and find that the optically thick disk truncates in BZ Cam and V592 Cas consistent with transition to an advective hot flow structure. V592 Cas also exhibits a quasiperiodic oscillation at ${1.4}_{-0.3}^{+2.6}$ mHz. In general, we find that the two NLs portray spectral and noise characteristics as expected from advective hot accretion flows at low radiative efficiency.

Keywords: accretion; white dwarf stars; stellar accretion disks; spectroscopy; plasma astrophysics; non-thermal radiation sources; x-ray binary stars; x-ray astronomy; x-ray sources; cataclysmic variable stars; nova-like variable stars; stellar winds
Dissonance in Harmony: The UV/Optical Periodic Outbursts of ASASSN-14ko Exhibit Repeated Bumps and Rebrightenings

ASASSN-14ko was identified as an abnormal periodic nuclear transient with a potential decreasing period. Its outbursts in the optical and UV bands have displayed a consistent and smooth "fast rise and slow decay" pattern since its discovery, which has recently experienced an unexpected alteration in the last two epochs, as revealed by our proposed high-cadence Swift observations. The new light curve profiles show a bump during the rising stages and a rebrightening during the declining stages, making them much broader and symmetrical than the previous ones. In the last two epochs, there is no significant difference in the X-ray spectral slope compared to the previous one, and its overall luminosity is lower than those of the previous epochs. The energy released in the early bump and rebrightening phases (∼1050 erg) could be due to collision of the stripped stream from partial tidal disruption events with an expanded accretion disk. We also discussed other potential explanations, such as disk instability and star–disk collisions. Further high-cadence multiwavelength observations of subsequent cycles are encouraged to comprehend the unique periodic source with its new intriguing features.

Keywords: tidal disruption; supermassive black holes; black hole physics; accretion
Waves and Turbulence in the Very Local Interstellar Medium: From Macroscales to Microscales

Voyager 1 (V1) has been exploring the heliospheric boundary layer in the very local interstellar medium (VLISM) since 2012 August. The measurements revealed a spectrum of fluctuations over a vast range of space and timescales, but the nature of these fluctuations continues to be an intriguing question. Numerous manifestations of turbulence cannot be explained using a single phenomenology. Weak shocks and compressions are the prominent features of the VLISM. We use high-resolution (48 s) measurements to perform a multiscale analysis of turbulence at V1 between the years of 2013.36 and 2019.0 (124-144 au from the Sun). On relatively large scales, wave trains of mixed compressible/transverse nature with the correlation scale in the range of 15-100 days dominate the spectrum of fluctuations. The observed magnetic field profiles are suggestive of a Burgers-like (f-2) turbulence phenomenology induced by solar activity. We demonstrate that the level of large-scale compressible fluctuations is still significant in late 2018. We analyze the turbulence down to small scales comparable to the ion inertial length and show that magnetic compressibility is always large on these scales. Besides the shock-induced turbulence measured from 2014.486, the intensity and intermittency of small-scale fluctuations have been growing smoothly since 2018.5. Our analysis suggests that local processes are contributing to the production of turbulence on small scales. We present the estimates of transport coefficients in the plasma traversed by V1. The range of scales is identified where V1 measurements are affected by the contribution from pickup ions.

Keywords: interstellar magnetic fields; heliopause; heliosphere