adsabs/SciX_UAT_keywords huggingface dataset:
The NANOGrav 12.5 yr Data Set: Wideband Timing of 47 Millisecond Pulsars

We present a new analysis of the profile data from the 47 millisecond pulsars comprising the 12.5 yr data set of the North American Nanohertz Observatory for Gravitational Waves, which is presented in a parallel paper (Alam et al., hereafter NG12.5). Our reprocessing is performed using "wideband" timing methods, which use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements from broadband observations, and novel analysis techniques. In particular, the wideband DM measurements are used to constrain the DM portion of the timing model. We compare the ensemble timing results to those in NG12.5 by examining the timing residuals, timing models, and noise-model components. There is a remarkable level of agreement across all metrics considered. Our best-timed pulsars produce encouragingly similar results to those from NG12.5. In certain cases, such as high-DM pulsars with profile broadening or sources that are weak and scintillating, wideband timing techniques prove to be beneficial, leading to more precise timing model parameters by 10%-15%. The high-precision, multiband measurements of several pulsars indicate frequency-dependent DMs. Compared to the narrowband analysis in NG12.5, the TOA volume is reduced by a factor of 33, which may ultimately facilitate computational speed-ups for complex pulsar timing array analyses. This first wideband pulsar timing data set is a stepping stone, and its consistent results with NG12.5 assure us that such data sets are appropriate for gravitational wave analyses.

Keywords: millisecond pulsars; pulsar timing method; rotation powered pulsars; binary pulsars; radio pulsars; pulsars; gravitational waves; astronomy data analysis; interstellar medium
XMM-Newton X-Ray Observations of the Unusual Wolf-Rayet Star WR 66

We summarize results of an XMM-Newton X-ray observation of the WN8h-type Wolf-Rayet star WR 66 which shows unusual 3.5-4.1 hr optical variations. One possible explanation is a compact companion (cc) which, if present, could give rise to luminous X-ray emission. WR 66 was marginally detected and its inferred X-ray luminosity (Lx) is orders of magnitude below that expected from wind accretion onto a neutron star, but is comparable to that of the WN8h stars WR 16 and WR 124. If luminous X-ray emission from an accreting WR+cc system is present then it is absorbed and escapes detection. Other explanations of the faintly detected X-ray emission of WN8h stars are not ruled out.

Keywords: wolf-rayet stars
The AGORA High-resolution Galaxy Simulations Comparison Project. VI. Similarities and Differences in the Circumgalactic Medium

We analyze the circumgalactic medium (CGM) for eight commonly-used cosmological codes in the AGORA collaboration. The codes are calibrated to use identical initial conditions, cosmology, heating and cooling, and star formation thresholds, but each evolves with its own unique code architecture and stellar feedback implementation. Here, we analyze the results of these simulations in terms of the structure, composition, and phase dynamics of the CGM. We show properties such as metal distribution, ionization levels, and kinematics are effective tracers of the effects of the different code feedback and implementation methods, and as such they can be highly divergent between simulations. This is merely a fiducial set of models, against which we will in the future compare multiple feedback recipes for each code. Nevertheless, we find that the large parameter space these simulations establish can help disentangle the different variables that affect observable quantities in the CGM, e.g., showing that abundances for ions with higher ionization energy are more strongly determined by the simulation's metallicity, while abundances for ions with lower ionization energy are more strongly determined by the gas density and temperature.

Keywords: circumgalactic medium; hydrodynamical simulations; computational astronomy; astronomical simulations
Stable Mass Transfer Can Explain Massive Binary Black Hole Mergers with a High-spin Component

Recent gravitational-wave observations showed that binary black hole (BBH) mergers with massive components are more likely to have high effective spins. In the model of isolated binary evolution, BH spins mainly originate from the angular momenta of the collapsing cores before BH formation. Both observations and theories indicate that BHs tend to possess relatively low spins; the origin of fast-spinning BHs remains a puzzle. We investigate an alternative process that stable Case A mass transfer may significantly increase BH spins during the evolution of massive BH binaries. We present detailed binary evolution calculations and find that this process can explain the observed high spins of some massive BBH mergers under the assumption of mildly super-Eddington accretion.

Keywords: gravitational waves; compact binary stars; black holes; stellar evolution
Fast Reconstruction of 3D Density Distribution around the Sun Based on the MAS by Deep Learning

This study is the first attempt to generate a three-dimensional (3D) coronal electron density distribution based on the pix2pixHD model, whose computing time is much shorter than that of the magnetohydrodynamic (MHD) simulation. For this, we consider photospheric solar magnetic fields as input, and electron density distribution simulated with the MHD Algorithm outside a Sphere (MAS) at a given solar radius is taken as output. We consider 155 pairs of Carrington rotations as inputs and outputs from 2010 June to 2022 April for training and testing. We train 152 deep-learning models for 152 solar radii, which are taken up to 30 solar radii. The artificial intelligence (AI) generated 3D electron densities from this study are quite consistent with the simulated ones from lower radii to higher radii, with an average correlation coefficient 0.97. The computing time of testing data sets up to 30 solar radii of 152 deep-learning models is about 45.2 s using the NVIDIA TITAN XP graphics-processing unit, which is much less than the typical simulation time of MAS. We find that the synthetic coronagraphic images estimated from the deep-learning models are similar to the Solar Heliospheric Observatory (SOHO)/Large Angle and Spectroscopic Coronagraph C3 coronagraph data, especially during the solar minimum period. The AI-generated coronal density distribution from this study can be used for space weather models on a near-real-time basis.

Keywords: the sun; solar photosphere; astronomy data analysis; astronomy image processing
On the Effects of UV Photons/X-Rays on the Chemistry of the Sgr B2 Cloud

The lines of HOC+, HCO, and CO+ are considered good tracers of photon-dominated regions (PDRs) and X-ray-dominated regions. We study these tracers toward regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO+ versus HOC+, HCO, and CO+ in dense H II gas, where UV photons dominate the heating and chemistry of the gas. The HOC+, HCO, and CO+ abundances and the above ratios are compared with those of chemical modeling, finding that high-temperature chemistry, a cosmic-ray ionization rate of 10-16 s-1, and timescales >105.0 yr explain well the HOC+ abundances in quiescent Sgr B2 regions, while shocks are also needed to explain the highest HCO abundances derived for these regions. The CO+ is mainly formed in PDRs, since the highest CO+ abundances of ∼(6-10) × 10-10 are found in H II regions with electron densities >540 cm-3 and CO+ emission is undetected in quiescent gas. Among the ratios, the HCO+/HCO ratio is sensitive to the electron density, as it shows different values in dense and diffuse H II regions. We compare SiO J = 2-1 emission maps of Sgr B2 with X-ray maps from 2004 and 2012. One known spot shown on the 2012 X-ray map is likely associated with molecular gas at velocities of 15-25 km s-1. We also derive the X-ray ionization rate of ∼10-19 s-1 for Sgr B2 regions pervaded by X-rays in 2004, which is quite low to affect the chemistry of the molecular gas.

Keywords: galaxy nuclei; interstellar medium; photodissociation regions; molecular clouds
Latitudinal Distribution of Ethane Precipitation on Titan Modulated by Topography and Orbital Forcing and Its Implication for Titan's Surface Evolution

A general circulation model with geography constrained by Cassini is used to predict how ethane precipitation in Titan's lower stratosphere varies with latitude, season, and orbital forcing over the past 100 kyr. Ethane precipitation is generally more prevalent near the winter pole, where stratospheric ethane is transported downward toward the cold trap, and this general pattern is relatively insensitive to orbital parameter variations and geography. However, eccentricity-driven seasonal temperature variations modulate the seasonal asymmetry of ethane precipitation to some extent. The annual ethane precipitation does not monotonically increase from equator to pole but maximizes at selected sites, preferentially over empty deep basins such as Hagal Planitia. Local enhancement of ethane precipitation is caused by katabatic winds from plateau to basin and an associated regional-scale thermally direct circulation over the slope, which induces strong adiabatic cooling near the tropopause. The observed putative ethane clouds off the poles are evidence that ethane condensation is affected by topography. Preferential ethane precipitation over basins may increase the irregularity of Titan's shape by isostatic crustal subsidence after substitution of enclathrated methane by percolated ethane.

Keywords: saturnian satellites; planetary atmospheres; planetary surfaces
What Would Happen if We Were About 1 pc Away from a Supermassive Black Hole?

We consider a hypothetical planet with the same mass m, radius R, angular momentum S, oblateness J2, semimajor axis a, eccentricity e, inclination I, and obliquity ɛ of the Earth orbiting a main-sequence star with the same mass ${M}_{\star }$ and radius ${R}_{\star }$ of the Sun at a distance ${r}_{\bullet }\simeq 1\,{\rm{pc}}$ from a supermassive black hole in the center of the hosting galaxy with the same mass ${M}_{\bullet }$ of, say, M87*. We preliminarily investigate some dynamical consequences of its presence in the neighborhood of such a stellar system on the planet's possibility of sustaining complex life over time. In particular, we obtain general analytic expressions for the long-term rates of change, doubly averaged over both the planetary and the galactocentric orbital periods ${P}_{{\rm{b}}}$ and ${P}_{\bullet }$ , of e, I, ɛ, which are the main quantities directly linked to stellar insolation. We find that, for certain orbital configurations, the planet's perihelion distance $q=a\left(1-e\right)$ may greatly shrink and even lead to, in some cases, an impact with the star. I may also notably change, with variations even of the order of tens of degrees. On the other hand, ɛ does not seem to be particularly affected, being shifted, at most, by $\simeq 0\buildrel{\circ}\over{.} 02$ over 1 Myr. Our results strongly depend on the eccentricity ${e}_{\bullet }$ of the galactocentric motion.

Keywords: black holes; exoplanets; celestial mechanics; astrobiology; gravitation
MEM_GE: A New Maximum Entropy Method for Image Reconstruction from Solar X-Ray Visibilities

Maximum Entropy is an image reconstruction method conceived to image a sparsely occupied field of view, therefore it is particularly effective at achieving super-resolution effects. Although widely used in image deconvolution, this method has been formulated in radio astronomy for the analysis of observations in the spatial frequency domain, and an Interactive Data Language code has been implemented for image reconstruction from solar X-ray Fourier data. However, this code relies on a non-convex formulation of the constrained optimization problem addressed by the Maximum Entropy approach, and this sometimes results in unreliable reconstructions characterized by unphysical shrinking effects. This paper introduces a new approach to Maximum Entropy based on the constrained minimization of a convex functional. In the case of observations recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the resulting code provides the same super-resolution effects of the previous algorithm, while also working properly when that code produces unphysical reconstructions. We also obtain results via testing the algorithm with synthetic data simulating observations of the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter. The new code is available in the HESSI folder of the Solar SoftWare (SSW) tree.

Keywords: the sun; solar flares; solar x-ray flares; astronomical techniques; experimental techniques; radio transient sources
A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55

We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete to M V ∼ (‑7, ‑10) mag for galaxies at D = (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of ${2.2}_{-0.12}^{+0.05}\,\mathrm{Mpc}$ , a potential satellite of the Local Volume galaxy NGC 55, separated by 47' (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absolute V-band magnitude of $-{8.0}_{-0.3}^{+0.5}\,\mathrm{mag}$ and an azimuthally averaged physical half-light radius of ${2.2}_{-0.4}^{+0.5}\,\mathrm{kpc}$ , making this one of the lowest surface brightness galaxies ever found with $\mu =32.3\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$ . This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host.

Keywords: local group; low surface brightness galaxies; dwarf galaxies
GRB 211211A: a Prolonged Central Engine under a Strong Magnetic Field Environment

Recently, a kilonova-associated gamma-ray burst (GRB 211211A), whose light curve consists of a precursor (~0.2 s), a hard spiky emission (~10 s), and a soft long extended emission (~40 s), has attracted great attention. Kilonova association could prove its merger origin, while the detection of the precursor can be used to infer at least one highly magnetized neutron star (NS) being involved in the merger. In this case, a strong magnetic flux Φ is expected to surround the central engine of GRB 211211A. Here we suggest that when Φ is large enough, the accretion flow could be halted far from the innermost stable radius, which will significantly prolong the lifetime of the accretion process, and so the GRB duration. For example, we show that as long as the central black hole (BH) is surrounded by a strong magnetic flux Φ ~ 1029cm2 G, an accretion flow with ${\dot{M}}_{\mathrm{ini}}\simeq 0.1{M}_{\odot }\,{{\rm{s}}}^{-1}$ could be halted at 40 times the gravitational radius and be slowly transferred into the black hole on the order of ~10 s, which naturally explains the duration of hard spiky emission. After most of the disk mass has been accreted onto the BH, the inflow rate will be reduced, so a long and soft extended emission is expected when a new balance between the magnetic field and the accretion current is reconstructed at a larger radius. Our results further support that the special behavior of GRB 211211A is mainly due to the strong magnetic field of its progenitor stars.

Keywords: gamma-ray bursts
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): The Warm-envelope Origin of Hot Corinos

Hot corinos are of great interest due to their richness in interstellar complex organic molecules (COMs) and the consequent potential prebiotic connection to solar-like planetary systems. Recent surveys have reported an increasing number of detected hot corinos in Class 0/I protostars; however, the relationships between their physical properties and the hot-corino signatures remain elusive. In this study, our objective is to establish a general picture of the detectability of hot corinos by identifying the origins of the hot-corino signatures in the sample of young stellar objects (YSOs) obtained from the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps project. We apply spectral energy distribution modeling to our sample and identify the physical parameters of the modeled YSOs directly, linking the detection of hot-corino signatures to the envelope properties of the YSOs. Imaging simulations of the methanol emission further support this scenario. We therefore posit that the observed COM emission originates from the warm inner envelopes of the sample YSOs, based on both the warm region size and the envelope density profile. The former is governed by the source luminosity and is additionally affected by the disk and cavity properties, while the latter is related to the evolutionary stages. This scenario provides a framework for detecting hot-corino signatures toward luminous Class 0 YSOs, with fewer detections being observed toward similarly luminous Class I sources.

Keywords: astrochemistry; interstellar molecules; star forming regions; low mass stars; protostars
A Massive Young Runaway Star in W49 North

We analyzed high-angular resolution 45.5 GHz images of the W49 North massive star-forming region obtained in 1998 and 2016 with the Very Large Array. Most of the ultracompact H II regions show no detectable changes over the time interval of the observations. However, subcomponents B1, B2, G2a, and G2c have increased its peak flux densities by values in the range of 3.8%-21.4%. Most interestingly, the cometary region C clearly shows proper motions that at the distance of the region are equivalent to a velocity of 76 ± 6 km s-1 in the plane of the sky. We interpret this region as the ionized bowshock produced by a runaway O6 ZAMS star that was ejected from the eastern edge of Welch's ring about 6400 yr ago.

Keywords: radio astrometry; proper motions; extragalactic radio sources
Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds

We report on the first uniform and systematic study of dust and molecular gas in nearby molecular clouds. We use surveys of dust extinction and emission to determine the opacity and map the distribution of the dust within a dozen local clouds in order to derive a uniform set of basic cloud properties. We find (1) the average dust opacity <κ d,353> = 0.8 cm2 g-1 with variations of a factor of ~2 between clouds, (2) cloud probability density functions are exquisitely described by steeply falling power laws with a narrow range of slope, and (3) a tight ${M}_{\mathrm{GMC}}\sim {R}_{\mathrm{GMC}}^{2}$ scaling relation for the cloud sample, indicative of a cloud population with an exactingly constant average surface density above a common fixed boundary. We compare these results to uniformly analyzed CO surveys. We measure the CO mass conversion factors and assess the efficacy of CO for tracing the physical properties of molecular clouds. We find <α CO> = 4.31 ± 0.67 M ⊙ (K km s-1 pc2)-1 (corresponding to X CO = 1.97 ×1020 cm-2(K km s-1)-1). We demonstrate that CO observations are a poor tracer of column density and structure on sub-cloud spatial scales. On cloud scales, CO observations can provide measurements consistent with those of the dust, provided data are analyzed in a similar, self-consistent fashion. Measurements of average giant molecular cloud surface density are sensitive to choice of cloud boundary. Care must be exercised to adopt common fixed boundaries when comparing surface densities for cloud populations within and between galaxies.

Keywords: giant molecular clouds; interstellar dust extinction; molecular gas
Testing Lyα Emission-line Reconstruction Routines at Multiple Velocities in One System

The 1215.67 Å H I Lyα emission line dominates the ultraviolet flux of low-mass stars, including the majority of known exoplanet hosts. Unfortunately, strong attenuation by the interstellar medium (ISM) obscures the line core in most stars, requiring the intrinsic Lyα flux to be reconstructed based on fits to the line wings. We present a test of the widely used Lyα emission-line reconstruction code LYAPY using phase-resolved, medium-resolution STIS G140M observations of the close white dwarf-M dwarf binary EG UMa. The Doppler shifts induced by the binary orbital motion move the Lyα emission line in and out of the region of strong ISM attenuation. Reconstructions of each spectrum should produce the same Lyα profile regardless of phase, under the well-justified assumption that there is no intrinsic line variability between observations. Instead, we find that the reconstructions underestimate the Lyα flux by almost a factor of 2 for the lowest velocity, most attenuated spectrum, due to a degeneracy between the intrinsic Lyα and ISM profiles. Our results imply that many stellar Lyα fluxes derived from G140M spectra reported in the literature may be underestimated, with potential consequences for, for example, estimates of extreme-ultraviolet stellar spectra and ultraviolet inputs into simulations of exoplanet atmospheres.

Keywords: m dwarf stars; white dwarf stars; common envelope binary stars; ultraviolet astronomy; planet hosting stars
Latitudinal Asymmetry in the Dayside Atmosphere of WASP-43b

We present two-dimensional near-infrared temperature maps of the canonical hot Jupiter WASP-43b using a phase-curve observation with JWST NIRSpec/G395H. From the white-light planetary transit, we improve constraints on the planet's orbital parameters and measure a planet-to-star radius ratio of . Using the white-light phase curve, we measure a longitude of maximum brightness of east of the substellar point and a phase-curve offset of . We also find a ≈4σ detection of a latitudinal hotspot offset of , the first significant detection of a nonequatorial hotspot in an exoplanet atmosphere. We show that this detection is robust to variations within planetary parameter uncertainties, but only if the transit is used to improve constraints, showing the importance of transit observations to eclipse mapping. Maps retrieved from the NRS1 and NRS2 detectors are similar, with hotspot locations consistent between the two detectors at the 1σ level. Our JWST data show brighter (hotter) nightsides and a dimmer (colder) dayside at the shorter wavelengths relative to fits to Spitzer 3.6 and 4.5 μm phase curves. Through comparison between our phase curves and a set of general circulation models, we find evidence for clouds on the nightside and atmospheric drag or high metallicity reducing the eastward hotspot offset.

Keywords: exoplanets; hot jupiters; exoplanet atmospheres