adsabs/SciX_UAT_keywords huggingface dataset:
The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core

We present the first mid-infrared (MIR) detections of HNC and ${{\rm{H}}}^{13}\mathrm{CN}$ in the interstellar medium, and numerous resolved HCN rovibrational transitions. Our observations span 12.8-22.9 μm toward the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). In particular, ∼5 km s-1 resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the ${{\rm{H}}}^{13}\mathrm{CN}$ R branch. This allows direct measurement of the species' excitation temperatures, column densities, and relative abundances. HNC and ${{\rm{H}}}^{13}\mathrm{CN}$ exhibit a local standard of rest velocity of -7 km s-1 that may be associated with an outflow from nearby radio source I and an excitation temperature of about 100 K. We resolve two velocity components for HCN, the primary component also being at -7 km s-1 with a temperature of 165 K. The hottest component, which had never before been observed, is at 1 km s-1 with a temperature of 309 K. This is the closest component to the hot core's center measured to date. The derived ${}^{12}{\rm{C}}{/}^{13}{\rm{C}}=13\pm 2$ is below expectation for Orion's Galactocentric distance, but the derived HCN/HNC = 72 ± 7 is expected for this extreme environment. Compared to previous sub-millimeter and millimeter observations, our SOFIA line survey of this region shows that the resolved MIR molecular transitions are probing a distinct physical component and isolating the chemistry closest to the hot core.

Keywords: infrared astronomy; interstellar medium; star formation; molecular spectroscopy; spectral line identification; molecular physics
Testing Densities and Refractive Indices of Extraterrestrial Ice Components Using Molecular Structures—Organic Compounds and Molar Refractions

The use of infrared spectra to determine molecular abundances of icy astronomical objects and to study their chemistry requires laboratory measurements of reference spectra and related quantities, such as the index of refraction (n) and density (ρ) of candidate ices. Here we present new n and ρ measurements on ices involving over 30 C-, H-, and O-containing compounds, both acyclic and cyclic, representing seven chemical families. We examine the results in a way that is rare in the astrochemical literature, namely one in which data from an ice formed from molecules of a particular chemical family are compared to measurements on another member of the same family, such as of a homologous series or a pair of isomers. Apart from the intrinsic usefulness of the n and ρ data, a structure-based comparison can help establish trends and identify possibly spurious results. As liquid-phase data sometimes are used in low-temperature astrochemical work in the absence of solid-phase measurements, we compare our new ice results to those for the corresponding room-temperature liquids. We emphasize the use of our n and ρ data to compute the molar refraction (RM) for each of our ices, and how the resulting RM values compare to those expected from molecular structures. The use of calculated RM values and measured n values to calculate ice densities, in the absence of direct measurements, is also addressed.

Keywords: astrochemistry; laboratory astrophysics; molecular spectroscopy
FOXSI-2 Solar Microflares. II. Hard X-ray Imaging Spectroscopy and Flare Energetics

We study the nature of energy release and transfer for two sub-A class solar microflares observed during the second Focusing Optics X-ray Solar Imager (FOXSI-2) sounding rocket flight on 2014 December 11. FOXSI is the first solar-dedicated instrument to utilize focusing optics to image the Sun in the hard X-ray (HXR) regime, sensitive to energies of 4-20 keV. Through spectral analysis of the microflares using an optically thin isothermal plasma model, we find evidence for plasma heated to ∼10 MK and emission measures down to ∼1044 cm-3. Though nonthermal emission was not detected for the FOXSI-2 microflares, a study of the parameter space for possible hidden nonthermal components shows that there could be enough energy in nonthermal electrons to account for the thermal energy in microflare 1, indicating that this flare is plausibly consistent with the standard thick-target model. With a solar-optimized design and improvements in HXR focusing optics, FOXSI-2 offers approximately five times greater sensitivity at 10 keV than the Nuclear Spectroscopic Telescope Array for typical microflare observations and allows for the first direct imaging spectroscopy of solar HXRs with an angular resolution at scales relevant for microflares. Harnessing these improved capabilities to study small-scale events, we find evidence for spatial and temporal complexity during a sub-A class flare. This analysis, combined with contemporaneous observations by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, indicates that these microflares are more similar to large flares in their evolution than to the single burst of energy expected for a nanoflare.

Keywords: solar x-ray flares; solar corona; solar flare spectra; active sun; the sun; solar instruments; x-ray telescopes
The Fundamental Plane in the LEGA-C Survey: Unraveling the M/L Ratio Variations of Massive Star-forming and Quiescent Galaxies at z ∼ 0.8

We explore the connection between the kinematics, structures and stellar populations of massive galaxies at 0.6 < z < 1.0 using the fundamental plane (FP). Combining stellar kinematic data from the Large Early Galaxy Astrophysics Census (LEGA-C) survey with structural parameters measured from deep Hubble Space Telescope imaging, we obtain a sample of 1419 massive ( $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 10.5$ ) galaxies that span a wide range in morphology, star formation activity, and environment, and therefore is representative of the massive galaxy population at z ∼ 0.8. We find that quiescent and star-forming galaxies occupy the parameter space of the g-band FP differently and thus have different distributions in the dynamical mass-to-light ratio (Mdyn/Lg), largely owing to differences in the stellar age and recent star formation history, and to a lesser extent, the effects of dust attenuation. In contrast, we show that both star-forming and quiescent galaxies lie on the same mass FP at z ∼ 0.8, with a comparable level of intrinsic scatter about the plane. We examine the variation in Mdyn/M* through the thickness of the mass FP, finding no significant residual correlations with stellar population properties, Sérsic index, or galaxy overdensity. Our results suggest that, at fixed size and velocity dispersion, the variations in Mdyn/Lg of massive galaxies reflect an approximately equal contribution of variations in M*/Lg, and variations in the dark matter fraction or initial mass function.

Keywords: galaxy evolution; galaxy structure; galaxy kinematics; galaxy dynamics
AstroSat View of the Newly Discovered X-Ray Transient MAXI J1803-298 in the Hard-intermediate State

We perform comprehensive temporal and spectral analysis of the newly discovered X-ray transient MAXI J1803-298 using an AstroSat target of opportunity observation on 2021 May 11 during its outburst. The source was found to be in the hard-intermediate state. We detect type C quasi-periodic oscillations (QPOs) at the frequencies of ~5.4 and ~6.3 Hz along with a subharmonic at ~2.8 Hz in the 3-15 keV band. The frequency and fractional rms amplitude of the QPO in the 15-30 keV band are found to be higher than those in the 3-15 keV band. We find soft lags of ~3.8 and ~6.8 ms for the respective QPOs at ~5.4 and ~6.3 Hz, whereas a soft lag of ~4.7 ms is found at the subharmonic frequency. The increase in the soft lags at the QPO frequencies with energy is also observed in other black hole transients and attributed to the inclination dependence of the lags. The rms energy spectra indicate the power-law component to be more variable than the disk and reflection components. We find a broad iron line with an equivalent width of ~0.17-0.19 keV and a reflection hump above ~12 keV in the energy spectrum. Based on the X-ray spectroscopy and considering the distance to the source as 8 kpc, the estimated mass (~8.5-16 M ⊙) and spin (a ≳ 0.7) of the black hole suggest that the source is likely to be a stellar mass Kerr black hole X-ray binary.

Keywords: high energy astrophysics; black hole physics; stellar mass black holes; stellar accretion disks; x-ray transient sources; x-ray sources; x-ray binary stars
Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud

We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ~20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm-3, and rotation measure (RM) of +456 rad m-2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523-7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ~1 mJy at 1400 MHz and ~25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ -3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds.

Keywords: pulsars; neutron stars; radio transient sources; radio continuum emission
Near-infrared Accretion Signatures from the Circumbinary Planetary-mass Companion Delorme 1 (AB)b

Accretion signatures from bound brown dwarf and protoplanetary companions provide evidence for ongoing planet formation, and accreting substellar objects have enabled new avenues to study the astrophysical mechanisms controlling the formation and accretion processes. Delorme 1 (AB)b, a ~30-45 Myr circumbinary planetary-mass companion, was recently discovered to exhibit strong Hα emission. This suggests ongoing accretion from a circumplanetary disk, somewhat surprising given canonical gas disk dispersal timescales of 5-10 Myr. Here, we present the first NIR detection of accretion from the companion in Paβ, Paγ, and Brγ emission lines from SOAR/TripleSpec 4.1, confirming and further informing its accreting nature. The companion shows strong line emission, with L line ≈ 1-6 × 10-8 L ⊙ across lines and epochs, while the binary host system shows no NIR hydrogen line emission (L line < 0.32-11 × 10-7 L ⊙). Observed NIR hydrogen line ratios are more consistent with a planetary accretion shock than with local line excitation models commonly used to interpret stellar magnetospheric accretion. Using planetary accretion shock models, we derive mass accretion rate estimates of ${\dot{M}}_{\mathrm{pla}}\sim 3$ -4 × 10-8 M J yr-1, somewhat higher than expected under the standard star formation paradigm. Delorme 1 (AB)b's high accretion rate is perhaps more consistent with formation via disk fragmentation. Delorme 1 (AB)b is the first protoplanet candidate with clear (signal-to-noise ratio ~5) NIR hydrogen line emission. * Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia e Inovações (MCTI/LNA) do Brasil, the US National Science Foundation's NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Keywords: planet formation; accretion; stellar accretion disks
Close Binary Companions to APOGEE DR16 Stars: 20,000 Binary-star Systems Across the Color-Magnitude Diagram

Many problems in contemporary astrophysics—from understanding the formation of black holes to untangling the chemical evolution of galaxies—rely on knowledge about binary stars. This, in turn, depends on the discovery and characterization of binary companions for large numbers of different kinds of stars in different chemical and dynamical environments. Current stellar spectroscopic surveys observe hundreds of thousands to millions of stars with (typically) few observational epochs, which allows for binary discovery but makes orbital characterization challenging. We use a custom Monte Carlo sampler (The Joker) to perform discovery and characterization of binary systems through radial velocities, in the regime of sparse, noisy, and poorly sampled multi-epoch data. We use it to generate posterior samplings in Keplerian parameters for 232,495 sources released in APOGEE Data Release 16. Our final catalog contains 19,635 high-confidence close-binary (P ≲ few years, a ≲ few $\mathrm{au}$ ) systems that show interesting relationships between binary occurrence rate and location in the color-magnitude diagram. We find notable faint companions at high masses (black hole candidates), at low masses (substellar candidates), and at very close separations (mass-transfer candidates). We also use the posterior samplings in a (toy) hierarchical inference to measure the long-period binary-star eccentricity distribution. We release the full set of posterior samplings for the entire parent sample of 232,495 stars. This set of samplings involves no heuristic "discovery" threshold and therefore can be used for myriad statistical purposes, including hierarchical inferences about binary-star populations and subthreshold searches.

Keywords: binary stars; close binary stars; radial velocity; spectroscopy; astronomy data analysis; bayesian statistics; astrostatistics; surveys
The Gas-phase Mass–Metallicity Relation for Massive Galaxies at z ∼ 0.7 with the LEGA-C Survey

The massive end of the gas-phase mass–metallicity relation (MZR) is a sensitive probe of active galactic nuclei (AGN) feedback that is a crucial but highly uncertain component of galaxy evolution models. In this paper, we extend the z ∼ 0.7 MZR by ∼0.5 dex up to log (M ⋆/M ⊙) ∼ 11.1. We use extremely deep VLT VIMOS spectra from the Large Early Galaxy Astrophysics Census (LEGA-C) survey to measure metallicities for 145 galaxies. The LEGA-C MZR matches the normalization of the z ∼ 0.8 DEEP2 MZR where they overlap, so we combine the two to create an MZR spanning from 9.3 to 11.1 log (M ⋆/M ⊙). The LEGA-C+DEEP2 MZR at z ∼ 0.7 is offset to slightly lower metallicities (0.05–0.13 dex) than the z ∼ 0 MZR, but it otherwise mirrors the established power-law rise at low/intermediate stellar masses and asymptotic flattening at high stellar masses. We compare the LEGA-C+DEEP2 MZR to the MZR from two cosmological simulations (IllustrisTNG and SIMBA), which predict qualitatively different metallicity trends for high-mass galaxies. This comparison highlights that our extended MZR provides a crucial observational constraint for galaxy evolution models in a mass regime where the MZR is very sensitive to choices about the implementation of AGN feedback.

Keywords: galaxy abundances; metallicity; galaxy evolution
Larmor Electric Field in Symmetric Magnetic Reconnection

The Larmor electric field (LEF) was previously suggested as a signature to identify the diffusion region in asymmetry reconnection. Using 2.5D particle-in-cell simulations, we show that the LEF also exists in symmetric reconnection, manifested as a transient structure upstream of the Hall electric field. The LEF emerges during the rapid growth phase of the reconnection rate and has opposite polarity to the Hall field. The half-width of the current sheet spontaneously decreases to the electron scale as the evolution of reconnection, which gives rise to the LEF. The current sheet later thickens to maintain the fast reconnection rate, which causes the disappearance of the LEF. We further find that the magnitude of LEF is sensitive to the initial half-width current sheet, the background plasma temperature and density, the guide-field strength, and the ion-electron mass ratio. Our results provide new insight into the dynamics around the diffusion region. The LEF can help satellites not only locate the diffusion region but also identify the onset phase of reconnection in the magnetotail.

Keywords: plasma physics; astronomical simulations; solar magnetic reconnection; space plasmas
Constraints on the Dust Size Distributions in the HD 163296 Disk from the Difference of the Apparent Dust Ring Widths between Two ALMA Bands

The dust size in protoplanetary disks is a crucial parameter for understanding planet formation, while the observational constraints on dust size distribution have large uncertainties. In this study, we present a new method to constrain the dust size distribution from the dust spatial distribution, utilizing the fact that larger dust grains are more spatially localized. We analyze Atacama Large Millimeter/submillimeter Array Band 6 (1.25 mm) and Band 4 (2.14 mm) high-resolution images and constrain the dust size distribution in the two rings of the HD 163296 disk. We find that the outer ring at 100 au appears narrower at longer wavelengths, while the inner ring at 67 au appears to have similar widths across the two wavelengths. We model dust rings trapped at gas pressure maxima, where the dust grains follow a power-law size distribution, and the dust grains of a specific size follow a Gaussian spatial distribution, with the width depending on the grain size. By comparing the observations with the models, we constrain the maximum dust size ${a}_{\max }$ and the exponent of the dust size distribution p. We constrain $0.9\ \mathrm{mm}\lt {a}_{\max }\lt 5\ \mathrm{mm}$ and p < 3.3 in the inner ring, and ${a}_{\max }\gt 3\,\times \,{10}^{1}\ \mathrm{mm}$ and 3.4 < p < 3.7 in the outer ring. The larger maximum dust size in the outer ring implies a spatial dependency in dust growth, potentially influencing the formation location of the planetesimals. We further discuss the turbulence strength α derived from the constrained dust spatial distribution, assuming equilibrium between turbulent diffusion and the accumulation of dust grains.

Keywords: protoplanetary disks; planet formation; submillimeter astronomy; dust continuum emission; dust physics
Discovery of Radial Spectral Hardening in the Hot Bubble of Planetary Nebula BD+30°3639 with Median Energy Imaging

We apply an imaging analysis technique to study the spatial distribution of the X-ray spectral hardness across the hot bubble of planetary nebula BD+30°3639. Hot bubble emission is typically photon starved, thus limiting the methods for spatial–spectral analysis; however, this technique uses the statistics of photon energies across the nebula to identify spatial variations in the X-ray spectral hardness. Using the median energy value of the X-ray photons, we identified a rise in median energy values toward the projected edge of the nebula, which we refer to as radial spectral hardening. We explored the origin of this radial spectral hardening with an X-ray spectral analysis of distinct regions of high and low median energy values. Given the results of the X-ray spectral fits and the fact that the hot bubble is embedded within a young, dense, planetary nebula, we conclude that the radial spectral hardening is due to an increased column density at the projected nebular edge.

Keywords: planetary nebulae; x-ray astronomy; astronomical techniques; astrostatistics; extinction
A Comparison of Millisecond Pulsar Populations between Globular Clusters and the Galactic Field

We have performed a systematic study of the rotational, orbital, and X-ray properties of millisecond pulsars (MSPs) in globular clusters (GCs) and compared their nature with those of the MSPs in the Galactic field (GF). We found that GC MSPs generally rotate slower than their counterparts in the GF. Different from the expectation of a simple recycling scenario, no evidence for the correlation between the orbital period and the rotation period can be found in the MSP binaries in GCs. There is also an indication that the surface magnetic field of GC MSPs is stronger than those in the GF. All these suggest dynamical interactions in GCs can alter the evolution of MSPs/their progenitors, which can leave an imprint on their X-ray emission properties. While the MSPs in both GF and GCs have similar distributions of X-ray luminosity and hardness, our sample supports the notion that these two populations follow different relations between the X-ray luminosity and spin-down power. We discuss this in terms of both the pulsar emission model and the observational bias.

Keywords: x-ray binary stars; x-ray astronomy; x-ray stars; binary pulsars; millisecond pulsars; pulsars; globular star clusters; x-ray sources
Statistical Fitting of Evolutionary Models to Rotation Rates of Sun-like Stars

We apply for the first time a two-dimensional fitting statistic, τ2, to rotational-evolution models (REMs) of stars (0.1-1.3 M⊙) on the period-mass plane. The τ2 statistic simultaneously considers all cluster rotation data to return a goodness of fit, allowing for data-driven improvement of REMs. We construct data sets for Upper Sco, the Pleiades, and Praesepe, to which we tune our REMs. We use consistently determined stellar masses (calculated by matching Ks magnitudes to isochrones) and literature rotation periods. As a first demonstration of the τ2 statistic, we find the best-fitting gyrochronology age for Praesepe, which is in good agreement with the literature. We then systematically vary three parameters that determine the dependence of our stellar wind torque law on the Rossby number in the saturated and unsaturated regimes, and the location of the transition between the two. By minimizing τ2, we find best-fit values for each parameter. These values vary slightly between clusters, mass determinations, and initial conditions, highlighting the precision of τ2 and its potential for constraining REMs, gyrochronology, and our understanding of stellar physics. Our resulting REMs, which implement the best-possible fitting form of a broken-power-law torque, are statistically improved on previous REMs using similar formulations, but still do not simultaneously describe the observed rotation distributions of the lowest masses, which have both slow and fast rotators by the Praesepe age, and the shape of the converged sequence for higher masses. Further complexity in the REMs is thus required to accurately describe the data.

Keywords: low mass stars; stellar rotation; stellar evolution