adsabs/SciX_UAT_keywords huggingface dataset:
Active Optical Control with Machine Learning: A Proof of Concept for the Vera C. Rubin Observatory

The Active Optics System of the Vera C. Rubin Observatory (Rubin) uses information provided by four wave front sensors to determine deviations between the reconstructed wave front and the ideal wave front. The observed deviations are used to adjust the control parameters of the optical system to maintain image quality across the 3°5 field of view. The baseline approach from the project is to obtain amplitudes of the Zernike polynomials describing the distorted wave front from out-of-focus images collected by the wave front sensors. These Zernike amplitudes are related via an "influence matrix" to the control parameters necessary to correct the wave front. In this paper, we use deep-learning methods to extract the control parameters directly from the images captured by the wave front sensors. Our neural net model uses anti-aliasing pooling to boost performance, and a domain-specific loss function to aid learning and generalization. The accuracy of the control parameters derived from our model exceeds Rubin requirements even in the presence of full-moon background levels and mis-centering of reference stars. Although the training process is time consuming, model evaluation requires only a few milliseconds. This low latency should allow for the correction of the optical configuration during the readout and slew interval between successive exposures.

Keywords: neural networks; convolutional neural networks; multiple mirror telescopes; optical telescopes; astronomical optics; observational astronomy; astronomical instrumentation
Low-surface-brightness Galaxies are Missing in the Observed Stellar Mass Function

We investigate the impact of the surface-brightness (SB) limit on the galaxy stellar mass functions (GSMFs) using galaxy catalogs generated from the Horizon Run 5 (HR5) simulation. We compare the stellar-to-halo-mass relation, GSMF, and size-stellar mass relation of the HR5 galaxies with observational data and other cosmological simulations. The mean SB of simulated galaxies are computed using their effective radii, luminosities, and colors. To examine the cosmic SB dimming effect, we compute k-corrections from the spectral energy distributions of individual simulated galaxy at each redshift, apply the k-corrections to the galaxies, and conduct mock surveys based on the various SB limits. We find that the GSMFs are significantly affected by the SB limits at the low-mass end. This approach can ease the discrepancy between the GSMFs obtained from simulations and observations at 0.6 ≲ z ≤ 2. We also find that a redshift survey with an SB selection limit of ${\left\langle {\mu }_{r}\right\rangle }^{e}=$ 25 mag arcsec-2 will miss 20% of galaxies with ${M}_{\star }^{g}={10}^{9}\,{M}_{\odot }$ at z = 0.625. The missing fraction of low-surface-brightness galaxies increases to 35%, 55%, and 80% at z = 0.9, 1.1, and 1.9, respectively, at the same SB limit.

Keywords: hydrodynamical simulations
From Supernova to Remnant: Tracking the Evolution of the Oldest Known X-Ray Supernovae

Core-collapse supernovae (SNe) expand into a medium created by winds from the pre-SN progenitor. The SN explosion and resulting shock wave(s) heat up the surrounding plasma, giving rise to thermal X-ray emission, which depends on the density of the emitting material. Tracking the variation of the X-ray luminosity over long periods of time thus allows for investigation of the kinematics of the SN shock waves, the structure of the surrounding medium, and the nature of the progenitor star. In this paper, X-ray observations of five of the oldest known X-ray SNe—SN 1970G, SN 1968D, SN 1959D, SN 1957D, and SN 1941C—are analyzed, with the aim of reconstructing their light curves over several decades. For those SNe for which we can extract multiepoch data, the X-ray luminosity appears to decline with time, although with large error bars. No increase in the X-ray emission from SN 1970G is found at later epochs, contrary to previous reports. All five SNe show X-ray luminosities that are of comparable magnitude. We compare the late-time X-ray luminosities of these SNe to those of supernova remnants (SNRs) in the Galaxy, which are a few hundred years old, and find that when the tentative decline is taken into account, the luminosity of the old SNe studied herein could fall below the luminosity of some of the younger SNRs within a few hundred years. However, the X-ray luminosity should begin to increase as the SNe expand in the Sedov phase, thus reaching that of the observed SNRs.

Keywords: core-collapse supernovae; supernovae; type ii supernovae; x-ray astronomy; x-ray point sources; x-ray transient sources; massive stars; stellar winds
A Collapsar Origin for GRB 211211A Is (Just Barely) Possible

Gamma-ray bursts (GRBs) have historically been divided into two classes. Short-duration GRBs are associated with binary neutron star mergers (NSMs), while long-duration bursts are connected to a subset of core-collapse supernovae (SNe). GRB 211211A recently made headlines as the first long-duration burst purportedly generated by an NSM. The evidence for an NSM origin was excess optical and near-infrared emission consistent with the kilonova observed after the gravitational-wave-detected NSM GW170817. Kilonovae derive their unique electromagnetic signatures from the properties of the heavy elements synthesized by rapid neutron capture (the r-process) following the merger. Recent simulations suggest that the "collapsar" SNe that trigger long GRBs may also produce r-process elements. While observations of GRB 211211A and its afterglow rule out an SN typical of those that follow long GRBs, an unusual collapsar could explain both the duration of GRB 211211A and the r-process-powered excess in its afterglow. We use semianalytic radiation transport modeling to evaluate low-mass collapsars as the progenitors of GRB 211211A-like events. We compare a suite of collapsar models to the afterglow-subtracted emission that followed GRB 211211A, and find the best agreement for models with high kinetic energies and an unexpected pattern of 56Ni enrichment. We discuss how core-collapse explosions could produce such ejecta, and how distinct our predictions are from those generated by more straightforward kilonova models. We also show that radio observations can distinguish between kilonovae and the more massive collapsar ejecta we consider here.

Keywords: gamma-ray bursts; explosive nucleosynthesis; core-collapse supernovae; r-process
Similarities between the X-Ray Light Curves of the 2016 and 2020 Eruptions of the Recurrent Nova LMC 1968

The latest eruption of the recurrent nova LMC 1968 was extensively observed by Swift with its X-ray Telescope instrument. A comparison with the Swift data set from the 2016 eruption shows that the X-ray evolution was remarkably similar just as the evolution of the optical photometry and spectroscopy was similar during previously observed eruptions. The only difference is a surprising decrease in the recurrence time. LMC 1968 is only the second nova for which Swift has observed the entire X-ray evolution more than once. At 50 kpc, it is close enough to be extensively observed in its next eruption.

Keywords: recurrent novae; x-ray binary stars; x-ray transient sources
Observations of Disintegrating Long-period Comet C/2019 Y4 (ATLAS): A Sibling of C/1844 Y1 (Great Comet)

We present a study of C/2019 Y4 (ATLAS) using Sloan gri observations from 2020 mid-January to early April. During this time span, the comet brightened with a growth in the effective cross-section of $\left(2.0\pm 0.1\right)\times {10}^{2}$ m2 s-1 from the beginning to ∼70 days preperihelion in late 2020 March, followed by a brightness fade and the comet gradually losing the central condensation. Meanwhile, the comet became progressively bluer, and was even bluer than the Sun (g - r ≈ 0.2) when the brightness peaked, likely due to activation of subterranean fresh volatiles exposed to sunlight. With the tailward bias-corrected astrometry we found an enormous radial nongravitational parameter, ${A}_{1}=\left(+2.25\pm 0.13\right)\times {10}^{-7}$ au day-2 in the heliocentric motion of the comet. Taking all of these findings into consideration, we conclude that the comet has disintegrated since 2020 mid-March. By no means was the split new to the comet, as we quantified that the comet had undergone another split event around last perihelion ∼5 kyr ago, during which its sibling C/1844 Y1 (Great Comet) was produced, with the in-plane component of the separation velocity ≳1 m s-1. We constrained that the nucleus of C/2019 Y4 before disintegration was ≳60 m in radius, and has been protractedly ejecting dust grains of ∼10-40 μm (assuming a dust bulk density of 0.5 g cm-3) with an ejection speed of ∼30 m s-1 in early 2020 March and increased to ∼80 m s-1 toward the end of the month for grains of ∼10 μm.

Keywords: long period comets; comets; small solar system bodies
Spin Change of Asteroid 2012 TC4 Probably by Radiation Torques

Asteroid 2012 TC4 is a small (∼10 m) near-Earth object that was observed during its Earth close approaches in 2012 and 2017. Earlier analyses of light curves revealed its excited rotation state. We collected all available photometric data from the two apparitions to reconstruct its rotation state and convex shape model. We show that light curves from 2012 and 2017 cannot be fitted with a single set of model parameters; the rotation and precession periods are significantly different for these two data sets, and they must have changed between or during the two apparitions. Nevertheless, we could fit all light curves with a dynamically self-consistent model assuming that the spin states of 2012 TC4 in 2012 and 2017 were different. To interpret our results, we developed a numerical model of its spin evolution in which we included two potentially relevant perturbations: (i) gravitational torque due to the Sun and Earth and (ii) radiation torque, known as the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. Despite our model simplicity, we found that the role of gravitational torques is negligible. Instead, we argue that the observed change of its spin state may be plausibly explained as a result of the YORP torque. To strengthen this interpretation, we verify that (i) the internal energy dissipation due to material inelasticity and (ii) an impact with a sufficiently large interplanetary particle are both highly unlikely causes of its observed spin state change. If true, this is the first case where the YORP effect has been detected for a tumbling body.

Keywords: asteroids; close encounters; near-earth objects; small solar system bodies
Star-forming versus Quiescent Regions in the Galaxy: A Case Study of ISM Properties Based on 18 cm OH and 12CO (1-0) Observations

We infer the density of hydrogen nuclei and optical depths associated with molecular gas in front of a star-forming region and in a quiescent region of the Galactic interstellar medium (ISM) using 18 cm OH and archival 3 mm 12CO observations, together with a diffuse cloud model from the literature. The results indicate that the volume densities of hydrogen nuclei are greatest near the star-forming region, intermediate in the CO-bright portions of the quiescent region, and lowest in the CO-dark portions of the quiescent region. Low volume density and low column density appear to be correlated with the presence of CO-dark molecular gas, which is primarily located in the vast space outside of star-forming regions. Molecular gas containing CO may exist in similar quantities both outside of and in the vicinity of star-forming regions; however, the CO emission radiates more efficiently in regions where the ISM is locally compressed, leading to the observational phenomenon of CO-dark and CO-bright molecular gas. We suggest that processes occurring as a natural consequence of star formation such as shock waves and stellar winds lead to compression of the gas into smaller pockets of higher volume density, and such "clumpy" structures will naturally emit more efficiently in CO owing to higher rates of collisional excitation. In this picture, the apparent prominence of CO emission in and near star-forming regions is itself a by-product of the star formation process.

Keywords: galaxy structure; interstellar medium; molecular clouds; molecular gas; radio spectroscopy; surveys
The Single-pulse Observation of PSR B2111+46 with the Five-hundred-meter Aperture Spherical Radio Telescope

We report the observations of periodic nulling in PSR B2111+46 at 1250 MHz with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The nulling fractions (NF) as well as nulling period of this pulsar were calculated. The NF and nulling period are 17% ± 1% and 62.49 ± 0.99 P 1, respectively, and the periodic nulling shows variations in periodicity with time. The durations of each consecutive burst and nulling were investigated, which show that the power-law distribution and the indices are -1.11 ± 0.04 and -2.08 ± 0.23. In the observed frequency band, the width of the profile is narrowed with the increase in frequency, and the degree of polarization has no obvious trend with the increase in frequency. We discovered a weak emission component in front of the leading component of this triple-type profile pulsar that was not observed in other bands and by other telescopes. With the fitting of rotation vector model, we obtained that the angles of the magnetic inclination α and the line of sight ζ are ~13.°0 and ~11.°6, respectively. The high-sensitivity observation of FAST improves our understanding of the emission of this pulsar.

Keywords: radio pulsars
Prebiotic Precursors of the Primordial RNA World in Space: Detection of NH2OH

One of the proposed scenarios for the origin of life is the primordial RNA world, which considers that RNA molecules were likely responsible for the storage of genetic information and the catalysis of biochemical reactions in primitive cells, before the advent of proteins and DNA. In the last decade, experiments in the field of prebiotic chemistry have shown that RNA nucleotides can be synthesized from relatively simple molecular precursors, most of which have been found in space. An important exception is hydroxylamine, NH2OH, which, despite several observational attempts, it has not been detected in space yet. Here we present the first detection of NH2OH in the interstellar medium toward the quiescent molecular cloud G+0.693-0.027 located in the Galactic Center. We have targeted the three groups of transitions from the J = 2-1, 3-2, and 4-3 rotational lines, detecting five transitions that are unblended or only slightly blended. The derived molecular abundance of NH2OH is (2.1 ± 0.9) × 10-10. From the comparison of the derived abundance of NH2OH and chemically related species, with those predicted by chemical models and measured in laboratory experiments, we favor the formation of NH2OH in the interstellar medium via hydrogenation of NO on dust grain surfaces, with possibly a contribution of ice-mantle NH3 oxidation processes. Further laboratory studies and quantum chemical calculations are needed to completely rule out the formation of NH2OH in the gas phase.

Keywords: pre-biotic astrochemistry; astrochemistry; astrobiology; interstellar molecules; galactic center
Factors That Determine the Power-law Index of an Energy Distribution of Solar Flares

The power-law index of an occurrence frequency distribution of flares as a function of energy is one of the most important indicators to evaluate the contribution of small-scale flares to coronal heating. For a few decades, many studies tried to derive the power-law index using various instruments and methods. However, these results are various and the cause of this uncertainty is unknown due to the variety of observation conditions. Therefore, we investigated the dependence of the index on the solar activity, coronal features, released energy range, and active region properties such as magnetic flux, twist, and size. Our findings are (1) annual power-law index derived from time series of total solar irradiance (Sun-as-a-star observation analysis) has a negative correlation with sunspot number; (2) power-law index in active region is smaller than that of the quiet Sun and coronal holes; (3) power-law index is almost constant in the energy range of 1025 ≲ E ≲ 1030 erg; and (4) active regions that have more magnetic free energy density, unsigned magnetic flux, and shear angle tend to have smaller power-law indices. Based on the results and energy-scaling law of Petschek-type reconnection, we suggest that the power-law index of sunspot-scale events is smaller than that of granule-scale events. Moreover, we indicated that sunspot-scale events follow CSHKP flare model whereas granule-scale events follow Parker's nanoflare model.

Keywords: solar active regions; solar corona; solar coronal heating; solar flares; solar physics; solar activity
Picky Partners: The Pairing of Component Masses in Binary Black Hole Mergers

We examine the relationship between individual black hole (BH) masses in merging binary black hole (BBH) systems. Analyzing the 10 BBH detections from LIGO/Virgo's first two observing runs, we find that the masses of the component BHs comprising each binary are unlikely to be randomly drawn from the same underlying distribution. Instead, the two BHs of a given binary prefer to be of comparable mass. We show that it is ∼5 times more likely that the component BHs in a given binary are always equal (to within 5%) than that they are randomly paired. If we assume that the probability of a merger between two BHs scales with the mass ratio q as qβ, so that β = 0 corresponds to random pairings, we find β > 0 is favored at credibility 0.987. By modeling the mass distribution, we find that the median mass ratio is q_{50 %}= 0.91-0.17+0.05 at 90% credibility. While the pairing between BHs depends on their mass ratio, we find no evidence that it depends on the total mass of the system. We predict that 99% of BBHs detected by LIGO/Virgo will have mass ratios q > 0.5. We conclude that merging black holes do not form random pairings; instead they are selective about their partners, preferring to mate with black holes of a similar mass. The details of these selective pairings provide insight into the underlying formation channels of merging binaries.

Keywords: astrophysical black holes; gravitational wave sources; massive stars; stellar remnants
The Behavior of HgMn Stars in the Far UV-Paper 27: HD 1909

The analysis of two spectra of the spectroscopic binary B9 Hg star HD 1909 recorded by the SWP camera on board the International Ultraviolet Explorer reveals one instance of variations of the far-ultraviolet flux of this star from 1300 up to 2000 Å. The first TESS lightcurve of HD 1909 on the MAST website is periodic with a period close to 7 days which is very close to an earlier period found for the variations of the Strömgren index u. The FUV variations, which occur over about 5 yr, could be caused by the motion of the lower mass companion.

Keywords: chemically peculiar stars; mercury-manganese stars
Oceanographic Considerations for Exoplanet Life Detection

Liquid water oceans are at the center of our search for life on exoplanets because water is a strict requirement for life as we know it. However, oceans are dynamic habitats—and some oceans may be better hosts for life than others. In Earth's ocean, circulation transports essential nutrients such as phosphate and is a first-order control on the distribution and productivity of life. Of particular importance is upward flow from the dark depths of the ocean in response to wind-driven divergence in surface layers. This "upwelling" returns essential nutrients that tend to accumulate at depth via sinking of organic particulates back to the sunlit regions where photosynthetic life thrives. Ocean dynamics are likely to impose constraints on the activity and atmospheric expression of photosynthetic life in exo-oceans as well, but we lack an understanding of how ocean dynamics may differ on other planets. We address this issue by exploring the sensitivity of ocean dynamics to a suite of planetary parameters using ROCKE-3D, a fully coupled ocean-atmosphere general circulation model. Our results suggest that planets that rotate slower and have higher surface pressure than Earth may be the most attractive targets for remote life detection because upwelling is enhanced under these conditions, resulting in greater nutrient supply to the surface biosphere. Seasonal deepening of the mixed layer on high-obliquity planets may also enhance nutrient replenishment from depth into the surface mixed layer. Efficient nutrient recycling favors greater biological activity, more biosignature production, and thus more detectable life. More generally, our results demonstrate the importance of considering oceanographic phenomena for exoplanet life detection and motivate future interdisciplinary contributions to the emerging field of exo-oceanography.

Keywords: astrobiology; exoplanets; ocean-atmosphere interactions
Twenty-five Years of Accretion onto the Classical T Tauri Star TW Hya

Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998-2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of 2.51 × 10-9 M ⊙ yr-1 and a Gaussian distribution with an FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Lyα. The accretion luminosities are well correlated with He line luminosities but poorly correlated with Hα and Hβ luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars.

Keywords: classical t tauri stars; stellar accretion disks; protoplanetary disks; high resolution spectroscopy; variable stars