adsabs/SciX_UAT_keywords huggingface dataset:
The ACTIONFINDER: An Unsupervised Deep Learning Algorithm for Calculating Actions and the Acceleration Field from a Set of Orbit Segments

We introduce the ACTIONFINDER, a deep learning algorithm designed to transform a sample of phase-space measurements along orbits in a static potential into action and angle coordinates. The algorithm finds the mapping from positions and velocities to actions and angles in an unsupervised way, by using the fact that points along the same orbit have identical actions. Here we present the workings of the method and test it on simple axisymmetric models, comparing the derived actions to those generated with the Torus Mapping technique. We show that it recovers the torus actions for halo-type orbits in a realistic model of the Milky Way to ~0.6% accuracy with as few as 1024 input phase-space measurements. These actions are much better conserved along orbits than those estimated with the Stäckel fudge. In our case, the reciprocal mapping from actions and angles to positions and velocities can also be learned. One of the advantages of the ACTIONFINDER is that it does not require the underlying potential to be known in advance-indeed it is designed to return the acceleration field. We expect the algorithm to be useful for analyzing the properties of dynamical systems in numerical simulations. However, our ultimate goal with this effort will be to apply it to real stellar streams to recover the Galactic acceleration field in a way that is relatively agnostic about the underlying dark matter properties or the behavior of gravity.

Keywords: celestial mechanics; neural networks
A Real-time View of Orbital Evolution in HM Cancri

HM Cancri is a double degenerate binary with the shortest orbital period presently known. The 5.36 minute period is seen as a large amplitude, soft X-ray modulation, likely resulting from a hot spot produced by direct impact accretion. With such a short orbital period it is expected to have a gravitational wave luminosity comparable to or larger than that in the X-ray, and its orbital frequency is known to be increasing at a rate consistent with the expected loss of angular momentum due to gravitational radiation. We use recent Neutron Star Interior Composition Explorer observations to extend its long-term X-ray timing baseline to almost 20 yr. Phase coherent timing of these new data combined with existing Chandra data demonstrates conclusively that the rate of orbital frequency increase is slowing, and we measure a nonzero ${\ddot{f}}_{0}=-8.95\pm 1.4\times {10}^{-27}$ Hz s-2, which is to our knowledge the first such measurement of its kind for any compact astrophysical binary. With the simultaneous high precision measurement of ${\dot{f}}_{0}=3.557\pm 0.005\times {10}^{-16}$ Hz s-1, we estimate that the system will reach its maximum orbital frequency of ${f}_{\max }\approx 3.1172091$ mHz in 1260 ± 200 yr, indicating that the system is close to its epoch of maximum orbital frequency. Assuming mass transfer is conservative, the measurement of $\ddot{f}\lt 0$ implies that the accretion rate from the donor is growing, with $-5.4\times {10}^{-10}\lt {\ddot{M}}_{2}\lt -4.0\times {10}^{-10}$ M⊙ yr-2. Further quantitative comparisons with theoretical models should enable more precise inferences regarding its current evolutionary state.

Keywords: white dwarf stars; compact binary stars; interacting binary stars; x-ray binary stars; accretion; orbital evolution; x-ray sources; am canum venaticorum stars
Tracing Molecular Gas Mass in z ≃ 6 Galaxies with [C II]

We investigate the fine-structure [C II] line at 158 μm as a molecular gas tracer by analyzing the relationship between molecular gas mass (M mol) and [C II] line luminosity (L [C II]) in 11,125 z ≃ 6 star-forming, main-sequence galaxies from the SIMBA simulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. Though most (~50%-100%) of the gas mass in our simulations is ionized, the bulk (>50%) of the [C II] emission comes from the molecular phase. We find a sublinear (slope 0.78 ± 0.01) $\mathrm{log}{L}_{[{\rm{C}}\,{\rm\small{II}}]}\mbox{--}\mathrm{log}{M}_{\mathrm{mol}}$ relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at z ≲ 6. We derive a median [C II]-to-M mol conversion factor of α [C II] ≃ 18 M ⊙/L ⊙. This is lower than the average value of ≃30 M ⊙/L ⊙ derived from observations, which we attribute to lower gas-phase metallicities in our simulations. Thus, a lower, luminosity-dependent conversion factor must be applied when inferring molecular gas masses from [C II] observations of low-mass galaxies. For our simulations, [C II] is a better tracer of the molecular gas than CO J = 1-0, especially at the lowest metallicities, where much of the gas is CO-dark. We find that L [C II] is more tightly correlated with M mol than with star formation rate (SFR), and both the $\mathrm{log}{L}_{[{\rm{C}}\,{\rm\small{II}}]}\mbox{--}\mathrm{log}{M}_{\mathrm{mol}}$ and $\mathrm{log}{L}_{[{\rm{C}}\,{\rm\small{II}}]}\mbox{--}\mathrm{log}\,\mathrm{SFR}$ relations arise from the Kennicutt-Schmidt relation. Our findings suggest that L [C II] is a promising tracer of the molecular gas at the earliest cosmic epochs.

Keywords: high-redshift galaxies; astronomical simulations; interstellar medium; molecular gas
Stellar Atmospheric Parameters of M-type Stars from LAMOST DR8

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Low Resolution Spectroscopic Survey (LRS) provides massive spectroscopic data on M-type stars, and the derived stellar parameters could bring vital help to various studies. We adopt the ULySS package to perform χ 2 minimization with model spectra generated from the MILES interpolator and determine the stellar atmospheric parameters for the M-type stars from LAMOST LRS Data Release 8. Comparison with the stellar parameters from the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP) suggests that most of our results have good consistency. For M dwarfs, we achieve dispersions better than 74 K, 0.19 dex, and 0.16 dex for T eff, $\mathrm{log}g$ , and [Fe/H], while for M giants, the internal uncertainties are 58 K, 0.32 dex, and 0.26 dex, respectively. Compared to ASPCAP we also find a systematic underestimation of ΔT eff = -176 K for M dwarfs and a systematic overestimation of ${\rm{\Delta }}\mathrm{log}g$ = 0.30 dex for M giants. However, such differences are less significant when we make a comparison with common stars from other literature, which indicates that systematic biases exist in the difference between ASPCAP and other measurements. A catalog of 763,136 spectra corresponding to 616,314 M-type stars with derived stellar parameters is presented. We determine the stellar parameters for stars with T eff higher than 2900 K, with $\mathrm{log}g$ from -0.24 dex to 5.9 dex. The typical precisions are 45 K, 0.25 dex, and 0.22 dex, for T eff, $\mathrm{log}g$ , and [Fe/H], respectively, which are estimated from duplicate observations of the same stars.

Keywords: m stars; late-type stars; stellar atmospheres; stellar physics; sky surveys; catalogs; atomic spectroscopy; spectroscopy
The Hubble Space Telescope Advanced Camera for Surveys Emission Line Survey of Andromeda. I. Classical Be Stars

We present results from a two epoch Hubble Space Telescope Hα emission line survey of the Andromeda galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We found 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch # 1 (epoch # 2), yielding an overall fractional Be content of 6.15% ± 0.26% (5.96% ± 0.25%). The fractional Be content decreased with spectral subtype from ∼23.6% ± 2.0% (∼23.9% ± 2.0%) for B0-type stars to ∼3.1% ± 0.34% (∼3.4% ± 0.35%) for B8-type stars in epoch # 1 (epoch # 2). We observed a clear population of cluster Be stars at early fractional main-sequence lifetimes, indicating that a subset of Be stars emerge onto the zero-age main sequence as rapid rotators. Be stars are 2.8× rarer in M31 for the earliest subtypes compared to the Small Magellanic Cloud, confirming that the fractional Be content decreases in significantly more metal-rich environments (like the Milky Way and M31). However, M31 does not follow a clear trend of Be fraction decreasing with metallicity compared to the Milky Way, which may reflect that the Be phenomenon is enhanced with evolutionary age. The rate of disk-loss or disk-regeneration episodes we observed, 22% ± 2% yr-1, is similar to that observed for seven other Galactic clusters reported in the literature, assuming these latter transient fractions scale by a linear rate. The similar number of disk-loss events (57) as disk-renewal events (43) was unexpected since disk dissipation timescales can be ∼2× the typical timescales for disk build-up phases.

Keywords: circumstellar disks; be stars; early-type stars; h alpha photometry
TOI-712: A System of Adolescent Mini-Neptunes Extending to the Habitable Zone

As an all-sky survey, NASA's Transiting Exoplanet Survey Satellite (TESS) mission is able to detect the brightest and rarest types of transiting planetary systems, including young planets that enable study of the evolutionary processes that occur within the first billion years. Here we report the discovery of a young, multiplanet system orbiting the bright K4.5V star, TOI-712 (V = 10.838, ${M}_{\star }={0.733}_{-0.025}^{+0.026}\,{M}_{\odot }$ , R ⋆ = 0.674 ± 0.016 R ⊙, ${T}_{\mathrm{eff}}={4622}_{-60}^{+61}$ K). From the TESS light curve, we measure a rotation period of 12.48 days and derive an age between about 500 Myr and 1.1 Gyr. The photometric observations reveal three transiting mini-Neptunes ( ${R}_{b}={2.049}_{-0.080}^{+0.120}\,{R}_{\oplus }$ , ${R}_{c}={2.701}_{-0.082}^{+0.092}\,{R}_{\oplus }$ , ${R}_{d}={2.474}_{-0.082}^{+0.090}\,{R}_{\oplus }$ ), with orbital periods of P b = 9.531 days, P c = 51.699 days, and P d = 84.839 days. After modeling the three-planet system, an additional Earth-sized candidate is identified, TOI-712.05 (P = 4.32 days, R P = 0.81 ± 0.11 R ⊕). We calculate that the habitable zone falls between 0.339 and 0.844 au (82.7 and 325.3 days), placing TOI-712 d near its inner edge. Among planetary systems harboring temperate planets, TOI-712 (T = 9.9) stands out as a relatively young star bright enough to motivate further characterization.

Keywords: exoplanets; mini neptunes; exoplanet evolution; exoplanet formation; transits; transit photometry; exoplanet dynamics; exoplanet systems
Water Masers as an Early Tracer of Star Formation

We present a study of the correlation between 22 GHz water maser emission and far-infrared/submillimeter (IR/sub-mm) sources. The generalized linear model (GLM) is used to predict H2O maser detection in a particular source with defined physical parameters. We checked the GLM predictions by observing a sample of selected sources with the Effelsberg 100 m telescope. In total, 359 sources were observed. H2O masers were detected in 124 sources, with 56 new detections. We found 22 sources with a significant flux variability. Using the GLM analysis, we estimate that 2392 ± 339 star formation regions (SFRs) in the Galaxy may harbor H2O masers detectable by single-dish observations at the noise level of ~0.05 Jy. Analyzing the luminosity-to-mass ratio (L/M) of the ATLASGAL and Hi-GAL clumps associated with different maser species, we find that 22 GHz water masers have significantly lower values of L/M in comparison to 6.7 GHz class II methanol and 1665 MHz OH masers. This implies that 22 GHz water masers may appear prior to 6.7 GHz methanol and OH masers in the evolutionary sequence of SFRs. From the analysis of physical offsets between host clumps and maser interferometric positions, we found no significant difference between the H2O and class II methanol maser offsets against the host clump position. We conclude that the tight association between water masers and IR/sub-mm sources may provide insight into the pumping conditions of these masers and the evolutionary stages of their onset.

Keywords: astronomy databases; water masers; astrophysical masers; submillimeter astronomy; far infrared astronomy; radio astronomy
Planetesimal Drift in Eccentric Disks: Possible Outward Migration

Radial drift of solid particles in the protoplanetary disk is often invoked as a threat to planet formation, as it removes solid material from the disk before it can be assembled into planets. However, it may also concentrate solids at particular locations in the disk, thus accelerating the coagulation process. Planetesimals are thought to drift much faster in an eccentric disk, due to their higher velocities with respect to the gas, but their drift rate has only been calculated using approximate means. In this work, we show that in some cases previous estimates of the drift rate, based on a modification of the results for an axisymmetric disk, are highly inaccurate. In particular, we find that under some easily realized circumstances, planetesimals may drift outwards, rather than inwards. This results in the existence of radii in the disk that act as stable attractors of planetesimals. We show that this can lead to a local enhancement of more than an order of magnitude in the surface density of planetesimals, even when a wide dispersion of planetesimal size is considered.

Keywords: exoplanet formation; eccentricity; protoplanetary disks; planetesimals; planet formation
The Quantitative Relation of the Time Profiles of Intensities in the Well-connected Solar Energetic Particle Events

In this work, the quantitative relation of the intensity time profiles in the well-connected energetic particle events has been identified. Focusing on the propagation processes of energetic protons in the energy channels of about 13-64 MeV, solar energetic particle (SEP) events observed by STEREO A, STEREO B, and SOHO have been studied. The intensities observed by the spacecraft with the best magnetic connection to the source region tend to rise the fastest and have the highest peak intensities. In the cases without multiple injections or significant acceleration of particles by interplanetary shocks, particle intensities with the highest peaks are fitted by using a solution of the diffusion equation, and the time profiles of particle intensities could be described by two parameters. By fitting 59 energetic proton events, we find that the two parameters satisfy a power-law model in different events, and the distribution of peak time is also obtained. The power-law model helps one to obtain a quantitative relation of SEP intensities with the fitting function, and the distribution of peak time could provide a basis for determining the magnetic connection between the spacecraft and the source region.

Keywords: solar energetic particles; interplanetary physics; solar particle emission; solar storm
Fleeting but Not Forgotten: The Imprint of Escaping Hydrogen Atmospheres on Super-Earth Interiors

Small, close-in exoplanets are divided into two subpopulations: super-Earths and sub-Neptunes. Most super-Earths are thought to have lost their primordially accreted hydrogen-dominated atmospheres via thermally driven winds. We consider the global chemical equilibrium of super-Earths and the lasting impacts of their fleeting hydrogen atmospheres. We find that hydrogen is efficiently sequestered into the interior, oxidizing iron and endogenously producing ∼0.5%–1.0% water by mass. As the atmospheres of super-Earths are continuously sculpted by mass loss and chemical equilibration, they remain hydrogen-dominated by mole (number) fraction but become steam-dominated by mass, which may be observable with JWST for planets transitioning across the radius valley. One of the main effects of efficient sequestration of hydrogen into the interior is to produce an underdense bulk interior compared to that of Earth. We predict bulk densities of super-Earths to be ∼5.0 g cm‑3 for a 1M ⊕ planet, which is consistent with high-precision mass measurements and also population-level inference analyses from atmospheric escape models.

Keywords: exoplanet evolution; exoplanet atmospheric evolution; exoplanet atmospheric composition; exoplanet structure
First Search for r-mode Gravitational Waves from PSR J0537-6910

We report results of the first search to date for continuous gravitational waves from unstable r-modes from the pulsar $\mathrm{PSR}\ {\rm{J}}0537\mbox{--}6910$ . We use data from the first two observing runs of the Advanced LIGO network. We find no significant signal candidate and set upper limits on the amplitude of gravitational-wave signals, which are within an order of magnitude of the spin-down values. We highlight the importance of having timing information at the time of the gravitational-wave observations, I.e., rotation frequency and frequency-derivative values, and glitch-occurrence times, such as those that a NICER campaign could provide.

Keywords: gravitational waves; pulsars; neutron stars
Calibrating Gamma-Ray Bursts by Using a Gaussian Process with Type Ia Supernovae

In this paper, we calibrate the Amati relation (the E p-E iso correlation) of gamma-ray bursts (GRBs) in a cosmology-independent way. By using a Gaussian process to reconstruct the smoothed luminosity distance from the Pantheon type Ia supernovae sample, we utilize the reconstructed results to calibrate the E p-E iso correlation with the Markov Chain Monte Carlo method and construct a Hubble diagram with the A220 GRB data, in which there are A118 GRB data with the higher qualities appropriate for cosmological purposes. With 98 GRBs at 1.4 < z ≤ 8.2 in the A118 sample and the observed Hubble data, we obtain Ωm = ${0.346}_{-0.069}^{+0.048}$ , h = ${0.677}_{-0.029}^{+0.029}$ for the flat ΛCDM model, and Ωm = ${0.314}_{-0.055}^{+0.072}$ , h = ${0.705}_{-0.069}^{+0.055}$ , w = $-{1.23}_{-0.64}^{+0.33}$ for the flat wCDM model, which are consistent with those from fitting the coefficients of the Amati relation and the cosmological parameters simultaneously.

Keywords: cosmology; gamma-ray bursts
Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra

H I Lyα (1215.67 Å) and the O I triplet (1302.17, 1304.86, and 1306.03 Å) are bright far-ultraviolet (FUV) emission lines that trace the stellar chromosphere. Observations of stellar Lyα and O I using the Hubble Space Telescope's (HST) most sensitive FUV spectrograph, the Cosmic Origins Spectrograph (COS), are contaminated with geocoronal emission, or airglow. This study demonstrates that airglow emission profiles as observed by COS are sufficiently stable to create airglow templates that can be reliably subtracted from the data, recovering the underlying stellar flux. We developed a graphical user interface to implement the airglow subtraction on a sample of 171 main-sequence F-, G-, K-, and M-type dwarfs from the COS data archive. Correlations between recovered stellar emission and measures of stellar activity were investigated. Several power-law relationships are presented for predicting the stellar Lyα and O I emission. The apparent brightness of the stellar emission relative to the airglow is a critical factor in the success or failure of an airglow subtraction. We developed a predictor for the success of an airglow subtraction using the signal-to-noise ratio of the nearby chromospheric emission line Si III (1206.51 Å). The minimum attenuated Lyα flux that was successfully recovered is 1.39 × 10-14 erg cm-2 s-1, and we recommend this as a minimum flux for COS Lyα recoveries.

Keywords: dwarf stars; main sequence stars; hubble space telescope; ultraviolet spectroscopy; stellar activity
GeV Emission in the Region of the Supernova Remnant G51.26+0.11

The supernova remnant G51.26+0.11 was recently discovered and little is known about its properties and environment. Using data from the Fermi Large Area Telescope we study the GeV emission seen in the direction of G51.26+0.11 to constrain the origin of the gamma-rays and their possible relation to this supernova remnant or to a star-forming region. We also search for emission from molecular gas in the region that could provide dense material for the production of gamma-rays. By modeling the multiwavelength spectrum of G51.26+0.11 from radio to gamma-rays we derive the properties of the particle populations that could produce the emission in several possible scenarios. We rule out the star-forming regions (such as G051.010+00.060) seen nearby as the origin of the GeV emission. The correspondence seen between the gamma-ray and radio morphologies supports a scenario in which G51.26+0.11 is the cause of the gamma-rays. The flat spectral energy distribution observed at GeV energies is best fit by hadronic or inverse Compton emission, while a bremsstrahlung model cannot properly account for the radio fluxes under a simple one-zone scenario. A pulsar wind nebula origin of the high-energy photons cannot be ruled out or confirmed.

Keywords: gamma-ray astronomy; gamma-rays
Spectroscopic Follow-up of Gaia Exoplanet Candidates: Impostor Binary Stars Invade the Gaia DR3 Astrometric Exoplanet Candidates

In this paper, we report on the follow-up of six potential exoplanets detected with Gaia astrometry and provide an overview of what is currently known about the nature of the entire Gaia astrometric exoplanet candidate sample, 72 systems in total. We discuss the primary false-positive scenario for astrometric planet detections: binary systems with alike components that produce small photocenter motions, mimicking exoplanets. These false positives can be identified as double-lined binaries (SB2) through analysis of high-resolution spectra. Doing so we find that three systems, Gaia DR3 1916454200349735680, Gaia DR3 2052469973468984192, and Gaia DR3 5122670101678217728, are indeed near-equal-mass double-star systems rather than exoplanetary systems. The spectra of the other two analyzed systems, HD 40503 and HIP 66074, are consistent with the exoplanet scenario in that no second set of lines can be found in the time series of publicly available high-resolution spectra. However, their Gaia astrometric solutions imply radial-velocity semiamplitudes ~3 (HD 40503) and ~15 (HIP 66074) larger than what was observed with ground-based spectrographs. The Gaia astrometry orbital solutions and ground-based radial-velocity measurements exhibit inconsistencies in six out of a total of 12 exoplanet candidate systems where such data are available, primarily due to substantial differences between observed ground-based radial-velocity semiamplitudes and those implied by the Gaia orbits. We investigated various hypotheses as to why this might be the case, and although we found no clear perpetrator, we note that a mismatch in orbital inclination offers the most straightforward explanation.

Keywords: exoplanet astronomy; astrometric exoplanet detection; exoplanets; brown dwarfs; astrometry; radial velocity; binary stars; astrometric binary stars; spectroscopic binary stars