adsabs/SciX_UAT_keywords huggingface dataset:
Two Populations of Carbon-enhanced Metal-poor Stars in the Disk System of the Milky Way

We present a chemodynamical analysis of low-resolution (R ~ 1300) spectroscopy of ~50,000 stars from the AAOmega Evolution of Galactic Structure survey, focusing on two key populations of (in total) 650 carbon-enhanced metal-poor (CEMP) stars within the disk system of the Milky Way: a mildly prograde population (Lz < 1000 kpc km s-1) and a strongly prograde population (Lz > 1000 kpc km s-1). Based on their chemical and kinematic characteristics, and on comparisons with similar populations found in the recent literature, we tentatively associate the former with an ex situ inner-halo population originating from either the Gaia Sausage or Gaia-Enceladus. The latter population is linked to the metal-weak thick disk. We discuss their implications in the context of the formation history of the Milky Way.

Keywords: milky way disk; milky way evolution; milky way formation; cemp stars; stellar kinematics
Early Evolution of Disk, Outflow, and Magnetic Field of Young Stellar Objects: Impact of Dust Model

The formation and early evolution of low-mass young stellar objects (YSOs) are investigated using three-dimensional non-ideal magnetohydrodynamics simulations. We investigate the evolution of YSOs up to $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation, at which protostellar mass reaches $\sim 0.1{M}_{\odot }$ . We particularly focus on the impact of the dust model on the evolution. We found that a circumstellar disk is formed in all simulations, regardless of the dust model. Disk size is approximately 10 au at the protostar formation epoch, and it increases to several tens of au at $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation. The disk mass is comparable to the central protostellar mass, and gravitational instability develops. In simulations with small dust sizes, the warp of the pseudodisk develops $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation. The warp strengthens magnetic braking in the disk and decreases disk size. Ion-neutral drift can occur in the infalling envelope when the typical dust size is $a\gtrsim 0.2\,\mu {\rm{m}}$ and the protostar (plus disk) mass is $M\gtrsim 0.1{M}_{\odot }$ . The outflow activity is anticorrelated to the dust size, and the strong outflow appears with small dust grains.

Keywords: protoplanetary disks; circumstellar disks; magnetohydrodynamical simulations
Atmospheric Temperature Inversions and He I 5876 Core Profile Structure in White Dwarfs

We report distinctive core profiles in the strongest optical helium line, He I λ5876, from high-resolution high-sensitivity observations of spectral type DB white dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES, we find the core appearance to be related to the degree of hydrogen and heavy element content in the atmosphere. New Ca K-line measurements or upper limits are reported for about half the sample stars. He I λ5876 emission cores with a self-reversed central component are present for those stars with relatively low hydrogen abundance, as well as relatively low atmospheric heavy element pollution. This self-reversed structure disappears for stars with higher degrees of pollution and/or hydrogen abundance, giving way to a single absorption core. From our model atmospheres, we show that the self-reversed emission cores can be explained by temperature inversions in the upper atmosphere. We propose that the transition to a single absorption core is due to the additional opacity from hydrogen and heavy elements that inhibits the temperature inversions. Our current models do not exactly match the effective temperature range of the phenomenon or the amplitude of the self-reversed structure, which is possibly a result of missing physics such as 3D treatment, convective overshoot, and/or non-LTE effects. The He I λ5876 line structure may prove to be a useful new diagnostic for calibrating temperature profiles in DB atmosphere models.

Keywords: white dwarf stars; db stars; stellar atmospheres; stellar atmospheric opacity; upper atmosphere; extrasolar rocky planets; stellar effective temperatures; high resolution spectroscopy
In Situ Geochronology for the Next Decade: Mission Designs for the Moon, Mars, and Vesta

Geochronology is an indispensable tool for reconstructing the geologic history of planets, essential to understanding the formation and evolution of our solar system. Bombardment chronology bounds models of solar system dynamics, as well as the timing of volatile, organic, and siderophile element delivery. Absolute ages of magmatic products provide constraints on the dynamics of magma oceans and crustal formation, as well as the longevity and evolution of interior heat engines and distinct mantle/crustal source regions. Absolute dating also relates habitability markers to the timescale of evolution of life on Earth. However, the number of terrains important to date on worlds of the inner solar system far exceeds our ability to conduct sample return from all of them. In preparation for the upcoming Decadal Survey, our team formulated a set of medium-class (New Frontiers) mission concepts to three different locations (the Moon, Mars, and Vesta) where sites that record solar system bombardment, magmatism, and habitability are uniquely preserved and accessible. We developed a notional payload to directly date planetary surfaces, consisting of two instruments capable of measuring radiometric ages, an imaging spectrometer, optical cameras to provide site geologic context and sample characterization, a trace-element analyzer to augment sample contextualization, and a sample acquisition and handling system. Landers carrying this payload to the Moon, Mars, and Vesta would likely fit into the New Frontiers cost cap in our study (~$1B). A mission of this type would provide crucial constraints on planetary history while also enabling a broad suite of complementary investigations.

Keywords: earth-moon system; selenology; mars; main belt asteroids; lunar geochronology; cosmochronology
Discovery of a 100 kpc Narrow Curved Twin Jet in the S-shaped Giant Radio Galaxy J0644+1043

We report the discovery of an S-shaped morphology of the radio galaxy J0644+1043 imaged with a 30 μJy beam‑1 sensitive 525 MHz broadband (bands 3 + 4) uGMRT map. Dedicated spectroscopic observations of the host galaxy carried out with the 2 m Rozhen telescope yielded a redshift of 0.0488, giving a projected linear size of the peculiar radio structure of over 0.7 Mpc. This giant radio galaxy is powered by a black hole of mass M ⊙, from the vicinity of which emanate well-collimated and knotty jets, each ∼100 kpc long. The entire radio structure, presumably due to the effective jet precession, is less than 50 Myr old, has a power of ∼6 × 1024 W Hz‑1 at 1.4 GHz, and has observed morphological characteristics that do not strictly conform to the traditional Fanaroff–Riley (FR) FR I or FR II categories.

Keywords: giant radio galaxies; active galaxies; non-thermal radiation sources
Black Hole Masses of Weak Emission Line Quasars Based on the Continuum Fit Method

We studied optical-ultraviolet spectral energy distribution of 10 weak emission-line quasars (WLQs) that lie at redshifts z = 0.19 and 1.43 < z < 3.48. The theoretical models of their accretion disk continua are created based on the Novikov-Thorne equations. It allows us to estimate masses of their supermassive black holes ( ${M}_{\mathrm{BH}}$ ) and accretion rates. We determined the virial factor for WLQs and note its anticorrelation with the FWHM of the Hβ emission line $(f\propto {\mathrm{FWHM}}^{\alpha },\alpha =-1.34\pm 0.37$ ). By comparison with the previously estimated BH masses, the underestimation of ${M}_{\mathrm{BH}}$ is noticed with a mean factor of 4-5, which depends on the measured full width. We proposed a new formula to estimate ${M}_{\mathrm{BH}}$ in WLQs based on their observed $\mathrm{FWHM}$ (Hβ) and luminosities at 5100 Å. In our opinion, WLQs are also normal quasars visible in a reactivation stage.

Keywords: quasars; active galactic nuclei; black holes
Prescriptions for Correcting Ultraviolet-based Redshifts for Luminous Quasars at High Redshift

High-redshift quasars typically have their redshift determined from rest-frame ultraviolet (UV) emission lines. However, these lines, and more specifically the prominent C IV λ1549 emission line, are typically blueshifted yielding highly uncertain redshift estimates compared to redshifts determined from rest-frame optical emission lines. We present near-infrared spectroscopy of 18 luminous quasars at 2.15 < z < 3.70 that allows us to obtain reliable systemic redshifts for these sources. Together with near-infrared spectroscopy of an archival sample of 44 quasars with comparable luminosities and redshifts, we provide prescriptions for correcting UV-based redshifts. Our prescriptions reduce velocity offsets with respect to the systemic redshifts by ∼140 km s-1 and reduce the uncertainty on the UV-based redshift by ∼25% with respect to the best method currently used for determining such values. We also find that the redshifts determined from the Sloan Digital Sky Survey Pipeline for our sources suffer from significant uncertainties, which cannot be easily mitigated. We discuss the potential of our prescriptions to improve UV-based redshift corrections given a much larger sample of high-redshift quasars with near-infrared spectra.

Keywords: galaxy distances; quasars; active galactic nuclei
Multiwavelength Evidence for a New Flare-mode Transitional Millisecond Pulsar

We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0-7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-ray to γ-ray flux. Together, these properties are consistent with the classification of the binary as a transitional millisecond pulsar (tMSP) in the subluminous disk state. Uniquely among the candidate tMSPs, 4FGL J0540.0-7552 shows consistent optical, X-ray, and γ-ray evidence for having undergone a state change, becoming substantially brighter in the optical and X-rays and fainter in GeV γ-rays sometime in mid-2013. In its current subluminous disk state, and like one other candidate tMSP in the Galactic field, 4FGL J0540.0-7552 appears to always be in an X-ray "flare mode," indicating that this could be common phenomenology for tMSPs.

Keywords: millisecond pulsars
Asteroid Thermal Inertia Estimates from Remote Infrared Observations: The Effects of Surface Roughness and Rotation Rate

The thermal inertia of an asteroid's surface can provide insight into regolith properties, such as the presence of a layer of fine dust, the density and thermal conductivity of a rocky surface, and, together with other observational data, mineralogy. Knowledge of the surface characteristics of asteroids is important for planetary defense initiatives and the extraction of resources ("asteroid mining"). A simple means of estimating asteroid thermal inertia has been proposed by Harris & Drube, which is suitable for application to large sets of thermal-infrared observational data, such as those obtained by infrared space telescopes. We compare results from the Harris-Drube estimator with recently published values of asteroid thermal inertia from detailed thermophysical modeling, and provide an explanation in terms of reduced surface roughness for some discrepant results. Smooth surfaces covered in fine dust may provide an explanation for the unexpectedly low values of thermal inertia derived from thermophysical modeling for some slowly rotating main-belt asteroids. In the case of near-Earth objects (NEOs) we show that results from the estimator are in good agreement with those from thermophysical modeling, with just a few exceptions. We discuss the special cases of the NEOs (101955) Bennu, (162173) Ryugu, and (29075) 1950 DA in the context of results from our estimator. Given the data requirements and complexity of thermophysical modeling, data-analysis tools based on relatively simple concepts can play an important role in allowing "quick-look" assessment of thermal-infrared data of asteroids, especially NEOs.

Keywords: main belt asteroids; near-earth objects; infrared astronomy; minor planets
The Behavior of Bp Si Stars in the Far UV-Paper V: HD 187473

The analysis of five spectra of the B9 SiSrEu HD 187473 recorded by the Short Wavelength Prime camera on board the International Ultraviolet Explorer reveals large amplitude variations of the far ultraviolet spectral energy distribution over a time interval of about half the rotation period. In contrast, the level of the mid-UV flux does not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The iron-peak elements, chromium, manganese and iron probably also contribute to these variations.

Keywords: chemically peculiar stars; bp stars
Kepler K2 Observations of the Faint, Understudied Polar SDSS J092122.84+203857.1

SDSS J092122.84+203857.1 is a polar-type cataclysmic variable system, consisting of a strongly magnetized white dwarf that accretes from its red dwarf companion. It is also one of just five polars known to have been observed by Kepler during its K2 mission. We analyzed the K2 short-cadence light curve of J0921 and identified a weak, but highly coherent, signal at a frequency of 17.099 cycles day-1, corresponding with the system's reported orbital period. We see no overall variation in the accretion rate across the K2 observation, and both our measurement of the period and the binned orbital profile are very consistent with previous ground-based data.

Keywords: cataclysmic variable stars; am herculis stars
A Novel Eccentricity Parameterization for Transit-only Models

We present a novel eccentricity parameterization for transit-only fits that allows us to efficiently sample the eccentricity and argument of periastron, while being able to generate a self-consistent model of a planet in a Keplerian orbit around its host star. With simulated fits of 330 randomly generated systems, we demonstrate that typical parameterizations often lead to inaccurate and overly precise determinations of the planetary eccentricity. However, our proposed parameterization allows us to accurately—and often precisely—recover the eccentricity for the simulated planetary systems with only transit data available.

Keywords: eccentricity; orbital elements; astronomical models; transit photometry
3D Selection of 167 Substellar Companions to Nearby Stars

We analyze 5108 AFGKM stars with at least five high-precision radial velocity points, as well as Gaia and Hipparcos astrometric data, utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000 days. Around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40 M Jup. We also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine substellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages, we estimate that an additional 10-57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.

Keywords: astrometric exoplanet detection; radial velocity; exoplanet detection methods; exoplanet astronomy; brown dwarfs; exoplanet catalogs
The Double White Dwarf Merger Progenitors of SDSS J2211+1136 and ZTF J1901+1458

Double white dwarf (DWD) mergers are possibly the leading formation channel of massive, rapidly rotating, high-field magnetic white dwarfs (HFMWDs). However, a direct link connecting a DWD merger to any observed HFMWD is still missing. We here show that the HFMWDs SDSS J221141.80+113604.4 (hereafter J2211+1136) and ZTF J190132.9+145808.7 (hereafter J1901+1458) might be DWD merger products. J2211+1136 is a 1.27 M ⊙ white dwarf (WD) with a rotation period of 70.32 s and a surface magnetic field of 15 MG. J1901+1458 is a 1.327-1.365 M ⊙ WD with a rotation period of 416.20 s, and a surface magnetic field in the range 600-900 MG. With the assumption of single-star evolution and the currently measured WD masses and surface temperatures, the cooling ages of J2211+1136 and J1901+1458 are, respectively, 2.61-2.85 Gyr and 10-100 Myr. We hypothesize that these WDs are DWD merger products and compute the evolution of the postmerged configuration formed by a central WD surrounded by a disk. We show that the postmerger system evolves through three phases depending on whether accretion, mass ejection (propeller), or magnetic braking dominates the torque onto the central WD. We calculate the time the WD spends in each of these phases and obtain the accretion rate and disk mass for which the WD rotational age, i.e., the total time elapsed since the merger to the instant where the WD central remnant reaches the current measured rotation period, agrees with the estimated WD cooling age. We infer the mass values of the primary and secondary WD components of the DWD merger that lead to a postmerger evolution consistent with the observations.

Keywords: stellar remnants; white dwarf stars; stellar mergers; compact binary stars; compact objects; stellar rotation
On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances

The presence of a liquid solvent is widely regarded as an essential prerequisite for habitability. We investigate the conditions under which worlds outside the habitable zones of stars are capable of supporting liquid solvents on their surface over geologically significant timescales via combined radiogenic and primordial heat. Our analysis suggests that super-Earths with radionuclide abundances that are ≳103 times higher than Earth can host long-lived water oceans. In contrast, the requirements for long-lived ethane oceans, which have been explored in the context of alternative biochemistries, are less restrictive: relative radionuclide abundances of ≳102 could be sufficient. We find that this class of worlds might be detectable (10σ detection over ∼10 day integration time at 12.8 μm) in principle by the James Webb Space Telescope at distances of ∼10 pc if their ages are ≲1 Gyr.

Keywords: astrobiology; exoplanet evolution; exoplanet surface composition; extrasolar rocky planets; free floating planets; habitable planets; planetary interior; planetary theory
OSSOS. XXIII. 2013 VZ70 and the Temporary Coorbitals of the Giant Planets

We present the discovery of 2013 VZ70, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey for 4.5 yr, the orbit of 2013 VZ70 is determined to high precision, revealing that it currently is in "horseshoe" libration with the planet. This coorbital motion will last at least thousands of years but ends ~10 kyr from now; 2013 VZ70 is thus another example of the already-known "transient coorbital" populations of the giant planets, with this being the first known prograde example for Saturn (temporary retrograde coorbitals are known for Jupiter and Saturn). We present a theoretical steady-state model of the scattering population of trans-Neptunian origin in the giant planet region (2-34 au), including the temporary coorbital populations of the four giant planets. We expose this model to observational biases using survey simulations in order to compare the model to the real detections made by a set of well-characterized outer solar system surveys. While the observed number of coorbitals relative to the scattering population is higher than predicted, we show that the number of observed transient coorbitals of each giant planet relative to each other is consistent with a trans-Neptunian source.

Keywords: kuiper belt; trans-neptunian objects; resonant kuiper belt objects; centaur group; small solar system bodies; trojan asteroids; jupiter trojans; neptune trojans; scattered disk objects; orbital resonances; asteroid dynamics; planetary dynamics
Dynamic Secondary Illumination in Permanent Shadows within Artemis III Candidate Landing Regions

Investigations that can be conducted at the Artemis III candidate landing regions will benefit from the knowledge of the thermal environment within permanently shadowed regions (PSRs). Within PSRs, secondary illumination controls the surface temperature, varying diurnally and seasonally, affecting the stability and concentration of volatiles cold-trapped within the PSRs. In this case study, we characterize the dynamic nature of secondary illumination at four PSRs that overlap five of the Artemis III candidate landing regions. Our analysis is based on secondary illumination model-generated images paired with PSR images acquired by ShadowCam on board the Korean Pathfinder Lunar Orbiter. We find that illumination and thermal conditions can change rapidly within the PSRs, and knowledge of time-variable secondary illumination can be decisive for the efficient design of investigations and sample collection operations at the PSRs.

Keywords: lunar science; lunar evolution; lunar surface
On the Observational Difference between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei

We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk-corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (αOX) and the monochromatic luminosity at 2500 Å (L2500Å) for both the super- and sub-Eddington subsamples. The best-fit αOX-L2500Å relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of αOX on both the Eddington ratio (LBol/LEdd) and black hole mass (MBH) parameters for our full sample. A multivariate linear regression analysis yields ${\alpha }_{\mathrm{OX}}=-0.13\mathrm{log}({L}_{\mathrm{Bol}}/{L}_{\mathrm{Edd}})-0.10\mathrm{log}{M}_{\mathrm{BH}}-0.69$ <!-- --> , with a scatter similar to that of the αOX-L2500Å relation. The hard (rest-frame >2 keV) X-ray photon index (Γ) is strongly correlated with LBol/LEdd for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk-corona connections in AGNs.

Keywords: accretion; x-ray active galactic nuclei; radio quiet quasars