adsabs/SciX_UAT_keywords huggingface dataset:
Superhabitability of High-obliquity and High-eccentricity Planets

Planetary obliquity and eccentricity influence climate by shaping the spatial and temporal patterns of stellar energy incident at a planet's surface, affecting both the annual mean climate and magnitude of seasonal variability. Previous work has demonstrated the importance of both planetary obliquity and eccentricity for climate and habitability, but most studies have not explicitly modeled the response of life to these parameters. While exaggerated seasons may be stressful to some types of life, a recent study found an increase in marine biological activity for moderately high obliquities <45° assuming an Earth-like eccentricity. However, it is unclear how life might respond to obliquities >45°, eccentricities much larger than Earth's, or the combination of both. To address this gap, we use cGENIE-PlaSim, a 3D marine biogeochemical model coupled to an atmospheric general circulation model, to investigate the response of Earth-like marine life to a large range of obliquities (0°-90°) and eccentricities (0-0.4). We find that marine biological activity increases with both increasing obliquity and eccentricity across the parameter space we considered, including the combination of high obliquity and high eccentricity. We discuss these results in the context of remote biosignatures, and we argue that planets with high obliquity and/or eccentricity may be superhabitable worlds that are particularly favorable for exoplanet life detection.

Keywords: exoplanets; habitable planets; planetary climates; astrobiology; biosignatures
Discovery of Three Candidate Magnetar-powered Fast X-Ray Transients from Chandra Archival Data

It was proposed that a remnant stable magnetar could be formed in a binary neutron-star merger, leading to a fast X-ray transient (FXT) that can last for thousands of seconds. Recently, Xue et al. suggested that CDF-S XT2 was exactly such a kind of source. If confirmed, such emission can be used to search for electromagnetic counterparts to gravitational wave events from binary neutron-star mergers that have short gamma-ray bursts and the corresponding afterglows seen off-axis and thus too weak to be detected. Here we report the discovery of three new FXTs, XRT 170901, XRT 030511, and XRT 110919, from a preliminary search over Chandra archival data. Similar to CDF-S XT2, these new FXTs had a very fast rise (less than a few tens of seconds) and a plateau of X-ray flux of ~1.0 × 10-12 erg s-1 cm-2 lasting for 1-2 ks, followed by a steep decay. Their optical/IR counterparts, if present, are very weak, arguing against a stellar flare origin for these FXTs. For XRT 170901, we identified a faint host galaxy with the source at the outskirts, very similar to CDF-S XT2. Therefore, our newly discovered FXTs are also strong candidates for magnetar-powered X-ray transients resulting from binary neutron star mergers.

Keywords: gamma-ray bursts; neutron stars; magnetars; x-ray transient sources
On the Tidal History and Future of the Earth-Moon Orbital System

Earth's rotation rate and the evolution of the Earth-Moon system have been controlled by tidal dissipation in Earth's ocean. Attempts to model the tidal history have shown incomplete compatibility with observations and unclear isolation of the most important controlling factors. Here it is shown that a relatively simple model with no explicit description of the continents (their effects are instead parameterized) can accurately reproduce the available observations (lunar distance and month, Earth's rotation and deceleration rates) describing the tidal evolution over the past 2.5 billion yr and also evade the paradox of an early Moon falling within the Roche limit. Notably, the model reproduces an observed dissipation peak 400 million yr ago. The model involves fitting two input parameters (the effective ocean depth h and the nondimensional dissipation timescale $\tilde{T}$ , the latter of which can be related to the more typically used quality factor Q). The best-fit values (h = 2.3 km and $\tilde{T}=40$ , corresponding to Q ≈ 20-28) derived empirically from the model correspond well with the plausibly expected values (h ≈ 2.5 km and Q ≈ 20) derived using independent reasoning and observations. The model shows very clearly that the tidal evolution has been primarily controlled by the rate of resonance in the ocean response, not the evolving amplitude of the tidal forces or forcing frequency. More closely, it also shows that the effect of Earth's rotation on the Lamb parameter (or nondimensional wave speed) has driven the evolution, and that changes in frequency or other parameters have been much less important.

Keywords: ocean tides; ocean planets; earth-moon system; orbital evolution; lunar evolution; natural satellite dynamics
Juno Spacecraft Measurements of Jupiter's Gravity Imply a Dilute Core

The Juno spacecraft measured Jupiter's gravity field and determined the even and odd zonal harmonics, J n , with unprecedented precision. However, interpreting these observations has been a challenge because it is difficult to reconcile the unexpectedly small magnitudes of the moments J 4 and J 6 with conventional interior models that assume a large, distinct core of rock and ice. Here we show that the entire set of gravity harmonics can be matched with models that assume an ab initio equation of state, wind profiles, and a dilute core of heavy elements that are distributed as far out as 63% of the planet's radius. In the core region, heavy elements are predicted to be distributed uniformly and make up only 18% by mass because of dilution with hydrogen and helium. Our models are consistent with the existence of primary and secondary dynamo layers that will help explain the complexity of the observed magnetic field.

Keywords: solar system gas giant planets
Estimating Atmospheric Parameters of DA White Dwarf Stars with Deep Learning

The determination of atmospheric parameters of white dwarf stars (WDs) is crucial for researches on them. Traditional methodology is to fit the model spectra to observed absorption lines and report the parameters with the lowest χ2 error, which strongly relies on theoretical models that are not always publicly accessible. In this work, we construct a deep learning network to model-independently estimate ${T}_{\mathrm{eff}}$ and log g of DA stars (DAs), corresponding to WDs with hydrogen-dominated atmospheres. The network is directly trained and tested on the normalized flux pixels of full optical wavelength range of DAs spectroscopically confirmed in the Sloan Digital Sky Survey. Experiments in test yield that the rms error for ${T}_{\mathrm{eff}}$ and log g approaches 900 K and 0.1 dex, respectively. This technique is applicable for those DAs with ${T}_{\mathrm{eff}}$ from 5000 to 40,000 K and log g from 7.0 to 9.0 dex. Furthermore, the applicability of this method is verified for the spectra with degraded resolution of ∼200. So it is also practical for the analysis of DAs that will be detected by the Chinese Space Station Telescope.

Keywords: da stars; spectroscopy; astronomy data analysis
IllustrisTNG Snapshots for 10 Gyr of Dynamical Evolution of Brightest Cluster Galaxies and Their Host Clusters

We explore the redshift evolution of the dynamical properties of massive clusters and their brightest cluster galaxies (BCGs) at z < 2 based on the IllustrisTNG-300 simulation. We select 270 massive clusters with M 200 < 1014 M ⊙ at z = 0 and trace their progenitors based on merger trees. From 67 redshift snapshots covering z < 2, we compute the 3D subhalo velocity dispersion as a cluster velocity dispersion (σ cl). We also calculate the 3D stellar velocity dispersion of the BCGs (σ *,BCG). Both σ cl and σ *,BCG increase as the universe ages. The BCG velocity dispersion grows more slowly than the cluster velocity dispersion. Furthermore, the redshift evolution of the BCG velocity dispersion shows dramatic changes at some redshifts resulting from dynamical interaction with neighboring galaxies (major mergers). We show that σ *,BCG is comparable with σ cl at z > 1, offering an interesting observational test. The simulated redshift evolution of σ cl and σ *,BCG generally agrees with an observed cluster sample for z < 0.3, but with large scatter. Future large spectroscopic surveys reaching to high redshift will test the implications of the simulations for the mass evolution of both clusters and their BCGs.

Keywords: brightest cluster galaxies; galaxy clusters; magnetohydrodynamical simulations
The Distribution and Accessibility of Geologic Targets near the Lunar South Pole and Candidate Artemis Landing Sites

Transformative lunar science will be driven by the accessibility, recovery, and return to Earth of geological specimens. Isolated boulders, rock exposures, and rocky craters at the lunar south pole all provide opportunities for geologic characterization and sampling of the lunar crust. Here, we present the results of orbital geological mapping of the region surrounding the south pole using Lunar Reconnaissance Orbiter Narrow Angle Camera images (0.5-2 m pixel-1). We mapped the distribution of isolated boulders (86,896), rocky craters (3556), and rock exposures (7553) around potential Artemis landing sites 001 and 004 (NASA 2020), which are within or near one of the Artemis III candidate landing regions. We found that boulder abundance decreases with increasing distance from the rim of Shackleton crater. From that correlation, we infer that most of the boulders and rock exposures near Shackleton were deposited as ejecta by the Shackleton impact, and by later the reworking of that material during smaller impact events. We additionally assessed the accessibility of the mapped features, and documented geologic targets located on shallow (<15°) slopes, including those on the Shackleton crater rim and on the "Connecting Ridge" between Shackleton and Henson crater. Such targets could be sampled by a future mission to the lunar south pole region. Our catalog of mapped features is made available to the lunar community.

Keywords: lunar science; planetary geology; lunar impacts; lunar craters
An Intensity Mapping Detection of Aggregate CO Line Emission at 3 mm

We present a detection of molecular gas emission at z ∼ 1-5 using the technique of line intensity mapping. We make use of a pair of 3 mm interferometric data sets, the first from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field, and the second from a series of Atacama Compact Array (ACA) observations conducted between 2016 and 2018, targeting the COSMOS field. At 100 GHz, we measure nonzero power at 97.8% and 99.9% confidence in the ACA and ALMA data sets, respectively. In the joint result, we reject the zero-power hypothesis at 99.99% confidence, finding ${\tilde{I}}_{s}^{2}(\nu )=770\pm 210\,\mu {{\rm{K}}}^{2}\,\mathrm{Hz}\,\mathrm{sr}$ . After accounting for sample variance effects, the estimated spectral shot power is ${\tilde{I}}_{s}^{2}(\nu )={1010}_{-390}^{+550}\,\mu {{\rm{K}}}^{2}\,\mathrm{Hz}\,\mathrm{sr}$ . We derive a model for the various line species our measurement is expected to be sensitive to, and estimate the shot power to be ${120}_{-50}^{+70}\,\mu {{\rm{K}}}^{2}\,{h}^{-3}\,{{\rm{Mpc}}}^{3}$ , ${210}_{-80}^{+110}\,\mu {{\rm{K}}}^{2}\,{h}^{-3}\,{{\rm{Mpc}}}^{3}$ , and ${100}_{-40}^{+50}\,\mu {{\rm{K}}}^{2}\,{h}^{-3}\,{{\rm{Mpc}}}^{3}$ for CO(2-1) at z = 1.3, CO(3-2) at z = 2.5, and CO(4-3) at z = 3.6, respectively. Using line ratios appropriate for high-redshift galaxies, we find these results to be in good agreement with those from the CO Power Spectrum Survey. Adopting αCO = 3.6 M⊙ (K km s-1 pc2)-1, we estimate a cosmic molecular gas density of ${\rho }_{{{\rm{H}}}_{2}}(z)$ ∼ 108 M⊙ Mpc-3 between z = 1-3.

Keywords: molecular gas; early universe; star formation; cosmological evolution
White Dwarfs in Close Binaries: A Systematic Search for Mass-transfer Systems and Supernova Ia Progenitors in the APOGEE Survey

We have created a new and unique database, the APOGEE-Galaxy Evolution Explorer (GALEX)-Gaia catalog, to study white dwarfs in close binaries, and, in particular, to: (1) create a minimally biased sample of white dwarf-main sequence (WDMS) systems derived from the combination of GALEX, Gaia, and the dual hemisphere, multi-epoch, high-resolution, infrared APOGEE-1 and -2 spectroscopic surveys, and (2) exploit this catalog to vastly increase the number of well-characterized WDMS systems having derived dynamical parameters (e.g., masses, separation, orbital periods, etc.) as well as precision multi-element chemical compositions by exploiting the high resolution, multi-epoch data from APOGEE. This catalog will significantly further our understanding of compact binary evolution.

Keywords: compact binary stars; common envelope evolution; white dwarf stars; surveys
How Does Background Air Pressure Influence the Inner Edge of the Habitable Zone for Tidally Locked Planets in a 3D View?

We examine the effect of varying background N2 surface pressure (labeled as pN2) on the inner edge of the habitable zone for 1:1 tidally locked planets around M dwarfs, using the three-dimensional (3D) atmospheric general circulation model (AGCM) ExoCAM. In our experiments, the rotation period is fixed when varying the stellar flux, in order to more clearly isolate the role of pN2. We find that the stellar flux threshold for the runaway greenhouse is a non-monotonous function of pN2. This is due to the competing effects of five processes: pressure broadening, heat capacity, lapse rate, relative humidity, and clouds. These competing processes increase the complexity in predicting the location of the inner edge of the habitable zone. For a slow-rotation orbit of 60 Earth days, the critical stellar flux for the runaway greenhouse onset is 1700-1750, 1900-1950, and 1750-1800 W m-2 under 0.25, 1.0, and 4.0 bar of pN2, respectively, suggesting that the magnitude of the effect of pN2 is within ≈13%. For a rapid rotation orbit, the effect of varying pN2 on the inner edge is smaller, within a range of ≈7%. Moreover, we show that Rayleigh scattering effect as varying pN2 is unimportant for the inner edge due to the masking effect of cloud scattering and to the strong shortwave absorption by water vapor under hot climates. Future work using AGCMs having different cloud and convection schemes and cloud-resolving models having explicit cloud and convection are Required to revise this problem.

Keywords: exoplanet atmospheres; planetary atmospheres; extrasolar rocky planets; astrobiology; habitable planets
An X-Ray Luminosity-dependent "Changing-look" Phenomenon in UGC 3223

The nature of the rare "Changing-look" (CL) phenomenon in active galactic nuclei (AGNs) is still under debate. We present Swift/XRT and UVOT follow-up observations of UGC 3223, a newly discovered repeat CL-AGN with type transitions of S1.5 → S2 → S1.8 occurring in a period of about 30 yr. By comparing the values previously reported in the ROSAT All-sky Survey and in the second Swift-XRT Point Source catalog, we clearly find that the X-ray flux tightly follows the optical spectral transition, in which a spectral type closer to a Seyfert 1 type is associated with a higher X-ray flux. An invariable X-ray spectral shape is, however, found in the CL phenomenon of the object. An extremely low Eddington ratio of ∼2 × 10-4 can be obtained from the X-ray luminosity for its Seyfert 2 state, which suggests the disk-wind broad-line region model best explains the CL phenomenon. A variation of the total UV emission is not revealed when compared to the previous Galaxy Evolution Explorer NUV observation, since the UVOT images indicate that ∼90% UV emission comes from intensive star formation in the host galaxy.

Keywords: active galactic nuclei; x-ray active galactic nuclei; seyfert galaxies
Serial Flaring in an Active Region: Exploring Why Only One Flare Is Eruptive

Over a four hour period between 2014 June 12-13 a series of three flares were observed within AR 12087. This sequence of flares started with a non-eruptive M-class flare, followed by a non-eruptive C-class flare, and finally ended with a second C-class flare that had an associated filament eruption. In this paper we combine spectroscopic analysis of Interface Region Imaging Spectrometer observations of the Si IV line during the three flares along with a series of nonlinear force-free field (NLFFF) extrapolations in order to investigate the conditions that lead the final flare to be eruptive. From this analysis it is found to be unlikely that the eruption was triggered by either kink instability or by tether-cutting reconnection, allowing the flux rope to rise into a region where it would be susceptible to the torus instability. The NLFFF modeling does, however, suggest that the overlying magnetic field has a fan-spine topology, raising the possibility that breakout reconnection occurring during the first two flares weakened the overlying field, allowing the flux rope to erupt in the subsequent third flare.

Keywords: solar flare spectra; solar physics; solar active regions; solar activity; solar active region magnetic fields; solar active region filaments; solar flares
JWST Measurements of 13C, 18O, and 17O in the Atmosphere of Super-Jupiter VHS 1256 b

Isotope ratios have recently been measured in the atmospheres of directly imaged and transiting exoplanets from ground-based observations. The arrival of JWST allows us to characterize exoplanetary atmospheres in further detail and opens up wavelengths inaccessible from the ground. In this work we constrain the carbon and oxygen isotopes 13C, 18O, and 17O from CO in the atmosphere of the directly imaged companion VHS 1256 b through retrievals of the ~4.1-5.3 μm NIRSpec G395H/F290LP observations from the early-release science program (ERS 1386). We detect and constrain 13C16O, 12C18O, and 12C17O at 32σ, 16σ, and 10σ confidence respectively, thanks to the very high signal-to-noise observations. We find the ratio of abundances are more precisely constrained than their absolute values, with ${}^{12}{\rm{C}}{/}^{13}{\rm{C}}={62}_{-2}^{+2}$ , in between previous measurements for companions (~30) and isolated brown dwarfs (~100). The oxygen isotope ratios are ${}^{16}{\rm{O}}{/}^{18}{\rm{O}}={425}_{-28}^{+33}$ and ${}^{16}{\rm{O}}{/}^{17}{\rm{O}}={1010}_{-100}^{+120}$ . All of the ratios are lower than the local interstellar medium and solar system, suggesting that abundances of the more minor isotopes are enhanced compared to the primary. This could be driven by isotope fractionation in protoplanetary disks, which can potentially alter the carbon and oxygen ratios through isotope selective photodissociation, gas/ice partitioning, and isotopic exchange reactions. In addition to CO, we constrain 1H ${}_{2}^{16}{\rm{O}}$ and 12C16O2 (the primary isotopologues of both species), but find only upper limits on 12C1H4 and 14N1H3. This work highlights the power of JWST to constrain isotopes in exoplanet atmospheres, with great promise in determining formation histories in the future.

Keywords: exoplanet atmospheric composition; isotopic abundances; direct imaging; extrasolar gaseous giant planets
Identification of a Helium Donor Star in NGC 247 ULX-1

With Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE) observations, we detected highly variable helium emission lines from the optical counterpart of the supersoft ultraluminous X-ray source (ULX) NGC 247 ULX-1. No Balmer lines can be seen in the source spectrum. This is the first evidence for the presence of a helium donor star in ULXs, consistent with a prediction that helium donor stars may be common in ULXs. The helium lines with an FWHM of about 200 km s-1 are likely produced on the outer accretion disk. Their strong variation implies that the central X-ray source can be significantly obscured to the outer disk. Also, a ring or a double-ring structure is revealed in the MUSE image. It is unknown whether or not it is related to the progenitor of the ULX binary.

Keywords: ultraluminous x-ray sources; x-ray binary stars; companion stars; hydrogen deficient stars; stellar accretion disks
A Systematic Study of the Frequency Evolution Behavior of Pulsar Pulse Profiles

The frequency evolution behavior of radio pulse profiles is an important clue for the radiation mechanism of a pulsar. Combined with the latest results of the European Pulsar Network and the Australia Telescope National Facility data, we systematically study the evolution of W50 (the full width of the pulse profile at 50% of the pulsar amplitude) for 74 pulsars with frequencies from tens to thousands of megahertz. We find that 71 pulsars show "absorption" features, which indicates that the absorption is an universal phenomenon in the pulsar population and independent of the type of pulsar profile. It is found that for most pulsars, the absorption features appear in the frequency range of 100-800 MHz, and the evolution trend of W50 at frequencies less than ~100 MHz and larger than ~800 MHz can be described as a power-law function.We quantify the absorption intensity and analyze the correlation between the absorption intensity and the pulsar parameters (such as the spin period, magnetic field, and age of the pulsar). It is found that there is no direct correlation between them. Our results will provide good samples and clues for the study of the physical mechanism of the absorption phenomenon.

Keywords: radio pulsars
Multiple Peaks and a Long Precursor in the Type IIn Supernova 2021qqp: An Energetic Explosion in a Complex Circumstellar Environment

We present optical photometry and spectroscopy of the Type IIn supernova (SN) 2021qqp. Its unusual light curve is marked by a long precursor for ≈300 days, a rapid increase in brightness for ≈60 days, and then a sharp increase of ≈1.6 mag in only a few days to a first peak of M r ≈ ‑19.5 mag. The light curve then declines rapidly until it rebrightens to a second distinct peak of M r ≈ ‑17.3 mag centered at ≈335 days after the first peak. The spectra are dominated by Balmer lines with a complex morphology, including a narrow component with a width of ≈1300 km s‑1 (first peak) and ≈2500 km s‑1 (second peak) that we associate with the circumstellar medium (CSM) and a P Cygni component with an absorption velocity of ≈8500 km s‑1 (first peak) and ≈5600 km s‑1 (second peak) that we associate with the SN–CSM interaction shell. Using the luminosity and velocity evolution, we construct a flexible analytical model, finding two significant mass-loss episodes with peak mass loss rates of ≈10 and ≈5 M ⊙ yr‑1 about 0.8 and 2 yr before explosion, respectively, with a total CSM mass of ≈2–4 M ⊙. We show that the most recent mass-loss episode could explain the precursor for the year preceding the explosion. The SN ejecta mass is constrained to be ≈5–30 M ⊙ for an explosion energy of ≈(3–10) × 1051 erg. We discuss eruptive massive stars (luminous blue variable, pulsational pair instability) and an extreme stellar merger with a compact object as possible progenitor channels.

Keywords: supernovae; core-collapse supernovae; type ii supernovae; massive stars; stellar mass loss; circumstellar matter