adsabs/SciX_UAT_keywords huggingface dataset:
Ultra–short-period WD Binaries Are Not Undergoing Strong Tidal Heating

Double white dwarf (WD) binaries are increasingly being discovered at short orbital periods where strong tidal effects and significant tidal heating signatures may occur. We assume that the tidal potential of the companion excites outgoing gravity waves within the WD primary, the dissipation of which leads to an increase in the WD's surface temperature. We compute the excitation and dissipation of the waves in cooling WD models in evolving MESA binary simulations. Tidal heating is self-consistently computed and added to the models at every time step. As a binary inspirals to orbital periods less than ∼20 minutes, the WD's behavior changes from cooling to heating, with temperature enhancements that can exceed 10,000 K compared with nontidally heated models. We compare a grid of tidally heated WD models to observed short-period systems with hot WD primaries. While tidal heating affects their T eff, it is likely not the dominant luminosity. Instead, these WDs are probably intrinsically young and hot, implying that the binaries formed at short orbital periods. The binaries are consistent with undergoing common envelope evolution with a somewhat low efficiency α CE. We delineate the parameter space where the traveling wave assumption is most valid, noting that it breaks down for WDs that cool sufficiently, where standing waves may instead be formed.

Keywords: white dwarf stars; tidal interaction; close binary stars; stellar evolutionary models; common envelope evolution
Dual-target Signal Simulation of Very Long baseline Interferometry for Chang'E-5

Very long baseline interferometry (VLBI) is an important deep-space tracking technology from radio astronomy. A mission that uses VLBI, China's lunar sample-return mission Chang'E-5 (CE-5) collects soil samples on the lunar surface, arrives at a rendezvous point, and docks in the lunar orbit through cooperation of the Orbiter and the Ascender. During rendezvous and docking, the Chinese VLBI network (CVN) used same beam VLBI (SBI) to observe two high-velocity probes simultaneously. However, before the launching of the CE-5, CVN lacked the capability to examine dynamic dual-target tracking ability of SBI mode because there were no similar space probes can be used in tests of upgraded VLBI data-processing system. This study proposes a method to simulate VLBI signals and acquire relevant data from the dual-target probe and calibration quasar signals recorded by each station according to the orbits and beacons of probes, station coordinates, etc. The real-time data-processing capability of the system is verified by processing the simulated data during rendezvous and docking. The consistency between simulation and VLBI data-processing was consistent to better than 0.05 ns. This method is universal and can also be used in VLBI simulation and orbital analysis of other deep-space probes.

Keywords: very long baseline interferometers; astronomical simulations; interferometric correlation; lunar probes
Unveiling Hidden Stellar Aggregates in the Milky Way: 1656 New Star Clusters Found in Gaia EDR3

We report 1656 new star clusters found in the Galactic disk (∣b∣ < 20°) beyond 1.2 kpc, using Gaia EDR3 data. Based on an unsupervised machine-learning algorithm, DBSCAN, and following our previous studies, we utilized a unique method to do the data preparation and obtain the clustering coefficients, which proved to be an effective way to search blindly for star clusters. We tabulate the physical parameters and member stars of the new clusters, and present some interesting examples, including a globular cluster candidate. The cluster parameters and member stars are available in machine-readable format in the online journal. We examine the new discoveries and discuss their statistical properties. The proper-motion dispersions and radii of the star clusters are the same as those previously reported. The new clusters beyond 1.2 kpc are older than those in the solar neighborhood, and the new objects found in the third Galactic quadrant present the lowest line-of-sight extinctions. Combined with our previous results, the total population of new clusters and candidates detected through our method is 2541, corresponding to 55% of all newly published clusters in the Gaia era. The number of cataloged Gaia star clusters was also increased to nearly 6000. In the near future, it will be necessary to make a unified confirmation and member star determination for all reported clusters.

Keywords: open star clusters; star clusters
The Dynamics of Interstellar Asteroids and Comets within the Galaxy: An Assessment of Local Candidate Source Regions for 1I/'Oumuamua and 2I/Borisov

The low velocity of interstellar asteroid 1I/'Oumuamua with respect to our galaxy's local standard of rest implies that it is young. Adopting the young age hypothesis, we assess possible origin systems for this interstellar asteroid and for 2I/Borisov, though the latter's higher speed means it is unlikely to be young. First, their past trajectories are modeled under gravitational scattering by galactic components ("disk heating") to assess how far back one can trace them. The stochastic nature of disk heating means that a back integration can only expect to be accurate to within 15 pc and 2 km s-1 at -10 Myr, dropping steeply to 400 pc and 10 km s-1 at -100 Myr, sharply limiting our ability to determine a precise origin. Nevertheless, we show that 'Oumuamua's origin system likely is currently within 1 kpc of Earth, in the local Orion Arm. Second, we back integrate 'Oumuamua's trajectory in order to assess source regions, emphasizing young systems and moving groups. Though disk heating allows for only a statistical link to source regions, 'Oumuamua passed through a considerable subset of the Carina and Columba moving groups when those groups were forming. This makes them perhaps the most plausible source region, if 'Oumuamua was ejected during planet formation or via intra-cluster interactions. We find three stars in the Ursa Major group, one brown dwarf, and seven other stars to have plausible encounters with 2I/Borisov, within 2 pc and 30 km s-1. These encounters' high relative speeds mean none are likely to be the home of 2I/Borisov.

Keywords: comets; asteroids; milky way galaxy
A Spectroscopic Study of Mars-analog Materials with Amorphous Sulfate and Chloride Phases: Implications for Detecting Amorphous Materials on the Martian Surface

The Chemistry and Mineralogy X-ray diffraction (XRD) instrument aboard the Curiosity rover consistently identifies amorphous material at Gale Crater, which is compositionally variable, but often includes elevated sulfur and iron, suggesting that amorphous ferric sulfate (AFS) may be present. Understanding how desiccating ferric sulfate brines affect the spectra of Martian material analogs is necessary for interpreting complex/realistic reaction assemblages. Visible and near-infrared reflectance (VNIR), mid-infrared attenuated total reflectance (MIR, FTIR-ATR), and Raman spectra, along with XRD data are presented for basaltic glass, hematite, gypsum, nontronite, and magnesite, each at three grain sizes (<25, 25-63, and 63-180 μm), mixed with ferric sulfate (+/-NaCl), deliquesced, then rapidly desiccated in 11% relative humidity or via vacuum. All desiccated products are partially or completely XRD amorphous; crystalline phases include starting materials and trace precipitates, leaving the bulk of the ferric sulfate in the amorphous fraction. Due to considerable spectral masking, AFS detectability is highly dependent on spectroscopic technique and minerals present. This has strong implications for remote and in situ observations of Martian samples that include an amorphous component. AFS is only identifiable in VNIR spectra for magnesite, nontronite, and gypsum samples; hematite and basaltic glass samples appear similar to pure materials. Sulfate features dominate Raman spectra for nontronite and basaltic glass samples; the analog material dominates Raman spectra of hematite and gypsum samples. MIR data are least affected by masking, but basaltic glass is almost undetectable in MIR spectra of those mixtures. NaCl produces similar FTIR-ATR and Raman features, regardless of analog material.

Keywords: planetary mineralogy; planetary science; surface processes; planetary geology; spectroscopy; vibrational spectroscopy
Cosmology-independent Estimate of the Hubble Constant and Spatial Curvature using Time-delay Lenses and Quasars

With the distance sum rule in the Friedmann-Lemaître-Robertson-Walker metric, model-independent constraints on both the Hubble constant H0 and spatial curvature ${{\rm{\Omega }}}_{K}$ can be obtained using strong lensing time-delay data and Type Ia supernovae (SNe Ia) luminosity distances. This method is limited by the relatively low redshifts of SNe Ia, however. Here, we propose using quasars as distance indicators, extending the coverage to encompass the redshift range of strong lensing systems. We provide a novel and improved method of determining H0 and ${{\rm{\Omega }}}_{K}$ simultaneously. By applying this technique to the time-delay measurements of seven strong lensing systems and the known ultraviolet versus X-ray luminosity correlation of quasars, we constrain the possible values of both H0 and ${{\rm{\Omega }}}_{K}$ , and find that ${H}_{0}={75.3}_{-2.9}^{+3.0}$ km ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ and ${{\rm{\Omega }}}_{K}=-{0.01}_{-0.17}^{+0.18}$ . The measured ${{\rm{\Omega }}}_{K}$ is consistent with zero spatial curvature, indicating that there is no significant deviation from a flat universe. If we use flatness as a prior, we infer that ${H}_{0}={75.3}_{-1.9}^{+1.9}$ km ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , representing a precision of 2.5%. If we further combine these data with the 1048 current Pantheon SNe Ia, our model-independent constraints can be further improved to ${H}_{0}={75.3}_{-2.9}^{+3.0}$ km ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ and ${{\rm{\Omega }}}_{K}={0.05}_{-0.14}^{+0.16}$ . In every case, we find that the Hubble constant measured with this technique is strongly consistent with the value (∼74 km ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ ) measured using the local distance ladder, as opposed to the value optimized by Planck.

Keywords: distance indicators; hubble constant; type ia supernovae; quasars; observational cosmology; cosmological parameters; strong gravitational lensing
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q band

The Earth's magnetic field induces Zeeman splitting of the magnetic dipole transitions of molecular oxygen in the atmosphere, which produces polarized emission in the millimeter-wave regime. This polarized emission is primarily circularly polarized and manifests as a foreground with a dipole-shaped sky pattern for polarization-sensitive ground-based cosmic microwave background experiments, such as the Cosmology Large Angular Scale Surveyor (CLASS), which is capable of measuring large angular scale circular polarization. Using atmospheric emission theory and radiative transfer formalisms, we model the expected amplitude and spatial distribution of this signal and evaluate the model for the CLASS observing site in the Atacama Desert of northern Chile. Then, using two years of observations at 32°3 to 43.7 GHz from the CLASS Q-band telescope, we present a detection of this signal and compare the observed signal to that predicted by the model. We recover an angle between magnetic north and true north of -5°5 ± 0°6, which is consistent with the expectation of -5°9 for the CLASS observing site. When comparing dipole sky patterns fit to both simulated and data-derived sky maps, the dipole directions match to within a degree, and the measured amplitudes match to within ∼20%.

Keywords: cosmic microwave background radiation; observational cosmology; polarimeters; astronomical instrumentation; atmospheric effects
A Novel Analytic Atmospheric T(τ) Relation for Stellar Models

Stellar models often use relations between the temperature T and optical depth τ to evaluate the structure of their optically thin outer layers. We fit a novel analytic function to the Hopf function q(τ) of a radiation-coupled hydrodynamics simulation of near-surface convection with solar parameters by Trampedach et al. The fit is accurate to within 0.82% for the solar simulation and to within 13% for all the simulations that are not on either the low-temperature or low-gravity edges of the grid of simulations.

Keywords: stellar atmospheres; stellar physics; stellar structures; stellar surfaces
A HaloSat Analysis of the Cygnus Superbubble

The Cygnus Superbubble (CSB) is a region of soft X-ray emission approximately 13 degrees wide in the direction of the local spiral arm. Such a large region might be the result of strong stellar winds and supernovae from nearby stellar nurseries, or it could be the result of a single event—a hypernova. HaloSat observed four nonoverlapping 10 degree diameter fields in the CSB region over the 0.4-7 keV band. The CSB absorption and temperature was found to be consistent over all four fields, with a weighted average of 6.1 × 1021 cm-2 and 0.190 keV, respectively. These observations suggest that the CSB is a cohesive object with a singular origin. The total thermal energy for the CSB is estimated at 4 × 1052 erg, based upon a shell-like physical model of the CSB. Absorption and distance estimates to Cyg OB associations are examined. The CSB absorption is found to be most consistent with the absorption seen in Cyg OB1, implying that the CSB lies at a similar distance of 1.1-1.4 kpc.

Keywords: hypernovae; supernova remnants; x-ray astronomy; ob associations
Comparing Short Gamma-Ray Burst Jet Structure Models

A structured gamma-ray burst (GRB) jet could explain the dimness of the prompt emission observed from GRB 170817A, but the exact form of this structure is still ambiguous. However, with the promise of future joint gravitational wave (GW) and GRB observations, we shall be able to examine populations of binary neutron star (BNS) mergers rather than on a case-by-case basis. We present an analysis that considers GW triggered BNS events both with and without short GRB counterparts assuming that events without a counterpart were observed off-axis. This allows for Bayes factors to be calculated to compare different jet structure models. We perform model comparison between a Gaussian and power-law apparent jet structure on simulated data to demonstrate that the correct model can be distinguished with a log Bayes factor of >5 after fewer than 100 events. Constraints on the apparent structure jet model parameters are also made. After 25(100) events the angular width of the core of a power-law jet structure can be constrained within a 90% credible interval of width ∼9.1(4.4)°, and the outer beaming angle to be within ∼19.9(8.5)°. Similarly, we show the width of a Gaussian jet structure to be constrained to ∼2.8(1.6)°.

Keywords: gamma-ray bursts; gravitational waves
Neutrinos and Gamma Rays from Galaxy Clusters Constrained by the Upper Limits of IceCube

Clusters of galaxies possess the capability to accelerate cosmic rays (CRs) to very high energy up to ~1018 eV due to their large size and magnetic field strength, which favor CR confinement for cosmological times. During their confinement, they can produce neutrinos and γ-rays out of interactions with the background gas and photon fields. In recent work, Hussain et al. have conducted three-dimensional cosmological magnetohydrodynamical simulations of the turbulent intracluster medium combined with multidimensional Monte Carlo simulations of CR propagation for redshifts ranging from z ~ 5 to z = 0 to study the multimessenger emission from these sources. They found that when CRs with a spectral index in the range 1.5-2.5 and cutoff energy ${E}_{\max }={10}^{16}\mbox{--}{10}^{17}$ eV are injected into the system, they make significant contributions to the diffuse background emission of both neutrinos and γ-rays. In this work, we have revisited this model and undertaken further constraints on the parametric space. This was achieved by incorporating the recently established upper limits on neutrino emission from galaxy clusters, as obtained by the IceCube experiment. We find that for CRs injected with spectral indices in the range 2.0-2.5, cutoff energy ${E}_{\max }={10}^{16}\mbox{--}{10}^{17}$ eV, and power corresponding to (0.1-1)% of the cluster luminosity, our neutrino flux aligns with the upper limits estimated by IceCube. Additionally, the resulting contribution from clusters to the diffuse γ-ray background remains significant with values of the order of ~10-5 MeV cm-2 s-1 sr-1 at energies above 500 GeV.

Keywords: neutrino astronomy
Effects of Scattering, Temperature Gradients, and Settling on the Derived Dust Properties of Observed Protoplanetary Disks

It is known that the millimeter dust thermal emission of protoplanetary disks is affected by scattering, such that for optically thick disks, the emission decreases with respect to the pure absorption case and the spectral indices can reach values below 2. The latter can also be obtained with temperature gradients. Using simple analytical models of radiative transfer in thin slabs, we quantify the effect of scattering, vertical temperature gradients, and dust settling on the emission and spectral indices of geometrically thin face-on accretion disks around young stars. We find that, in vertically isothermal disks with large albedo (ων ≳ 0.6), the emergent intensity can increase at optical depths between 10-2 and 10-1. We show that dust settling has important effects on the spectral indices in the optically thick regime, since the disk emission mainly traces small dust grains in the upper layers of the disk. The λ = 870 μm emission of these small grains can hide large grains at the disk midplane when the dust surface density is larger than ∼3.21 g cm-2. Finally, because of the change of the shape of the spectral energy distribution, optically thick disks at 1.3 mm and grains with sizes between 300 μm < amax < 1 mm have a 7 mm flux ∼60% higher than the extrapolation from higher millimeter frequencies, assumed when scattering is neglected. This effect could provide an explanation for the excess emission at λ = 7 mm reported in several disks.

Keywords: circumstellar dust; interstellar scattering; radiative transfer; radio continuum emission; protoplanetary disks
The Rapid Variability of Wave Electric Fields Within and Near Quasiperpendicular Interplanetary Shock Ramps: STEREO Observations

We present STEREO observations within 1500 proton gyroradii of 12 quasiperpendicular interplanetary shocks, with long-duration burst mode electric field acquisition by S/WAVES enabling observation of the evolution of waves throughout the entire ramp of interplanetary shocks. The shocks are low Mach number (Mf ∼ 1-5), with beta (β) ∼0.2-1.8. High variability in frequency, amplitude, and wave mode is observed upstream, downstream, and in shock ramps. Observations in every region include ion acoustic-like waves, electron cyclotron drift instability (ECDI) driven waves, electrostatic solitary waves, and high frequency whistler mode waves. We also show for the first time the existence of electrostatic waves with frequencies in the ion acoustic range, which are frequency dispersed in time and the first observations of ECDI-driven waves at interplanetary shocks. The waves are bursty, large amplitude (∼5->200 mV m-1), and seen in all three regions. All wave modes are more commonly observed downstream than upstream.

Keywords: interplanetary shocks; solar wind; space plasmas
MACE: A Machine-learning Approach to Chemistry Emulation

The chemistry of an astrophysical environment is closely coupled to its dynamics, the latter often found to be complex. Hence, to properly model these environments a 3D context is necessary. However, solving chemical kinetics within a 3D hydro simulation is computationally infeasible for even a modest parameter study. In order to develop a feasible 3D hydro-chemical simulation, the classical chemical approach needs to be replaced by a faster alternative. We present MACE, a Machine-learning Approach to Chemistry Emulation, as a proof-of-concept work on emulating chemistry in a dynamical environment. Using the context of AGB outflows, we have developed an architecture that combines the use of an autoencoder (to reduce the dimensionality of the chemical network) and a set of latent ordinary differential equations (that are solved to perform the temporal evolution of the reduced features). Training this architecture with an integrated scheme makes it possible to successfully reproduce a full chemical pathway in a dynamical environment. MACE outperforms its classical analog on average by a factor of 26. Furthermore, its efficient implementation in PyTorch results in a sublinear scaling with respect to the number of hydrodynamical simulation particles.

Keywords: astrochemistry; computational methods; astronomy software; chemical reaction network models; asymptotic giant branch stars; stellar winds
Unveiling Nongray Surface of Cloudy Exoplanets: The Influence of Wavelength-dependent Surface Albedo and Cloud Scattering Properties on Retrieval Solutions

Direct-imaging spectra hold rich information about a planet's atmosphere and surface, and several space-based missions aiming at such observations will become a reality in the near future. Previous spectral retrieval works have resulted in key atmospheric constraints under the assumption of a gray surface, but the effect of wavelength-dependent surface albedo on retrieval has not been shown. We explore the influence of the coupling effect of cloud and wavelength-dependent surface albedo on retrieval performance via modeling suites of Earth-like atmospheres with varying cloud and surface albedo parameterizations. Under the assumption of known cloud scattering properties, the surface spectral albedos can be reasonably recovered when the surface cover represents that of Earth-like vegetation or ocean, which may aid in characterizing the planet's habitability. When the cloud scattering properties cannot be assumed, we show that the degeneracy between the cloud properties and wavelength-dependent surface albedo leads to biased results of atmospheric and cloud properties. The multiepoch visible-band observations offer limited improvement in disentangling this degeneracy. However, the constraints on atmospheric properties from the combination of the UV band (R ~ 6) + visible band (R ~ 140) are consistent with input values to within 1σ. If short-bandpass data are not available, an alternative solution to reduce the retrieval uncertainties would be to have the prior constraints on the planetary cloud fraction with less than 20% uncertainty.

Keywords: exoplanet surface characteristics; exoplanet atmospheres; direct imaging; spectroscopy; bayesian statistics