adsabs/SciX_UAT_keywords huggingface dataset:
The Lunar Geophysical Network Landing Sites Science Rationale

The Lunar Geophysical Network (LGN) mission is proposed to land on the Moon in 2030 and deploy packages at four locations to enable geophysical measurements for 6-10 yr. Returning to the lunar surface with a long-lived geophysical network is a key next step to advance lunar and planetary science. LGN will greatly expand our primarily Apollo-based knowledge of the deep lunar interior by identifying and characterizing mantle melt layers, as well as core size and state. To meet the mission objectives, the instrument suite provides complementary seismic, geodetic, heat flow, and electromagnetic observations. We discuss the network landing site requirements and provide example sites that meet these requirements. Landing site selection will continue to be optimized throughout the formulation of this mission. Possible sites include the P-5 region within the Procellarum KREEP Terrane (PKT; (lat: 15°; long: -35°), Schickard Basin (lat: -44.°3; long: -55.°1), Crisium Basin (lat: 18.°5; long: 61.°8), and the farside Korolev Basin (lat: -2.°4; long: -159.°3). Network optimization considers the best locations to observe seismic core phases, e.g., ScS and PKP. Ray path density and proximity to young fault scarps are also analyzed to provide increased opportunities for seismic observations. Geodetic constraints require the network to have at least three nearside stations at maximum limb distances. Heat flow and electromagnetic measurements should be obtained away from terrane boundaries and from magnetic anomalies at locations representative of global trends. An in-depth case study is provided for Crisium. In addition, we discuss the consequences for scientific return of less than optimal locations or number of stations.

Keywords: lunar interior; lunar seismology; lunar composition; lunar rilles; lunar science; the moon
STARCNET: Machine Learning for Star Cluster Identification

We present a machine learning (ML) pipeline to identify star clusters in the multicolor images of nearby galaxies, from observations obtained with the Hubble Space Telescope as part of the Treasury Project LEGUS (Legacy ExtraGalactic Ultraviolet Survey). STARCNET (STAR Cluster classification NETwork) is a multiscale convolutional neural network (CNN) that achieves an accuracy of 68.6% (four classes)/86.0% (two classes: cluster/noncluster) for star cluster classification in the images of the LEGUS galaxies, nearly matching human expert performance. We test the performance of STARCNET by applying a pre-trained CNN model to galaxies not included in the training set, finding accuracies similar to the reference one. We test the effect of STARCNET predictions on the inferred cluster properties by comparing multicolor luminosity functions and mass-age plots from catalogs produced by STARCNET and by human labeling; distributions in luminosity, color, and physical characteristics of star clusters are similar for the human and ML classified samples. There are two advantages to the ML approach: (1) reproducibility of the classifications: the ML algorithm's biases are fixed and can be measured for subsequent analysis; and (2) speed of classification: the algorithm requires minutes for tasks that humans require weeks to months to perform. By achieving comparable accuracy to human classifiers, STARCNET will enable extending classifications to a larger number of candidate samples than currently available, thus increasing significantly the statistics for cluster studies. * Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: star clusters; young star clusters; interacting galaxies; galactic and extragalactic astronomy; young massive clusters; stellar astronomy
SBI++: Flexible, Ultra-fast Likelihood-free Inference Customized for Astronomical Applications

Flagship near-future surveys targeting 108-109 galaxies across cosmic time will soon reveal the processes of galaxy assembly in unprecedented resolution. This creates an immediate computational challenge on effective analyses of the full data set. With simulation-based inference (SBI), it is possible to attain complex posterior distributions with the accuracy of traditional methods but with a >104 increase in speed. However, it comes with a major limitation. Standard SBI requires the simulated data to have characteristics identical to those of the observed data, which is often violated in astronomical surveys due to inhomogeneous coverage and/or fluctuating sky and telescope conditions. In this work, we present a complete SBI-based methodology, SBI ++ , for treating out-of-distribution measurement errors and missing data. We show that out-of-distribution errors can be approximated by using standard SBI evaluations and that missing data can be marginalized over using SBI evaluations over nearby data realizations in the training set. In addition to the validation set, we apply SBI ++ to galaxies identified in extragalactic images acquired by the James Webb Space Telescope, and show that SBI ++ can infer photometric redshifts at least as accurately as traditional sampling methods-and crucially, better than the original SBI algorithm using training data with a wide range of observational errors. SBI ++ retains the fast inference speed of ~1 s for objects in the observational training set distribution, and additionally permits parameter inference outside of the trained noise and data at ~1 minute per object. This expanded regime has broad implications for future applications to astronomical surveys. (Code and a Jupyter tutorial are made publicly available at https://github.com/wangbingjie/sbi_pp.)

Keywords: algorithms; astrostatistics; computational astronomy
A Large Massive Quiescent Galaxy Sample at z ∼ 1.2

In this paper we present a simple color-magnitude selection and obtain a large sample of 33,893 massive quiescent galaxies at intermediate redshifts (1 < z < 1.5). We choose the longest wavelength available in the Hyper-Supreme-Cam (HSC) deep survey, the Y band and i - Y color, to select the 4000 Å Balmer jump in passive galaxies to the highest redshift possible within the survey. With the rich multiwavelength data in the HSC deep fields, we then confirm that the selected galaxies are in the targeted redshift range of 1 < z < 1.5, lie in the passive region of the UVJ diagram, and have high stellar masses at log(M*/M⊙) > 10.5, with a median of log(M*/M⊙) = 11.0. A small fraction of our galaxies is also covered by the HST CANDELS. Morphological analysis in the observed H band shows that the majority of this subsample are early-type galaxies. As massive early-type galaxies trace the high-density regions in the large-scale structure in the universe, our study provides a quick and simple way to obtain a statistically significant sample of massive galaxies in a relatively narrow redshift range. Our sample is 7-20× larger at the massive end (log(M*/M⊙) > 10.5) than any existing samples obtained in previous surveys. This is a pioneer study, and the technique introduced here can be applied to a future wide-field survey to study large-scale structure and to identify high-density regions and clusters.

Keywords: galaxies; high-redshift galaxies; catalogs
High-cadence Dispersed Spectral Analysis of Supernova Remnant 1987A

We present an analysis of the dispersed spectral data from 11 epochs (2011 March-2018 September) of supernova remnant (SNR) 1987A observations performed with Chandra. These observations were performed with the High Energy Transmission Grating (HETG) as part of our ongoing Chandra monitoring campaign of SNR 1987A, whose first-order dispersed spectrum provides a significantly greater energy resolution than the previously published zeroth-order spectrum. Our data sets with moderate exposure times of ∼50-70 ks per epoch cover the time period between deep Chandra HETG observations (with individual exposures >∼200 ks) taken in 2011 March and 2018 March. These data have a much higher cadence than the widely spaced deep high-resolution spectra, at the expense of total exposure time. While statistical uncertainties are large due to low photon count statistics in the observed first-order spectra, we find that spectral model parameters are generally in line with the shock wave propagating into the medium beyond the dense inner ring, as suggested by Frank et al. (2016). As the reverse shock begins ionizing the heavier elements of the supernova ejecta interior to the equatorial ring, spectral fit parameters are expected to change as the chemical makeup and physical properties of the shocked gas evolve. Based on our broadband spectral model fits, we find that abundance values appear to be constant in this time period. While our results are somewhat limited due to photon statistics, we demonstrate the utility of the dispersed HETG spectral analysis that can be performed with our regular Chandra monitoring observations of SNR 1987A.

Keywords: supernova remnants; x-ray astronomy; circumstellar gas; supernovae
Setting the Stage for the Search for Life with the Habitable Worlds Observatory: Properties of 164 Promising Planet-survey Targets

The Decadal Survey on Astronomy and Astrophysics 2020 has recommended that NASA realize a large IR/optical/UV space telescope optimized for high-contrast imaging and spectroscopy of ∼25 exo-Earths and transformative general astrophysics. The NASA Exoplanet Exploration Program (ExEP) has subsequently released a list of 164 nearby (d < 25 pc) targets deemed the most accessible to survey for potentially habitable exoplanets with the Habitable Worlds Observatory (HWO). We present a catalog of system properties for the 164 ExEP targets, including 1744 abundance measurements for 14 elements from the Hypatia Catalog and 924 photometry measurements spanning from 151.6 nm to 22 μm in the GALEX, Strömgren, Tycho, Gaia, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer bandpasses. We independently derive stellar properties for these systems by modeling their spectral energy distributions with Bayesian model averaging. Additionally, by consulting the literature, we identify TESS flare rates for 46 stars, optical variability for 78 stars, and X-ray emission for 46 stars in our sample. We discuss our catalog in the context of planet habitability and draw attention to key gaps in our knowledge where precursor science can help to inform HWO mission design trade studies in the near future. Notably, only 33 of the 164 stars in our sample have reliable space-based UV measurements, and only 40 have a mid-IR measurement. We also find that phosphorus, a bioessential element, has only been measured in 11 of these stars, motivating future abundance surveys. Our catalog is publicly available and we advocate for its use in future studies of promising HWO targets.

Keywords: exoplanet catalogs; exoplanet astronomy; planet hosting stars; astrobiology; space telescopes
Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf

We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J - K)MKO color of 2.97 ± 0.03 mag and a J MKO - W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH4 absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ-T0γ. We tentatively find that CWISE J0506+0738 is variable at 3-5 μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in the β Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

Keywords: brown dwarfs; l dwarfs; t dwarfs
Estimation of Thermal and Epithermal Neutron Fluences at the Lunar Surface from Isotopic Compositions of Rare Earth Elements

Thermalized neutrons arising at the surface of solar planets are produced from the interaction of cosmic rays with the nucleus consisting of surficial materials. The neutron energy spectrum in the range between thermal and epithermal regions at the lunar surface was investigated based on the combination of the isotopic variations of Sm and Gd caused by the thermal neutron-capture reactions in our previous study, with those of Dy, Er, and Yb caused by the epithermal neutron-capture reactions in this study. The detailed comparison of the systematic isotopic variations among Sm, Gd, Dy, Er, and Yb helps to construct a neutron energy spectrum at the surface of the Moon. Seven kinds of lunar soils at different depths of the drill core recovered from the Apollo 15 landing site (A-15) were used in this study. Isotopic variations of 164Dy/161Dy, 168Er/167Er, and 168Yb/174Yb were newly found in the A-15 samples, and showed the depth dependence caused by the interaction with cosmic-ray irradiation. In particular, the combination of the isotopic shifts of 168Er/167Er and 150Sm/149Sm could be effectively used to evaluate the epithermal neutron fluences of 5.4-8.1 × 1017 n cm-2 that were more than 10 times higher than thermal neutron fluences of 0.48-0.69 × 1017 n cm-2 reestimated in this study.

Keywords: galactic cosmic rays; lunar surface; isotope shifts
Spectra of Diffusion, Dispersion, and Dissipation for Kinetic Alfvénic and Compressive Turbulence: Comparison between Kinetic Theory and Measurements from MMS

We analyze measurements from Magnetospheric Multiscale mission to provide the spectra related with diffusion, dispersion, and dissipation, all of which are compared with predictions from plasma theory. This work is one example of magnetosheath turbulence, which is complex and diverse and includes more wave modes than the kinetic Alfvénic wave (KAW) mode studied here. The counter-propagation of KAW is identified from the polarities of cross-correlation spectra: CC(Ne, ∣B∣), CC(Ve⊥, B⊥), CC(Ve∥, B∥), and CC(Ne, Ve∥). We propose the concepts of turbulence ion and electron diffusion ranges (T-IDRs and T-EDRs) and identify them practically based on the ratio between electric field power spectral densities in different reference frames: PSD( $\delta {{\boldsymbol{E}}}_{{\rm{i}},\mathrm{local}}^{{\prime} }$ )/PSD(δEglobal) and PSD( $\delta {{\boldsymbol{E}}}_{{\rm{e}},\mathrm{local}}^{{\prime} }$ )/PSD(δEglobal). The outer scales of the T-IDR and T-EDR are observed to be at the wavenumber of kdi ∼ 0.2 and kde ∼ 0.1, where di and de are the proton and electron inertial lengths, respectively. The signatures of positive dispersion related to the Hall effect are illustrated observationally and reproduced theoretically with flat PSD(δEglobal) and steep PSD(δB), as well as a bifurcation between PSD(δVi) and PSD(δVe). We calculate the dissipation rate spectra, $\gamma \left(k\right)$ , which clearly show the commencement of dissipation around kdi ∼ 1. We find that the dissipation in this case is mainly converted to electron parallel kinetic energy, responsible for the electron thermal anisotropy with Te,∥/Te,⊥ > 1. The "3D" (diffusion, dispersion, and dissipation) characteristics of kinetic Alfvénic and compressive plasma turbulence are therefore summarized as follows: positive dispersion due to the Hall effect appears in the T-IDR, while dominant parallel dissipation with energy transferred to electrons occurs mainly in the T-EDR.

Keywords: solar wind; interplanetary turbulence; alfven waves
A Deep Search for Five Molecules in the 49 Ceti Debris Disk

Surprisingly strong CO emission has been observed from more than a dozen debris disks around nearby main-sequence stars. The origin of this CO is unclear, in particular whether it is left over from the protoplanetary disk phase or is second-generation material released from collisions between icy bodies like debris dust. The primary unexplored avenue for distinguishing the origin of the material is understanding its molecular composition. Here we present a deep search for five molecules (CN, HCN, HCO+, SiO, and CH3OH) in the debris disk around 49 Ceti. We take advantage of the high sensitivity of the Atacama Large Millimeter/submillimeter Array at Band 7 to integrate for 3.2 hr at modest spatial (1″) and spectral (0.8 km s-1) resolution. Our search yields stringent upper limits on the flux of all surveyed molecular lines, which imply abundances relative to CO that are orders of magnitude lower than those observed in protoplanetary disks and solar system comets, and also those predicted in outgassing models of second-generation material. However, if C I shielding is responsible for extending the lifetime of any CO produced in second-generation collisions as proposed by Kral et al., then the line ratios do not reflect true ice phase chemical abundances but rather imply that CO is shielded by its own photodissociation product, C I, and other molecules are rapidly photodissociated by the stellar and interstellar radiation field.

Keywords: debris disks; submillimeter astronomy; radio interferometry; molecular spectroscopy
Kilonovae Across the Nuclear Physics Landscape: The Impact of Nuclear Physics Uncertainties on r-process-powered Emission

Merging neutron stars produce "kilonovae"-electromagnetic transients powered by the decay of unstable nuclei synthesized via rapid neutron capture (the r-process) in material that is gravitationally unbound during inspiral and coalescence. Kilonova emission, if accurately interpreted, can be used to characterize the masses and compositions of merger-driven outflows, helping to resolve a long-standing debate about the origins of r-process material in the Universe. We explore how the uncertain properties of nuclei involved in the r-process complicate the inference of outflow properties from kilonova observations. Using r-process simulations, we show how nuclear physics uncertainties impact predictions of radioactive heating and element synthesis. For a set of models that span a large range in both predicted heating and final abundances, we carry out detailed numerical calculations of decay product thermalization and radiation transport in a kilonova ejecta with a fixed mass and density profile. The light curves associated with our models exhibit great diversity in their luminosities, with peak brightness varying by more than an order of magnitude. We also find variability in the shape of the kilonova light curves and their color, which in some cases runs counter to the expectation that increasing levels of lanthanide and/or actinide enrichment will be correlated with longer, dimmer, redder emission.

Keywords: r-process; neutron stars; stellar mergers; gravitational wave sources
A Nucleosynthetic Origin for the Southwestern Fe-rich Structure in Kepler's Supernova Remnant

Chandra X-ray observations of Kepler's supernova remnant indicate the existence of a high-speed Fe-rich ejecta structure in the southwestern region. We report strong K-shell emission from Fe-peak elements (Cr, Mn, Fe, Ni), as well as Ca, in this Fe-rich structure, implying that those elements could be produced in the inner area of the exploding white dwarf. We found Ca/Fe, Cr/Fe, Mn/Fe, and Ni/Fe mass ratios of 1.0%-4.1%, 1.0%-4.6%, 1%-11%, and 2%-30%, respectively. In order to constrain the burning regime that could produce this structure, we compared these observed mass ratios with those in 18 one-dimensional Type Ia nucleosynthesis models (including both near-MCh and sub-MCh explosion models). The observed mass ratios agree well with those around the middle layer of incomplete Si burning in Type Ia nucleosynthesis models with a peak temperature of ∼(5.0-5.3) × 109 K and a high metallicity, Z > 0.0225. Based on our results, we infer the necessity for some mechanism to produce protruding Fe-rich clumps dominated by incomplete Si-burning products during the explosion. We also discuss the future perspectives of X-ray observations of Fe-rich structures in other Type Ia supernova remnants.

Keywords: supernova remnants; interstellar medium; explosive nucleosynthesis; x-ray astronomy
Optical Properties of Interstellar Dust around the Orion A Molecular Cloud

We have studied optical properties of interstellar dust around the Orion A molecular cloud to investigate the size distribution and the composition of dust grains. Orion A is one of the most studied molecular clouds in the solar vicinity (d ≃ 400 pc). In this paper, we used optical and near-infrared photometric data. The optical data were obtained by BVRI bands imaging observations. The near-infrared data consisting of JHKS bands were taken from 2MASS point source catalog. We produced some color excess maps around Orion A and measured their ratios such as E(R - I)/E(B - V). In order to investigate dust properties, we compared the observed ratios with results of simulation performed by Naoi et al. who calculated the extinction in the optical to near-infrared wavelengths based on a standard dust model. They assumed a power-law grain-size distribution with an upper cutoff radius and assumed graphite and silicate as dominant components. As a result, we found that the upper cutoff radius around Orion A is ≃0.3 μm, and silicate predominates compared with graphite (with the fraction of silicate grater than 93%). In addition, we further derived the total-to-selective extinction ratio RV from the observed extinction of AV and the color excess E(B - V), and compared it with the model calculations. Dust properties (i.e., the upper cutoff radius and the ratio of graphite/silicate) derived from RV are almost consistent with those derived from the color excess ratios.

Keywords: interstellar dust; interstellar dust extinction; diffuse interstellar clouds; extinction; reddening law; optical observation; near infrared astronomy
Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis

We analyze five epochs of Neutron star Interior Composition Explorer (NICER) data of the black hole X-ray binary MAXI J1820+070 during the bright hard-to-soft state transition in its 2018 outburst with both reflection spectroscopy and Fourier-resolved timing analysis. We confirm the previous discovery of reverberation lags in the hard state, and find that the frequency range where the (soft) reverberation lag dominates decreases with the reverberation lag amplitude increasing during the transition, suggesting an increasing X-ray emitting region, possibly due to an expanding corona. By jointly fitting the lag-energy spectra in a number of broad frequency ranges with the reverberation model reltrans, we find the increase in reverberation lag is best described by an increase in the X-ray coronal height. This result, along with the finding that the corona contracts in the hard state, suggests a close relationship between spatial extent of the X-ray corona and the radio jet. We find the corona expansion (as probed by reverberation) precedes a radio flare by ∼5 days, which may suggest that the hard-to-soft transition is marked by the corona expanding vertically and launching a jet knot that propagates along the jet stream at relativistic velocities.

Keywords: low-mass x-ray binary stars; stellar mass black holes; high energy astrophysics; black hole physics; x-ray transient sources