adsabs/SciX_UAT_keywords huggingface dataset:
Modeling Cassini UVIS Interplanetary Hydrogen Lyα Observations from 1999 to 2017

The Cassini Orbiter Ultraviolet Imaging Spectrograph (UVIS) obtained interplanetary hydrogen Lyα observations from 1999 to 2017, with mid-2004 to 2017 observations obtained from Saturn orbit. During its Saturn orbital phase, the spacecraft moved from mostly downwind and sidewind in the heliosphere to upwind. We analyze the full set of observations with our existing hot hydrogen density model with a solar illumination model most recently used to study Solar and Heliospheric Observatory Solar Wind Anisotropy Experiment data and selected Cassini UVIS observations from 2003 to 2004. We find general agreement between data and model, but with evidence for a decline in UVIS Lyα sensitivity, with a significant decline in 2002 June during a starburn event and an overall roughly linear decline in sensitivity. While earlier work by Pryor et al. fit the UVIS Lyα data from 2003 to 2004 with a hydrogen density in the outer heliosphere (but after filtration at outer heliospheric boundaries) of 0.085 cm-3 using the UVIS laboratory sensitivity calibration, including the sensitivity decline found here leads to a revised hydrogen density estimate of n H = 0.14 ± 0.03 cm-3. This density estimate is consistent with a recent neutral hydrogen density estimate near the termination shock of 0.127 ± 0.015 cm-3 based on models of observations of pick-up hydrogen ions from the New Horizons spacecraft.

Keywords: heliosphere
Measured Optical Absorption Cross Sections of TiO

A laboratory emission spectrum of TiO in the visible and near-infrared regions (476-1176 nm) has been calibrated and corrected. High-resolution experimental absorption cross sections for TiO with natural isotopic abundance are provided at a temperature of about 2300 K. These cross sections have been compared with those derived from the ExoMol line list. The experimental cross sections can be used directly as a template for cross correlation TiO detection in hot Jupiter exoplanets.

Keywords: molecular spectroscopy; high resolution spectroscopy; line intensities; m stars; exoplanet atmospheric composition
The Effect of the Chromospheric Temperature on Coronal Heating

Recent observational and numerical studies show a variety of thermal structures in the solar chromosphere. Given that the thermal interplay across the transition region is a key to coronal heating, it is worth investigating how different thermal structures of the chromosphere yield different coronal properties. In this work, by MHD simulations of Alfvén-wave heating of coronal loops, we study how the coronal properties are affected by the chromospheric temperature. To this end, instead of solving the radiative transfer equation, we employ a simple radiative loss function so that the chromospheric temperature is easily tuned. When the chromosphere is hotter, because the chromosphere extends to a larger height, the coronal part of the magnetic loop becomes shorter, which enhances the conductive cooling. A larger loop length is therefore required to maintain the high-temperature corona against the thermal conduction. From our numerical simulations we derive a condition for the coronal formation with respect to the half loop length l loop in a simple form: ${l}_{\mathrm{loop}}\gt {{aT}}_{\min }+{l}_{\mathrm{th}}$ , where ${T}_{\min }$ is the minimum temperature in the atmosphere, and parameters a and l th have negative dependencies on the coronal field strength. Our conclusion is that the chromospheric temperature has a nonnegligible impact on coronal heating for loops with small lengths and weak coronal fields. In particular, the enhanced chromospheric heating could prevent the formation of the corona.

Keywords: solar corona; magnetohydrodynamical simulations; solar coronal loops
On the Particle Acceleration Mechanisms in a Double Radio Relic Galaxy Cluster, Abell 1240

We present a 368 ks deep Chandra observation of Abell 1240, a binary merging galaxy cluster at a redshift of 0.195 with two brightest cluster galaxies that may have passed each other 0.3 Gyr ago. Building upon previous investigations involving Giant Metrewave Radio Telescope, Very Large Array, and LOFAR data, our study focuses on two prominent extended radio relics at the northwest (NW) and southeast (SE) of the cluster core. By leveraging the high-resolution Chandra imaging, we have identified two distinct surface-brightness edges at ∼1 Mpc and 1.2 Mpc NW and SE of the cluster center, respectively, coinciding with the outer edges of both relics. Our temperature measurements suggest the edges to be shock front edges. The Mach numbers, derived from the gas density jumps, yield ${{ \mathcal M }}_{\mathrm{SE}}$ = ${1.49}_{-0.24}^{+0.22}$ for the SE shock and ${{ \mathcal M }}_{\mathrm{NW}}$ = ${1.41}_{-0.19}^{+0.17}$ for the NW shock. Our estimated Mach numbers are remarkably smaller compared to those derived from radio observations ( ${{ \mathcal M }}_{\mathrm{SE}}$ = 2.3 and ${{ \mathcal M }}_{\mathrm{NW}}$ = 2.4), highlighting the prevalence of a reacceleration scenario over direct acceleration of electrons from the thermal pool. Furthermore, we compare the observed temperature profiles across both shocks with those of predictions from collisional versus collisionless models. Both shocks favor the Coulomb collisional model, but we could not rule out a purely collisionless model due to pre-shock temperature uncertainties.

Keywords: galaxy clusters
Constraining the Halo Mass of Damped Lyα Absorption Systems (DLAs) at z = 2-3.5 Using the Quasar-CMB Lensing Cross-correlation

We study the cross-correlation of damped Lyα systems (DLAs) and their background quasars, using the most updated DLA catalog and the Planck 2018 CMB lensing convergence field. Our measurement suggests that the DLA bias ${b}_{\mathrm{DLA}}$ is smaller than 3.1, corresponding to $\mathrm{log}(M/{M}_{\odot }{h}^{-1})\leqslant 12.3$ at a confidence of 90%. These constraints are broadly consistent with Alonso et al. and previous measurements by cross-correlation between DLAs and the Lyα forest (e.g., Font-Ribera et al.; Prez-Rfols et al.). Further, our results demonstrate the potential of obtaining a more precise measurement of the halo mass of the high-redshift sources using next generation CMB experiments with a higher angular resolution. The python-based codes and data products of our analysis are available at https://github.com/LittleLin1999/CMB-lensingxDLA.

Keywords: cosmic microwave background radiation; quasars; large-scale structure of the universe; galaxy dark matter halos; intergalactic medium
Physical Model of Dust Polarization by Radiative Torque Alignment and Disruption and Implications for Grain Internal Structures

Dust polarization depends on mechanical properties of dust as well as on local environments. To understand how dust polarization varies with different properties, we model the wavelength-dependence polarization of starlight and polarized dust emission of aligned grains by simultaneously taking into account grain alignment and rotational disruption by radiative torques (RATs). We explore a wide range of the local radiation field and grain mechanical properties characterized by tensile strength (Smax). We find that the peak wavelength shifts to shorter wavelengths as the radiation strength (U) increases due to the enhanced alignment of small grains. Grain rotational disruption by RATs tends to decrease the optical-NIR polarization but increase the UV polarization of starlight due to the conversion of large grains into smaller ones. In particular, we find that the polarization degree at 850 μm (P850) does not increase monotonically with U or grain temperature (Td), but it depends on Smax of the grains. Our model can be tested with observations toward star-forming regions or molecular clouds irradiated by a nearby star, which have higher radiation intensities than the that of the average interstellar radiation field. Finally, we compare our predictions of the P850-Td relationship with Planck data and find that the observed decrease of P850 with Td can be explained when grain disruption by RATs is accounted for, suggesting that as interstellar grains are unlikely to have a compact structure, perhaps they have a composite one. The variation of the polarization degree with U (or Td) can provide a valuable constraint on the internal structure of cosmic dust.

Keywords: interstellar medium; starlight polarization; interstellar radiation field; interstellar dust extinction
Kiloparsec-scale ALMA Imaging of [C II] and Dust Continuum Emission of 27 Quasar Host Galaxies at z ∼ 6

We present a study of the [C II] 158 μm line and underlying far-infrared (FIR) continuum emission of 27 quasar host galaxies at z ∼ 6, traced by the Atacama Large Millimeter/submillimeter Array at a spatial resolution of ∼1 physical kpc. The [C II] emission in the bright, central regions of the quasars have sizes of 1.0-4.8 kpc. The dust continuum emission is typically more compact than [C II]. We find that 13/27 quasars (approximately one-half) have companion galaxies in the field, at projected separations of 3-90 kpc. The position of dust emission and the Gaia-corrected positions of the central accreting black holes are cospatial (typical offsets ≲0"1). This suggests that the central black holes are located at the bottom of the gravitational wells of the dark matter halos in which the $z\gt 6$ quasar hosts reside. Some outliers with offsets of ∼500 pc can be linked to disturbed morphologies, most likely due to ongoing or recent mergers. We find no correlation between the central brightness of the FIR emission and the bolometric luminosity of the accreting black hole. The FIR-derived star formation rate densities (SFRDs) in the host galaxies peak at the galaxies' centers, at typical values between 100 and 1000 M⊙ yr-1 kpc-2. These values are below the Eddington limit for star formation, but similar to those found in local ultraluminous infrared galaxies. The SFRDs drop toward larger radii by an order of magnitude. Likewise, the [C II]/FIR luminosity ratios of the quasar hosts are lowest in their centers (few ×10-4) and increase by a factor of a few toward the galaxies' outskirts, consistent with resolved studies of lower-redshift sources.

Keywords: observational cosmology; high-redshift galaxies; quasars; star formation
State of the Field: Binary Black Hole Natal Kicks and Prospects for Isolated Field Formation after GWTC-2

Advanced LIGO and Advanced Virgo's newly released GWTC-2 catalog of gravitational-wave detections offers unprecedented information about the spin magnitudes and orientations of merging binary black holes (BBHs). Notably, analysis of the BBH population suggests the presence of binaries whose component spins are significantly misaligned with respect to their orbital angular momenta. Significantly misaligned spins are typically predicted to be at odds with isolated field formation via standard common envelope (CE) evolution, and hence a "smoking gun" signature of dynamical binary formation inside dense stellar clusters. Here, we explore whether the LIGO/Virgo observation of spin-orbit misalignment indeed rules out the possibility that BBHs are formed entirely in the field via standard CE evolution. In particular, we seek to understand whether, by varying the natal kicks black holes receive upon formation, we can invoke the CE scenario to self-consistently explain both the observed spin distribution and merger rate of BBHs. We find that, if isolated black holes are born with small natal spins, then BBHs formed through CE require extreme natal kicks to match the observed BBH population, with a velocity dispersion $\sigma ={9.7}_{-5.9}^{+26.7}\times {10}^{2}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and σ > 260 km s-1 at 99% credibility. To avoid the need for extreme kicks, we argue that it is necessary to assume that isolated black holes are born with nonvanishing natal spins, that one or more alternative channels contribute to the observed BBH population, and/or that other unforeseen mechanisms serve to yield large spin-orbit misalignment in the field.

Keywords: gravitational waves; astrophysical black holes; astronomy data analysis; compact binary stars
Atmospheric Circulation in Simulations of the AGN-CGM Connection at Halo Masses 1013.5 M ⊙

Coupling between active galactic nuclei (AGNs) and the circumgalactic medium (CGM) is critical to the interplay between radiative cooling and feedback heating in the atmospheres of the universe's most massive galaxies. This paper presents a detailed analysis of numerical simulations showing how kinetic AGN feedback with a strong momentum flux interacts with the CGM. Our analysis shows that large-scale CGM circulation driven by that momentum flux plays an important role in reconfiguring the galactic atmosphere and regulating the atmosphere's central entropy level. We find that most of the AGN's energy output goes into lifting of circumgalactic gas rather than heating of atmospheric gas within the galaxy, consequently reconfiguring the CGM by replacing low-entropy gas originally in the core with higher-entropy gas from larger radii. Circulation of the CGM on ~10-100 kpc scales therefore plays a critical role in preventing overcooling of gas in these simulated galaxies, but leads to elevated entropy profiles ~1-10 kpc compared to the observed entropy profiles of massive elliptical galaxies in the same mass range. The simulations also show that our choices of accretion efficiency and jet opening angle significantly affect the AGN-CGM coupling. Reducing the jet opening angle to one-quarter of the fiducial opening angle increases the jet momentum flux, enabling it to drill through to larger radii without effectively coupling with the CGM at the center (r < 5 kpc). Outflows with a lower momentum flux decelerate and thermalize the bulk of their energy at smaller radii (r ≲ 10 kpc).

Keywords: active galactic nuclei; circumgalactic medium; galaxy groups; supermassive black holes; active galaxies; radio galaxies; stellar feedback
The R-Process Alliance: A Very Metal-poor, Extremely r-process-enhanced Star with [Eu/Fe] = + 2.2, and the Class of r-III Stars

We report the discovery of J1521-3538, a bright (V = 12.2), very metal-poor ([Fe/H] = -2.8) strongly r-process-enhanced field horizontal branch star, based on a high-resolution, high signal-to-noise Magellan/MIKE spectrum. J1521-3538 shows the largest r-process element overabundance in any known r-process-enhanced star, with [Eu/Fe] = +2.2, and its chemical abundances of 22 neutron-capture elements closely match the scaled solar r-process pattern. J1521-3538 is also one of few known carbon-enhanced metal-poor stars with r-process enhancement (CEMP-r stars), as found after correcting the measured C abundance for the star's evolutionary status. We propose to extend the existing classification of moderately enhanced ( $+0.3\leqslant {\rm{[Eu/Fe]}}\leqslant +1.0$ ) r-I and strongly r-process enhanced ( ${\rm{[Eu/Fe]}}\gt +1.0$ ) r-II stars to include an r-III class, for r-process stars such as J1521-3538, with ${\rm{[Eu/Fe]}}\gt +2.0$ and ${\rm{[Ba/Eu]}}\lt -0.5$ , or $\geqslant 100$ times the solar ratio of europium to iron. Using cosmochronometry, we estimate J1521-3538 to be $12.5\pm 5\,\mathrm{Gyr}$ and $8.9\pm 5\,\mathrm{Gyr}$ , using two different sets of initial production ratios. These ages are based on measurements of the Th line at 4019 Å and other r-process element abundances. This is broadly consistent with the old age of a low-mass, metal-poor field red horizontal branch star. J1521-3538 likely originated in a low-mass dwarf galaxy that was later accreted by the Milky Way, as evidenced by its highly eccentric orbit. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Based on observations obtained at the Gemini Observatory (Prop. IDs: GS-2015A-Q-205), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program(s) 092.D-0308(A).

Keywords: milky way stellar halo; nucleosynthesis; stellar abundances; population ii stars
Visual Explanation of a Deep Learning Solar Flare Forecast Model and Its Relationship to Physical Parameters

In this study, we present a visual explanation of a deep learning solar flare forecast model and its relationship to physical parameters of solar active regions (ARs). For this, we use full-disk magnetograms at 00:00 UT from the Solar and Heliospheric Observatory/Michelson Doppler Imager and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, physical parameters from the Space-weather HMI Active Region Patch (SHARP), and Geostationary Operational Environmental Satellite X-ray flare data. Our deep learning flare forecast model based on the Convolutional Neural Network (CNN) predicts "Yes" or "No" for the daily occurrence of C-, M-, and X-class flares. We interpret the model using two CNN attribution methods (guided backpropagation and Gradient-weighted Class Activation Mapping [Grad-CAM]) that provide quantitative information on explaining the model. We find that our deep learning flare forecasting model is intimately related to AR physical properties that have also been distinguished in previous studies as holding significant predictive ability. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of daily solar flare occurrence with TSS = 0.65, without any preprocessing to extract features from data. Second, using the attribution methods, we find that the polarity inversion line is an important feature for the deep learning flare forecasting model. Third, the ARs with high Grad-CAM values produce more flares than those with low Grad-CAM values. Fourth, nine SHARP parameters such as total unsigned vertical current, total unsigned current helicity, total unsigned flux, and total photospheric magnetic free energy density are well correlated with Grad-CAM values.

Keywords: the sun; solar flares; convolutional neural networks
Velocity Gradient in the Presence of Self-gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage

Understanding how star formation is regulated requires studying the energy balance between turbulence, magnetic fields, stellar feedback, and gravity within molecular clouds. However, identifying the transition region where the gravity takes over remains elusive. Recent studies of the Velocity Gradient Technique (VGT), which is an advanced tool for magnetic field studies, reveal that the gradients of spectroscopic observables change their directions by 90° with respect to the magnetic fields in the regions of gravitational collapse. In this study, we perform 3D MHD numerical simulations. We observe that star formation successfully proceeds in strongly magnetized and fully ionized media. We confirm that the self-gravity induces the change of gradients' orientation and gradients' high amplitude. We explore two ways of identifying collapsing self-gravitating regions through the double-peak feature in the histogram of gradients' orientation and the curvature of gradients. We show that velocity gradients' morphology and amplitude can be synthetically used to trace the convergent inflows. By comparing with the column density Probability Density Functions method, we show that VGT is a powerful new tool for studying the gas dynamics and tracing magnetic field in star-forming regions. By analogy with VGT, we extend the Intensity Gradient Technique (IGT) to locate the gravitational collapsing region and shocks. We demonstrate that the synergy of VGT and IGT can determine the collapsing stages in a star-forming region.

Keywords: interstellar magnetic fields; star formation; interstellar medium; star forming regions
Constraining the Structure under Lunar Impact Basins with Gravity

The lunar gravity field is used to estimate and constrain the depth of mass anomalies under 19 major lunar impact basins. We use radial gravitational spectra, consisting of accelerations computed either per spherical harmonic degree or cumulatively, at surface locations to obtain the distribution of the gravity signal with spherical harmonic degree and, by implication, to the likely depth below the surface. The results provide estimates for the maximum likely depths of the primary component to the mass anomalies under 19 basins. We find that the maximum depths of the primary source of mascon gravity on the lunar nearside are deeper than the depths for those on the farside when South Pole-Aitken (SPA) is excluded. All basin mass anomalies on the lunar nearside are in the mantle. The maximum depth of the primary source of the mass anomalies is <80 km, with the exception of SPA, whose dominant mass signature lies at a maximum depth of >200 km beneath the surface. The upper 20 km under all basins is largely devoid of anomalies, reflecting predominantly mixing and relaxation associated with impact melt combined with ejecta fallback, as well as homogenization associated with post-basin formation impact bombardment. Except for SPA, all basin anomalies merge with the deep interior at ~150 km or below, indicating the depth penetration of disruption of the density structure of the lunar interior associated with impact bombardment.

Keywords: lunar gravitational field
Spectral Diversities of Gamma-Ray Bursts in High-energy Bands: Hints from Turbulent Cascade

We statistically examine the gamma-ray burst (GRB) photon indices obtained by the Fermi-GBM and Fermi-LAT observations and compare the LAT GRB photon indices to the GBM GRB photon indices. We apply the jitter radiation to explain the GRB spectral diversities in the high-energy bands. In our model, the jitter radiative spectral index is determined by the spectral index of the turbulence. We classify GRBs into three classes depending on the shape of the GRB high-energy spectrum when we compare the GBM and LAT detections: the GRB spectrum is concave (GRBs turn out to be softer and are labeled as S-GRBs), the GRB spectrum is convex (GRBs turn out to be harder and are labeled as H-GRBs), and the GRBs have no strong spectral changes (labeled as N-GRBs). A universal Kolmogorov index 7/3 in the turbulent cascade is consistent with the photon index of the N-GRBs. The S-GRB spectra can be explained by the turbulent cascade due to the kinetic magnetic reconnection with the spectral index range of the turbulence from 8/3 to 3.0. The H-GRB spectra originate from the inverse turbulent cascade with the spectral index range of the turbulence from 2.0 to 3.5 that occurred during the large lengthscale magnetic reconnection. Thus, the GRB radiative spectra are diversified because the turbulent cascade modifies the turbulent energy spectrum. More observational samples are expected in the future to further identify our suggestions.

Keywords: gamma-ray bursts; magnetic fields; magnetohydrodynamics