adsabs/SciX_UAT_keywords huggingface dataset:
The High Helium Abundance and Charge States of the Interplanetary CME and Its Material Source on the Sun

Identifying the source of the material within coronal mass ejections (CMEs) and understanding CME onset mechanisms are fundamental issues in solar and space physics. Parameters relating to plasma composition, such as charge states and He abundance (AHe), may be different for plasmas originating from differing processes or regions on the Sun. Thus, it is crucial to examine the relationship between in situ measurements of CME composition and activity on the Sun. We study the CME that erupted on 2014 September 10, in association with an X1.6 flare, by analyzing Atmospheric Imaging Assembly imaging and Interface Region Imaging Spectrograph (IRIS) spectroscopic observations and its in situ signatures detected by Wind and Advanced Composition Explorer. We find that during the slow expansion and intensity increase of the sigmoid, plasma temperatures of 9 MK, and higher, first appear at the footpoints of the sigmoid, associated with chromospheric brightening. Then the high-temperature region extends along the sigmoid. IRIS observations confirm that this extension is caused by transportation of hot plasma upflow. Our results show that chromospheric material can be heated to 9 MK, and above, by chromospheric evaporation at the sigmoid footpoints before flare onset. The heated chromospheric material can transport into the sigmoidal structure and supply mass to the CME. The aforementioned CME mass supply scenario provides a reasonable explanation for the detection of high charge states and elevated AHe in the associated interplanetary CME. The observations also demonstrate that the quasi-steady evolution in the precursor phase is dominated by magnetic reconnection between the rising flux rope and the overlying magnetic field structure.

Keywords: solar-terrestrial interactions; solar corona; solar coronal mass ejections; solar flares; solar abundances
Is the High-Resolution Coronal Imager Resolving Coronal Strands? Results from AR 12712

Following the success of the first mission, the High-Resolution Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1) on 2018 May 29 from the White Sands Missile Range, NM, USA. On this occasion, 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec pixel-1. Using data captured by Hi-C 2.1 and co-aligned observations from SDO/AIA 17.1 nm, we investigate the widths of 49 coronal strands. We search for evidence of substructure within the strands that is not detected by AIA, and further consider whether these strands are fully resolved by Hi-C 2.1. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss are studied. A comparison is made between these low-emission strands and those from regions of higher emission within the target active region. It is found that Hi-C 2.1 can resolve individual strands as small as ≈202 km, though the more typical strand widths seen are ≈513 km. For coronal strands within the region of low emission, the most likely width is significantly narrower than the high-emission strands at ≈388 km. This places the low-emission coronal strands beneath the resolving capabilities of SDO/AIA, highlighting the need for a permanent solar observatory with the resolving power of Hi-C.

Keywords: solar corona; solar coronal loops; solar active regions
Disentangled Representation Learning for Astronomical Chemical Tagging

Modern astronomical surveys are observing spectral data for millions of stars. These spectra contain chemical information that can be used to trace the Galaxy's formation and chemical enrichment history. However, extracting the information from spectra and making precise and accurate chemical abundance measurements is challenging. Here we present a data-driven method for isolating the chemical factors of variation in stellar spectra from those of other parameters (i.e., Teff, log g, [Fe/H]). This enables us to build a spectral projection for each star with these parameters removed. We do this with no ab initio knowledge of elemental abundances themselves and hence bypass the uncertainties and systematics associated with modeling that rely on synthetic stellar spectra. To remove known nonchemical factors of variation, we develop and implement a neural network architecture that learns a disentangled spectral representation. We simulate our recovery of chemically identical stars using the disentangled spectra in a synthetic APOGEE-like data set. We show that this recovery declines as a function of the signal-to-noise ratio but that our neural network architecture outperforms simpler modeling choices. Our work demonstrates the feasibility of data-driven abundance-free chemical tagging.

Keywords: stellar astronomy; neural networks; stellar spectral lines
The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lyα Photons: A Case Study of a Protocluster Field at z = 3.1

We present a detailed characterization of the Lyα properties for 93 Lyα emitters (LAEs) at z ~ 3.1 selected from the D1 field of the Canada-France-Hawaii Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lyα image shows an extended Lyα halo (LAH) surrounding the galaxy with the exponential scale length 4.9 ± 0.7 kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lyα escape fraction, fesc, is 40% ± 26%. Combining the data set with existing measurements, we find a dependence of fesc on the galaxy's UV slope (β) and UV luminosity (LUV). The simultaneous use of both parameters allows prediction of fesc within 0.18 dex, a substantial improvement over 0.23 dex when only β is used. The correlation between fesc and E(B - V) suggests that Lyα photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lyα transmission is typically higher than that expected for continuum photons at a similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lyα transmission or production. Alternatively, the dust law may change with luminosity leading to an over- or underestimation of fesc. Finally, we report that protocluster LAEs tend to be bluer and more UV luminous than their field cousins, resulting in systematically higher fesc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

Keywords: galaxy evolution; galaxy formation; high-redshift galaxies
On the Intermittency of Hot Plasma Loops in the Solar Corona

A recent analysis has suggested that the heating of plasma loops in the solar corona depends not just on the Poynting flux but also on processes yet to be identified. This discovery reflects and refines earlier questions such as, Why and how are entire hydromagnetic structures only intermittently loaded with bright coronal plasma? The present work scrutinizes more chromospheric and coronal data, with the aim of finding reproducible observational constraints on coronal heating mechanisms. Six independent scans of chromospheric active-region magnetic fields are investigated and correlated to overlying hot plasma loops. For the first time, the footpoints of over 30 bright plasma loops are thus related to scalar proxies for the Poynting fluxes measured from the upper chromosphere. Although imperfect, the proxies all indicate a general lack of correlation between footpoint Poynting flux and loop brightness. Our findings consolidate the claim that unobserved physical processes are at work, which govern the heating of long-lived coronal loops.

Keywords: active sun; solar coronal heating; solar chromosphere; solar active region magnetic fields
Polarimetric Properties of Event Horizon Telescope Targets from ALMA

We present the results from a full polarization study carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) during the first Very Long Baseline Interferometry (VLBI) campaign, which was conducted in 2017 April in the λ3 mm and λ1.3 mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), respectively. We determine the polarization and Faraday properties of all VLBI targets, including Sgr A*, M87, and a dozen radio-loud active galactic nuclei (AGNs), in the two bands at several epochs in a time window of 10 days. We detect high linear polarization fractions (2%-15%) and large rotation measures (RM > 103.3-105.5 rad m-2), confirming the trends of previous AGN studies at millimeter wavelengths. We find that blazars are more strongly polarized than other AGNs in the sample, while exhibiting (on average) order-of-magnitude lower RM values, consistent with the AGN viewing angle unification scheme. For Sgr A* we report a mean RM of (-4.2 ± 0.3) × 105 rad m-2 at 1.3 mm, consistent with measurements over the past decade and, for the first time, an RM of (-2.1 ± 0.1) × 105 rad m-2 at 3 mm, suggesting that about half of the Faraday rotation at 1.3 mm may occur between the 3 mm photosphere and the 1.3 mm source. We also report the first unambiguous measurement of RM toward the M87 nucleus at millimeter wavelengths, which undergoes significant changes in magnitude and sign reversals on a one year timescale, spanning the range from -1.2 to 0.3 × 105 rad m-2 at 3 mm and -4.1 to 1.5 × 105 rad m-2 at 1.3 mm. Given this time variability, we argue that, unlike the case of Sgr A*, the RM in M87 does not provide an accurate estimate of the mass accretion rate onto the black hole. We put forward a two-component model, comprised of a variable compact region and a static extended region, that can simultaneously explain the polarimetric properties observed by both the EHT (on horizon scales) and ALMA (which observes the combined emission from both components). These measurements provide critical constraints for the calibration, analysis, and interpretation of simultaneously obtained VLBI data with the EHT and GMVA.

Keywords: magnetic fields; relativistic jets; active galactic nuclei; radio jets; polarimetry; interferometry; long baseline interferometry; galactic center; supermassive black holes; blazars; radio galaxies; quasars
The Impact of Type Ia Supernovae in Quiescent Galaxies. I. Formation of the Multiphase Interstellar Medium

A cool phase of the interstellar medium has been observed in many giant elliptical galaxies, but its origin remains unclear. We propose that uneven heating from Type Ia supernovae (SNe Ia), together with radiative cooling, can lead to the formation of the cool phase. The basic idea is that since SNe Ia explode randomly, gas parcels that are not directly heated by SN shocks will cool, forming multiphase gas. We run a series of idealized high-resolution numerical simulations and find that cool gas develops even when the overall SN heating rate H exceeds the cooling rate C by a factor as large as 1.4. We also find that the time for multiphase gas development depends on the gas temperature. When the medium has a temperature T = 3 × 106 K, the cool phase forms within one cooling time ${t}_{{\rm{c}},0}$ ; however, the cool phase formation is delayed to a few times ${t}_{{\rm{c}},0}$ for higher temperatures. The main reason for the delay is turbulent mixing. Cool gas formed this way would naturally have a metallicity lower than that of the hot medium. For constant H/C, there is more turbulent mixing for higher-temperature gas. We note that this mechanism of producing cool gas cannot be captured in cosmological simulations, which usually fail to resolve individual SN remnants.

Keywords: type ia supernovae; core-collapse supernovae; elliptical galaxies; galaxy evolution; interstellar medium; hydrodynamical simulations; shocks; galaxy chemical evolution
SpyderZ: An Efficient Support Vector Machine Library for Photometric Redshift Estimation and Redshift Probability Information

We present SpyderZ, a Python-based library for photometric redshift estimation using support vector machines (implemented with scikit-learn). Our approach discretizes redshift values into uniformly-sized bins and uses one-vs-one support vector classifiers with voting strategies to produce effective probability density functions (ePDFs) over redshift for each galaxy. These ePDFs, which are not constrained to be Gaussian or any other shape, allow for our model's predictions to be used quantitatively with uncertainty analysis methods, and have been shown to enable reliable catastrophic outlier detection. Adapted from the previous IDL package SpiderZ, SpyderZ offers training and evaluation speed optimizations on the order of 102, along with support for parallelization across CPU cores. Our library also offers in-built data sanity checks, result visualizations, metric calculations, cross validation, batch evaluations, and parallelized hyperparameter search (grid search and random search).

Keywords: redshift surveys; photometry; support vector machine
The Compact Structures of Massive z ∼ 0.7 Post-starburst Galaxies in the SQuIGG$\vec{L}$E Sample

We present structural measurements of 145 spectroscopically selected intermediate-redshift (z ~ 0.7), massive (M ⋆ ~ 1011 M ⊙) post-starburst galaxies from the $\mathrm{SQuIGG}\vec{L}{\rm{E}}$ sample measured using wide-depth Hyper Suprime-Cam i-band imaging. This deep imaging allows us to probe the sizes and structures of these galaxies, which we compare to a control sample of star-forming and quiescent galaxies drawn from the LEGA-C Survey. We find that post-starburst galaxies systematically lie ~0.1 dex below the quiescent mass-size (half-light radius) relation, with a scatter of ~0.2 dex. This finding is bolstered by nonparametric measures, such as the Gini coefficient and the concentration, which also reveal these galaxies to have more compact light profiles than both quiescent and star-forming populations at similar mass and redshift. The sizes of post-starburst galaxies show either negative or no correlation with the time since quenching, such that more recently quenched galaxies are larger or similarly sized. This empirical finding disfavors the formation of post-starburst galaxies via a purely central burst of star formation that simultaneously shrinks the galaxy and shuts off star formation. We show that the central densities of post-starburst and quiescent galaxies at this epoch are very similar, in contrast with their effective radii. The structural properties of z ~ 0.7 post-starburst galaxies match those of quiescent galaxies that formed in the early universe, suggesting that rapid quenching in the present epoch is driven by a similar mechanism to the one at high redshift.

Keywords: post-starburst galaxies; galaxy quenching; galaxy evolution; quenched galaxies; galaxies
Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) was designed to conduct a survey covering 14,000 deg2 over 5 yr to constrain the cosmic expansion history through precise measurements of baryon acoustic oscillations (BAO). The scientific program for DESI was evaluated during a 5 month survey validation (SV) campaign before beginning full operations. This program produced deep spectra of tens of thousands of objects from each of the stellar Milky Way Survey (MWS), Bright Galaxy Survey (BGS), luminous red galaxy (LRG), emission line galaxy (ELG), and quasar target classes. These SV spectra were used to optimize redshift distributions, characterize exposure times, determine calibration procedures, and assess observational overheads for the 5 yr program. In this paper, we present the final target selection algorithms, redshift distributions, and projected cosmology constraints resulting from those studies. We also present a One-Percent Survey conducted at the conclusion of SV covering 140 deg2 using the final target selection algorithms with exposures of a depth typical of the main survey. The SV indicates that DESI will be able to complete the full 14,000 deg2 program with spectroscopically confirmed targets from the MWS, BGS, LRG, ELG, and quasar programs with total sample sizes of 7.2, 13.8, 7.46, 15.7, and 2.87 million, respectively. These samples will allow exploration of the Milky Way halo, clustering on all scales, and BAO measurements with a statistical precision of 0.28% over the redshift interval z < 1.1, 0.39% over the redshift interval 1.1 < z < 1.9, and 0.46% over the redshift interval 1.9 < z < 3.5.

Keywords: cosmology; redshift surveys
Milky Way Thin and Thick Disk Kinematics with Gaia EDR3 and RAVE DR5

We present a detailed analysis of kinematics of the Milky Way disk in the solar neighborhood using the Gaia DR3 catalog. To determine the local kinematics of the stellar disks of the Milky Way we use a complete sample of 278,228 red giant branch (RGB) stars distributed in a cylinder, centered at the Sun with a 1 kpc radius and half-height of 0.5 kpc. We determine separately the kinematical properties of RGB stars for each Galactic hemisphere in search of possible asymmetries. The kinematical properties of the RGB stars reveal the existence of two kinematically distinct components: the thin disk with mean velocities V R , V ϕ , V Z of about -1, -239, 0 km s-1, correspondingly, and velocity dispersions σ R , σ ϕ , σ Z of 31, 20, and 11 km s-1, and the Thick disk with mean velocity components of about +1, -225, 0 km s-1, and velocity dispersions of 49, 35, and 22 km s-1. We find that up to 500 pc in height above/below the Galactic plane, Thick disk stars comprise about half the stars of the disk. Such a high amount of RGB stars with Thick disk kinematics points at the secular evolution scenario origin for the Thick disk of the Milky Way.

Keywords: milky way disk; stellar kinematics; galaxy structure
Characterizing the Atmospheric Dynamics of HD 209458b-like Hot Jupiters Using AI-driven Image Recognition/Categorization

In order to understand the results of recent observations of exoplanets, models have become increasingly complex. Unfortunately, this increases both the computational cost and output size of said models. We intend to explore if AI image recognition can alleviate this burden. We used DYNAMICO to run a series of HD 209458-like models with different orbital radii. Training data for a number of features of interest was selected from the initial outputs of these models. This was used to train a pair of multi-categorization convolutional neural networks (CNNs), which we applied to our outer-atmosphere-equilibrated models. The features detected by our CNNs revealed that our models fall into two regimes: models with shorter orbital radii exhibit significant global mixing that shapes the dynamics of the entire atmosphere, whereas models with longer orbital-radii exhibit negligible mixing except at mid-pressures. Here the initial nondetection of any trained features revealed a surprise: a nightside hot spot. Analysis suggests that this occurs when rotational influence is sufficiently weak that divergent flows from the dayside to the nightside dominate over rotational-driven transport, such as the equatorial jet. We suggest that image classification may play an important role in future, computational, atmospheric studies. However special care must be paid to the data feed into the model, from the color map, to training the CNN on features with enough breadth and complexity that the CNN can learn to detect them. However, by using preliminary studies and prior models, this should be more than achievable for future exascale calculations, allowing for a significant reduction in future workloads and computational resources.

Keywords: exoplanet atmospheres; exoplanet atmospheric structure
Examining AGN UV/Optical Variability beyond the Simple Damped Random Walk

We present damped harmonic oscillator (DHO) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey Stripe 82 region. DHO is a second-order continuous-time autoregressive moving-average process, which can be fully described using four independent parameters: a natural oscillation frequency (ω 0), a damping ratio (ξ), a characteristic perturbation timescale (τ perturb), and an amplitude for the perturbing white noise (σ ϵ ). The asymptotic variability amplitude of a DHO process is quantified by σ DHO-a function of ω 0, ξ, τ perturb, and σ ϵ . We find that both τ perturb and σ ϵ follow different dependencies with rest-frame wavelength (λ RF) on either side of 2500 Å, whereas σ DHO follows a single power-law relation with λ RF. After correcting for wavelength dependence, σ DHO exhibits anticorrelations with both the Eddington ratio and the black hole mass, while τ perturb-with a typical value of days in the rest frame-shows an anticorrelation with the bolometric luminosity. Modeling active galactic nuclei (AGN) variability as a DHO offers more insight into the workings of accretion disks close to the supermassive black holes at the center of AGN. The newly discovered short-term variability (characterized by τ perturb and σ ϵ ) and its correlation with bolometric luminosity pave the way for new algorithms that will derive fundamental properties (e.g., Eddington ratio) of AGN using photometric data alone.

Keywords: quasars; active galactic nuclei; supermassive black holes; time series analysis; surveys
Particle Dynamics in 3D Self-gravitating Disks. II. Strong Gas Accretion and Thin Dust Disks

Observations suggest that protoplanetary disks have moderate accretion rates onto the central young star, especially at early stages (e.g., HL Tau), indicating moderate disk turbulence. However, recent ALMA observations suggest that dust is highly settled, implying weak turbulence. Motivated by such tension, we carry out 3D stratified local simulations of self-gravitating disks, focusing on the settling of dust particles in actively accreting disks. We find that gravitationally unstable disks can have moderately high accretion rates while maintaining a relatively thin dust disk for two reasons. First, accretion stress from the self-gravitating spirals (self-gravity stress) can be stronger than the stress from turbulence (Reynolds stress) by a factor of 5-20. Second, the strong gravity from the gas to the dust decreases the dust scale height by another factor of ∼2. Furthermore, the turbulence is slightly anisotropic, producing a larger Reynolds stress than the vertical dust diffusion coefficient. Thus, gravitoturbulent disks have unusually high vertical Schmidt numbers (Scz) if we scale the total accretion stress with the vertical diffusion coefficient (e.g., Scz ∼ 10-100). The reduction of the dust scale height by the gas gravity should also operate in gravitationally stable disks (Q > 1). Gravitational forces between particles become more relevant for the concentration of intermediate dust sizes, forming dense clouds of dust. After comparing with HL Tau observations, our results suggest that self-gravity and gravity among different disk components could be crucial for solving the conflict between the protoplanetary disk accretion and dust settling, at least at the early stages.

Keywords: protoplanetary disks; hydrodynamics; gravitation; circumstellar dust