adsabs/SciX_UAT_keywords huggingface dataset:
Application and Interpretation of Deep Learning for Identifying Pre-emergence Magnetic Field Patterns

Magnetic flux generated within the solar interior emerges to the surface, forming active regions (ARs) and sunspots. Flux emergence may trigger explosive events—such as flares and coronal mass ejections, and therefore understanding emergence is useful for space-weather forecasting. Evidence of any pre-emergence signatures will also shed light on subsurface processes responsible for emergence. In this paper, we present a first analysis of EARs from the Solar Dynamics Observatory/Helioseismic Emerging Active Regions dataset using deep convolutional neural networks (CNN) to characterize pre-emergence surface magnetic field properties. The trained CNN classifies between pre-emergence line-of-sight magnetograms and a control set of nonemergence magnetograms with a true skill statistic (TSS) score of approximately 85% about 3 hr prior to emergence and approximately 40% about 24 hr prior to emergence. Our results are better than a baseline classification TSS obtained using discriminant analysis (DA) of only the unsigned magnetic flux, although a multivariable DA produces TSS values consistent with the CNN. We develop a network-pruning algorithm to interpret the trained CNN and show that the CNN incorporates filters that respond positively as well as negatively to the unsigned magnetic flux of the magnetograms. Using synthetic magnetograms, we demonstrate that the CNN output is sensitive to the length scale of the magnetic regions, with small-scale and intense fields producing maximum CNN output and possibly a characteristic pre-emergence pattern. Given increasing popularity of deep learning, the techniques developed here to interpret the trained CNN—using network pruning and synthetic data—are relevant for future applications in solar and astrophysical data analysis.

Keywords: solar magnetic flux emergence; convolutional neural networks; solar active region magnetic fields; astronomy data analysis
A New Spin on an Old Black Hole: NuSTAR Spectroscopy of EXO 1846-031

The black hole candidate EXO 1846-031 underwent an outburst in 2019, after at least 25 yr in quiescence. We observed the system using NuSTAR on 2019 August 3. The 3-79 keV spectrum shows strong relativistic reflection features. Our baseline model gives a nearly maximal black hole spin value of $a={0.997}_{-0.002}^{+0.001}$ (1σ statistical errors). This high value nominally excludes the possibility of the central engine harboring a neutron star. Using several models, we test the robustness of our measurement to assumptions about the density of the accretion disk, the nature of the corona, the choice of disk continuum model, and the addition of reflection from the outer regions of the accretion disk. All tested models agree on a very high black hole spin value and a high value for the inclination of the inner accretion disk of $\theta \approx 73^\circ $ . We discuss the implications of this spin measurement in the population of stellar mass black holes with known spins, including LIGO and Virgo events.

Keywords: black hole physics; low-mass x-ray binary stars; x-ray binary stars; accretion; stellar accretion disks
GASP. XXXIII. The Ability of Spatially Resolved Data to Distinguish among the Different Physical Mechanisms Affecting Galaxies in Low-density Environments

Galaxies inhabit a wide range of environments and therefore are affected by different physical mechanisms. Spatially resolved maps combined with the knowledge of the hosting environment are very powerful for classifying galaxies by physical process. In the context of the GAs Stripping Phenomena in galaxies (GASP), we present a study of 27 non-cluster galaxies: 24 of them were selected for showing asymmetries and disturbances in the optical morphology, suggestive of gas stripping; 3 of them are passive galaxies and were included to characterize the final stages of galaxy evolution. We therefore provide a panorama of the different processes taking place in low-density environments. The analysis of VLT/MUSE data allows us to separate galaxies into the following categories: galaxy-galaxy interactions (2 galaxies), mergers (6), ram pressure stripping (4), cosmic web stripping (2), cosmic web enhancement (5), gas accretion (3), and starvation (3). In one galaxy we identify the combination of merger and ram pressure stripping. Only 6/27 of these galaxies have just a tentative classification. We then investigate where these galaxies are located on scaling relations determined for a sample of undisturbed galaxies. Our analysis shows the successes and limitations of a visual optical selection in identifying the processes that deplete galaxies of their gas content and probes the power of IFU data in pinning down the acting mechanism.

Keywords: galaxies; field galaxies; galaxy evolution; galaxy formation; galaxy groups; star formation; stellar kinematics
Revisited Cold Gas Content with Atomic Carbon [C I] in z = 2.5 Protocluster Galaxies

We revisit the cold gas contents of galaxies in a protocluster at z = 2.49 using the lowest neutral atomic carbon transition [C I] 3P1 - 3P0 from Atacama Large Millimeter/submillimeter Array observations. We aim to test if the same gas-mass calibration adopted in field galaxies can be applied to protocluster galaxies. Five galaxies out of 16 targeted galaxies are detected in the [C I] line, and these are all previously detected in CO (3-2) and CO (4-3) and three in 1.1 mm dust continuum. We investigate the line luminosity relations between CO and [C I] in the protocluster and compare with other previous studies. We then compare the gas mass based on three gas tracers of [C I], CO(3-2), and dust if at least one of the last two tracers are available. Using the calibration adopted for field main-sequence galaxies, the [C I]-based gas measurements are lower than or comparable to the CO-based gas measurements by -0.35 dex at the lowest with the mean deviation of -0.14 dex. The differences between [C I]- and the dust- based measurements are relatively mild by up to 0.16 dex with the mean difference of 0.02 dex. Taking these all together with calibration uncertainties, with the [C I] line, we reconfirm our previous findings that the mean gas fraction is comparable to field galaxies for a stellar-mass range of $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })=[10.6,11.3]$ <!-- --> . However, at least for these secure five detections, the depletion timescale decreases more rapidly with stellar mass than field galaxies that might be related to earlier quenching in dense environments.

Keywords: interstellar medium; high-redshift galaxy clusters; galaxy evolution; star formation
Modeling Unresolved Binaries of Open Clusters in the Color-Magnitude Diagram. I. Method and Application of NGC 3532

The binary properties of open clusters place crucial constraints on star formation theory and clusters' dynamical evolution. We develop a comprehensive approach that models the color-magnitude diagram (CMD) of the cluster members as a mixture of single stars and photometric unresolved binaries. This method enables us to infer the binary properties, including the binary fraction fb and binary mass ratio distribution index γq when a power law is assumed, with high accuracy and precision, which was unfeasible in conventional methods. We employ a modified Gaussian process to determine the main-sequence ridgeline and its scatter from the observed CMD as model input. As a first example, we apply the method to the open cluster NGC 3532 with the Gaia DR2 photometry. For the cluster members within a magnitude range corresponding to FGK dwarfs, we obtain fb = 0.267 ± 0.019 and γq = -0.10 ± 0.22 for binaries with mass ratio q > 0.2. The fb value is consistent with the previous work on NGC 3532 and smaller than that of field stars. The close-to-zero γq indicates that the mass ratios of binaries follow a nearly uniform distribution. For the first time, we unveil that the stars with smaller mass or in the inner region tend to have lower fb and a more positive value of γq due to the lack of low mass ratio binaries. The clear dependences of binary properties on mass and radius are most likely caused by the internal dynamics. In this scheme, binaries with smaller primary mass or lower mass ratio have smaller binding energy; hence, they are more vulnerable to dynamical disruption, especially in the inner region where stars interact more frequently.

Keywords: open star clusters; binary stars; mixture model
Nonequilibrium Equation of State in Stellar Atmospheres

In the stellar chromospheres, radiative energy transport is dominated by only the strongest spectral lines. For these lines, the approximation of local thermodynamic equilibrium (LTE) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. To calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated explicitly, including all time-dependent terms. We develop a numerical method to solve the evolution equation for the atomic-level populations in a time-implicit way, keeping all time-dependent terms to first order. We show that the linear approximation of the time dependence of the populations can handle very large time steps without losing accuracy. We reproduce the benchmark solutions from earlier, well-established works in terms of non-LTE kinetic equilibrium solutions and typical ionization/recombination timescales in the solar chromosphere.

Keywords: radiative magnetohydrodynamics; radiative transfer; radiative transfer simulations; stellar atmospheres; computational methods; solar atmosphere; stellar chromospheres; ionization; solar chromosphere; recombination; spectroscopy; theoretical techniques
Properties of Solar Rossby Waves from Normal Mode Coupling and Characterizing Its Systematics

Rossby waves play an important role in mediating the angular momentum of rotating spherical fluids, creating weather on Earth and tuning exoplanet orbits in distant stellar systems. Their recent discovery in the solar convection zone provides an exciting opportunity to appreciate the detailed astrophysics of Rossby waves. Large-scale Rossby waves create subtle drifts in acoustic oscillations in the convection zone, which we measure using helioseismology to image properties of Rossby waves in the interior. We analyze 20 yr of space-based observations, from 1999 to 2018, to measure Rossby-mode frequencies, line widths, and amplitudes. Spatial leakage affects the measurements of normal-mode eigenfunction coupling (which we refer to as "normal-mode coupling" in this paper) and complicates the analysis of separating out specific harmonic degree and azimuthal number of features on the Sun. Here we demonstrate a novel approach to overcome this difficulty and test it by performing synthetic tests. We find that the rms velocity of the modes is of the order of 0.5 m s-1 at the surface.

Keywords: helioseismology; astronomical techniques; internal waves; solar photosphere; solar interior; observational astronomy
Radiation-induced D-to-H Exchange in Ices Containing Ethane or Benzene: Reactions and Rate Constants

The rate constants for radiation-induced deuterium to hydrogen (D-to-H) exchange were recently measured for CD4 in H2O and C2D6 in H2O at 20 K. In the current study, rate constants for radiation-induced D-to-H exchange were obtained for C6D6 in H2O at 20, 50, and 100 K. The rate constants for D-to-H exchange for an organic molecule in water were found to be an order of magnitude greater for benzene than ethane. Additionally, D-to-H exchange for benzene was found to be far more favorable than the production of any other radiolysis product, a result that contrasts with our previous findings for methane and ethane. Finally, rate constants were obtained for C2D6 in H2O at 50 K. For all ice mixtures, increasing the temperature of the experiment yielded a larger rate constant. There is a notable difference in the magnitude of the response of the rate constant for D-to-H exchange as a function of temperature for C2D6 versus C6D6 containing ices. The results suggest that radiation will have an asymmetric effect on D-to-H exchange between different types of organic compounds and water ice matrices. These results suggest that the radiation history of an extraterrestrial sample will influence the D/H ratios of its organic compounds.

Keywords: astrochemistry; reaction rates
The Dragonfly Wide Field Survey. I. Telescope, Survey Design, and Data Characterization

We present a description of the Dragonfly Wide Field Survey (DWFS), a deep photometric survey of a wide area of sky. The DWFS covers 330 deg2 in the equatorial GAMA fields and the Stripe 82 fields in the SDSS g and r bands. It is carried out with the 48-lens Dragonfly Telephoto Array, a telescope that is optimized for the detection of low surface brightness emission. The main goal of the survey is to study the dwarf galaxy population beyond the Local Group. In this paper, we describe the survey design and show early results. We reach 1σ depths of μg ≈ 31 mag arcsec-2 on arcminute scales and show that Milky Way satellites such as Sextans, Bootes, and Ursa Major should be detectable out to D ≳ 10 Mpc. We also provide an overview of the elements and operation of the 48-lens Dragonfly telescope and a detailed description of its data reduction pipeline. The pipeline is fully automated, with individual frames subjected to a rigorous series of quality tests. The sky subtraction is performed in two stages, ensuring that emission features with spatial scales up to ∼0°9 × 0°6 are preserved. The DWFS provides unparalleled sensitivity to low surface brightness features on arcminute scales.

Keywords: surveys; galaxy counts; dwarf galaxies; automated telescopes; low surface brightness galaxies; galaxies; field galaxies
Measurement of the Rate Distribution of the Population of Repeating Fast Radio Bursts: Implications for Progenitor Models

The discovery of many repeating fast radio bursts (FRBs) by the Canadian Hydrogen Intensity Mapping Experiment, the high rate of individual bursts, and the observation of repeat bursts from a bright FRB initially detected by the Australian Square Kilometre Array Pathfinder (ASKAP) suggest a significant population of repeating FRBs. Here, we analyze the rate distribution of this population using results from follow-up observations of the Commensal Real-time ASKAP Fast Transients Survey. Characterizing a repeating FRB by its burst rate R0 above an energy of 1038 erg, we consider a volumetric density Φ(R0) with rate distribution $d{\rm{\Phi }}\propto {R}_{0}^{\zeta }{{dR}}_{0}$ . We use maximum-likelihood methods to constrain ζ < -1.94 at 90% confidence. We discuss how this constraint can be used to limit different classes of progenitor models for repeating FRBs: it excludes FRBs with burst rate proportional to neutron star spin-down power with braking index n ≤ 14, I.e., magnetic dipole radiation (n = 3); and it excludes some scenarios for FRB emission from magnetars, and the magnetic field interactions of compact binaries.

Keywords: radio transient sources; neutron stars; magnetars; astrostatistics; radio bursts; compact binary stars
Mass-Velocity Dispersion Relation by Using the Gaia Data and Its Effect on Interpreting Short-duration and Degenerate Microlensing Events

Gravitational microlensing, the lensing of stars in the Milky Way with other stars, has been used for exploring compact dark matter objects, exoplanets, and black holes. The duration of microlensing events, the so-called Einstein crossing time, is a function of distance, mass, and velocities of lens objects. Lenses with different ages and masses might have various characteristic velocities inside the Galaxy and this might lead to our misinterpretation of microlensing events. In this work, we use the Gaia archived data to find a relation between the velocity dispersion and mass, and the age of stars. This mass-velocity dispersion relation confirms the known age-velocity relation for early-type and massive stars, and additionally reveals a dependence of stellar velocity dispersion on the mass for low-mass and late-type stars at a 2σ-3σ level. By considering this correlation, we simulate short-duration microlensing events due to brown dwarfs. From this simulation, we conclude that lens masses are underestimated by ~2.5%-5.5% while modeling short-duration and degenerate microlensing events with the Bayesian analysis.

Keywords: gravitational microlensing exoplanet detection; stellar types; gravitational microlensing
Witnessing a Transformation to Blue-cored Dwarf Early-type Galaxies in Filaments and the Cluster Outskirts: Gas-phase Abundances and Internal Kinematics Perspectives

The presence of transitional dwarf galaxies in filaments and cluster outskirts may be closely related to preprocessing in the filament; however, the underlying mechanism is not yet comprehensively understood. We present the spatially resolved chemical and kinematical properties of three blue-cored dwarf early-type galaxies (dE(bc)s) in the Virgo cluster and Virgo-related filaments (Crater and Virgo III) using the Sydney-AAO Multi-object Integral-field spectrograph galaxy Survey. We map the spatial distribution of Hα, oxygen abundance (O/H), nitrogen-to-oxygen abundance ratio (N/O), stellar population age, and gas-stellar internal kinematics. We find irregular shapes of enhanced star-forming regions from the centers to the outlying regions of blue cores in dE(bc)s. These regions are relatively metal poor compared with the surrounding regions, rendering the overall metallicity gradient of each galaxy positive. Furthermore, they exhibit higher N/O ratios at a given O/H relative to their surroundings, implying metal-poor gas infall by external processes. The equivalent width of the Hα emission line in metal-poor regions indicates young age of star formation, 6-8 Myr. The disturbed ionized gas velocity field, one of the most prominent features of galaxy mergers is also discovered in two dE(bc)s. We propose that a moderately dense filament environment is favorable for the formation of blue cores in dEs, in which dE(bc)s in filaments may have already been transformed before they fall into the Virgo cluster. This process may contribute to the composition of galaxy population at the outskirts of the cluster.

Keywords: extragalactic astronomy; star formation; galaxy chemical evolution; galaxy evolution; large-scale structure of the universe; dwarf elliptical galaxies; stellar kinematics
Surveying the X-Ray Behavior of Novae as They Emit γ-Rays

The detection of GeV γ-ray emission from Galactic novae by the Fermi-Large Area Telescope has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to ∼107 K, resulting in detectable X-ray emission. In this paper, we investigate 13 γ-ray emitting novae observed with the Neil Gehrels Swift Observatory, searching for 1-10 keV X-ray emission concurrent with γ-ray detections. We also analyze γ-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence of hot shocked plasma, but not until the γ-rays have faded below detectability. We suggest that the delayed rise of the X-ray emission is due to large absorbing columns and/or X-ray suppression by corrugated shock fronts. The only nova in our sample with a concurrent X-ray/γ-ray detection is also the only embedded nova (V407 Cyg). This exception supports a scenario where novae with giant companions produce shocks with external circumbinary material and are characterized by lower density environments, in comparison with novae with dwarf companions where shocks occur internal to the dense ejecta.

Keywords: classical novae; novae; x-ray astronomy; cataclysmic variable stars; white dwarf stars; gamma-ray astronomy; gamma-ray transient sources; symbiotic binary stars; high energy astrophysics; observational astronomy; shocks
MOSEL: Strong [OIII] 5007 Å Emitting Galaxies at (3 < z < 4) from the ZFOURGE Survey

To understand how strong emission-line galaxies (SELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target SELGs from the ZFOURGE imaging survey that have blended Hβ+[O III] rest-frame equivalent widths of >230 Å and 2.5 < ${z}_{\mathrm{phot}}$ < 4.0. Using Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than Ks = 25 mag as part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our spectroscopic success rate is ∼53% and ${z}_{\mathrm{phot}}$ uncertainty is ${\sigma }_{z}$ = [Δz/(1+z)] = 0.0135. We confirm 31 ELGs at $3\lt {z}_{\mathrm{spec}}\lt 3.8$ , and show that SELGs have spectroscopic rest-frame [O III]5007 Å equivalent widths of 100-500 Å and tend to be lower-mass systems [ $\mathrm{log}({M}_{\star }/{M}_{\odot })$ ∼ 8.2-9.6] compared with more typical star-forming galaxies. The SELGs lie ∼0.9 dex above the star-forming main sequence at z ∼ 3.5 and have high inferred gas fractions of ${f}_{\mathrm{gas}}$ ≳ 60%, i.e., the inferred gas masses can easily fuel a starburst to double stellar masses within ∼10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that (1) strong [O III]5007 Å emission signals an early episode of intense stellar growth in low-mass [ ${M}_{\star }\lt 0.1\,{M}^{\star }$ ] galaxies and (2) many, if not most, galaxies at z > 3 go through this starburst phase. If true, low-mass galaxies with strong [O III]5007 Å emission (EWrest > 200 Å) may be an increasingly important source of ionizing UV radiation at z > 3.

Keywords: emission line galaxies; galaxy evolution; galaxy formation; starburst galaxies; galaxy properties; near infrared astronomy
ASKAP-EMU Discovery of New Galactic SNR Candidate: Unicycle (G312.65+2.87)

We present the serendipitous discovery of a low surface brightness Galactic supernova remnant candidate, Unicycle (G312.65+2.87). Unicycle was initially discovered in the Evolutionary Map of the Universe large-scale radio survey at 943.5 MHz. We measure a diffuse shell (D = 288″ × 300″) and an integrated flux density of S I 944 MHz = 150 ± 20 mJy. We estimate the most likely intrinsic diameters of 30 < D < 36 pc or 42 < D < 47 pc, corresponding to distances of 10 < d < 12 kpc or 14 < d < 16 kpc, placing it within either the Scutum–Centaurus or outer Sagittarius spiral arms.

Keywords: supernova remnants; radio continuum emission; milky way galaxy
Robust Field-level Inference of Cosmological Parameters with Dark Matter Halos

We train graph neural networks on halo catalogs from Gadget N-body simulations to perform field-level likelihood-free inference of cosmological parameters. The catalogs contain ≲5000 halos with masses ≳1010 h -1 M ⊙ in a periodic volume of ${(25\,{h}^{-1}\,\mathrm{Mpc})}^{3}$ ; every halo in the catalog is characterized by several properties such as position, mass, velocity, concentration, and maximum circular velocity. Our models, built to be permutationally, translationally, and rotationally invariant, do not impose a minimum scale on which to extract information and are able to infer the values of Ωm and σ 8 with a mean relative error of ~6%, when using positions plus velocities and positions plus masses, respectively. More importantly, we find that our models are very robust: they can infer the value of Ωm and σ 8 when tested using halo catalogs from thousands of N-body simulations run with five different N-body codes: Abacus, CUBEP3M, Enzo, PKDGrav3, and Ramses. Surprisingly, the model trained to infer Ωm also works when tested on thousands of state-of-the-art CAMELS hydrodynamic simulations run with four different codes and subgrid physics implementations. Using halo properties such as concentration and maximum circular velocity allow our models to extract more information, at the expense of breaking the robustness of the models. This may happen because the different N-body codes are not converged on the relevant scales corresponding to these parameters.

Keywords: cosmology; sigma8; density parameters; cosmological parameters from large-scale structure