adsabs/SciX_UAT_keywords huggingface dataset:
Effects of Radial Distances on Small-scale Magnetic Flux Ropes in the Solar Wind

Small-scale magnetic flux ropes (SFRs) in the solar wind have been studied for decades. Statistical analysis utilizing various in situ spacecraft measurements is the main observational approach to investigating the generation and evolution of these small-scale structures. Based on the Grad-Shafranov reconstruction technique, we use the automated detection algorithm to build the databases of these small-scale structures via various spacecraft measurements at different heliocentric distances. We present the SFR properties, including the magnetic field and plasma parameters at different radial distances from the Sun near the ecliptic plane. It is found that the event occurrence rate is still of the order of a few hundreds per month, the duration and scale-size distributions follow power laws, and the flux-rope axis orientations are approximately centered around the local Parker spiral directions. In general, most SFR properties exhibit radial decays. In addition, with various databases established, we derive scaling laws for the changes in average field magnitude, event counts, and SFR scale sizes, with respect to the radial distances, ranging from ∼0.3 au for Helios to ∼7 au for the Voyager spacecraft. The implications of our results for comparisons with the relevant theoretical works and for applications to the Parker Solar Probe mission are discussed.

Keywords: solar wind; interplanetary turbulence; magnetohydrodynamics; astronomy data analysis; astronomy databases
The Gaia-ASAS-SN Classical Cepheid Sample. I. Sample Selection

We present a well-defined and characterized all-sky sample of classical Cepheids in the Milky Way, obtained by combining two time-domain all-sky surveys: Gaia DR2 (Gaia Collaboration et al. 2018) and All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014). We first use parallax and variability information from Gaia to select ~30,000 bright (G < 17) Cepheid candidates with MK < - 1. We then analyze their ASAS-SN V-band light curves, determining periods and classifying the light curves using their Fourier parameters. This results in ~1900 likely Galactic Cepheids, which we estimate to be ≳90% complete and pure within our adopted selection criteria. This is the largest all-sky sample of Milky Way Cepheids that has such a well-characterized selection function, needed for population modeling and for systematic spectroscopic follow-up foreseen with Sloan Digital Sky Survey-V. About 130 of these potential Cepheids have not been documented in the literature even as possible candidates.

Keywords: cepheid variable stars; milky way galaxy
Toward Microarcsecond Astrometry for the Innermost Wobbling Jet of the BL Lacertae Object OJ 287

The BL Lacertae object OJ 287 is a very unusual quasar producing a wobbling radio jet and some double-peaked optical outbursts with a possible period of about 12 yr for more than one century. This variability is widely explained by models of binary supermassive black holes (SMBHs) or precessing jets/disks from a single SMBH. To enable an independent and nearly bias-free investigation on these possible scenarios, we explored the feasibility of extremely high-precision differential astrometry on its innermost restless jet at millimeter wavelengths. Through revisiting some existing radio surveys and very long baseline interferometry (VLBI) data at frequencies from 1.4 to 15.4 GHz and performing new Very Long Baseline Array observations at 43.2 GHz, we find that the radio source J0854+1959, 7.'1 apart from OJ 287 and with no clearly seen optical and infrared counterparts, could provide a nearly ideal reference point to track the complicated jet activity of OJ 287. The source J0854+1959 has a stable GHz-peaked radio spectrum and shows a jet structure consisting of two discrete, milliarcsecond-scale-compact and steep-spectrum components and showing no proper motion over about 8 yr. The stable VLBI structure can be interpreted by an episodic, optically thin, and one-sided jet. With respect to its 4.1 mJy peak feature at 43.2 GHz, we have achieved an astrometric precision at the state-of-art level, about 10 μas. These results indicate that future VLBI astrometry on OJ 287 could allow us to accurately locate its jet apex and activity boundary, align its restless jet structure over decades without significant systematic bias, and probe various astrophysical scenarios.

Keywords: supermassive black holes; very long baseline interferometry; radio jets; radio continuum emission
A New Detached Binary USNO-B1.0 1421-0485411 with the Secondary Component having Large Albedo

USNO-B1.0 1421-0485411 is an eclipsing binary system newly discovered in the Yunnan-Hong Kong wide-field photometric survey. Its orbital period is 1.295 days. Based on the V- and R-band photometric data collected at Kunming 1.0 m telescope and spectroscopic data observed at Lijiang 2.4 m telescope, we used the Wilson-Devinney program to determine the physical parameters of the binary system. The results show that the mass and radius are 2.21 M ⊙ and 1.70 R ⊙ for the A0V primary component, and 2.11 M ⊙ and 1.77 R ⊙ for the A4-5V secondary one. The observed light curves show higher shoulders around the secondary eclipse, which can originate from hot spots, circumstellar materials, abnormal albedo of the secondary component, etc. Through analyzing and modeling, a quite large albedo (~1.89) of the secondary component was considered to be the most possible reason for this phenomenon. The position of the two components on the H-R diagram implies that the binary is in main-sequence stage.

Keywords: close binary stars; photometry; spectroscopy; fundamental parameters of stars
Stellar Collapse Diversity and the Diffuse Supernova Neutrino Background

The diffuse cosmic supernova neutrino background (DSNB) is an observational target of the gadolinium-loaded Super-Kamiokande (SK) detector and the forthcoming JUNO and Hyper-Kamiokande detectors. Current predictions are hampered by our still incomplete understanding of the supernova (SN) explosion mechanism and of the neutron star (NS) equation of state and maximum mass. In our comprehensive study we revisit this problem on grounds of the landscapes of successful and failed SN explosions obtained by Sukhbold et al. and Ertl et al. with parameterized one-dimensional neutrino engines for large sets of single-star and helium-star progenitors, with the latter serving as a proxy for binary evolution effects. Besides considering engines of different strengths, leading to different fractions of failed SNe with black hole (BH) formation, we also vary the NS mass limit and the spectral shape of the neutrino emission and include contributions from poorly understood alternative NS formation channels, such as accretion-induced and merger-induced collapse events. Since the neutrino signals of our large model sets are approximate, we calibrate the associated degrees of freedom by using state-of-the-art simulations of proto-NS cooling. Our predictions are higher than other recent ones because of a large fraction of failed SNe with long delay to BH formation. Our best-guess model predicts a DSNB ${\bar{\nu }}_{{\rm{e}}}$ <!-- --> -flux of ${28.8}_{-10.9}^{+24.6}$ <!-- --> cm-2 s-1 with ${6.0}_{-2.1}^{+5.1}$ <!-- --> cm-2 s-1 in the favorable measurement interval of [10, 30] MeV and ${1.3}_{-0.4}^{+1.1}$ <!-- --> cm-2 s-1 with ${\bar{\nu }}_{{\rm{e}}}$ <!-- --> energies > 17.3 MeV, which is roughly a factor of two below the current SK limit. The uncertainty range is dominated by the still insufficiently constrained cosmic rate of stellar core-collapse events.

Keywords: diffuse radiation; supernova neutrinos; core-collapse supernovae; massive stars; black holes
Exploring the Origin of Solar Energetic Electrons. I. Constraining the Properties of the Acceleration Region Plasma Environment

Solar flare electron acceleration is an efficient process, but its properties (mechanism, location) are not well constrained. Via hard X-ray (HXR) emission, we routinely observe energetic electrons at the Sun, and sometimes we detect energetic electrons in interplanetary space. We examine if the plasma properties of an acceleration region (size, temperature, density) can be constrained from in situ observations, helping to locate the acceleration region in the corona, and infer the relationship between electrons observed in situ and at the Sun. We model the transport of energetic electrons, accounting for collisional and non-collisional effects, from the corona into the heliosphere (to 1.0 au). In the corona, electrons are transported through a hot, over-dense region. We test if the properties of this region can be extracted from electron spectra (fluence and peak flux) at different heliospheric locations. We find that cold, dense coronal regions significantly reduce the energy at which we see the peak flux and fluence for distributions measured out to 1.0 au, the degree of which correlates with the temperature and density of plasma in the region. Where instrument energy resolution is insufficient to differentiate the corresponding peak values, the spectral ratio of [7-10) to [4-7) keV can be more readily identified and demonstrates the same relationship. If flare electrons detected in situ are produced in, and/or transported through, hot, over-dense regions close to HXR-emitting electrons, then this plasma signature should be present in their lower-energy spectra (1-20 keV), observable at varying heliospheric distances with missions such as Solar Orbiter.

Keywords: solar flares; solar energetic particles; heliosphere; active solar corona
Lagrangian Perspectives on the Small-scale Structure of Alfvénic Turbulence and Stochastic Models for the Dispersion of Fluid Particles and Magnetic Field Lines in the Solar Wind

Lagrangian perspectives on the small-scale structure of anisotropic Alfvénic turbulence are adopted. We are interested in relating the statistical properties of the Eulerian field increments evaluated along the fluid particle trajectories, in the direction perpendicular to the guiding magnetic field and along the magnetic field lines. We establish the basis for a unified multifractal phenomenology of Eulerian and Lagrangian Alfvénic turbulence. The critical balance condition is generalized to structure functions of an order different than 2. A Lagrangian perspective is not only useful for investigating the small-scale structure of Alfvénic turbulence, it is also tailored to the modeling of large-scale turbulent transport. Therefore, we develop Lagrangian stochastic models for the dispersion of fluid particles and magnetic field lines in the solar wind. The transport models are based on the integrated Ornstein–Uhlenbeck process that is not Markov, yielding smooth stochastic fluid particle trajectories and magnetic field lines. Brownian diffusion is recovered by tending the integral scale parameter to zero while keeping the diffusivity finite.

Keywords: interplanetary turbulence; solar wind; solar energetic particles; magnetohydrodynamics
Filling the Magnetospheres of Weak Pulsars

Recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using particle-in-cell techniques. These ab initio simulations seem to indicate that pair creation through photon-photon collision at the light cylinder is required to sustain the pulsar engine. However, for many rotation-powered pulsars, pair creation operates effectively only near the stellar surface where magnetic field is high. How these "weak pulsars" fill their magnetospheres without efficient photon-photon pair conversion in the outer magnetosphere is still an open question. In this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. When pair production is very efficient near the star, the pulsar magnetosphere converges to previously reported solutions. However, in the intermediate regime, where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with a quasi-period about half of the rotation period. This new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core versus conal emission patterns observed in pulsar radio signals.

Keywords: plasma astrophysics; rotation powered pulsars; magnetic fields; neutron stars
Spiral Structure Boosts Star Formation in Disk Galaxies

We investigate the impact of spiral structure on global star formation using a sample of 2226 nearby bright disk galaxies. Examining the relationship between spiral arms, star formation rate (SFR), and stellar mass, we find that arm strength correlates well with the variation of SFR as a function of stellar mass. Arms are stronger above the star-forming galaxy main sequence (MS) and weaker below it: arm strength increases with higher $\mathrm{log}(\mathrm{SFR}/{\mathrm{SFR}}_{\mathrm{MS}})$ , where SFRMS is the SFR along the MS. Likewise, stronger arms are associated with higher specific SFR. We confirm this trend using the optical colors of a larger sample of 4378 disk galaxies, whose position on the blue cloud also depends systematically on spiral arm strength. This link is independent of other galaxy structural parameters. For the subset of galaxies with cold gas measurements, arm strength positively correlates with H I and H2 mass fraction, even after removing the mutual dependence on $\mathrm{log}(\mathrm{SFR}/{\mathrm{SFR}}_{\mathrm{MS}})$ , consistent with the notion that spiral arms are maintained by dynamical cooling provided by gas damping. For a given gas fraction, stronger arms lead to higher $\mathrm{log}(\mathrm{SFR}/{\mathrm{SFR}}_{\mathrm{MS}})$ , resulting in a trend of increasing arm strength with shorter gas depletion time. We suggest a physical picture in which the dissipation process provided by gas damping maintains spiral structure, which, in turn, boosts the star formation efficiency of the gas reservoir.

Keywords: galaxy evolution; spiral arms; spiral galaxies; galaxy structure; star formation; interstellar medium
Element Abundances in the Unshocked Ejecta of Cassiopeia A

We analyze and model the infrared spectrum of the Cassiopeia A supernova remnant with the aim of determining the masses of various elements in the unshocked ejecta. In this way, we complement the survey of the X-ray-emitting ejecta to provide a complete census of the elemental composition of the Cas A ejecta. We calculate photoionization-recombination equilibria to determine the ionization balance of various elements in the ejecta as a function of density using the X-ray and UV emission from the forward and reverse shocks as the ionizing radiation. With the assumption that all emission lines are principally excited at the ejecta density that maximizes their emission, we can convert observed line intensities into element masses. We find that the majority of the ∼3 M⊙ ejecta have already been through the reverse shock and are seen today in X-rays. A minority, ∼0.47 ± 0.05 M⊙, with uncertainties quoted here coming from the data fitting procedure only, are still expanding inside the reverse shock and emitting in the infrared. This component is comprised mainly of O, Si, and S, with no Fe readily detectable. Incorporating uncertainties estimated to come from our modeling, we quote $0.47{\pm }_{0.24}^{0.47}$ M⊙. We speculate that up to a further 0.07 M⊙ of Fe may be present in diffuse gas in the inner ejecta, depending on the Fe charge state.

Keywords: supernova remnants; core-collapse supernovae; chemical abundances; shocks; plasma astrophysics; high energy astrophysics
The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass–Metallicity Relation for Low-mass Galaxies at z ∼ 1–2

Using more than 100 galaxies in the MUSE Ultra Deep Field with spectroscopy from the Hubble Space Telescope's (HST) Wide Field Camera 3 and the Very Large Telescope's Multi Unit Spectroscopic Explorer, we extend the gas-phase mass–metallicity relation (MZR) at z ≈ 1–2 down to stellar masses of M ⋆ ≈ 107.5 M ⊙. The sample reaches 6 times lower in stellar mass and star formation rate (SFR) than previous HST studies at these redshifts, and we find that galaxy metallicities decrease to log(O/H) + 12 ≈ 7.8 ± 0.1 (15% solar) at log(M ⋆/M ⊙) ≈ 7.5, without evidence of a turnover in the shape of the MZR at low masses. We validate our strong-line metallicities using the direct method for sources with [O III] λ4363 and [O III] λ1666 detections, and find excellent agreement between the techniques. The [O III] λ1666-based metallicities double existing measurements with a signal-to-noise ratio ≥ 5 for unlensed sources at z > 1, validating the strong-line calibrations up to z ∼ 2.5. We confirm that the MZR resides ∼0.3 dex lower in metallicity than local galaxies and is consistent with the fundamental metallicity relation if the low-mass slope varies with SFR. At lower redshifts (z ∼ 0.5) our sample reaches ∼0.5 dex lower in SFR than current calibrations and we find enhanced metallicities that are consistent with extrapolating the MZR to lower SFRs. Finally, we detect only an ∼0.1 dex difference in the metallicities of galaxies in groups versus isolated environments. These results are based on robust calibrations and reach the lowest masses and SFRs that are accessible with HST, providing a critical foundation for studies with the Webb and Roman Space Telescopes.

Keywords: star formation; metallicity; high-redshift galaxies; galaxy environments; galaxy evolution; galaxy chemical evolution; galaxy abundances
DESI z ≳ 5 Quasar Survey. I. A First Sample of 400 New Quasars at z 4.7-6.6

We report the first results of a high-redshift (z ≳ 5) quasar survey using the Dark Energy Spectroscopic Instrument (DESI). As a DESI secondary target program, this survey is designed to carry out a systematic search and investigation of quasars at 4.8 < z < 6.8. The target selection is based on the DESI Legacy Imaging Surveys (the Legacy Surveys) DR9 photometry, combined with the Pan-STARRS1 data and J-band photometry from public surveys. A first quasar sample has been constructed from the DESI Survey Validation 3 (SV3) and first-year observations until 2022 May. This sample includes more than 400 new quasars at redshift 4.7 ≤ z < 6.6, down to 21.5 magnitude (AB) in the z band, discovered from 35% of the entire target sample. Remarkably, there are 220 new quasars identified at z ≥ 5, more than one-third of existing quasars previously published at this redshift. The observations so far result in an average success rate of 23% at z > 4.7. The current spectral data set has already allowed analysis of interesting individual objects (e.g., quasars with damped Lyα absorbers and broad absorption line features), and statistical analysis will follow the survey's completion. A set of science projects will be carried out leveraging this program, including quasar luminosity function, quasar clustering, intergalactic medium, quasar spectral properties, intervening absorbers, and properties of early supermassive black holes. Additionally, a sample of 38 new quasars at z ~ 3.8-5.7 discovered from a pilot survey in the DESI SV1 is also published in this paper.

Keywords: quasars; surveys; broad-absorption line quasar
From Images to Dark Matter: End-to-end Inference of Substructure from Hundreds of Strong Gravitational Lenses

Constraining the distribution of small-scale structure in our universe allows us to probe alternatives to the cold dark matter paradigm. Strong gravitational lensing offers a unique window into small dark matter halos (<1010 M ⊙) because these halos impart a gravitational lensing signal even if they do not host luminous galaxies. We create large data sets of strong lensing images with realistic low-mass halos, Hubble Space Telescope (HST) observational effects, and galaxy light from HST's COSMOS field. Using a simulation-based inference pipeline, we train a neural posterior estimator of the subhalo mass function (SHMF) and place constraints on populations of lenses generated using a separate set of galaxy sources. We find that by combining our network with a hierarchical inference framework, we can both reliably infer the SHMF across a variety of configurations and scale efficiently to populations with hundreds of lenses. By conducting precise inference on large and complex simulated data sets, our method lays a foundation for extracting dark matter constraints from the next generation of wide-field optical imaging surveys.

Keywords: strong gravitational lensing; cosmology; dark matter; convolutional neural networks; hierarchical models; dark matter distribution
The Rapid Optical Variability of the Nearby Radio-loud AGN Pictor A: Introducing the Quaver Pipeline for AGN Science with TESS

The sampling strategy of the Transiting Exoplanet Survey Satellite (TESS) makes TESS light curves extremely valuable for investigating the high cadence optical variability of active galactic nuclei (AGN). However, because the TESS instrument was primarily designed for exoplanet science, the use of the satellite for other applications requires careful treatment of the data. In this paper, we introduce Quaver, a new software tool designed specifically to extract TESS light curves of extended and faint sources presenting stochastic variability. We then use this new tool to extract light curves of the nearby radio-loud AGN Pictor A, and perform a temporal and power spectral analysis of its high-cadence optical variability. The obtained light curves are well fit with a damped random walk (DRW) model, exhibiting both stochastic AGN variations and flaring behavior. The DRW characteristic timescales are τ DRW ~ 3-6 days during more quiet periods, and τ DRW ~ 0.8 day for periods with strong flares, even when the flares themselves are masked from the DRW fit. The observed timescales are consistent with the dynamical, orbital, and thermal timescales expected for the low black hole mass of Pictor A.

Keywords: active galactic nuclei; radio active galactic nuclei; astronomy software
Asteroseismic Study of KUV03442+0719 with Parallax Constraints

Hydrogen atmosphere white dwarf KUV03442+0719 was first reported as a pulsator by Gianninas et al. in 2006. Follow-up campaigns by Su et al. revealed more periods. Some spectroscopic results suggest that KUV03442+0719 has a slightly below-average mass and an effective temperature of 11,000 K. However, Gaia data (parallax and magnitude) suggest that it may be a low-mass white dwarf. Such an object would have a helium core. We perform asteroseismic fitting of KUV03442+0719, modeling it both as a carbon/oxygen normal mass white dwarf, and a helium-core low-mass white dwarf. To perform the study, we perform a grid search with WDEC models, refined by simplex minimization of the best fits. Both analyses result in best-fit models that are comparable in terms of quality of fit. More pulsation data would be required to allow us to distinguish between the two scenarios. We present and contrast our results with expectations from stellar evolution. We also provide analytic formulae for a temperature-dependent mass-radius relationship for helium-core white dwarfs.

Keywords: white dwarf stars; periodic variable stars; compact objects; da stars; asteroseismology; stellar astronomy; stellar oscillations