adsabs/SciX_UAT_keywords huggingface dataset:
Flare Activity and Magnetic Feature Analysis of the Flare Stars. II. Subgiant Branch

We present an investigation of the magnetic activity and flare characteristics of the subgiant stars mostly from F and G spectral types and compare the results with the main-sequence (MS) stars. The light curve of 352 stars on the subgiant branch (SGB) from the Kepler mission is analyzed in order to infer stability, relative coverage, and contrast of the magnetic structures and also flare properties using three flare indexes. The results show the following. (i) Relative coverage and contrast of the magnetic features along with rate, power, and magnitude of flares increase on the SGB due to the deepening of the convective zone and more vigorous magnetic field production. (ii) Magnetic activity of the F- and G-type stars on the SGB does not show dependency on the rotation rate and does not obey the saturation regime. This is the opposite of what we saw for the MS, in which the G-, K-, and M-type stars show clear dependency on the Rossby number. (iii) The positive relationship between the magnetic features' stability and their relative coverage and contrast remains true on the SGB; though, it has a lower dependency coefficient in comparison with the MS. (iv) Magnetic proxies and flare indexes of the SGB stars increase with increasing relative mass of the convective zone.

Keywords: magnetic stars; flare stars; stellar activity; f subgiant stars; g subgiant stars; k subgiant stars; main sequence; starspots
Asymmetric Distribution of the Solar Photospheric Magnetic-Field Values

Understanding the characteristics of the solar magnetic field is essential for interpreting solar activities and dynamo. In this research, we investigated the asymmetric distribution of the solar photospheric magnetic-field values, using synoptic charts constructed from space-borne high-resolution magnetograms. It is demonstrated that the Lorentzian function describes the distribution of magnetic-field values in the synoptic charts much better than the Gaussian function and this should reflect the gradual decay process from strong to weak magnetic fields. The asymmetry values are calculated under several circumstances, and the results generally show two periodicities related to the variation of the solar B0 angle and the solar cycle, respectively. We argue that it is the small-scale magnetic fields, the inclination of the solar axis, the emergence and evolution of magnetic flux, and the polar fields that are responsible for the features of asymmetry values. We further determined the polar-field reversal time of solar cycles 23 and 24 with the flip of asymmetry values. Specifically, for cycle 24, we assert that the polar polarities of both hemispheres reversed at the same time-in 2014 March; as to cycle 23, the reversal time of the S-hemisphere is 2001 March, while the determination of the N-hemisphere is hampered by missing data.

Keywords: solar magnetic fields; solar photosphere; solar activity
The Supersonic Project: Lighting Up the Faint End of the JWST UV Luminosity Function

The James Webb Space Telescope (JWST) is capable of probing extremely early eras of our Universe, when the supersonic relative motions between dark matter and baryonic overdensities modulate structure formation (z ≳ 10). We study low-mass galaxy formation, including this "stream velocity," using high-resolution AREPO hydrodynamics simulations and present theoretical predictions of the UV luminosity function (UVLF) and galaxy stellar mass function down to extremely faint and low-mass galaxies (M UV ≳ -15, 104 M ⊙ ≤ M * ≤ 108 M ⊙). We show that, although the stream velocity suppresses early star formation overall, it induces a short period of rapid star formation in some larger dwarfs, leading to an enhancement in the faint end of the UVLF at z = 12. We demonstrate that JWST observations are close to this enhanced regime and propose that the UVLF may constitute an important probe of the stream velocity at high redshift for JWST and future observatories.

Keywords: high-redshift galaxies; primordial galaxies; luminosity function; james webb space telescope; hydrodynamical simulations
Sudden Extreme Obscuration of a Sun-like Main-sequence Star: Evolution of the Circumstellar Dust around ASASSN-21qj

ASASSN-21qj is a distant Sun-like star that recently began an episode of deep dimming events after no prior recorded variability. Here we examine archival and newly obtained optical and near-infrared data of this star. The deep aperiodic dimming and absence of previous infrared excess are reminiscent of KIC 8462852 ("Boyajian's Star"). The observed occultations are consistent with a circumstellar cloud of submicron-sized dust grains composed of amorphous pyroxene, with a minimum mass of 1.50 ± 0.04 × 10-9 M ⊕ derived from the deepest occultations, and a minimum grain size of ${0.29}_{-0.18}^{+0.01}\,\mu {\rm{m}}$ assuming a power-law size distribution. We further identify the first evidence of near-infrared excess in this system from NEOWISE 3.4 and 4.6 μm observations. The excess emission implies a total circumstellar dust mass of around 10-6 M ⊕, comparable to the extreme, variable disks associated with terrestrial planet formation around young stars. The quasiperiodic recurrence of deep dips and the inferred dust temperature (ranging from 1800 to 700 K across the span of observations) independently point to an orbital distance of ≃0.2 au for the dust, supporting the occulting material and excess emission being causally linked. The origin of this extended, opaque cloud is surmised to be the breakup of one or more exocometary bodies.

Keywords: exocomets; circumstellar dust; solar analogs
Monster Radiative Shocks in the Perturbed Magnetospheres of Neutron Stars

Magnetospheres of neutron stars can be perturbed by star quakes, interaction in a binary system, or sudden collapse of the star. The perturbations are typically in the kilohertz band and excite magnetohydrodynamic waves. We show that compressive magnetospheric waves steepen into monster shocks, possibly the strongest shocks in the Universe. The shocks are radiative, i.e., the plasma energy is radiated before it crosses the shock. As the kilohertz wave with the radiative shock expands through the magnetosphere, it produces a bright X-ray burst. Then, it launches an approximately adiabatic blast wave, which will expand far from the neutron star. These results suggest a new mechanism for X-ray bursts from magnetars and support the connection of magnetar X-ray activity with fast radio bursts. Similar shocks may occur in magnetized neutron-star binaries before they merge, generating an X-ray precursor of the merger. Powerful radiative shocks are also predicted in the magnetosphere of a neutron star when it collapses into a black hole, producing a bright X-ray transient.

Keywords: x-ray transient sources; neutron stars; magnetars; radiative processes; radio bursts; plasma astrophysics
The String Theory Swampland in the Euclid, Square Kilometer Array, and Vera Rubin Observatory Era

This article aims to draw the attention of astronomers to the ability of future cosmological surveys to put constraints on string theory. The fact that "quantum gravity" might be constrained by large-scale astrophysical observations is a remarkable fact that has recently concentrated a great amount of interest. In this work, we focus on future observatories and investigate their capability to put string theory, which is sometimes said to be "unfalsifiable," under serious pressure. We show that the combined analysis of the Square Kilometer Array, Euclid, and the Vera Rubin observatory—together with Planck results—could substantially improve the current limits on the relevant string swampland parameter. In particular, our analysis leads to a nearly model-independent prospective upper bound on the quintessence potential, $| V^{\prime} | /V\lt 0.16$ , in strong contradiction of the so-called de Sitter conjecture. Some lines of improvements for the very long run are also drawn, together with generic prospective results, underscoring the efficiency of this approach. The conjectures used in this work are discussed pedagogically, together with the cosmological models chosen in the analysis.

Keywords: cosmology; dark energy; quintessence
GJ 9404 b: A Confirmed Eccentric Planet, and not a Candidate

Eccentric orbits can be decomposed into a series of sine curves which affects how the false alarm probability is computed when using traditional periodograms on radial-velocity data. Here we show that a candidate exoplanet orbiting the M dwarf GJ 9404, identified by the HADES survey using data from the HARPS-N spectrograph, is in fact a bona fide planet on a highly eccentric orbit. Far from a candidate, GJ 9404b is detected with a high confidence. We reach our conclusion using two methods that assume Keplerian functions rather than sines to compute a detection probability, a Bayes Factor, and the false-inclusion probability periodogram. We compute these using nested sampling with kima.

Keywords: radial velocity; exoplanets; nested sampling; keplerian orbit
The Behavior of Bp He-weak Stars in the Far UV-Paper 2: HD 125823

The analysis of seventeen spectra of the Bp He-weak star HD 125823 recorded by the SWP camera on board the International Ultraviolet Explorer reveals no variations of the far-ultraviolet spectral energy distribution of this star over a time interval of three years. However line variations are present in the range 1400 up to 1600 Å which can be partly attributed to variations of lines of Si II and Si III. This confirms that silicon is not distributed in a uniform manner over the surface but the horizontal gradients of the silicon abundance are probably not large.

Keywords: chemically peculiar stars; helium-weak stars
Multiple-wavelength Correlation and Variation Study for 3C 279 at Various Timescales

The study on variation phenomena of blazars can shed light on the jet activity and structures. We collect nearly ten years γ-ray, X-ray, optical, and radio light curves of the target 3C 279, and use the local cross-correlation function to perform the correlation analysis among them. Based on lags among different wavelengths, we obtain that the optical as well as the X-ray emitting regions are ${32.5}_{-0.9}^{+2.9}$ and ${8.4}_{-4.4}^{+7.7}$ pc away from the jet base, and are upstream of the radio core region. The optical and γ-ray emitting regions are not completely co-spatial. We select several periods to study various variation phenomena at long-term, short-term, and very-short-term timescales. We find a redder when brighter trend of the optical color index at the quiescent state and a bluer when brighter trend at the active state. We also find a softer when brighter trend of the γ-ray at low luminosity and a possible harder when brighter trend at high luminosity. The correlation between the optical polarization and fluxes is complex. We find an anticorrelation for one long-term flare, and positive correlations for two short-term flares. The stack of the multiple optical components can explain the anticorrelation, while the appearance of a dominating component can explain the positive correlations. The disk plus many jet components scenario can explain the complex optical variation behaviors for 3C 279. As a remarkable intermediate synchrotron peaked blazar target, 3C 279 play an important role to understand the classification and transition between the low synchrotron peaked and high synchrotron peaked subclass of blazars, since its variation phenomena shows the indication of connection between these two categories.

Keywords: quasars; galaxy jets; gamma-ray sources
Hybrid Emission Modeling of GRB 221009A: Shedding Light on TeV Emission Origins in Long GRBs

Observations of long-duration gamma-ray bursts (GRBs) with TeV emission during their afterglow have been on the rise. Recently, GRB 221009A, the most energetic GRB ever observed, was detected by the Large High Altitude Air Shower Observatory experiment in the energy band 0.2-7 TeV. Here, we interpret its afterglow in the context of a hybrid model in which the TeV spectral component is explained by the proton-synchrotron process while the low-energy emission from optical to X-ray is due to synchrotron radiation from electrons. We constrained the model parameters using the observed optical, X-ray, and TeV data. By comparing the parameters of this burst and of GRB 190114C, we deduce that the VHE emission at energies ≥1 TeV in the GRB afterglow requires large explosion kinetic energy, E ≳ 1054 erg and a reasonable circumburst density, n ≳ 10 cm-3. This results in a small injection fraction of particles accelerated to a power law, ~10-2. A significant fraction of shock energy must be allocated to a near equipartition magnetic field, ϵ B ~ 10-1, while electrons should only carry a small fraction of this energy, ϵ e ~ 10-3. Under these conditions required for a proton-synchrotron model, namely ϵ B ≫ ϵ e , the SSC component is substantially subdominant over proton-synchrotron as a source of TeV photons. These results lead us to suggest that proton-synchrotron process is a strong contender for the radiative mechanisms explaining GRB afterglows in the TeV band.

Keywords: gamma-ray bursts; gamma-ray transient sources; high energy astrophysics
Spatial Scales and Time Variation of Solar Subsurface Convection

Spectral analysis of the spatial structure of solar subphotospheric convection is carried out for subsurface flow maps constructed using the time-distance helioseismological technique. The source data are obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory from 2010 May to 2020 September. A spherical harmonic transform is applied to the horizontal velocity divergence field at depths from 0 to 19 Mm. The range of flow scales is fairly broad in the shallow layers and narrows as the depth increases. The horizontal flow scales increase rapidly with depth, from supergranulation to giant-cell values, and indicate the existence of large-scale convective motions in the near-surface shear layer. The results can naturally be interpreted in terms of a superposition of differently scaled flows localized at different depth intervals. There is some tendency toward the emergence of meridionally elongated (banana-shaped) convection structures in the deep layers. The total power of the convective flows is anticorrelated with the sunspot number variation over the solar activity cycle in shallow subsurface layers, and positively correlated at larger depths, which is suggestive of the depth redistribution of the convective flow energy due to the action of magnetic fields.

Keywords: helioseismology; solar granulation; solar activity
Sympathetic Partial Filament Eruptions Caused by the Interaction between Two Nearby Filaments

To better understand the physical connections in sympathetic solar eruptions, we investigated the interaction between two nearby filaments and their successive partial eruptions in the active region (AR) NOAA 12866 on 2021 September 9 by using data from the Solar Dynamics Observatory and the New Vacuum Solar Telescope. Based on Hα and extreme ultraviolet observations, we found that the right part of one filament (F1) became active first and experienced an obvious rolling motion. Then the whole body of the filament became wider and expanded toward another filament (F2). They collided with each other, and the interaction between them was accompanied by the brightening and bidirectional flows that appeared between them. This implies that magnetic reconnection occurred between the threads of two filaments. The interaction resulted in a rightward motion of F2 at first, and then its activation, and finally part of it erupted. Furthermore, when the erupted F2 deflected rapidly toward the middle part of F1, the left part of F1 erupted with its overlying magnetic fields pushed by F2. These observational results imply that these successive eruptions within a short time are physically linked, and this was caused by the interaction of the filaments. Nonlinear force-free field extrapolation reveals that the magnetic structure of the filament F1 was composed of several magnetic flux ropes with different twists. These results further advance our understanding of partial filament eruptions and sympathetic solar eruptions.

Keywords: solar filaments; solar filament eruptions; solar active regions
The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions

With the release of Gaia DR2, it is now possible to measure the proper motions (PMs) of the lowest-mass, ultrafaint satellite galaxies in the Milky Way's (MW) halo for the first time. Many of these faint satellites are posited to have been accreted as satellites of the Magellanic Clouds (MCs). Using their six-dimensional phase-space information, we calculate the orbital histories of 13 ultrafaint satellites and five classical dwarf spheroidals in a combined MW+LMC+SMC potential to determine which galaxies are dynamically associated with the MCs. These 18 galaxies are separated into four classes: (I) long-term Magellanic satellites that have been bound to the MCs for at least the last two consecutive orbits around the MCs (Carina 2, Carina 3, Horologium 1, Hydrus 1); (II) Magellanic satellites that were recently captured by the MCs < 1 Gyr ago (Reticulum 2, Phoenix 2); (III) MW satellites that have interacted with the MCs (Sculptor 1, Tucana 3, Segue 1); and (IV) MW satellites (Aquarius 2, Canes Venatici 2, Crater 2, Draco 1, Draco 2, Hydra 2, Carina, Fornax, Ursa Minor). Results are reported for a range of MW and LMC masses. Contrary to previous work, we find no dynamical association between Carina, Fornax, and the MCs. Finally, we determine that the addition of the SMC's gravitational potential affects the longevity of satellites as members of the Magellanic system (long-term versus recently captured), but it does not change the total number of Magellanic satellites.

Keywords: local group; milky way galaxy; magellanic clouds; dwarf galaxies; galaxy dynamics
Strategies for Obtaining Robust Spectral Energy Distribution Fitting Parameters for Galaxies at z ∼ 1 and z ∼ 2 in the Absence of Infrared Data

Robust estimation of star formation rates (SFRs) at higher redshifts (z ≳ 1) using UV–optical–near-infrared (NIR) photometry is contingent on the ability of spectral energy distribution (SED) fitting to constrain the dust attenuation, stellar metallicity, and star formation history (SFH) simultaneously. IR-derived dust luminosities can help break the degeneracy between these parameters, but IR data are often not available. Here, we explore strategies for SED fitting at z ≳ 1 in the absence of IR data using a sample of log M * > 10.2 star-forming galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) for which 24 μm data are available. We adopt the total IR luminosity (L TIR) obtained from 24 μm as the "ground truth," which allows us to assess how well it can be recovered (as L dust) from UV–optical–NIR SED fitting. We test a variety of dust attenuation models, stellar population synthesis models, metallicity assumptions, and SFHs separately to identify which assumptions maximize the agreement (correlation and linearity) between L TIR and L dust. We find that a flexible dust attenuation law performs best. For stellar populations, we find that Bruzual & Charlot models are favored over those of Eldridge et al. Fixing the stellar metallicity at solar value is preferred to other fixed values or leaving it as a free parameter. For SFHs, we find that minimizing the variability in the recent (<100 Myr) SFH improves the agreement with L TIR. Finally, we provide a catalog of galaxy parameters (including M * and SFR) for CANDELS galaxies with $\mathrm{log}{M}_{* }\gt 8$ and 0.7 < z < 1.3, obtained using the models we found to be the most robust.

Keywords: galaxy formation; galaxy evolution; galaxy masses; galaxy properties; star formation; spectral energy distribution; model selection; astronomical models; metallicity; stellar populations; high-redshift galaxies; galaxies
He-rich Hot Subdwarf Stars Observed in Gaia DR3 and LAMOST DR7: Carbon and Nitrogen Abundances and Kinematics

We conducted an analysis of the abundances of He, C, and N in 210 He-rich hot subdwarfs observed within both the Gaia Data Release 3 (DR3) and LAMOST DR7 data sets. This analysis involved fitting the LAMOST spectra with TLUSTY/SYNSPEC non-LTE synthetic spectra. By examining the Galactic spatial positions, velocity vectors, and orbital parameters of these stars, we determined their Galactic population memberships utilizing LAMOST radial velocities and Gaia DR3 parallaxes along with proper motions. Our investigation revealed two positive correlations of C and one positive correlation of N with respect to the He abundance. We found a clear C abundance dichotomy where approximately 82% of the stars show N enrichment above the solar value. Moreover, we observed a bimodal distribution of C abundances, prominently evident in both the Galactic thin and thick disks but absent in the halo population. Furthermore, we found that the scenario of the merger channel of double helium white dwarfs is inadequate to explain the formation of C-deficient He-rich hot subdwarfs.

Keywords: subdwarf stars
KIC 10736223: An Algol-type Eclipsing Binary That Has Just Undergone the Rapid Mass-transfer Stage

This paper reports the discovery of an Algol system KIC 10736223 that just passed the rapid mass transfer stage. From the light-curve and radial-velocity modeling we find KIC 10736223 to be a detached Algol system with the less-massive secondary nearly filling its Roche lobe. Based on the short-cadence Kepler data, we analyzed intrinsic oscillations of the pulsator and identified six secured independent δ Scuti-type pulsation modes (f1, f3, f9, f19, f42, and f48). We compute two grids of theoretical models to reproduce the δ Scuti frequencies, and find that fitting results of mass-accreting models agree well with those of single-star evolutionary models. The fundamental parameters of the primary star yielded with asteroseismology are $M={1.57}_{-0.09}^{+0.05}$ M⊙, Z = 0.009 ± 0.001, $R={1.484}_{-0.028}^{+0.016}$ R⊙, $\mathrm{log}g={4.291}_{-0.009}^{+0.004}$ , ${T}_{\mathrm{eff}}={7748}_{-378}^{+230}$ K, and L = ${7.136}_{-1.519}^{+1.014}$ L⊙. The asteroseismic parameters match well with the dynamical parameters derived from the binary model. Moreover, our asteroseismic results show that the pulsator is an almost unevolved star with an age between 9.46 and 11.65 Myr for single-star evolutionary models and 2.67-3.14 Myr for mass-accreting models. Therefore, KIC 10736223 may be an Algol system that has just undergone the rapid mass-transfer process.

Keywords: asteroseismology; stellar oscillations; delta scuti variable stars; eclipsing binary stars
Center for Astrophysics Optical Infrared Science Archive. I. FAST Spectrograph

We announce the public release of 141,531 moderate-dispersion optical spectra of 72,247 objects acquired over the past 25 yr with the FAST Spectrograph on the Fred L. Whipple Observatory 1.5 m Tillinghast telescope. We describe the data acquisition and processing so that scientists can understand the spectra. We highlight some of the largest FAst Spectrograph for the Tillinghast Telescope (FAST) survey programs, and make recommendations for use. The spectra have been placed in a Virtual Observatory-accessible archive and ready for download.

Keywords: astronomy data analysis; astronomy data reduction; astronomy databases; spectroscopy; radial velocity; galaxy radial velocities; optical astronomy