adsabs/SciX_UAT_keywords huggingface dataset:
The Lyα Emission in Solar Flares. I. A Statistical Study on Its Relationship with the 1-8 ŠSoft X-Ray Emission

We statistically study the relationship between the Lyα and 1-8 Å soft X-ray (SXR) emissions from 658 M- and X-class solar flares observed by the Geostationary Operational Environmental Satellite during 2006-2016. Based on the peak times of the two wave band emissions, we divide the flares into three types. Type I (III) has an earlier (a later) peak time in the Lyα emission than that in the SXR emission, while type II has nearly the same peak time (within the time resolution of 10 s) between the Lyα and SXR emissions. In these 658 flares, we find that there are 505 (76.8%) type I flares, 10 (1.5%) type II flares, and 143 (21.7%) type III flares, and that the three types appear to have no dependence on the flare duration, flare location, or solar cycle. Besides the main peak, the Lyα emission of the three type flares also shows sub-peaks which can appear in the impulsive or gradual phase of the flare. It is found that the main-peak (for type I) and subpeak (for type III) emissions of Lyα that appear in the impulsive phase follow the Neupert effect in general. This indicates that such Lyα emissions are related to the nonthermal electron beam heating. While the main-peak (for type III) and subpeak (for type I) emissions of Lyα that appear in the gradual phase are supposed to be primarily contributed by the thermal plasma that cools down.

Keywords: solar activity; solar chromosphere; solar corona; solar flares; solar ultraviolet emission; solar x-ray emission
Unveiling an Old Disk around a Massive Young Leaking Blueberry in SDSS-IV MaNGA

Extreme emission-line galaxies, such as blue compact dwarfs (BCDs), Green Peas (GPs), and blueberries in the local universe are potential candidates for understanding the nature of galaxies that reionized the early universe. Being low-mass, metal-poor starburst systems, they are understood to be local analogs of the high-redshift Lyman continuum and Lyα emitters (LAEs). Even with their proximity to us, we know little about their spatially resolved properties; while most blueberries and GPs are indeed compact, they remain unresolved. Here, we report the detection of a disk-like lower-surface-brightness (LSB) stellar host with a very old population around a blueberry LAE system using broad i-band imaging and integral field spectroscopic data from the SDSS and SDSS-IV MaNGA surveys, respectively. The LSB stellar host is structurally similar to that observed around local starburst BCDs. Furthermore, the kinematics of the studied blueberry source bears signs of misalignment between the gas and stellar components. Our findings establish an intriguing thread connecting the blueberry and an LSB disk with an old stellar population and suggest that blueberries and their high-redshift counterparts such as GPs do not represent peculiar cases of dwarf galaxy evolution. In fact, with respect to the structural properties of their host galaxies, they are compatible with a common evolutionary track of the main population of local BCDs.

Keywords: compact galaxies; compact dwarf galaxies
On the Interacting/Active Lifetime of Supernova Fallback Disks around Isolated Neutron Stars

The fallback disk model is widely accepted to explain long-period neutron stars (NSs) that cannot be simulated by magnetic dipole radiation. However, there was no confirmed detection of disks from the newly discovered long-period pulsars GLEAM-X 162759.5-523504.3 and GPM J1839-10 and the slowest known isolated NS 1E 161348-5055. This might be because the disks have either been in a noninteracting/inactive state where their emission is too weak to be detected or have been disrupted. In this work, we conduct simulations to examine the lifetime of supernova fallback disks around isolated NSs. We assume that the disks' mass varies in a self-similar way, and their interaction with the NS occurs only in an interacting/active state. Our results reveal that nearly all the interacting lifetimes for the disks are shorter than 105 yr, while the existence lifetimes are considerably longer.

Keywords: magnetars; neutron stars; debris disks; stellar rotation
Revisiting the Galactic X-Ray Binary MAXI J1631-479: Implications for High Inclination and a Massive Black Hole

X-ray spectroscopy of Galactic black hole binaries serves as a powerful tool to gain an overall understanding of the system. Not only can the properties of the accretion disk be studied in detail, the fundamental properties of the black hole such as spin and mass can also be measured. In this work we carry out a comprehensive spectral analysis of the X-ray binary MAXI J1631-479 using data from NICER and NuSTAR observatories. We trace the evolution of the accretion disk properties, such as density, ionization, and Fe abundance, as the source transitions from a disk-dominated soft state to a power-law-dominated hard intermediate state. As expected the disc ionization increased with hardness while the density and abundance (at solar values) remained unchanged. We provide strong constraints on the spin of the black hole (a > 0.996) and the inclination of the inner disk (50°-70°). We also use the soft-state NICER observations to constrain the black hole mass using distance estimates from optical observations. We find the probable mass of the black hole to be much higher than its X-ray binary counterparts with a conservative lower limit of 15 ${M}_{\odot }$ at 4.5 kpc.

Keywords: accretion; stellar mass black holes; low-mass x-ray binary stars
Investigating the Origins of Hot Neptunes from Radial Velocity Data

Hot Neptunes are extrasolar planets that are similar in size to Neptune in our solar system but are much closer to their host stars, completing an orbit in 10 days or less. The origin of hot Neptunes is not fully understood. A potential large third body at a distance can lead to the migration of long-period planets to become much closer to the host star, and such a dynamical process helps explain the origin of hot Jupiters. We investigate whether hot Neptunes could share a similar origin by analyzing radial velocity data from multiple sources for a sample of 34 hot Neptune systems. Hot Neptune systems appear to have similar values of linear trend to hot Jupiter systems. We perform a maximum likelihood analysis to constrain the mass and distance distribution of the putative third body. The overall fraction of hot Neptune systems with third bodies is consistent with unity, higher than 71% at the 2σ level. On average, the mass and distance distribution of the third bodies for hot Neptune systems is consistent with that for hot Jupiter systems. Our results suggest that hot-Neptune systems share the same origin mechanism as hot Jupiters, e.g., through the gravitational effect of third bodies.

Keywords: exoplanet evolution; exoplanet dynamics; exoplanet formation; exoplanet migration
A Study of Eight Visual-spectroscopic Southern Binaries Using Recent SOAR Observations

Speckle observations performed between 2019 and 2022 with the HRCam attached to the 4.1 m SOAR telescope (Cerro Pachón, Chile) permitted to improve visual orbits of the southern binaries WDS 01243-0655 (BU 1163), WDS 09275-5806 (CHR 240), WDS 12114-1647 (S 643 AaAb), WDS 13317-0219 (HDS 1895), WDS 15282-0921 (BAG 25 AaAb), WDS 17304-0104 (STF 2173), WDS 19598-0957 (HO 276), and WDS 21274-0701 (HDS 3053). All of them are spectroscopic binaries, of which six are SB2, so relevant information about their individual masses has been obtained. Moreover, comparison between different values of their parallaxes (orbital, dynamic, and ANAPAR, a color-dependent model suitable for binary systems attending to the exact locations of the components on the MS in the HR diagram) with those provided by Hipparcos and Gaia missions, along with comments for each binary are presented. The luminosity determination of the 16 components allowed us to estimate their approximate age and position on the HR diagram as well.

Keywords: orbit determination; orbits; stellar astronomy; stellar dynamics; stellar evolutionary tracks; stellar masses; stellar parallax; binary stars; visual binary stars; spectroscopic binary stars
Ba-enhanced Dwarf and Subgiant Stars in the LAMOST Galactic Surveys

Ba-enhanced stars are interesting probes of stellar astrophysics and Galactic formation history. In this work, we investigate the chemistry and kinematics of a large sample of Ba-enhanced ([Ba/Fe]>1.0) dwarf and subgiant stars with 5000 < T eff < 6700 K from LAMOST. We find that both stellar internal evolution processes and external mass exchange due to binary evolution are responsible for the origins of the Ba enhancement of our sample stars. About one third of them exhibit C and N enhancement and an ultraviolet brightness excess, indicating they are products of binary evolution. The remaining Ba-enhanced stars with normal C and N abundances are mostly warm stars with T eff > 6000 K. They are likely the consequences of stellar internal element transport processes, but they show very different element patterns to hotter Am/Fm stars. Our results reveal a substantially lack of high-[α/Fe], Ba-enhanced stars in the [Fe/H]-[α/Fe] plane, which we dub as a "high-[α/Fe] desert". We suggest it is due to a lower efficiency for producing Ba-enhanced stars by low-mass asymptotic giant branch progenitors in binary systems. Our results call for detailed modeling of these Ba-enhanced stellar peculiarities, in the context of both stellar internal element transport and external mass accretion.

Keywords: chemically peculiar stars; barium stars; stellar evolution; stellar populations; binary stars; chemical abundances; surveys
Chemical Diversity on Small Scales: Abundance Analysis of the Tucana V Ultrafaint Dwarf Galaxy

The growing number of Milky Way satellites detected in recent years has introduced a new focus for stellar abundance analysis. Abundances of stars in satellites have been used to probe the nature of these systems and their chemical evolution. However, for most satellites, only centrally located stars have been examined. This paper presents an analysis of three stars in the Tucana V system, one in the inner region and two at ∼10' (7–10 half-light radii) from the center. We find a remarkable chemical diversity between the stars. One star exhibits enhancements in rapid neutron-capture elements (an r-I star), and another is highly enhanced in C, N, and O but with low neutron-capture abundances (a CEMP-no star). The metallicities of the stars analyzed span more than 1 dex from [Fe/H] = ‑3.55 to ‑2.46. This, combined with a large abundance range of other elements like Ca, Sc, and Ni, confirms that Tuc V is an ultrafaint dwarf (UFD) galaxy. The variation in abundances, highlighted by [Mg/Ca] ratios ranging from +0.89 to ‑0.75, among the stars demonstrates that the chemical enrichment history of Tuc V was very inhomogeneous. Tuc V is only the second UFD galaxy in which stars located at large distances from the galactic center have been analyzed, along with Tucana II. The chemical diversity seen in these two galaxies, driven by the composition of the noncentral member stars, suggests that distant member stars are important to include when classifying faint satellites and that these systems may have experienced more complex chemical enrichment histories than previously anticipated.

Keywords: stellar abundances; dwarf galaxies; milky way stellar halo
Preferential Acceleration of Heavy Ions in a Spontaneously Fragmenting Flare Current Sheet

We study the ion acceleration in a mesoscale, spontaneously fragmenting flare current sheet (SFCS) characterized by the presence of a plasmoid cascade. The main subject of our investigation is to determine whether and how plasmoid cascades at intermediate scales in a fragmented current sheet of a solar flare can impact the (preferential) acceleration of specific ions. The time evolution of the SFCS is obtained from high-resolution 2.5D MHD simulations. The ion trajectories (in the background fields resulting from the MHD model), energies, and pitch angles are calculated using a relativistic test-particle code based on the half-acceleration-rotation-half-acceleration method. For light ions, the main acceleration effects of electromagnetic fields within the SFCS are analyzed using the guiding center approximation. We identify regions with the most-efficient ion acceleration within the SFCS, the accelerator efficiency, and spectra of the accelerated ions. The influence of the charge-to-mass ratio on ion behavior is also studied and resulting ion abundances are compared with observational data. The main ion acceleration takes place in the regions with a strong polarization term, which is part of the first-order Fermi acceleration. Because the term is mass dependent, heavier ions undergo preferential acceleration. The ion energy spectra, abundance-enhancement factors, and differential fluxes, obtained from the model, exhibit power-law profiles, in agreement with observed solar energetic particle events. Nonetheless, the obtained slopes for the abundance-enhancement factor do not exactly match the observed data. The computed slopes and profiles are not sensitive to changes in the initial plasma temperature.

Keywords: active solar corona; solar flares; solar abundances; solar magnetic reconnection; solar energetic particles
Investigating the Physical Properties and Fragmentation of the AFGL 333-Ridge

We present multiwavelength data to investigate the physical properties and fragmentation of AFGL 333-Ridge. A statistical analysis of velocity dispersion indicates that turbulence is the dominant motion in the ridge. However, the linear mass density (1124.0 M ⊙/pc) of AFGL 333-Ridge far exceeds its critical value of 406.5 M ⊙/pc, suggesting that additional motions are required to prevent the filament radial collapse. Using the getsources algorithm, we identified 14 cores from the Herschel maps, including two protostellar cores and 12 starless cores. All of these starless cores are gravitationally bound, and are therefore considered to be prestellar cores. Based on their radius-mass relation, 11 of 14 cores have the potential to form massive stars. Moreover, the seven cores in two subfilaments of AFGL 333-Ridge seem to constitute two necklace-like chains with a spacing length of 0.51 and 0.45 pc, respectively. Compared the spacing length with theoretical prediction lengths by Jeans and cylindrical fragmentations, we argued that the combination of turbulence and thermal pressure may lead to the fragmentation of the two subfilaments into the cores.

Keywords: interstellar filaments
Using Data Imputation for Signal Separation in High-contrast Imaging

To characterize circumstellar systems in high-contrast imaging, the fundamental step is to construct a best point-spread function (PSF) template for the noncircumstellar signals (I.e., starlight and speckles) and separate it from the observation. With existing PSF construction methods, the circumstellar signals (e.g., planets, circumstellar disks) are unavoidably altered by overfitting and/or self-subtraction, making forward modeling a necessity to recover these signals. We present a forward modeling-free solution to these problems with data imputation using sequential nonnegative matrix factorization (DI-sNMF), which first converts this signal separation problem to a "missing data" problem in statistics by flagging the regions that host circumstellar signals as missing data, then attributes PSF signals to these regions. We mathematically prove it to have negligible alteration to circumstellar signals when the imputation region is relatively small, which thus enables precise measurement of these circumstellar objects. We apply it to simulated point-source and circumstellar disk observations to demonstrate its proper recovery of them. We apply it to Gemini Planet Imager K1-band observations of the debris disk surrounding HR 4796A, finding a tentative trend that the dust is more forward scattering as the wavelength increases. We expect DI-sNMF to be applicable to other general scenarios where the separation of signals is needed.

Keywords: astronomy data analysis; debris disks; protoplanetary disks; coronagraphic imaging; dimensionality reduction; multivariate analysis
Toward Astrometric Constraints on a Supermassive Black Hole Binary in the Early-type Galaxy NGC 4472

The merger of two galaxies, each hosting a supermassive black hole (SMBH) of mass 106 M ⊙ or more, could yield a bound SMBH binary. For the early-type galaxy NGC 4472, we study how astrometry with a next-generation Very Large Array could be used to monitor the reflex motion of the primary SMBH of mass M pri, as it is tugged on by the secondary SMBH of mass ${M}_{\sec }$ . Casting the orbit of the putative SMBH binary in terms of its period P, semimajor axis a bin, and mass ratio $q={M}_{\sec }/{M}_{\mathrm{pri}}\leqslant 1$ , we find the following: (1) Orbits with fiducial periods of P = 4 yr and 40 yr could be spatially resolved and monitored. (2) For a 95% accuracy of 2 μas per monitoring epoch, subparsec values of a bin could be accessed over a range of mass ratios notionally encompassing major $\left(q\gt \tfrac{1}{4}\right)$ and minor $\left(q\lt \tfrac{1}{4}\right)$ galaxy mergers. (3) If no reflex motion is detected for M pri after 1 (10) yr of monitoring, an SMBH binary with period P = 4 (40) yr and mass ratio q > 0.01 (0.003) could be excluded. This would suggest no present-day evidence for a past major merger like that recently simulated, where scouring by a q ~ 1 SMBH binary formed a stellar core with kinematic traits like those of NGC 4472. (4) Astrometric monitoring could independently check the upper limits on q from searches for continuous gravitational waves from NGC 4472.

Keywords: active galactic nuclei; early-type galaxies; supermassive black holes; interferometry
Identifying Flare-indicative Photospheric Magnetic Field Parameters from Multivariate Time-series Data of Solar Active Regions

Photospheric magnetic field parameters are frequently used to analyze and predict solar events. Observation of these parameters over time, i.e., representing solar events by multivariate time-series (MVTS) data, can determine relationships between magnetic field states in active regions and extreme solar events, e.g., solar flares. We can improve our understanding of these events by selecting the most relevant parameters that give the highest predictive performance. In this study, we propose a two-step incremental feature selection method for MVTS data using a deep-learning model based on long short-term memory (LSTM) networks. First, each MVTS feature (magnetic field parameter) is evaluated individually by a univariate sequence classifier utilizing an LSTM network. Then, the top performing features are combined to produce input for an LSTM-based multivariate sequence classifier. Finally, we tested the discrimination ability of the selected features by training downstream classifiers, e.g., Minimally Random Convolutional Kernel Transform and support vector machine. We performed our experiments using a benchmark data set for flare prediction known as Space Weather Analytics for Solar Flares. We compared our proposed method with three other baseline feature selection methods and demonstrated that our method selects more discriminatory features compared to other methods. Due to the imbalanced nature of the data, primarily caused by the rarity of minority flare classes (e.g., the X and M classes), we used the true skill statistic as the evaluation metric. Finally, we reported the set of photospheric magnetic field parameters that give the highest discrimination performance in predicting flare classes.

Keywords: solar flares; space weather; time series analysis; solar active region magnetic fields; multivariate analysis; solar physics
Tidal Disruption Event Hosts Are Green and Centrally Concentrated: Signatures of a Post-merger System

We study the properties of the galaxies hosting the first 19 tidal disruption events (TDEs) detected with the Zwicky Transient Facility (ZTF) within the context of a carefully constructed, representative host galaxy sample. We find that the ZTF sample of TDE hosts is dominated by compact "green valley" galaxies. After we restrict the comparison sample to galaxies with a similar concentration, as measured by the Sérsic index, we find this green valley overrepresentation is even larger. That is, concentrated red sequence galaxies are not producing TDEs at elevated levels. We present host galaxy spectra that show that E + A galaxies are overrepresented in the ZTF sample by a factor of ≈22, which is lower than previous TDE host galaxy studies have found. We find that this overrepresentation can be fully accounted for when taking into account the masses, colors, and Sérsic indices of the ZTF TDE hosts. The combination of both green colors and high Sérsic index of the typical TDE host galaxy could be explained if the TDE rate is temporarily enhanced following a merger that leads to a higher central concentration of stars.

Keywords: black hole physics; galaxy nuclei
Revisiting FUSE O VI Emission in Galaxy Halos

A significant fraction of baryons in galaxies are in the form of diffuse gas of the circumgalactic medium (CGM). One critical component of the multiphases of CGM, the so-called "coronal" warm-hot phase gas (105-106 K) traced by O VI 1031.93, 1037.62 Å resonance lines, has rarely been detected in emission from galaxy halos other than that of the Milky Way. Here we report four additional detections of O VI emission gas in the halos of nearby edge-on galaxies, NGC 4631 and NGC 891, using archival Far Ultraviolet Spectroscopic Explorer data and an updated data pipeline. We find the most intense O VI emission to be from fields forming a vertical line near the center of NGC 4631, despite the close proximity to the disk of two other fields. The detected O VI emission surface brightness is about (1.1 ± 0.3) × 10-18 to (3.9 ± 0.8) × 10-18 erg s-1 cm-2 arcsec-2. The spatial distribution of the five 30″ × 30″ O VI detection fields in NGC 4631 can be interpreted as the existence of filamentary structures of more intense O VI emission superimposed within a diffuse and faint O VI halo in star-forming galaxies. Volume-filled O VI emission mapping is greatly needed to determine the structure and prevalence of warm-hot gas and the role it plays in the cycling of gas between the galaxy disk and the halo. Finally, we present the sensitivity of future funded and proposed UV missions (LUVOIR-A, LUVOIR-B, CETUS, and Aspera) to the detection of diffuse and faint O VI emission in nearby galaxy halos.

Keywords: circumgalactic medium; extragalactic astronomy; galaxy structure