adsabs/SciX_UAT_keywords huggingface dataset:
Probing the Line-locking Signatures within the C IV Broad Absorption Line in Quasar SDSS J092345+512710

Quasar SDSS J092345.19+512710.1 (hereafter J0923+5127) shows two broad absorption line (BAL) systems. The blue one at ∼14,000 km s-1, called BAL system A, has been reported to show a synchronized kinematic shift of its C IV and Si IV BALs. In this paper, we mainly concentrate on the red one at ∼4000 km s-1, called BAL system B, which can be resolved into multiple narrow absorption lines (NALs). We identify 11 NAL systems from BAL system B and find that these blended NALs show complex line-locking phenomena, which offers evidence for the idea that radiation pressure plays an important role in the dynamics of these clumpy outflow clouds.

Keywords: quasars; broad-absorption line quasar; quasar absorption line spectroscopy
A Search for Technosignatures around 31 Sun-like Stars with the Green Bank Telescope at 1.15-1.73 GHz

We conducted a search for technosignatures in 2018 and 2019 April with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused on regions surrounding 31 Sun-like stars near the plane of the Galaxy. We present the results of our search for narrowband signals in this data set, as well as improvements to our data processing pipeline. Specifically, we applied an improved candidate signal detection procedure that relies on the topographic prominence of the signal power, which nearly doubles the signal detection count of some previously analyzed data sets. We also improved the direction-of-origin filters that remove most radio frequency interference (RFI) to ensure that they uniquely link signals observed in separate scans. We performed a preliminary signal injection and recovery analysis to test the performance of our pipeline. We found that our pipeline recovers 93% of the injected signals over the usable frequency range of the receiver and 98% if we exclude regions with dense RFI. In this analysis, 99.73% of the recovered signals were correctly classified as technosignature candidates. Our improved data processing pipeline classified over 99.84% of the ∼26 million signals detected in our data as RFI. Of the remaining candidates, 4539 were detected outside of known RFI frequency regions. The remaining candidates were visually inspected and verified to be of anthropogenic nature. Our search compares favorably to other recent searches in terms of end-to-end sensitivity, frequency drift rate coverage, and signal detection count per unit bandwidth per unit integration time.

Keywords: search for extraterrestrial intelligence; technosignatures; astrobiology; exoplanets; solar analogs; radio astronomy; milky way galaxy
A Partial Filament Eruption in Three Steps Induced by External Magnetic Reconnection

We present an investigation of partial filament eruption on 2012 June 17 in the active region NOAA 11504. For the first time, we observed the vertical splitting process during the partial eruption with high-resolution narrowband images at 10830 Å. The active filament was rooted in a small δ-sunspot of the active region. Particularly, it underwent the partial eruption in three steps, i.e., the precursor, the first eruption, and the second eruption, while the latter two were associated with a C1.0 flare and a C3.9 flare, respectively. During the precursor, slow magnetic reconnection took place between the filament and the adjoining loops that also rooted in the δ-sunspot. The continuous reconnection not only caused the filament to split into three groups of threads vertically but also formed a new filament, which was growing and accompanied brightening took place around the site. Subsequently, the growing filament erupted together with one group splitted threads, resulted in the first eruption. At the beginning of the first eruption, a subsequent magnetic reconnection occurred between the erupting splitted threads and another ambient magnetic loop. After about 3 minutes, the second eruption occurred as a result of the eruption of two larger unstable filaments induced by the magnetic reconnection. The high-resolution observation provides a direct evidence that magnetic reconnection between filament and its ambient magnetic fields could induce the vertical splitting of the filament, resulting in partial eruption.

Keywords: solar active region filaments; solar filaments; solar filament eruptions; magnetic fields; solar magnetic reconnection; solar active region magnetic fields
Lithium in Kepler Red Giants: Defining Normal and Anomalous

The orders-of-magnitude variations in the lithium abundances of evolved stars have long been a puzzle. Diluted signals, ambiguous evolutionary states, and unknown masses have made it challenging to both map the expected lithium signals and explain the anomalously lithium-rich stars. Using a set of asteroseismically characterized evolved stars, we show here that the base lithium abundance in red giant stars is mass-dependent, with higher-mass stars having higher "normal" lithium abundances, while highly lithium-enhanced stars may cluster around 0.8 or 1.8 M ☉. We confirm previous studies that have shown that lithium enhancement and rapid rotation are often coincident but find that the actual correlation between lithium abundance and rotation rate, whether surface, internal, or radial differential rotation, is weak. Our data support previous assertions that most lithium-rich giants are in the core-helium-burning phase. We also note a tentative correlation between the highest lithium abundances and unusual carbon-to-nitrogen ratios, which is suggestive of binary interactions, though we find no simple correlation between lithium richness and indicators of binarity.

Keywords: red giant stars; lithium stars; stellar rotation
Multiwavelength Observations of a B-class Flare Using XSM, AIA, and XRT

We present multiwavelength observations by Chandrayaan-2/Solar X-ray Monitor, Solar Dynamics Observatory/Atmospheric Imaging Assembly, and Hinode/X-Ray Telescope (XRT) of a B-class flare observed on 2021 February 25, originating from an active region (AR 12804) near the northwest limb. The microflare lasts for ~30 minutes and is composed of hot loops reaching temperatures of 10 MK. We report excellent agreement (within 20%) for the average effective temperatures obtained at the flare peak from all the three instruments, which have different temperature sensitivities. The XRT filter combination of Be-thin and Be-med provides an excellent opportunity to measure the high temperatures in such microflare events. The elemental abundances during the evolution of the microflare are also studied and observed to drop toward photospheric values at the flare peak time, compared to coronal values during the rise and decay phase. This is consistent with previous XSM studies.

Keywords: solar corona
Insight-HXMT Views Her X-1: Probing the Dependence of the Cyclotron Line Energy on Flux and Time

Recent observations of Her X-1 with NuSTAR (as well as with INTEGRAL, Swift, and Astrosat) have provided evidence that the nearly 20 yr-long decay of the cyclotron line energy since ~1994 has ended and that a stable value has replaced the decay. Using the observations of the Hard X-ray Modulation Telescope (Insight-HXMT) performed between 2017 July and 2020 February, we analyze the spectra of Her X-1 in its main-on state, focusing on tracing the evolution of cyclotron line energy. While our analysis of eight main-on observations with Insight-HXMT (two in coordination with NuSTAR) shows significant differences with the results of NuSTAR, two earlier findings are confirmed: the positive correlation between the cyclotron line energy and the X-ray flux (source luminosity) and the constancy of the flux-normalized cyclotron line energy during 2017-2020-albeit with significant uncertainty about the absolute value.

Keywords: accretion; x-ray binary stars
Discovery of Two Pulsating Extremely Low-mass Pre-white Dwarf Candidates in the TESS Eclipsing Binaries

We report the discovery of two new pulsating extremely low-mass pre-white dwarf (pre-ELMV) candidates in the Transiting Exoplanet Survey Satellite (TESS) eclipsing binaries, TIC 149160359 and TIC 416264037. Their light curves show a typical feature of EL CVn-type binaries. The light-curve modeling indicates that they are both detached systems with very low-mass ratios (q ≃ 0.1). Based on the photometric solutions, the masses and radii of the two main-sequence primary components are estimated, and those of the secondaries are deduced. The results show that the less-massive components of the two binaries are both probably thermally bloated, pre-ELMVs. Apart from the eclipsing light changes, short-period light variations are clearly shown in their residual light curves. We have made the Fourier analysis of their light-curve residuals with the Period04 program. TIC 149160359 was found to pulsate in 21 independent frequencies, 17 of which are between 21 and 35 day-1 and the others are between 63 and 77 day-1. The Fourier amplitude spectrum of TIC 416264037 also shows two frequency concentration ranges. Out of nine independent frequencies, seven reside within the low-frequency range of 12.5-19.9 day-1. Two pulsating signals, f 4 = 122.2698 day-1 and f 10 = 112.3603 day-1, were detected in the high-frequency region. These low-frequency signals that are detected on TIC 149160359 and TIC 416264037 are probably due to the intrinsic pulsations of their δ Sct-type primary components. However, the high-frequency signals are likely to come from the pulsations of the pre-ELM WD components. This brings the number of pre-ELMV candidates to 12.

Keywords: eclipsing binary stars; white dwarf stars; delta scuti variable stars
An XMM-Newton View of the Symbiotic Stars HM Sge, NQ Gem, and PU Vul

We present the analysis of archival XMM-Newton observations of the symbiotic stars HM Sge, NQ Gem, and PU Vul. The EPIC-pn spectra hint at the presence of emission lines, which are further confirmed in the first-order RGS spectra of the three sources. Spectral modeling of the EPIC-pn data discloses unprecedented characteristics; for instance, the best fit to the EPIC-pn spectrum of the β-type symbiotic star PU Vul reveals the presence of two-plasma components. We report the discovery of an extremely soft spectral component in the EPIC-pn spectrum of the β-type symbiotic star HM Sge, which we suggest is produced by periodic mass ejections such as jets. Consequently, we suggest that a simple β-type classification no longer applies to HM Sge. Finally, the spectrum of the β/δ-type symbiotic star NQ Gem cannot be fitted by a two-temperature plasma model as performed by previous authors. The model requires extra components to fit the 1.0-4.0 keV energy range. More sophisticated models to β/δ-type symbiotic stars are needed in order to peer into the accretion process from such systems.

Keywords: symbiotic binary stars; stellar accretion; white dwarf stars; low mass stars
Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet Background

The diffuse ultraviolet background radiation has been mapped over most of the sky with 2' resolution using data from the Galaxy Evolution Explorer survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the Planck survey. We use only high Galactic latitude ( $| b| \gt 60^\circ $ ) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range of 0.02 ≤ z ≤ 0.72, which we further subdivide into four redshift bins. In analyzing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with z < 0.3. We then stacked these z < 0.3 clusters to find a statistically significant excess of 12 ± 2.3 photon cm-2 s-1 sr-1 Å-1 over the median of ∼380 photon cm-2 s-1 sr-1 Å-1 measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of ∼1 Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.

Keywords: galaxy clusters; ultraviolet astronomy; cosmic background radiation
Three-polarizer Treatment of Linear Polarization in Coronagraphs and Heliospheric Imagers

Linearly polarized light has been used to view the solar corona for over 150 years. While the familiar Stokes representation for polarimetry is complete, it is best matched to a laboratory setting and therefore is not the most convenient representation either for coronal instrument design or for coronal data analysis. Over the last 100 years of development of coronagraphs and heliospheric imagers, various representations have been used for both direct measurement and analysis. These systems include famous representations such as the (B, pB) system, which is analogous to the Stokes system in solar observing coordinates, and also internal representations such as in-instrument Stokes parameters with fixed or variable "vertical" direction, and brightness values through a particular polarizing optic or set thereof. Many polarimetric instruments currently use a symmetric three-polarizer measurement and representation system (which we refer to as "(M, Z, P)") to derive the (B, pB) or Stokes parameters. We present a symmetric derivation of (B, pB) and Stokes parameters from (M, Z, P), analyze the noise properties of (M, Z, P) in the context of instrument design, develop (M, Z, P) as a useful intermediate system for data analysis including background subtraction, and draw a helpful analogy between linear polarimetric systems and the large existing body of work on photometric colorimetry.

Keywords: polarimetry; solar k corona; color equation; polarimeters; solar instruments
AstroLLaMA-Chat: Scaling AstroLLaMA with Conversational and Diverse Datasets

We explore the potential of enhancing LLM performance in astronomy-focused question-answering through targeted, continual pre-training. By employing a compact 7B-parameter LLaMA-2 model and focusing exclusively on a curated set of astronomy corpora-comprising abstracts, introductions, and conclusions-we achieve notable improvements in specialized topic comprehension. While general LLMs like GPT-4 excel in broader question-answering scenarios due to superior reasoning capabilities, our findings suggest that continual pre-training with limited resources can still enhance model performance on specialized topics. Additionally, we present an extension of AstroLLaMA: the fine-tuning of the 7B LLaMA model on a domain-specific conversational data set, culminating in the release of the chat-enabled AstroLLaMA for community use. Comprehensive quantitative benchmarking is currently in progress and will be detailed in an upcoming full paper. The model, AstroLLaMA-Chat, is now available at https://huggingface.co/universeTBD, providing the first open-source conversational AI tool tailored for the astronomy community.

Keywords: astronomy software; publicly available software; astronomical instrumentation
Why "Solar Tsunamis" Rarely Leave Their Imprints in the Chromosphere

Solar coronal waves frequently appear as bright disturbances that propagate globally from the eruption center in the solar atmosphere, just like the tsunamis in the ocean on Earth. Theoretically, coronal waves can sweep over the underlying chromosphere and leave an imprint in the form of Moreton wave, due to the enhanced pressure beneath their coronal wave front. Despite the frequent observations of coronal waves, their counterparts in the chromosphere are rarely detected. Why the chromosphere rarely bears the imprints of solar tsunamis remained a mystery since their discovery three decades ago. To resolve this question, all coronal waves and associated Moreton waves in the last decade have been initially surveyed, though the detection of Moreton waves could be hampered by utilizing the low-quality Hα data from the Global Oscillations Network Group. Here, we present eight cases (including five in the Appendix) of the coexistence of coronal and Moreton waves in inclined eruptions where it is argued that the extreme inclination is key to providing an answer to address the question. For all these events, the lowest part of the coronal wave front near the solar surface appears very bright, and the simultaneous disturbances in the solar transition region and the chromosphere predominantly occur beneath the bright segment. Therefore, evidenced by observations, we propose a scenario for the excitation mechanism of the coronal-Moreton waves in highly inclined eruptions, in which the lowest part of a coronal wave can effectively disturb the chromosphere even for a weak (e.g., B-class) solar flare.

Keywords: solar coronal waves; solar activity; solar corona; solar atmosphere
Solar Neighborhood Exoplanet Host Stars within a Galactic Context

Ages, metallicities, and Galactic orbit parameters are considered for those stars with Henry Draper catalog designations that have been discovered to host planetary systems. There are quite a few such stars with above-solar metallicity and ages up to 4 Gyr older than the Sun. Some planet-hosting stars have Galactic orbits that take them within 4 kpc of the Galactic Center, while a substantial fraction attain displacements from the Galactic mid-plane consistent with the thick disk.

Keywords: planet hosting stars; milky way disk
Stars on the Verge: Investigating Semiregular Light Variations and Changing Multiperiods of the Luminous Red Supergiant μ Cephei from over 175 yr of Photometry

μ Cephei is a 4th mag semi-regular variable M2Ia star. It is among the largest, most luminous red supergiants in our galactic neighborhood and a probable SN-II core-collapse progenitor. Analyses of ~175 yr of photometry were conducted. The observations are mostly from the AAVSO database. Period analyses were conducted using the Period Analysis Software (Peranso-3) package. The CLEANest and Wavelet (WWZ) programs were utilized. Two dominant "periods" were found: P = 870 ± 50 days (~2.39 yr) and a long period of ~5300 ± 155 days (~14.5 yr). The long period was prominent during the first ~90 yr but weakened and was followed by multiple transitory periods ranging from ~3000 to 4600 days. μ Cephei has interesting features including multiple periods, period-splitting, period-merging and period-decays.

Keywords: red supergiant stars; stellar pulsations
Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion

The faint and ultrafaint dwarf galaxies in the Local Group form the observational bedrock upon which our understanding of small-scale cosmology rests. In order to understand whether this insight generalizes, it is imperative to use resolved-star techniques to discover similarly faint satellites in nearby galaxy groups. We describe our search for ultrafaint galaxies in the M81 group using deep ground-based resolved-star data sets from Subaru's Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the M81 group and identify five additional extremely low surface brightness candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to M V ~ - 6 (similar to current limits for Andromeda satellites). These candidates' luminosities and sizes are similar to known Local Group dwarf galaxies Tucana B, Canes Venatici I, Hercules, and Boötes I. Most of these candidates are likely to be real, based on tests of our techniques on blank fields. Intriguingly, all of these candidates are spatially clustered around NGC 3077, which is itself an M81 group satellite in an advanced state of tidal disruption. This is somewhat surprising, as M81 itself and its largest satellite M82 are both substantially more massive than NGC 3077 and, by virtue of their greater masses, would have been expected to host as many or more ultrafaint candidates. These results lend considerable support to the idea that satellites of satellites are an important contribution to the growth of satellite populations around Milky Way-mass galaxies.

Keywords: dwarf galaxies; dwarf spheroidal galaxies; galaxy groups
Rest-frame Near-infrared Sizes of Galaxies at Cosmic Noon: Objects in JWST's Mirror Are Smaller than They Appeared

Galaxy sizes and their evolution over cosmic time have been studied for decades and serve as key tests of galaxy formation models. However, at z ≳ 1 these studies have been limited by a lack of deep, high-resolution rest-frame infrared imaging that accurately traces stellar mass distributions. Here, we leverage the new capabilities of the James Webb Space Telescope (JWST) to measure the 4.4 μm sizes of ~1000 galaxies with $\mathrm{log}{M}_{* }/{M}_{\odot }\geqslant 9$ and 1.0 ≤ z ≤ 2.5 from public CEERS imaging in the Extended Groth Strip deep field. We compare the sizes of galaxies measured from NIRCam imaging at 4.4 μm (λ rest ~ 1.6 μm) with sizes measured at 1.5 μm (λ rest ~ 5500 Å). We find that, on average, galaxy half-light radii are ~9% smaller at 4.4 μm than 1.5 μm in this sample. This size difference is markedly stronger at higher stellar masses and redder rest-frame V - J colors: galaxies with M * ~ 1011 M ⊙ have 4.4 μm sizes that are ~30% smaller than their 1.5 μm sizes. Our results indicate that galaxy mass profiles are significantly more compact than their rest-frame optical light profiles at cosmic noon, and demonstrate that spatial variations in age and attenuation are important, particularly for massive galaxies. The trend we find here impacts our understanding of the size growth and evolution of galaxies, and suggests that previous studies based on rest-frame optical light may not have captured the mass-weighted structural evolution of galaxies. This paper represents a first step toward a new understanding of the morphologies of early massive galaxies enabled by JWST's infrared window into the distant universe.

Keywords: galaxy evolution; galaxy formation; galaxy radii
The "Snow Line" on Venus's Maxwell Montes: Varying Elevation Implies a Dynamic Atmosphere

Radar images of Venus's tallest mountain range, Maxwell Montes, show a sharp increase in radar reflectivity, a "snow line," at high elevation. This snow line has been inferred to represent a single common elevation (and thus temperature and pressure) above which metallic or semimetal compounds are present on the surface, either as direct precipitates from the atmosphere or from atmosphere-rock chemical reactions. Here, we show that Maxwell's snow line is not at a constant elevation-it is ~3.5 km higher in the NW than the SE. The best explanation is that atmospheric composition is not constant across Maxwell. The higher snow line elevation to the NW can be interpreted as a snow shadow, produced as winds from the SE cross Maxwell and becomes progressively depleted in its snow-producing component.

Keywords: venus; radar observations; planetary boundary layers; planetary mineralogy