adsabs/SciX_UAT_keywords huggingface dataset:
Measuring He I Stark Line Shapes in the Laboratory to Examine Differences in Photometric and Spectroscopic DB White Dwarf Masses

Accurate helium White Dwarf (DB) masses are critical for understanding the star's evolution. DB masses derived from the spectroscopic and photometric methods are inconsistent. Photometric masses agree better with currently accepted DB evolutionary theories and are mostly consistent across a large range of surface temperatures. Spectroscopic masses rely on untested He I Stark line-shape and Van der Waals broadening predictions, show unexpected surface temperature trends, and are thus viewed as less reliable. To test this conclusion, we present in this paper detailed He I Stark line-shape measurements at conditions relevant to DB atmospheres (T electron ≈12,000-17,000 K, n electron ≈ 1017 cm-3). We use X-rays from Sandia National Laboratories' Z-machine to create a uniform ≈120 mm long hydrogen-helium mixture plasma. Van der Waals broadening is negligible at our experimental conditions, allowing us to measure He I Stark profiles only. Hβ, which has been well-studied in our platform and elsewhere, serves as the n e diagnostic. We find that He I Stark broadening models used in DB analyses are accurate within errors at tested conditions. It therefore seems unlikely that line-shape models are solely responsible for the observed spectroscopic mass trends. Our results should motivate the WD community to further scrutinize the validity of other spectroscopic and photometric input parameters, like atmospheric structure assumptions and convection corrections. These parameters can significantly change the derived DB mass. Identifying potential weaknesses in any input parameters could further our understanding of DBs, help elucidate their evolutionary origins, and strengthen confidence in both spectroscopic and photometric masses.

Keywords: white dwarf stars; db stars; laboratory astrophysics; atomic physics; plasma physics
New Constraints on Titan's Stratospheric n-Butane Abundance

Curiously, n-butane has yet to be detected at Titan, though it is predicted to be present in a wide range of abundances that span over 2.5 orders of magnitude. We have searched infrared spectroscopic observations of Titan for signals from n-butane (n-C4H10) in Titan's stratosphere. Three sets of Cassini Composite Infrared Spectrometer Focal Plane 4 (1050-1500 cm-1) observations were selected for modeling, having been collected from different flybys and pointing latitudes. We modeled the observations with the Nonlinear Optimal Estimator for MultivariatE Spectral AnalySIS radiative transfer tool. Temperature profiles were retrieved for each of the data sets by modeling the ν 4 emission from methane near 1305 cm-1. Then, incorporating the temperature profiles, we retrieved abundances of all of Titan's known trace gases that are active in this spectral region, reliably reproducing the observations. We then systematically tested a set of models with varying abundances of n-butane, investigating how the addition of this gas affected the fits. We did this for several different photochemically predicted abundance profiles from the literature, as well as for a constant-with-altitude profile. Ultimately, though we did not produce any firm detection of n-butane, we derived new upper limits on its abundance specific to the use of each profile and to multiple different ranges of stratospheric altitudes. These results will tightly constrain the C4 chemistry of future photochemical modeling of Titan's atmosphere and also motivate the continued search for n-butane and its isomer, isobutane.

Keywords: titan; saturnian satellites; solar system; planetary science; planetary atmospheres; atmospheric composition; natural satellite atmospheres
How Cost Impacts Equitable Participation in Astronomy Outreach Events

The International Astronomical Youth Camp (IAYC) is an astronomy education outreach event with more than 50 yr of history and over 1700 unique participants from 81 nationalities. The International Workshop for Astronomy e.V. is the non-profit organization behind the IAYC, established in 1979 and based in Germany. The IAYC's unprecedented longevity in a rapidly globalizing world has meant that financial inequities decreases the reach of the camp to people from the Global South compared to Global North countries. Though nationalities represented per camp has increased steadily since its inception, the share of participants from eastern Europe and Africa has dropped, while those from western Europe and North America have increased. This note examines how camp cost, location, and leadership affects nationality diversity among participants, and how astronomy outreach events must reckon with funding for less privileged participants with limited access to resources.

Keywords: astronomy education
Eccentricity Distribution beyond the Snow Line and Implications for Planetary Habitability

A fundamental question in the study of planetary system demographics is: how common is the solar system architecture? The primary importance of this question lies in the potential of planetary systems to create habitable environments, and dissecting the various components of solar system evolution that contributed to a sustainable temperate surface for Earth. One important factor in that respect is volatile delivery to the inner system and the dependence on giant planets beyond the snow line as scattering agents, particularly as such cold giant planets are relatively rare. Here, we provide an investigation of the eccentricity distribution for giant planet populations both interior and exterior to their system snow lines. We show that the median eccentricity for cold giants is 0.23, compared with a far more circular orbital regime for inner planets. We further present the results of a dynamical simulation that explores the particle scattering potential for a Jupiter analog in comparison with a Jupiter whose eccentricity matches that of the median cold giant eccentricity. These simulations demonstrate that the capacity for such an eccentric cold giant system to scatter volatiles interior to the snow line is significantly increased compared with the Jupiter analog case, resulting in a far greater volume of Earth-crossing volatiles. Thus, many of the known systems with cold giant planets may harbor water worlds interior to the snow line.

Keywords: habitable zone; exoplanets; exoplanet systems; exoplanet dynamics; exoplanet evolution; orbits; orbital evolution; solar system; solar system gas giant planets; solar system evolution
Tracing Dark Energy History with Gamma-Ray Bursts

Observations of gamma-ray bursts up to z ∼ 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble's diagram and then we estimate the set (Ωm, ΩΛ) in the framework of flat and non-flat ΛCDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4σ, i.e., H0 = (67.4 ± 0.5) km s-1 Mpc-1 and H0 = (74.03 ± 1.42) km s-1 Mpc-1. We show our new sample provides tighter constraints on Ωm since at z ≤ 1.2 we see that w(z) agrees within 1σ with the standard value w = -1. The situation is the opposite at larger z, where gamma-ray bursts better fix w(z) that seems to deviate from w = -1 at 2σ and 4σ level, depending on the redshift bins. In particular, we investigate the w(z) evolution through a piecewise formulation over seven redshift intervals. From our fitting procedure we show that at z ≥ 1.2 the case w < -1 cannot be fully excluded, indicating that dark energy's influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper.

Keywords: standard candles; dark energy; gamma-ray bursts
A Search for Rapid Mid-infrared Variability in Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

Fermi-LAT's detection of γ-rays from narrow-line Seyfert 1 galaxies (NLS1s) has received increasing attention. Understanding these γ-NLS1s is of interest because they have some properties similar to blazars, which are known to show rapid and large-amplitude variability. Based on the largest sample of γ-NLS1s (25 sources), we carried out a systematic search for rapid mid-infrared (MIR, 3.4 and 4.6 μm) variability using the multiepoch data of the Wide-field Infrared Survey Explorer (WISE). We also compared a few variability properties between γ-NLS1s and γ-ray blazars. Our main results are as follows. (1) Thirteen γ-NLS1s showed significant (>3σ) rapid variability in at least one of the two MIR bands. The MIR emission of these sources is dominated by the synchrotron emission of relativistic electrons in the jet. (2) The γ-NLS1s with flat radio spectra are more variable than those not detected in γ-rays. (3) The γ-NLS1s tend to show smaller amplitude of variability as well as lower duty cycle relative to γ-ray blazars. (4) The γ-NLS1s tend to show a trend of bluer-when-brighter on both intraday and long timescales, similar to γ-ray blazars. (5) The γ-NLS1s that are more variable on long timescales have larger amplitudes of variability and higher duty cycles on intraday timescales. (6) In the majority of cases, the γ-NLS1s fall in the WISE Gamma-ray Blazar Strip (WGS). However, we noted migrations outside of the WGS due to significant variability.

Keywords: seyfert galaxies; infrared astronomical satellite; infrared photometry; gamma-ray sources
The Ultraviolet Deep Imaging Survey of Galaxies in the Bootes Void. I. Catalog, Color-Magnitude Relations, and Star Formation

We present a deep far and near-ultraviolet (FUV and NUV) wide-field imaging survey of galaxies in the Bootes void using the Ultraviolet Imaging Telescope on board AstroSat. Our data reach 5σ limiting magnitudes for point sources at 23.0 and 24.0 AB mag in the FUV and NUV, respectively. We report a total of six star-forming galaxies residing in the Bootes void alongside the full catalog, and of these, three are newly detected in our FUV observation. Our void galaxy sample spans a range of UV colors (-0.35 mag ≤ FUV-NUV ≤ 0.68 mag) and absolute magnitudes (-14.16 mag ≤ MNUV ≤ -18.65 mag). In addition, Sloan Digital Sky Survey and Two Micron All Sky Survey archival data are being used to study UV, optical, and infrared color-magnitude relations for our galaxies in the void. We investigate the nature of bimodal color distribution, morphologies, and star formation of the void galaxies. Most of the galaxies in our sample are fainter and less massive than L* galaxies, with Mr > -20 mag. Our analysis reveals a dominant fraction of bluer galaxies over the red ones in the void region probed. The internal and Galactic extinction corrected FUV star formation rates (SFRs) in our void galaxy catalog varies in a large range of 0.05-51.01 M⊙ yr-1, with a median of 3.96 M⊙ yr-1. We find a weak effect of the environment on the SFRs of galaxies. Implications of our findings are discussed.

Keywords: star formation; ultraviolet surveys; catalogs; voids; galaxy properties
Magnetohydrodynamic Wave Mode Identification in Circular and Elliptical Sunspot Umbrae: Evidence for High-order Modes

In this paper, we provide clear direct evidence of multiple concurrent higher-order magnetohydrodynamic (MHD) modes in circular and elliptical sunspots by applying both proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques on solar observational data. These techniques are well documented and validated in the areas of fluid mechanics, hydraulics, and granular flows but are relatively new to the field of solar physics. While POD identifies modes based on orthogonality in space and provides a clear ranking of modes in terms of their contribution to the variance of the signal, DMD resolves modes that are orthogonal in time. The clear presence of the fundamental slow sausage and kink body modes, as well as higher-order slow sausage and kink body modes, have been identified using POD and DMD analysis of the chromospheric Hα line at 6562.808 Å for both the circular and elliptical sunspots. Additionally, for the various slow body modes, evidence for the presence of the fast surface kink mode was found in the circular sunspot. All of the MHD mode patterns were cross-correlated with their theoretically predicted counterparts, and we demonstrated that ellipticity cannot be neglected when interpreting MHD wave modes. The higher-order MHD wave modes are even more sensitive to irregularities in umbral cross-sectional shapes; hence, this must be taken into account for more accurate modeling of the modes in sunspots and pores.

Keywords: sunspots; solar physics; wavelet analysis; umbra
Constraints on Sub-Neptune Planet Candidate KOI-972.01 via Joint Variability/Gravity-darkening Analysis

We analyze Kepler photometry of transiting planet candidate KOI-972.01, accounting for both stellar variability and gravity darkening. KOI-972.01 stands out because of its small radius, less than that of Neptune, and because of its intermediate orbit period at 13.12 days, long enough to avoid significant tidal evolution, and thus it represents an underexplored exoplanet class. The parent star of KOI-972.01 is a rapidly rotating δ-Scuti variable, complicating transit lightcurve interpretation but also offering a potential independent source of stellar parameters. We measure the stellar rotation period (16.2 hr) by identifying the stellar rotation frequency and subsequently place a constraint on the stellar obliquity of no greater than 10°, but have difficulty isolating individual oscillation modes in the periodogram owing to time variation of the δ-Scuti oscillations. After subtracting the stellar oscillations, lightcurve fits place the transiting object radius at 3.07 ± 0.09 R⊕, but the shallow transit prevents useful constraints on the system's spin-orbit alignment.

Keywords: exoplanet formation; exoplanet astronomy; exoplanet evolution; exoplanet systems; mini neptunes; planetary alignment; gravity darkening
Limiting the Abundance of LIGO/Virgo Black Holes with Microlensing Observations of Quasars of Finite Size

We present a simple but general argument that strongly limits the abundance of primordial black holes (PBHs) (or other unknown population of compact objects) with masses similar to those determined by LIGO/Virgo from BH binary mergers. We show that quasar microlensing can be very sensitive to the mass of the lenses, and that it is able to distinguish between stars and BHs of high mass, when the finite size of the source is taken into account. A significant presence of massive BHs would produce frequent high-flux magnifications (except for unrealistically large sources), which have been very rarely observed. On the contrary, a typical stellar population would induce flux magnifications consistent with the observations. This result excludes PBHs (or any type of compact object) in the mass range determined by LIGO/Virgo as the main dark matter constituents in the lens galaxies.

Keywords: cosmology; dark matter; primordial black holes; astrophysical black holes; quasar microlensing; gravitational lensing
Observational Evidence for Enhanced Black Hole Accretion in Giant Elliptical Galaxies

We present a study of the relationship between black hole accretion rate (BHAR) and star formation rate (SFR) in a sample of giant elliptical galaxies. These galaxies, which live at the centers of galaxy groups and clusters, have star formation and black hole activity that is primarily fueled by gas condensing out of the hot intracluster medium. For a sample of 46 galaxies spanning five orders of magnitude in BHAR and SFR, we find a mean ratio of ${\mathrm{log}}_{10}(\mathrm{BHAR}/\mathrm{SFR})=-1.45\pm 0.2$ , independent of the methodology used to constrain both SFR and BHAR. This ratio is significantly higher than most previously published values for field galaxies. We investigate whether these high BHAR/SFR ratios are driven by high BHAR, low SFR, or a different accretion efficiency in radio galaxies. The data suggest that the high BHAR/SFR ratios are primarily driven by boosted black hole accretion in spheroidal galaxies compared to their disk counterparts. We propose that the angular momentum of the cool gas is the primary driver in suppressing BHAR in lower-mass galaxies, with massive galaxies accreting gas that has condensed out of the hot phase on nearly radial trajectories. Additionally, we demonstrate that the relationship between specific BHAR and SFR (sBHAR and sSFR) has much less scatter over six orders of magnitude in both parameters, due to competing dependence on morphology between the MBH-M* and BHAR-SFR relations. In general, active galaxies selected by typical techniques have sBHAR/sSFR ∼ 10, while galactic nuclei with no clear AGN signatures have sBHAR/sSFR ∼ 1, consistent with a universal MBH-Mspheroid relation.

Keywords: brightest cluster galaxies; galaxy clusters; galaxy groups; active galactic nuclei; radio active galactic nuclei; x-ray active galactic nuclei; black hole physics; supermassive black holes; giant elliptical galaxies
A Dynamic Deep-learning Model for Generating a Magnetogram Sequence from an SDO/AIA EUV Image Sequence

The solar magnetic field dominates solar activities in the solar atmosphere, such as solar flares and coronal mass ejections (CMEs). The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) has been in operation from 2010, providing a full-disk photospheric magnetogram. However, with a single view of observation, SDO/HMI cannot provide a global view of the Sun at the same time, so the farside of the Sun is blind to us. The Solar Terrestrial Relations Observatory (STEREO) provides two different views of the Sun with complementary viewing angles relative to SDO/HMI. However, it did not carry a magnetograph, but an extreme-ultraviolet (EUV) imager. Fortunately, deep learning has been proved to generate a solar farside magnetogram from STEREO farside EUV observation. Although a single generated magnetogram is morphologically very similar to ground truth, the sequence of the generated magnetogram has noticeable magnetic field fluctuation, which cannot be ignored when it is displayed as a time series, especially at an active region. This fluctuation is represented by sudden magnetic polarity reversal and drifting of magnetic field distribution. To mitigate this problem, a novel dynamic deep-learning model by integrating a convolutional gated recurrent units (convGRU) model into a pix2pix baseline is proposed in this paper. It can generate a sequence of a magnetogram with smooth transition among consecutive magnetograms by exploring spatio-temporal information of an input EUV image sequence. From both quantitative and qualitative comparisons, the proposed model can generate a magnetogram sequence more close to real observation.

Keywords: solar active regions; convolutional neural networks; detection
Star Photometry for DECam Legacy Survey and Sloan Digital Sky Survey Images Based on Convolutional Neural Networks

Flux is one of the most fundamental parameters in astrophysics, and aperture photometry and point-spread function (PSF) photometry are commonly used methods to obtain the flux. With the continuous development of astronomical equipment that has generated massive data, researchers have to find more effective methods to obtain stellar fluxes. However, current photometric software such as SExtractor are very sensitive to the configuration parameters and are difficult to configure. We propose a new photometric model based on deep learning called sf-convolutional neural network (CNN) to extract aperture fluxes and PSF fluxes. For the simulated data including 5727 stars, the experimental results show that sf-CNN can predict fluxes better than SExtractor. The mean absolute error (MAE) values of sf-CNN and SExtractor for predicting PSF fluxes are 0.0034 and 0.0134, respectively. On the 6293 mixed stars in DECam Legacy Survey Data Release (DR) 9, the MAE values of the predicted PSF fluxes are 0.0075 and 0.0177, respectively. The PSF accuracy of the sf-CNN model is significantly higher than that of SExtractor. Additionally, the MAE values of the predicted aperture fluxes on 6215 mixed stars and 1341 blends of stars in Sloan Digital Sky Survey DR 12 illustrate that the accuracy of sf-CNN is still the highest. Meanwhile, the results indicate that sf-CNN outperforms VGG16 and ResNet50. Furthermore, sf-CNN is 100-200 times faster than Photutils on RTX 3070 GPU and 20-40 times faster than Photutils on I7 12700 CPU. sf-CNN can calculate fluxes efficiently and accurately only by setting a few parameters and may thus become a fundamental tool for the era of big data in astronomy.

Keywords: stellar photometry; convolutional neural networks; surface photometry; fundamental parameters of stars; ccd photometry
Large-scale Volcanism and the Heat Death of Terrestrial Worlds

Large-scale volcanism has played a critical role in the long-term habitability of Earth. Contrary to widely held belief, volcanism, rather than impactors, has had the greatest influence on and bears most of the responsibility for large-scale mass extinction events throughout Earth's history. We examine the timing of large igneous provinces (LIPs) throughout Earth's history to estimate the likelihood of nearly simultaneous events that could drive a planet into an extreme moist or runaway greenhouse, leading to the end of volatile cycling and causing the heat death of formerly temperate terrestrial worlds. In one approach, we make a conservative estimate of the rate at which sets of near-simultaneous LIPs (pairs, triplets, and quartets) occur in a random history statistically the same as Earth's. We find that LIPs closer in time than 0.1-1 million yr are likely; significantly, this is less than the time over which terrestrial LIP environmental effects are known to persist. In another approach, we assess the cumulative effects with simulated time series consisting of randomly occurring LIP events with realistic time profiles. Both approaches support the conjecture that environmental impacts of LIPs, while narrowly avoiding grave effects on the climate history of Earth, could have been responsible for the heat death of our sister world Venus.

Keywords: volcanism; planetary climates; venus; earth (planet)