adsabs/SciX_UAT_keywords huggingface dataset:
The Full Kepler Phase Curve of the Eclipsing Hot White Dwarf Binary System KOI-964

We analyze the full Kepler phase curve of KOI-964, a binary system consisting of a hot white dwarf on an eclipsing orbit around an A-type host star. Using all 18 quarters of long-cadence photometry, we carry out a joint light-curve fit and obtain improved phase-curve amplitudes, occultation depths, orbital parameters, and transit ephemeris over the previous results of Carter et al. A periodogram of the residuals from the phase-curve fit reveals an additional stellar variability signal from the host star with a characteristic period of 0.620276 ± 0.000011 days and a full amplitude of 24 ± 2 ppm. We also present new Keck/HIRES radial velocity observations, which we use to measure the orbit and obtain a mass ratio of q = 0.106 ± 0.012. Combining this measurement with the results of a stellar isochrone analysis, we find that the masses of the host star and white dwarf companion are 2.23 ± 0.12 M ⊙ and {0.236}-0.027+0.028 {M}⊙ , respectively. The effective temperatures of the two components are {9940}-230+260 K and 15,080 ± 400 K, respectively, and we determine the age of the system to be {0.21}-0.08+0.11 Gyr. We use the measured system properties to compute predicted phase-curve amplitudes and find that while the measured Doppler-boosting and mutual illumination components agree well with theory, the ellipsoidal distortion amplitude is significantly underestimated. We detail possible explanations for this discrepancy, including interactions between the dynamical tide of the host star and the tidal bulge and possible nonsynchronous rotation of the host star.

Keywords: eclipsing binary stars
A Comptonized Fireball Bubble Fits the Second Extragalactic Magnetar Giant Flare GRB 231115A

Magnetar giant flares (MGFs), originating from noncatastrophic magnetars, share noteworthy similarities with some short gamma-ray bursts (GRBs). However, understanding their detailed origin and radiation mechanisms remains challenging due to limited observations. The discovery of MGF GRB 231115A, the second extragalactic MGF located in the Cigar galaxy at a luminosity distance of ∼3.5 Mpc, offers yet another significant opportunity for gaining insights into the aforementioned topics. This Letter explores its temporal properties and conducts a comprehensive analysis of both the time-integrated and time-resolved spectra through empirical and physical model fitting. Our results reveal certain properties of GRB 231115A that bear resemblances to GRB 200415A. We employ a Comptonized fireball bubble model, in which the Compton cloud, formed by the magnetar wind with high density e ±, undergoes Compton scattering and inverse Compton scattering, resulting in reshaped thermal spectra from the expanding fireball at the photosphere radius. This leads to dynamic shifts in dominant emission features over time. Our model successfully fits the observed data, providing a constrained physical picture, such as a trapped fireball with a radius of ∼1.95 × 105 cm and a high local magnetic field of 2.5 × 1016 G. The derived peak energy and isotropic energy of the event further confirm the burst's MGF origin and its contribution to the MGF-GRB sample. We also discuss prospects for further gravitational wave detection associated with MGFs, given their high-event-rate density (∼8 × 105 Gpc‑3 yr‑1) and ultrahigh local magnetic field.

Keywords: gamma-ray bursts; magnetars
Searching for Giant Exoplanets around M-dwarf Stars (GEMS) I: Survey Motivation

Recent discoveries of transiting giant exoplanets around M-dwarf stars (GEMS), aided by the all-sky coverage of TESS, are starting to stretch theories of planet formation through the core-accretion scenario. Recent upper limits on their occurrence suggest that they decrease with lower stellar masses, with fewer GEMS around lower-mass stars compared to solar-type. In this paper, we discuss existing GEMS both through confirmed planets, as well as protoplanetary disk observations, and a combination of tests to reconcile these with theoretical predictions. We then introduce the Searching for GEMS survey, where we utilize multidimensional nonparameteric statistics to simulate hypothetical survey scenarios to predict the required sample size of transiting GEMS with mass measurements to robustly compare their bulk-density with canonical hot Jupiters orbiting FGK stars. Our Monte Carlo simulations predict that a robust comparison requires about 40 transiting GEMS (compared to the existing sample of ∼15) with 5σ mass measurements. Furthermore, we discuss the limitations of existing occurrence estimates for GEMS and provide a brief description of our planned systematic search to improve the occurrence rate estimates for GEMS.

Keywords: exoplanet astronomy; exoplanet formation; exoplanet detection methods; radial velocity; transit photometry
Turbulence Properties of Interplanetary Coronal Mass Ejections in the Inner Heliosphere: Dependence on Proton Beta and Flux Rope Structure

Interplanetary coronal mass ejections (ICMEs) have low proton beta across a broad range of heliocentric distances and a magnetic flux rope structure at large scales, making them a unique environment for studying solar wind fluctuations. Power spectra of magnetic field fluctuations in 28 ICMEs observed between 0.25 and 0.95 au by Solar Orbiter and Parker Solar Probe have been examined. At large scales, the spectra were dominated by power contained in the flux ropes. Subtraction of the background flux rope fields increased the mean spectral index from -5/3 to -3/2 at kd i ≤ 10-3. Rope subtraction also revealed shorter correlation lengths in the magnetic field. The spectral index was typically near -5/3 in the inertial range at all radial distances regardless of rope subtraction and steepened to values consistently below -3 with transition to kinetic scales. The high-frequency break point terminating the inertial range evolved approximately linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale, as expected for plasma at low proton beta. Magnetic compressibility at inertial scales did not show any significant correlation with radial distance, in contrast to the solar wind generally. In ICMEs, the distinctive spectral properties at injection scales appear mostly determined by the global flux rope structure while transition-kinetic properties are more influenced by the low proton beta; the intervening inertial range appears independent of both ICME features, indicative of a system-independent scaling of the turbulence.

Keywords: solar coronal mass ejections; interplanetary magnetic fields; interplanetary turbulence; solar wind
Model-based Performance Characterization of Software Correlators for Radio Interferometer Arrays

Correlation for radio interferometer array applications, including Very Long Baseline Interferometry (VLBI), is a multidisciplinary field that traditionally involves astronomy, geodesy, signal processing, and electronic design. In recent years, however, high-performance computing has been taking over electronic design, complicating this mix with the addition of network engineering, parallel programming, and resource scheduling, among others. High-performance applications go a step further by using specialized hardware like Graphics Processing Units (GPUs) or Field Programmable Gate Arrays (FPGAs), challenging engineers to build and maintain high-performance correlators that efficiently use the available resources. Existing literature has generally benchmarked correlators through narrow comparisons on specific scenarios, and the lack of a formal performance characterization prevents a systematic comparison. This combination of ongoing increasing complexity in software correlation together with the lack of performance models in the literature motivates the development of a performance model that allows us not only to characterize existing correlators and predict their performance in different scenarios but, more importantly, to provide an understanding of the trade-offs inherent to the decisions associated with their design. In this paper, we present a model that achieves both objectives. We validate this model against benchmarking results in the literature, and provide an example for its application for improving cost-effectiveness in the usage of cloud resources.

Keywords: theoretical models; astronomy software; interferometric correlation; radio astronomy; radio interferometry; distributed computing
Prompt Emission and Early Optical Afterglow of Very-high-energy Detected GRB 201015A and GRB 201216C: Onset of the External Forward Shock

We present a detailed prompt emission and early optical afterglow analysis of the two very-high-energy (VHE) detected bursts GRB 201015A and GRB 201216C, and their comparison with a subset of similar bursts. Time-resolved spectral analysis of multistructured GRB 201216C using the Bayesian binning algorithm revealed that during the entire duration of the burst, the low-energy spectral index (α pt) remained below the limit of the synchrotron line of death. However, statistically some of the bins supported the additional thermal component. Additionally, the evolution of spectral parameters showed that both the peak energy (E p) and α pt tracked the flux. These results were further strengthened using the values of the physical parameters obtained by synchrotron modeling of the data. Our earliest optical observations of both bursts using the F/Photometric Robotic Atmospheric Monitor Observatorio del Roque de los Muchachos and Burst Observer and Optical Transient Exploring System robotic telescopes displayed a smooth bump in their early optical light curves, consistent with the onset of the afterglow due to synchrotron emission from an external forward shock. Using the observed optical peak, we constrained the initial bulk Lorentz factors of GRB 201015A and GRB 201216C to Γ0 = 204 and Γ0 = 310, respectively. The present early optical observations are the earliest known observations constraining outflow parameters and our analysis indicate that VHE detected bursts could have a diverse range of observed luminosity within the detectable redshift range of present VHE facilities.

Keywords: gamma-ray bursts
Evaluating the V-band Photometric Metallicity with Fundamental Mode RR Lyrae in the Kepler Field

The aim of this work is to evaluate the performance of photometric metallicity [Fe/H], determined based on V-band light curves photometrically transformed from the gr-band light curves. We tested this by using a set of homogeneous samples of fundamental mode RR Lyrae located in the Kepler field. It was found that the color term is necessary in such photometric transformation. We demonstrated that when including the color term the determined photometric [Fe/H] are in good agreement with the spectroscopic [Fe/H], either based on the calibrated or the transformed V-band light curves. We also tested the impact of Blazhko RR Lyrae in determining the photometric [Fe/H], and found that Blazhko RR Lyrae can give consistent photometric [Fe/H]. Finally, we derived independent gVr-band [Fe/H]-ϕ 31-P relations (where ϕ 31 and P are the Fourier parameter and pulsation period, respectively) using our light curves. The V-band relation is in good agreement with the most recent determination given in the literature.

Keywords: rr lyrae variable stars; metallicity; light curves
As a Matter of Dynamical Range - Scale Dependent Energy Dynamics in MHD Turbulence

Magnetized turbulence is ubiquitous in many astrophysical and terrestrial plasmas but no universal theory exists. Even the detailed energy dynamics in magnetohydrodynamic (MHD) turbulence are still not well understood. We present a suite of subsonic, super-Alfvénic, high plasma beta MHD turbulence simulations that only vary in their dynamical range, i.e., in their separation between the large-scale forcing and dissipation scales, and their dissipation mechanism (implicit large eddy simulation, ILES, and direct numerical simulation (DNS)). Using an energy transfer analysis framework we calculate the effective numerical viscosities and resistivities, and demonstrate that all ILES calculations of MHD turbulence are resolved and correspond to an equivalent visco-resistive MHD turbulence calculation. Increasing the number of grid points used in an ILES corresponds to lowering the dissipation coefficients, i.e., larger (kinetic and magnetic) Reynolds numbers for a constant forcing scale. Independently, we use this same framework to demonstrate that-contrary to hydrodynamic turbulence-the cross-scale energy fluxes are not constant in MHD turbulence. This applies both to different mediators (such as cascade processes or magnetic tension) for a given dynamical range as well as to a dependence on the dynamical range itself, which determines the physical properties of the flow. We do not observe any indication of convergence even at the highest resolution (largest Reynolds numbers) simulation at 20483 cells, calling into question whether an asymptotic regime in MHD turbulence exists, and, if so, what it looks like.

Keywords: magnetohydrodynamical simulations; magnetohydrodynamics; plasma astrophysics; magnetic fields; theoretical techniques; computational methods
Thermal Emission and Radioactive Lines, but No Pulsar, in the Broadband X-Ray Spectrum of Supernova 1987A

Supernova 1987A offers a unique opportunity to study an evolving supernova in unprecedented detail over several decades. The X-ray emission is dominated by interactions between the ejecta and the circumstellar medium, primarily the equatorial ring (ER). We analyze 3.3 Ms of NuSTAR data obtained between 2012 and 2020, and two decades of XMM-Newton data. Since ~2013, the flux below 2 keV has declined, the 3-8 keV flux has increased but has started to flatten, and the emission above 10 keV has remained nearly constant. The spectra are well described by a model with three thermal shock components. Two components at 0.3 and 0.9 keV are associated with dense clumps in the ER, and a 4 keV component may be a combination of emission from diffuse gas in the ER and the surrounding low-density H II region. We disfavor models that involve nonthermal X-ray emission and place constraints on nonthermal components, but cannot firmly exclude an underlying power law. Radioactive lines show a ${}^{44}\mathrm{Ti}$ redshift of ${670}_{-380}^{+520}$ $\,\mathrm{km}\,{{\rm{s}}}^{-1}$, ${}^{44}\mathrm{Ti}$ mass of ${1.73}_{-0.29}^{+0.27}\times {10}^{-4}$ ${M}_{\odot}$, and ${}^{55}\mathrm{Fe}$ mass of $\lt 4.2\times {10}^{-4}$ ${M}_{\odot}$. The 35-65 keV luminosity limit on the compact object is $2\times {10}^{34}$ erg s-1, and $\lt 15 \% $ of the 10-20 keV flux is pulsed. Considering previous limits, we conclude that there are currently no indications of a compact object, aside from a possible hint of dust heated by a neutron star in recent ALMA images.

Keywords: circumstellar matter; core-collapse supernovae; cosmic ray sources; explosive nucleosynthesis; shocks; supernova remnants
OGLE-2018-BLG-1269Lb: A Jovian Planet with a Bright I = 16 Host

We report the discovery of a planet in the microlensing event OGLE-2018-BLG-1269 with a planet-host mass ratio q ∼ 6 × 10-4, i.e., 0.6 times smaller than the Jupiter/Sun mass ratio. Combined with the Gaia parallax and proper motion, a strong one-dimensional constraint on the microlens parallax vector allows us to significantly reduce the uncertainties of lens physical parameters. A Bayesian analysis that ignores any information about light from the host yields that the planet is a cold giant $({M}_{2}={0.69}_{-0.22}^{+0.44}\,{M}_{{\rm{J}}})$ orbiting a Sun-like star $({M}_{1}={1.13}_{-0.35}^{+0.72}\,{M}_{\odot })$ at a distance of ${D}_{{\rm{L}}}={2.56}_{-0.62}^{+0.92}\,\mathrm{kpc}$ . The projected planet-host separation is ${a}_{\perp }={4.61}_{-1.17}^{+1.70}\,\mathrm{au}$ . Using Gaia astrometry, we show that the blended light lies $\lesssim 12\,\mathrm{mas}$ from the host and therefore must be either the host star or a stellar companion to the host. An isochrone analysis favors the former possibility at >99.6%. The host is therefore a subgiant. For host metallicities in the range of $0.0\leqslant [\mathrm{Fe}/{\rm{H}}]\leqslant +0.3$ , the host and planet masses are then in the range of $1.16\leqslant {M}_{1}/{M}_{\odot }\leqslant 1.38$ and $0.74\leqslant {M}_{2}/{M}_{{\rm{J}}}\leqslant 0.89$ , respectively. Low host metallicities are excluded. The brightness and proximity of the lens make the event a strong candidate for spectroscopic follow-up both to test the microlensing solution and to further characterize the system.

Keywords: gravitational microlensing; gravitational microlensing exoplanet detection
The Rate and Spatial Distribution of Novae in M31 as Determined by a 20 Year Survey

A long-term (1995-2016) survey for novae in the nearby Andromeda galaxy (M31) was conducted as part of the Research-Based Science Education initiative. During the course of the survey 180 nights of observation were completed at Kitt Peak, Arizona. A total of 262 novae were either discovered or confirmed, 40 of which have not been previously reported. Of these, 203 novae form a spatially complete sample detected by the KPNO/WIYN 0.9 m telescope within a $20^{\prime} \times 20^{\prime} $ field centered on the nucleus of M31. An additional 50 novae are part of a spatially complete sample detected by the KPNO 4 m telescope within a larger $36^{\prime} \times 36^{\prime} $ field. Consistent with previous studies, it is found that the spatial distribution of novae in both surveys follows the bulge light of M31 somewhat more closely than the overall background light of the galaxy. After correcting for the limiting magnitude and the spatial and temporal coverage of the surveys, a final nova rate in M31 is found to be $R={40}_{-4}^{+5}$ yr-1, which is considerably lower than recent estimates. When normalized to the K-band luminosity of M31, this value yields a luminosity-specific nova rate, ν K = 3.3 ± 0.4 yr ${}^{-1}\,{[{10}^{10}\,{L}_{\odot ,K}]}^{-1}$ . By scaling the M31 nova rate using the relative infrared luminosities of M31 and our Galaxy, a nova rate of ${R}_{{\rm{G}}}={28}_{-4}^{+5}$ yr-1 is found for the Milky Way.

Keywords: classical novae; cataclysmic variable stars; galaxies; novae; time domain astronomy
Photoelectron Butterfly Pitch-angle Distributions in the Martian Ionosphere Based on MAVEN Observations

Using pitch-angle-resolved electron fluxes recorded by the Mars Atmosphere and Volatile Evolution spacecraft over 5 yr, we present a detailed analysis of the occurrence patterns of photoelectron butterfly pitch-angle distributions (PADs) in the Martian ionosphere. Statistical analysis indicates that Martian photoelectron butterfly PADs favorably occur near the moderate crustal magnetic fields with a strength of 10-30 nT on the dayside and 10-15 nT on the nightside. The nightside occurrence rates are much higher. Furthermore, dayside butterfly PADs prefer to occur near the vertical magnetic field lines in the ionosphere, and the significant day-to-night transport of photoelectrons evades the nightside strongest magnetic anomaly regions. These features strongly support the idea that Martian photoelectron butterfly PADs are more likely to occur in eclipse or near the terminator and that they mainly form due to the adiabatic evolution of photoelectrons that transport along the closed cross-terminator magnetic field lines. Despite the negligible energy dependence in the darkness, the occurrence rate of dayside butterfly PADs observed at higher altitudes and near the subsolar region increases with energy, presumably related to the increased proportion of electrons from the solar wind when measured at relatively higher electron energies, which, however, is limitedly understood and deserves future investigation. Our comprehensive observations suggest the diverse influence of Martian magnetic topology on the ionospheric plasma in different spatial regions, and, in turn, analysis of their influence allows us a better understanding of the intricate Martian global magnetic system.

Keywords: mars; solar-planetary interactions; planetary ionospheres
The Recurrent Nova IM Normae: A UV Spectroscopic Twin of T Pyxidis

We present an HST COS spectrum of the short orbital period recurrent nova IM Normae. We compare its far-ultraviolet spectrum with the HST COS spectrum of the recurrent nova T Pyxidis, both spectra obtained in deep quiescence. Despite the poor signal-to-noise ratio of the IM Nor spectrum, it seems clear that the two recurrent novae are quite similar to each other. This conclusion is consistent with optical similarities in their light curves. In terms of distinctions, the presence of higher excitation features such as O V (1371) and N V (1240) in IM Nor may suggest that the accretion disk is hotter and the accretion rate is higher than those of T Pyx.

Keywords: cataclysmic variable stars; stellar accretion; white dwarf stars; recurrent novae; type ia supernovae
X-Ray Constraints on the Hot Gas Content of Early-type Galaxies in Virgo

We present a systematic study of the diffuse hot gas around early-type galaxies (ETGs) residing in the Virgo cluster, based on archival Chandra observations. Our representative sample consists of 79 galaxies with low-to-intermediate stellar masses (M* ≈ 109-11 M⊙), a mass range that has not been extensively explored with X-ray observations thus far. We detect diffuse X-ray emission in only eight galaxies and find that in five cases a substantial fraction of the detected emission can be unambiguously attributed to truly diffuse hot gas, based on their spatial distribution and spectral properties. For the individually nondetected galaxies, we constrain their average X-ray emission by performing a stacking analysis, finding a specific X-ray luminosity of ${L}_{X}/{M}_{* }\sim {10}^{28}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{M}_{\odot }^{-1}$ , which is consistent with unresolved stellar populations. The apparent paucity of truly diffuse hot gas in these low- and intermediate-mass ETGs may be the result of efficient ram pressure stripping by the hot intracluster medium. However, we also find no significant diffuse hot gas in a comparison sample of 57 field ETGs of similar stellar masses, for which archival Chandra observations with similar sensitivity are available. This points to the alternative possibility that galactic winds evacuate the hot gas from the inner region of low- and intermediate-mass ETGs, regardless of the galactic environment. Nevertheless, we do find strong morphological evidence for ongoing ram pressure stripping in two galaxies (NGC 4417 and NGC 4459). A better understanding of the roles of ram pressure stripping and galactic winds in regulating the hot gas content of ETGs invites sensitive X-ray observations for a large galaxy sample.

Keywords: virgo cluster; early-type galaxies; x-ray astronomy; extended radiation sources; galaxy environments