adsabs/SciX_UAT_keywords huggingface dataset:
Photosphere Recession and Luminosity of Homologous Explosions Revisited

By assuming the photosphere located at the outmost edge of the ejecta, Arnett et al. (1980, 1982, 1989) presented the light curves of homologous explosions in supernovae analytically and numerically to include recombination effects. Actually as homologous expansion proceeds, the photosphere recedes deeper into the ejecta. In this situation, the photosphere radius increases at early times and decreases later on, which can be described by a simple method proposed by Liu et al. To study how the photosphere recession affects the luminosity evolution, we impose a boundary condition on the photosphere to determine the spatial and time distribution of the temperature of the ejecta, which is clarified to be reasonable. We find that the photosphere recession reduces the luminosity compared with the previous result without the recession, which can be tested with observations of Type-IIP supernovae.

Keywords: core-collapse supernovae
Claimed Detection of PH3 in the Clouds of Venus Is Consistent with Mesospheric SO2

The observation of a 266.94 GHz feature in the Venus spectrum has been attributed to phosphine (PH3) in the Venus clouds, suggesting unexpected geological, chemical, or even biological processes. Since both PH3 and sulfur dioxide (SO2) are spectrally active near 266.94 GHz, the contribution to this line from SO2 must be determined before it can be attributed, in whole or part, to PH3. An undetected SO2 reference line, interpreted as an unexpectedly low SO2 abundance, suggested that the 266.94 GHz feature could be attributed primarily to PH3. However, the low SO2 and the inference that PH3 was in the cloud deck posed an apparent contradiction. Here we use a radiative transfer model to analyze the PH3 discovery, and explore the detectability of different vertical distributions of PH3 and SO2. We find that the 266.94 GHz line does not originate in the clouds, but above 80 km in the Venus mesosphere. This level of line formation is inconsistent with chemical modeling that assumes generation of PH3 in the Venus clouds. Given the extremely short chemical lifetime of PH3 in the Venus mesosphere, an implausibly high source flux would be needed to maintain the observed value of 20 ± 10 ppb. We find that typical Venus SO2 vertical distributions and abundances fit the JCMT 266.94 GHz feature, and the resulting SO2 reference line at 267.54 GHz would have remained undetectable in the ALMA data due to line dilution. We conclude that nominal mesospheric SO2 is a more plausible explanation for the JCMT and ALMA data than PH3.

Keywords: venus; radiative transfer; biosignatures
Dynamical Structures Associated with High-Order and Secondary Resonances in the Spin–Orbit Problem

In our solar system, spin–orbit resonances are common under Sun–planet, planet–satellite, and binary asteroid configurations. In this work, high-order and secondary spin–orbit resonances are investigated by taking numerical and analytical approaches. Poincaré sections as well as two types of dynamical maps are produced, showing that there are complicated structures in the phase space. To understand numerical structures, we adopt the theory of perturbative treatments to formulate resonant Hamiltonian for describing spin–orbit resonances. The results show that there is an excellent agreement between analytical and numerical structures. It is concluded that the main V-shape structure arising in the parameter space $(\dot{\theta },\alpha )$ is sculpted by the synchronous primary resonance, those minute structures inside the V-shape region are dominated by secondary resonances and those structures outside the V-shape region are governed by high-order resonances. Finally, the analytical approach is applied to binary asteroid systems (65803) Didymos and (4383) Suruga to reveal their phase-space structures.

Keywords: celestial mechanics; perturbation methods
Magnetic Switchback Occurrence Rates in the Inner Heliosphere: Parker Solar Probe and 1 au

The subject of switchbacks, defined either as large angular deflections or polarity reversals of the magnetic field, has generated substantial interest in the space physics community since the launch of the Parker Solar Probe (PSP) in 2018. Previous studies have characterized switchbacks in several different ways and have been restricted to data available from the first few orbits. Here, we analyze the frequency of occurrence of switchbacks per unit distance for the first full eight orbits of PSP. In this work, events that reverse the sign of the magnetic field relative to a regional average are considered switchbacks. A significant finding is that the rate of occurrence falls off sharply approaching the Sun near 0.2 au (40 R ⊙) and rises gently from 0.2 au outward. The analysis is varied for different magnetic field cadences and for different local averages of the ambient field, confirming the robustness of the results. We discuss implications for the mechanisms of switchback generation. A publicly available database has been created with the identified reversals.

Keywords: interplanetary magnetic fields; interplanetary medium; interplanetary turbulence
Taming the TuRMoiL: The Temperature Dependence of Turbulence in Cloud–Wind Interactions

Turbulent radiative mixing layers play an important role in many astrophysical contexts where cool (≲104 K) clouds interact with hot flows (e.g., galactic winds, high-velocity clouds, infalling satellites in halos and clusters). The fate of these clouds (as well as many of their observable properties) is dictated by the competition between turbulence and radiative cooling; however, turbulence in these multiphase flows remains poorly understood. We have investigated the emergent turbulence arising in the interaction between clouds and supersonic winds in hydrodynamic ENZO-E simulations. In order to obtain robust results, we employed multiple metrics to characterize the turbulent velocity, v turb. We find four primary results when cooling is sufficient for cloud survival. First, v turb manifests clear temperature dependence. Initially, v turb roughly matches the scaling of sound speed on temperature. In gas hotter than the temperature where cooling peaks, this dependence weakens with time until v turb is constant. Second, the relative velocity between the cloud and wind initially drives rapid growth of v turb. As it drops (from entrainment), v turb starts to decay before it stabilizes at roughly half its maximum. At late times, cooling flows appear to support turbulence. Third, the magnitude of v turb scales with the ratio between the hot phase sound-crossing time and the minimum cooling time. Finally, we find tentative evidence for a length scale associated with resolving turbulence. Underresolving this scale may cause violent shattering and affect the cloud's large-scale morphological properties.

Keywords: galaxy evolution; hydrodynamical simulations; interstellar clouds; circumgalactic medium; galactic winds
Discovery of a Young, Highly Scattered Pulsar PSR J1032-5804 with the Australian Square Kilometre Array Pathfinder

We report the discovery of a young, highly scattered pulsar in a search for highly circularly polarized radio sources as part of the Australian Square Kilometre Array Pathfinder Variables and Slow Transients survey. In follow-up observations with the Parkes radio telescope, Murriyang, we identified PSR J1032‑5804 and measured a period of 78.7 ms, a dispersion measure of 819 ± 4 pc cm‑3, a rotation measure of ‑2000 ± 1 rad m‑2, and a characteristic age of 34.6 kyr. We found a pulse scattering timescale at 3 GHz of ∼22 ms, implying a timescale at 1 GHz of ∼3845 ms, which is the third most scattered pulsar known and explains its nondetection in previous pulsar surveys. We discuss the identification of a possible pulsar wind nebula and supernova remnant in the pulsar's local environment by analyzing the pulsar spectral energy distribution and the surrounding extended emission from multiwavelength images. Our result highlights the possibility of identifying extremely scattered pulsars from radio continuum images. Ongoing and future large-scale radio continuum surveys will offer us an unprecedented opportunity to find more extreme pulsars (e.g., highly scattered, highly intermittent, and highly accelerated), which will enhance our understanding of the characteristics of pulsars and the interstellar medium.

Keywords: neutron stars; galactic radio sources; radio pulsars; interstellar scattering
PEARLS: A Potentially Isolated Quiescent Dwarf Galaxy with a Tip of the Red Giant Branch Distance of 30 Mpc

A wealth of observations have long suggested that the vast majority of isolated classical dwarf galaxies (M * = 107–109 M ⊙) are currently star forming. However, recent observations of the large abundance of "ultra-diffuse galaxies" beyond the reach of previous large spectroscopic surveys suggest that our understanding of the dwarf galaxy population may be incomplete. Here we report the serendipitous discovery of an isolated quiescent dwarf galaxy in the nearby Universe, which was imaged as part of the JWST PEARLS Guaranteed Time Observation program. Remarkably, individual red-giant branch stars are visible in this near-IR imaging, suggesting a distance of 30 ± 4 Mpc, and a wealth of archival photometry point to an sSFR of 2 × 10‑11 yr‑1 and star formation rate of 4 × 10‑4 M ⊙ yr‑1. Spectra obtained with the Lowell Discovery Telescope find a recessional velocity consistent with the Hubble Flow and >1500 km s‑1 separated from the nearest massive galaxy in Sloan Digital Sky Survey suggesting that this galaxy was either quenched from internal mechanisms or had a very high-velocity (≳1000 km s‑1) interaction with a nearby massive galaxy in the past. This analysis highlights the possibility that many nearby quiescent dwarf galaxies are waiting to be discovered and that JWST has the potential to resolve them.

Keywords: low surface brightness galaxies; james webb space telescope; dwarf galaxies; stellar populations; galaxy evolution
Insight-HXMT Observation of 4U 1608-52: Evidence of Interplay between a Thermonuclear Burst and Accretion Environment

A Type I burst could influence the accretion process through radiation pressure and Comptonization both for the accretion disk and the corona/boundary layer of an X-ray binary, and vice versa. We investigate the temporal evolution of a bright photospheric radius expansion (PRE) burst of 4U 1608-52 detected by Insight-HXMT in 1-50 keV, with the aim to study the interplay between the burst and persistent emission. Apart from the emission from the neutron star (NS) surface, we find residuals in both the soft (<3 keV) and hard (>10 keV) X-ray bands. Time-resolved spectroscopy reveals that the excess can be attributed to either an enhanced preburst/persistent emission or the Comptonization of the burst emission by the corona/boundary layer. The Comptonization model is a convolution thermal-Comptonization model (thcomp in XSPEC), and the Comptonization parameters are fixed at the values derived from the persistent emission. We find, during the PRE phase, after the enhanced preburst/persistent emission or the Comptonization of the burst emission is removed, the NS surface emission shows a plateau and then a rise until the photosphere touches down on the NS surface, resulting in a flux peak at that moment. We speculate that the findings above correspond to the lower part of the NS surface that is obscured by the disk being exposed to the line of sight due to the evaporation of inner disk by the burst emission. The consistency between the f a model and convolution thermal-Comptonization model indicates the interplay between thermonuclear bursts and accretion environments. These phenomena do not usually show up in conventional blackbody model fittings, which may be due to the low count rate and narrow energy coverage in previous observations.

Keywords: x-ray bursters
The Line Variability of 78 Vir (A2p SrCrEu) in the Far-ultraviolet

Line variations are studied in the far-ultraviolet spectra of 78 Vir collected with International Ultraviolet Explorer at phases of far-UV maximum and at phases of far-UV minimum. The far-UV spectrum of 78 Vir is populated with low-excitation transitions of light elements and iron-peak elements. The low excitation C I and N I lines are stronger at phases of far-UV minimum. Carbon appears to be underabundant and aluminum very underabundant in the atmosphere of 78 Vir. The lines of Si I and Si II are stronger at phases of far-UV minimum. Many lines which strengthen at phases of far-UV minimum are due to low-excitation lines of Fe II and Cr II which suggests that both iron and chromium are unevenly distributed over the surface of 78 Vir.

Keywords: chemically peculiar stars; ap stars
A Search for Lensed Lyα Emitters within the Early HETDEX Data Set

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a large-volume spectroscopic survey without preselection of sources, searching ~540 deg2 for Lyα emitting galaxies (LAEs) at 1.9 < z < 3.5. Taking advantage of such a wide-volume survey, we perform a pilot study using early HETDEX data to search for lensed Lyα emitters (LAEs). After performing a proof of concept using a previously known lensed LAE covered by HETDEX, we perform a search for previously unknown lensed LAEs in the HETDEX spectroscopic sample. We present a catalog of 26 potential LAEs lensed by foreground, red, non-star-forming galaxies at z ~ 0.4-0.7. We estimate the magnification for each candidate system, finding 12 candidates to be within the strong lensing regime (magnification μ > 2). Follow-up observations of these potential lensed LAEs have the potential to confirm their lensed nature and explore these distant galaxies in more detail.

Keywords: gravitational lensing; lyman-alpha galaxies
New Observations of the IR Emission Corona from the 2019 July 2 Eclipse Flight of the Airborne Infrared Spectrometer

The Airborne Infrared Spectrometer (AIR-Spec) was commissioned during the 2017 total solar eclipse, when it observed five infrared coronal emission lines from a Gulfstream V research jet owned by the National Science Foundation and operated by the National Center for Atmospheric Research. The second AIR-Spec research flight took place during the 2019 July 2 total solar eclipse across the south Pacific. The 2019 eclipse flight resulted in seven minutes of observations, during which the instrument measured all four of its target emission lines: S XI 1.393 μm, Si X 1.431 μm, S XI 1.921 μm, and Fe IX 2.853 μm. The 1.393 μm S XI line was detected for the first time, and probable first detections were made of Si XI 1.934 μm and Fe X 1.947 μm. The 2017 AIR-Spec detection of Fe IX was confirmed and the first observations were made of the Fe IX line intensity as a function of solar radius. Telluric absorption features were used to calibrate the wavelength mapping, instrumental broadening, and throughput of the instrument. AIR-Spec underwent significant upgrades in preparation for the 2019 eclipse observation. The thermal background was reduced by a factor of 30, providing a 5.5× improvement in signal-to-noise ratio, and the postprocessed pointing stability was improved by a factor of 5 to <10″ rms. In addition, two imaging artifacts were identified and resolved, improving the spectral resolution and making the 2019 data easier to interpret.

Keywords: solar coronal lines; solar instruments; total eclipses; spectrometers; solar e corona
The Directional Isotropy of LIGO–Virgo Binaries

We demonstrate how to constrain the degree of absolute alignment of the total angular momenta of LIGO–Virgo binary black holes, looking for a special direction in space that would break isotropy. We also allow for inhomogeneities in the distribution of black holes over the sky. Making use of dipolar models for the spatial distribution and orientation of the sources, we analyze 57 signals with false-alarm rates ≤1 yr‑1 from the third LIGO–Virgo observing run. Accounting for selection biases, we find the population of LIGO–Virgo black holes to be consistent with both homogeneity and isotropy. We additionally find the data to constrain some directions of alignment more than others, discuss the interpretation of this measurement, and produce posteriors for the directions of total angular momentum of all binaries in our set. While our current constraints are weak, the fact that such a small number of detections can already yield a measurement suggests that this will be a powerful tool in the future; we explore this prospect with a number of simulated catalogs of varying size. All code and data are made publicly available at https://github.com/maxisi/gwisotropy/.

Keywords: gravitational waves; gravitational wave astronomy
A Shortcut to Calculate SPAM Limb-darkening Coefficients

We release a new grid of stellar limb-darkening coefficients (LDCs, using the quadratic, power-2 and claret-4 laws) and intensity profiles for the Kepler, U, B, V and R passbands, based on STAGGER model atmospheres. The data can be downloaded from Zenodo: https://doi.org/10.5281/zenodo.5593162. We compare the newly released LDCs, computed by ExoTETHyS, with previously published values, based on the same atmospheric models using a so-called "SPAM" procedure. The SPAM method relies on synthetic light curves in order to compute the LDCs that best represent the photometry of exoplanetary transits. We confirm that ExoTETHyS achieves the same objective with a much simpler algorithm.

Keywords: limb darkening; transit photometry; transmission spectroscopy; exoplanet systems; stellar atmospheres; eclipsing binary stars
Flare-induced Sunquake Signatures in the Ultraviolet as Observed by the Atmospheric Imaging Assembly

Sunquakes (SQs) have been routinely observed in the solar photosphere, but it is only recently that signatures of these events have been detected in the chromosphere. We investigate whether signatures of SQs are common in ultraviolet (UV) continua that sample the solar plasma several hundred km above where SQs are typically detected. We analyze observations from the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) 1600 and 1700 Å passbands, for SQ signatures induced by the flares of Solar Cycle 24. We base our analysis on the 62 SQs detected in the recent statistical study presented by Sharykin & Kosovichev. We find that 9 out of 62 SQ candidates produced a response that is clearly detected in running-difference images from the AIA 1600 and 1700 Å channels. A binary frequency filter with a width of 2 mHz, centered on 6 mHz, was applied to the data. The first signature of each SQ was detected at distances between 5.2 and 25.7 Mm from the associated flare ribbon. Time-distance and regression analysis allowed us to calculate the apparent transverse velocities of the SQs in the UV data sets and found maximum velocities as high as 41 km s-1, 87 Mm away from the SQ source. Our analysis shows that flare-induced SQ signatures can be detected in the SDO/AIA 1600 and 1700 Å passbands, hinting at their presence in the lower chromosphere. There was no apparent correlation between GOES flare classification and the appearance of the SQ at these heights.

Keywords: solar physics; helioseismology; solar atmosphere
Discovery of a New Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V

We present the discovery of Boötes V, a new ultra-faint dwarf galaxy (UFD) candidate. This satellite is detected as a resolved overdensity of stars during an ongoing search for new Local Group dwarf galaxy candidates in the UNIONS photometric data set. It has a physical half-light radius of ${26.9}_{-5.4}^{+7.5}$ pc, a V-band magnitude of -4.5 ± 0.4 mag, and resides at a heliocentric distance of approximately 100 kpc. We use Gaia DR3 astrometry to identify member stars, characterize the systemic proper motion, and confirm the reality of this faint stellar system. The brightest star in this system was followed up using Gemini GMOS-N long-slit spectroscopy and is measured to have a metallicity of [Fe/H] = -2.85 ± 0.10 dex and a heliocentric radial velocity of v r = 5.1 ± 13.4 km s-1. Boötes V is larger (in terms of scale radius), more distant, and more metal-poor than the vast majority of globular clusters. It is likely that Boötes V is an UFD, though future spectroscopic studies will be necessary to definitively classify this object.

Keywords: dwarf galaxies; local group; broad band photometry; milky way stellar halo
An Earth-like Stellar Wind Environment for Proxima Centauri c

A new planet has been recently discovered around Proxima Centauri. With an orbital separation of ∼1.44 au and a minimum mass of about $7\,{M}_{\oplus }$ , Proxima c is a prime direct imaging target for atmospheric characterization. The latter can only be performed with a good understanding of the space environment of the planet, as multiple processes can have profound effects on the atmospheric structure and evolution. Here, we take one step in this direction by generating physically realistic numerical simulations of Proxima's stellar wind, coupled to a magnetosphere and ionosphere model around Proxima c. We evaluate their expected variation due to the magnetic cycle of the host star, as well as for plausible inclination angles for the exoplanet orbit. Our results indicate stellar wind dynamic pressures comparable to present-day Earth, with a slight increase (by a factor of 2) during high-activity periods of the star. A relatively weak interplanetary magnetic field at the distance of Proxima c leads to negligible stellar wind Joule heating of the upper atmosphere (about 10% of the solar wind contribution on Earth) for an Earth-like planetary magnetic field (0.3 G). Finally, we provide an assessment of the likely extreme conditions experienced by the exoplanet candidate Proxima d, tentatively located at 0.029 au with a minimum mass of 0.29 M⊕.

Keywords: stellar winds; stellar magnetic fields; planetary magnetospheres; stellar mass loss; interplanetary magnetic fields; stellar activity; super earths; exoplanets
Gamma-Ray Thermalization and Leakage from Millisecond Magnetar Nebulae: Toward a Self-consistent Model for Superluminous Supernovae

Superluminous supernovae (SLSNe) are massive star explosions that are too luminous to be powered by traditional energy sources, such as the radioactive decay of 56Ni. Instead, they may be powered by a central engine, such as a millisecond pulsar or magnetar, whose relativistic wind inflates a nebula of high-energy particles and radiation behind the expanding supernova ejecta. We present three-dimensional Monte Carlo radiative transfer calculations of SLSNe that follow the production of high-energy emission in the nebula and its subsequent thermalization into optical radiation within the surrounding ejecta and, conversely, determine the gamma-ray emission that escapes the ejecta without thermalizing. We identify a novel mechanism by which γγ pair creation in the upstream pulsar wind regulates the mean energy of particles entering the nebula over the first several years after the explosion, rendering our results on this timescale insensitive to the (uncertain) intrinsic wind pair multiplicity. To explain the observed late-time steepening of SLSN optical light curves as being the result of gamma-ray leakage, we find that the nebular magnetization must be very low, ${\varepsilon }_{{\rm{B}}}\lesssim {10}^{-6}\mbox{--}{10}^{-4}$ . For higher ${\varepsilon }_{{\rm{B}}}$ , the more efficiently thermalized lower-energy synchrotron emission would overproduce the late-time (≳1 yr) optical radiation, inconsistent with observations. For magnetars to remain as viable contenders for powering SLSNe, we conclude that either magnetic dissipation in the wind/nebula is extremely efficient or the spin-down luminosity decays significantly faster than the canonical dipole rate ∝t-2 in a way that coincidentally mimics gamma-ray escape.

Keywords: transient sources; high energy astrophysics; gamma-rays; gamma-ray sources; non-thermal radiation sources; core-collapse supernovae; gamma-ray transient sources; radiative transfer simulations