adsabs/SciX_UAT_keywords huggingface dataset:
AU Microscopii in the Far-UV: Observations in Quiescence, during Flares, and Implications for AU Mic b and c

High-energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry and mass loss. The active ~22 Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore, this system provides a unique opportunity to quantify the effects of stellar X-ray and UV irradiation on planetary atmospheres as a function of both age and orbital separation. In this paper, we present over 5 hr of far-UV (FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Å) on the Hubble Space Telescope (HST). We provide an itemization of 120 emission features in the HST/COS FUV spectrum and quantify the flux contributions from formation temperatures ranging from 104 to 107 K. We detect 13 flares in the FUV white-light curve with energies ranging from 1029 to 1031 erg s. The majority of the energy in each of these flares is released from the transition region between the chromosphere and the corona. There is a 100× increase in flux at continuum wavelengths λ < 1100 Å in each flare, which may be caused by thermal Bremsstrahlung emission. We calculate that the baseline atmospheric mass-loss rate for AU Mic b is ~108 g s-1, although this rate can be as high as ~1014 g s-1 during flares with ${L}_{\mathrm{flare}}\simeq {10}^{33}$ erg s-1. Finally, we model the transmission spectra for AU Mic b and c with a new panchromatic spectrum of AU Mic and motivate future JWST observations of these planets.

Keywords: stellar activity; stellar flares; hubble space telescope; ultraviolet astronomy; m dwarf stars; exoplanet atmospheres
A Speckle Interferometric Search for a Companion to the RR Lyrae Star UV Oct

We obtained high-resolution, diffraction limited imaging of the candidate binary RR Lyrae UV Oct using Gemini-South/Zorro. We detect no companions between 0"1 and 1"2, with a contrast of Δm ∼ 5 mag, placing a mass constraint for any possible main sequence companion of m < 0.67M⊙.

Keywords: rr lyrae variable stars; speckle interferometry
Ultrahigh-energy Cosmic-Ray Interactions as the Origin of Very High-energy γ-Rays from BL Lacertae Objects

We explain the observed multiwavelength photon spectrum of a number of BL Lacertae (BL Lac) objects detected at very high energy (VHE, E ≳ 30 GeV), using a lepto-hadronic emission model. The one-zone leptonic emission is employed to fit the synchrotron peak. Subsequently, the SSC spectrum is calculated, such that it extends up to the highest energy possible for the jet parameters considered. The data points beyond this energy, and also in the entire VHE range are well explained using a hadronic emission model. The ultrahigh-energy cosmic rays (UHECRs, E ≳ 0.1 EeV) escaping from the source interact with the extragalactic background light (EBL) during propagation over cosmological distances to initiate electromagnetic cascade down to ∼1 GeV energies. The resulting photon spectrum peaks at ∼1 TeV energies. We consider a random turbulent extragalactic magnetic field (EGMF) with a Kolmogorov power spectrum to find the survival rate of UHECRs within 0°1 of the direction of propagation in which the observer is situated. We restrict ourselves to an rms value of EGMF, Brms ∼ 10-5 nG, for a significant contribution to the photon spectral energy distribution from UHECR interactions. We found that UHECR interactions on the EBL and secondary cascade emission can fit gamma-ray data from the BL Lac objects we considered at the highest energies. The required luminosity in UHECRs and corresponding jet power are below the Eddington luminosities of the supermassive black holes in these BL Lac objects.

Keywords: high energy astrophysics; blazars; relativistic jets; gamma-rays; ultra-high-energy cosmic radiation; extragalactic magnetic fields
Relations of Rotation and Chromospheric Activity to Stellar Age for FGK Dwarfs from Kepler and LAMOST

The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index $\mathrm{log}{R}_{\mathrm{HK}}^{+}$ , 6077 rotation periods P rot, and variability amplitudes S ph, based on data from LAMOST DR7, Kepler, and Gaia Data Release 3. We find a pronounced correlation among P rot, age, and [Fe/H] throughout the main-sequence phase for F dwarfs. However, the decrease of $\mathrm{log}{R}_{\mathrm{HK}}^{+}$ over time is not significant except for those with [Fe/H] < ‑0.1. For G dwarfs, both P rot and $\mathrm{log}{R}_{\mathrm{HK}}^{+}$ are reliable age probes in the ranges ∼2–11 Gyr and ∼2–13 Gyr, respectively. K dwarfs exhibit a prominent decrease in $\mathrm{log}{R}_{\mathrm{HK}}^{+}$ within the age range of ∼3–13 Gyr when the relation of P rot–τ is invalid. These relations are very important for promptly estimating the age of a vast number of stars, thus serving as a powerful tool in advancing the fields of exoplanet properties, stellar evolution, and Galactic archeology.

Keywords: stellar rotation; stellar activity; stellar chromospheres; stellar ages
The Compact UV Size of Green Pea Galaxies As Local Analogs of High-redshift Lyα-Emitters

We study the dependence of Lyα escape from galaxies on UV continuum size and luminosity using a sample of 40 Green Pea (GP) galaxies, which are the best local analogs of high-redshift Lyα emitters (LAEs). We use the Cosmic Origins Spectrograph near-ultraviolet images from the Hubble Space Telescope to measure the UV size and luminosity with 0"047 spatial resolution. Like most galaxies the GPs show a log-normal size distribution. They also show a positive correlation between size and UV-continuum luminosity. The slope of the size-continuum luminosity relation for GPs is consistent with those of continuum-selected star-forming galaxies (SFGs) at low and high redshifts. A distinctive feature of GPs is a very compact typical radius of 0.33 kpc with a population spread (1σ) of 0.19 kpc. The peak of the size distribution and the intercept of the size-luminosity relation of GPs are noticeably smaller than those of continuum-selected SFGs at similar redshifts. There are statistically significant anticorrelations found between the circularized half-light radius (rcir,50), the Lyα equivalent width (EW(Lyα)), and the Lyα escape faction ( ${f}_{{esc}}^{{Ly}\alpha }$ ), suggesting that small UV-continuum radii are crucial for Lyα emission. GPs and high-redshift LAEs have similar sizes, once spatial resolution effects are properly considered. Our results show that a compact small size is crucial for escape of Lyα photons, and that Lyα emitters show constant characteristic size independent of their redshift.

Keywords: compact galaxies; starburst galaxies; galaxy formation; galaxy evolution; galaxy structure; star formation; reionization
The Orion OB Association as a Generator for the Hot Circumgalactic Medium

Feedback from star formation may play a key role in energizing the hot, diffuse, X-ray emitting circumgalactic medium (CGM). We observed the diffuse hot gas on the interior of the Orion-Eridanus Superbubble (OES) produced by feedback from the Orion OB association. Using HaloSat, a CubeSat X-ray observatory, we cover the majority of the OES using 11 HaloSat fields, each with a 10° diameter. We find the gas is well described by two thermal plasma components. There are regions of enhanced emission measure (EM) that coincide with the Eridanus X-ray Enhancement and the Orion OB association. Individual field temperatures are statistically consistent with the weighted average of all of the OES fields: a warm temperature kT w = 0.17 ± 0.02 keV and a hot temperature kT h = 0.79 ± 0.12 keV. The gas is overpressured in comparison with typical interstellar medium pressures, and the rate of energy injected by Orion OB1 can sufficiently power growth of the superbubble. The gas's radiative cooling timescale (~30 Myr) is long in comparison with the rate of hot gas production. The temperatures and EMs of the gas agree with properties of the bulk CGM elsewhere in the Milky Way. If we take the OES as a typical superbubble, these factors together suggest that the hot CGM is energized by star formation activity.

Keywords: superbubbles; circumgalactic medium; galaxy structure; stellar feedback
Using Asteroseismology to Calibrate the Physical Parameters of Confirmed Exoplanets and Their Evolved Host Stars

Asteroseismology offers a profound window into stellar interiors and has emerged as a pivotal technique in exoplanetary research. This study harnesses the Transiting Exoplanet Survey Satellite observations to reveal, for the first time, the asteroseismic oscillations of four exoplanet-hosting stars. Through meticulous analysis, we extracted their asteroseismic signatures, enabling the precise determination of stellar masses, radii, luminosities, and surface gravities. These parameters exhibit markedly reduced uncertainties compared to those derived from spectroscopic methods. Crucially, the exoplanets orbiting these stars were initially identified via radial velocity measurements. The refinement of host stellar masses necessitates a corresponding adjustment in planetary characteristics. Employing asteroseismology, we recalibrated the exoplanets' minimum masses and semimajor axes—a novel approach in the field. For instance, the exoplanet HD 5608 b's minimum mass, denoted as , was ascertained to be 1.421 ± 0.091M J through the integration of asteroseismic and radial velocity data. Similarly, two planets within the 7 CMa system yielded values of 1.940 ± 0.064M J and 0.912 ± 0.067M J , respectively. Two planets in the HD 33844 system presented figures of 1.726 ± 0.145M J and 1.541 ± 0.182M J , while the HIP 67851 system's planets registered at 1.243 ± 0.139M J and a notably higher 5.387 ± 0.699M J . This investigation extends beyond mere parameter refinement, it underscores the synergy between asteroseismology and exoplanetology, yielding unprecedented precision in system metrics. Focusing on a quartet of K-type giants in advanced evolutionary phases, our work positions these systems as invaluable astrophysical laboratories, offering insights into the potential trajectory of our own solar system's fate.

Keywords: exoplanets; asteroseismology; planet hosting stars; evolved stars
New Light on an Old Problem of the Cores of Solar Resonance Lines

We reexamine a 50+ yr old problem of deep central reversals predicted for strong solar spectral lines, in contrast to the smaller reversals seen in observations. We examine data and calculations for the resonance lines of H I, Mg II, and Ca II, the self-reversed cores of which form in the upper chromosphere. Based on 3D simulations, as well as data for the Mg II lines from the Interface Region Imaging Spectrograph (IRIS), we argue that the resolution lies not in velocity fields on scales in either of the micro- or macroturbulent limits. Macroturbulence is ruled out using observations of optically thin lines formed in the upper chromosphere, and by showing that it would need to have unreasonably special properties to account for critical observations of the Mg II resonance lines from the IRIS mission. The power in "turbulence" in the upper chromosphere may therefore be substantially lower than earlier analyses have inferred. Instead, in 3D calculations horizontal radiative transfer produces smoother source functions, smoothing out intensity gradients in wavelength and in space. These effects increase in stronger lines. Our work will have consequences for understanding the onset of the transition region, for understanding the energy in motions available for heating the corona, and for the interpretation of polarization data in terms of the Hanle effect applied to resonance line profiles.

Keywords: solar physics; radiative processes; solar chromosphere; solar chromospheric heating
Extended Stellar Populations in Ultrafaint Dwarf Galaxies

The possible existence of stellar halos in low-mass galaxies is being intensely discussed nowadays after some recent discoveries of stars located in the outskirts of dwarf galaxies of the Local Group. RR Lyrae stars can be used to identify the extent of these structures, taking advantage of the minimization of foreground contamination they provide. In this work we use RR Lyrae stars obtained from Gaia DR3, the Dark Energy Survey, the Zwicky Transient Facility, and Pan-STARRS1 to explore the outskirts of 45 ultrafaint dwarf galaxies. We associate the stars with a host galaxy based on their angular separations, magnitudes, and proper motions. We find a total of 120 RR Lyrae stars that belong to 21 different galaxies in our sample. We report seven new RR Lyrae stars in six ultrafaint dwarf galaxies (Hydrus I, Ursa Major I, Ursa Major II, Grus II, Eridanus II, and Tucana II). We found a large number of new possible members in Bootes I and Bootes III as well, but some of them may actually belong to the nearby Sagittarius stream. Adding to our list of 120 RR Lyrae stars the observations of other ultrafaint dwarf galaxies that were beyond the reach of our search, we find that at least 10 of these galaxies have RR Lyrae stars located at distances greater than four times their respective half-light radius, which implies that at least 33% of the 30 ultrafaint dwarfs with a population of RR Lyrae stars have extended stellar populations.

Keywords: rr lyrae variable stars; dwarf galaxies; galaxy stellar halos; local group
The Increasingly Strange Polarimetric Behavior of the Barbarian Asteroids

Polarization phase-curve measurements provide a unique constraint on the surface properties of asteroids that are complementary to those from photometry and spectroscopy and have led to the identification of the "Barbarian" asteroids as a class of objects with highly unusual surfaces. We present new near-infrared polarimetric observations of six Barbarian asteroids obtained with the WIRC+Pol instrument on the Palomar Hale telescope. We find a dramatic change in polarimetric behavior from visible to near-infrared for these objects, including a change in the polarimetric inversion angle that is tied to the index of refraction of the surface material. Our observations support a two-phase surface composition consisting of high albedo and high index of refraction inclusions with a small optical size scale embedded in a dark matrix material more closely related to C-complex asteroids. These results are consistent with the interpretation that the Barbarians are remnants of a population of primitive bodies that formed shortly after calcium-aluminum-rich inclusion (CAIs). Near-infrared polarimetry provides a direct test of the constituent grains of asteroid surfaces.

Keywords: asteroids; asteroid surfaces; polarimetry
The Halo Spin Transition As a Probe of Dark Energy

We present numerical evidence supporting the claim that the mass-dependent transitions of the halo spin orientations from the intermediate to the minor principal directions of the local tidal fields can in principle be useful discriminators of dark energy models. We first define a spin transition zone as the mass range of the halos, ${\rm{\Delta }}{m}_{{\rm{t}}}$ , for which the intrinsic spin alignments with the minor tidal principal directions become as strong as that with the intermediate principal directions. Then, utilizing the halo samples from the DEUS simulations performed separately for the WMAP7 ΛCDM, phantom dark energy, and quintessence models, we investigate if and how the three different dark energy models differ in ${\rm{\Delta }}{m}_{{\rm{t}}}$ . It is shown that the differences in ${\rm{\Delta }}{m}_{{\rm{t}}}$ among the three dark energy models are significant enough to discriminate the models from one another and robust against the variations of the smoothing scale of the tidal field and redshift. Noting that a narrower spin transition zone is more powerful as a probe of dark energy, we also show that the spin transition zones become narrower at higher redshifts in the filamentary environments and, for the case of the tidal fields, smoothed on smaller scales. Our result is consistent with the scenario that ${\rm{\Delta }}{m}_{{\rm{t}}}$ is mainly determined by how fast the nonlinear evolution of the tidal field proceeds, which in turn sensitively depends on the background cosmology.

Keywords: large-scale structure of the universe; cosmological models
New Constraints on Pluto's Sputnik Planitia Ice Sheet from a Coupled Reorientation-Climate Model

We present a coupled reorientation and climate model, to understand how true polar wander (TPW) and atmospheric condensation worked together to create the Sputnik Planitia (SP) ice sheet and reorient it to its present-day location on Pluto. SP is located at 18°N, 178°E, very close to the anti-Charon point, and it has been previously shown that this location can be explained by TPW reorientation of an impact basin as it fills with N2 ice. We readdress that hypothesis while including a more accurate treatment of Pluto's climate and orbital obliquity cycle. Our model again finds that TPW is a viable mechanism for the formation and present-day location of SP. We find that the initial impact basin could have been located north of the present-day location, at latitudes between 35°N and 50°N. The empty basin is constrained to be 2.5-3 km deep, with enough N2 available to form at most a 1-2 km thick ice sheet. Larger N2 inventories reorient too close to the anti-Charon point. After reaching the final location, the ice sheet undergoes short periods of sublimation and recondensation on the order of 10 m of ice, due to Pluto's variable obliquity cycle, which drives short periods of reorientation of a few kilometers. The obliquity cycle also has a role in the onset of infilling; some initial basin locations are only able to begin accumulating N2 ice at certain points during the obliquity cycle. We also explore the sensitivity of the coupled model to albedo, initial obliquity, and Pluto's orbit.

Keywords: pluto; planetary climates; planetary interior; surface ices
The Cassiopeia Filament: A Blown Spur of the Local Arm

We present wide-field and high-sensitivity CO(1-0) molecular line observations toward the Cassiopeia region, using the 13.7 m millimeter telescope of the Purple Mountain Observatory. The CO observations reveal a large-scale highly filamentary molecular cloud within the Galactic region of 132.°0 ≥ l ≥ 122.°0 and -1.°0 ≤ b ≤ 3.°0 and the velocity range from approximately +1 to +4 km s-1. The measured length of the large-scale filament, referred to as the Cassiopeia Filament, is ~390 pc. The observed properties of the Cassiopeia Filament, such as length, column density, and velocity gradient, are consistent with those synthetic large-scale filaments in the inter-arm regions. Based on its observed properties and location on the Galactic plane, we suggest that the Cassiopeia Filament is a spur of the Local arm, which is formed due to the galactic shear. The western end of the Cassiopeia Filament shows a giant arc-like molecular gas shell, which extends in the velocity range from roughly -1 to +7 km s-1. Finger-like structures, with systematic velocity gradients, are detected in the shell. The CO kinematics suggest that the large shell is expanding at a velocity of ~6.5 km s-1. Both the shell and finger-like structures outline a giant bubble with a radius of ~16 pc, which is likely produced by the stellar wind from the progenitor star of a supernova remnant. The observed spectral line widths suggest that the whole Cassiopeia Filament was quiescent initially until its west part was blown by the stellar wind and became supersonically turbulent.

Keywords: interstellar medium; interstellar filaments; giant molecular clouds; stellar wind bubbles
Charge States, Helium Abundance, and FIP Bias of the Interplanetary CMEs Classified by Flares and Hot Channels

Identifying the material source of coronal mass ejections (CMEs) is crucial for understanding the generation mechanisms of CMEs. The composition parameters of interplanetary coronal mass ejections (ICMEs) associated with different activities on the Sun may be diverse, as the materials come from distinct regions or are generated by different processes. We classified ICMEs into three types by associated activities on the Sun, with (T1) and without (T3) flares and hot channels, and only associated with flares (T2). The composition parameters of each type of ICMEs were analyzed. We found that all CMEs with hot channels are accompanied by flares, and strong flares are all associated with hot channels in our database. The average length of the filaments in T1 cases are much shorter than those in T3 cases. The average charge states of iron (Q Fe) and helium abundance (A He) for T3 ICMEs are less than 12% and 7%, respectively. The Q Fe and A He for T1 ICMEs present clear bimodal distributions with the minimum between two peaks at 12% and 7%, respectively. Nearly two-thirds of the hot plasma (with higher Q Fe) inside ICMEs is associated with higher A He. The Q Fe and A He are both positively correlated with the flare intensities. The A He and filament scales are not explicitly linked to each other. The statistical results demonstrate that the material contribution of the filaments to ICMEs is low and more than half of the hot materials inside ICMEs originate from the chromosphere in our database. We suggest that they are heated by the chromospheric evaporation process at the hot channel (flux rope) footpoint regions before and/or during the flaring process.

Keywords: solar coronal mass ejections; solar flares; solar abundances
Floor of Cosmogenic Neutrino Fluxes above 1017 eV

The search for neutrinos with energies greater than 1017 eV is being actively pursued. Although normalization of the dominant neutrino flux is highly uncertain, a floor level is guaranteed by the interactions of extragalactic cosmic rays with milky Way gas. We estimate that this floor level gives an energy flux of ${E}^{2}{\phi }_{\nu }\,\simeq {10}^{-{13}_{-0.5}^{+0.5}}\,\mathrm{GeV}\,{\mathrm{cm}}^{-2}\,{\mathrm{sr}}^{-1}\,{{\rm{s}}}^{-1}$ at 1018 eV, where uncertainties arise from the modeling of the gas distribution and the experimental determination of the mass composition of ultra–high-energy cosmic rays on Earth. Based on a minimal model of cosmic-ray production to explain the mass-discriminated energy spectra observed on Earth above 5 × 1018 eV, we also present generic estimates of the neutrino fluxes expected from extragalactic production that generally exceed the aforementioned guaranteed floor. The prospects for detecting neutrinos above 1018 eV remain challenging, however, unless proton acceleration to the highest energies is at play in a subdominant population of cosmic-ray sources or new physical phenomena are at work.

Keywords: astrophysical processes; cosmic rays; non-thermal radiation sources