adsabs/SciX_UAT_keywords huggingface dataset:
Solar Wind Magnetic Field Line Dispersal: Multispacecraft Analysis and Comparison with Theoretical Results

The dominance of the global over the relative, cross-field transport of magnetic field lines (MFLs), up to scales of a couple of hours in the solar wind (SW), has been predicted both theoretically and numerically, in the approximation of self-similar, single-level power spectra of magnetic fluctuations. Here the predictions for the MFL relative cross-field transport or dispersal are tested against the results of in situ data analysis, using 23 yr of field and flow measurements on board ACE and Wind. The theoretical results are confirmed/refined by nonlinear theoretical computations and corrected to include the effects of power-level variability or intermittency. Other than confirming earlier theoretical findings at the separation scales ρ between a few ×1010 cm and the large-separation limit, with a ballistic regime followed by decorrelation and transition to diffusion in the $(\mathrm{ln}\rho ,\theta )$ -space, the new study reveals two new supradiffusive regimes in $\mathrm{ln}\rho $ and clock angle θ for the MFL dispersal, distinct from a drift-induced supradiffusion found earlier, and distinct from each other. The first supradiffusion, of the nonlinear computations, is a simple nonlinear effect, which cannot be recovered by data analysis at two spacecraft of fixed separation on the analysis timescale. The second supradiffusion, of the data analysis, is much stronger for ρ < few × 1010 cm than the two previous supradiffusions, and it becomes stronger at shorter separations. It follows the ballistic regime without transition through diffusion and is recovered by multiscale, theoretical estimates. It is a Lévy-type supradiffusion, due to the intermittency observed in the SW.

Keywords: solar wind; interplanetary physics; interplanetary magnetic fields; space plasmas; plasma astrophysics
Detector Count Rate Nonlinearity Determination Using Signal Intermodulation

Detectors that use HgCdTe exhibit Count Rate Non-Linearity (CRNL), where the integrated photon-generated charge in a pixel has an undesirable variation with photon arrival rate, at fixed delivered photon dose. Correcting for this is essential to meet the science goals of the Roman Space Telescope. The CRNL effect is distinct from signal-level-dependent (but photon-rate-independent) nonlinearity. We describe a potential method for measuring CRNL, by illuminating the sensor with two modulated light sources running at different frequencies, f1 and f2. The CRNL-modified generation of photocharge in the material produces a variation in the accumulated charge versus time with Fourier components at the beat frequencies (f1 - f2) and (f1 + f2). Successive non-destructive read-up-the-ramp measurements could perhaps be used to quantify CRNL, and distinguish it from nonlinearities in the downstream electronics. A pair of LEDs driven with square waves at different frequencies are appropriate sources.

Keywords: astronomical detectors; flux calibration
Hubble Space Telescope Reveals Spectacular Light Echoes Associated with the Stripped-envelope Supernova 2016adj in the Iconic Dust Lane of Centaurus A

We present a multiband sequence of Hubble Space Telescope images documenting the emergence and evolution of multiple light echoes (LEs) linked to the stripped-envelope supernova (SN) 2016adj located in the central dust lane of Centaurus A. Following point-spread function subtraction, we identify the earliest LE emission associated with an SN at only +34 days past the epoch of the B-band maximum. Additional HST images extending through +578 days cover the evolution of LE1 taking the form of a ring, while images taken on +1991 days reveal not only LE1 but also segments of a new inner LE ring (LE2) as well as two additional outer LE rings (LE3 and LE4). Adopting the single-scattering formalism, the angular radii of the LEs suggest they originate from discrete dust sheets in the foreground of the SN. This information, combined with measurements of color and optical depth of the scattering surfaces, informs a scenario with multiple sheets of clumpy dust characterized by a varying degree of holes. In this case, the larger the LE's angular radii, the farther in the foreground of the SN its dust sheet is located. However, an exception to this is LE2, which is formed by a dust sheet located in closer proximity to the SN than the dust sheets producing LE1, LE3, and LE4. The delayed appearance of LE2 can be attributed to its dust sheet having a significant hole along the line of sight between the SN and Earth.

Keywords: type ic supernovae; core-collapse supernovae
Revised Extinctions and Radii for 1.5 Million Stars Observed by APOGEE, GALAH, and RAVE

Asteroseismology has become widely accepted as a benchmark for accurate and precise fundamental stellar properties. It can therefore be used to validate and calibrate stellar parameters derived from other approaches. Meanwhile, one can leverage large-volume surveys in photometry, spectroscopy, and astrometry to infer stellar parameters over a wide range of evolutionary stages, independently of asteroseismology. Our pipeline, SEDEX (https://github.com/Jieyu126/SEDEX), compares the spectral energy distribution predicted by the MARCS and BOSZ model spectra with 32 photometric bandpasses, combining data from nine major, large-volume photometric surveys. We restrict the analysis to targets with available spectroscopy from the APOGEE, GALAH, and RAVE surveys to lift the temperature-extinction degeneracy. The cross-survey atmospheric parameter and uncertainty estimates are homogenized with artificial neural networks. Validation of our results with CHARA interferometry, Hubble Space Telescope CALSPEC spectrophotometry, and asteroseismology shows that we achieve high precision and accuracy. We present a catalog of improved interstellar extinction ( ${\sigma }_{{A}_{V}}\simeq $ 0.14 mag) and stellar radii (σ R /R ≃ 7.4%) for ~1.5 million stars in the low-to-high-extinction (A V ≲ 6 mag) fields observed by the spectroscopic surveys. We derive global extinctions for 184 Gaia DR2 open clusters and confirm the differential extinction in NGC 6791 and NGC 6819, which have been subject to extensive asteroseismic analysis. Furthermore, we report 36,854 double-lined spectroscopic main-sequence binary candidates. This catalog will be valuable for providing constraints on detailed modeling of stars and for constructing 3D dust maps of the Kepler field, the TESS Continuous Viewing Zones, and the PLATO long-duration observation fields.

Keywords: interstellar extinction; stellar properties; astronomical techniques; ab photometry; photometry; spectral energy distribution
Modeling the Formation of Selk Impact Crater on Titan: Implications for Dragonfly

Selk crater is an ~80 km diameter impact crater on the Saturnian icy satellite Titan. Melt pools associated with impact craters like Selk provide environments where liquid water and organics can mix and produce biomolecules like amino acids. It is partly for this reason that the Selk region has been selected as the area that NASA's Dragonfly mission will explore and address one of its primary goals: to search for biological signatures on Titan. Here we simulate Selk-sized impact craters on Titan to better understand the formation of Selk and its melt pool. We consider several structures for the icy target material by changing the thickness of the methane clathrate layer, which has a substantial effect on the target thermal structure and crater formation. Our numerical results show that a 4 km diameter impactor produces a Selk-sized crater when 5-15 km thick methane clathrate layers are considered. We confirm the production of melt pools in these cases and find that the melt volumes are similar regardless of methane clathrate layer thickness. The distribution of the melted material, however, is sensitive to the thickness of the methane clathrate layer. In the case of a 10-15 km thick methane clathrate layer, the melt pool appears as a torus-like shape that is a few kilometers deep, and as a shallower layer in the case of a 5 km thick clathrate layer. Melt pools of this thickness may take tens of thousands of years to freeze, allowing more time for complex organics to form.

Keywords: titan; saturnian satellites; planetary surfaces; impact phenomena; methane
The Effect of the Fluctuating Interplanetary Magnetic Field on the Cosmic Ray Intensity Profile of the Ground-level Enhancement (GLE) Events

We numerically integrate the equations of motion of a large number of GeV protons, released impulsively near the Sun, in order to study their time-intensity behavior at the location of an observer at 1 au. This is relevant to the interpretation of Ground Level Enhancements (GLEs) detected by neutron monitors on Earth. Generally, the observed time-intensity profiles reveal a single sharp rise, followed by slow decay. However, in the 1989 October 22 GLE event, there was an initial sharp spike followed by a secondary smaller spike in the particle intensity. We consider whether the propagation of the high-energy protons in a large-scale turbulent interplanetary magnetic field (IMF) can lead to this unusual time-intensity profile. The IMF model includes large-scale magnetic turbulence and a heliospheric current sheet. Ad-hoc scattering is used to mimic the effect of smaller-scale fluctuations resulting in pitch-angle scattering. Proton fluxes as a function of time and location for an observer are determined for various turbulence parameters, IMF polarities, and the size of the particle source near the Sun. We find that the fluctuating IMF leads to considerable variation in the arrival location of the particles crossing 1 au, and the time-intensity profile depends significantly on the observer's location and can have multiple peaks. An alternate explanation for the unusual structure in the 1989 October 22 GLE event is provided. Our findings show that the large-scale turbulent IMF enhances the access of the high-energy protons to the HCS at the early time of the event, which leads to efficient cross-field transport.

Keywords: solar energetic particles; interplanetary magnetic fields; interplanetary turbulence; solar flares; solar coronal mass ejections; solar coronal mass ejection shocks
Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

We present the median-stacked Lyman-α (Lyα) surface brightness profiles of 968 spectroscopically selected Lyα emitting galaxies (LAEs) at redshifts 1.9 < z < 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Lyα detections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM <1.″4), excluding active galactic nuclei. The Lyα luminosities of the LAEs are 1042.4-1043 erg s-1. We detect faint emission in the median-stacked radial profiles at the level of $(3.6\pm 1.3)\times {10}^{-20}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ from the surrounding Lyα halos out to r ≃ 160 kpc (physical). The shape of the median-stacked radial profile is consistent at r < 80 kpc with that of much fainter LAEs at 3 < z < 4 observed with the Multi Unit Spectroscopic Explorer (MUSE), indicating that the median-stacked Lyα profiles have similar shapes at redshifts 2 < z < 4 and across a factor of 10 in Lyα luminosity. While we agree with the results from the MUSE sample at r < 80 kpc, we extend the profile over a factor of two in radius. At r > 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation at z = 3. This suggests that the surface brightness of a Lyα halo at r ≲ 100 kpc is dominated by resonant scattering of Lyα photons from star-forming regions in the central galaxy, whereas at r > 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos.

Keywords: lyman-alpha galaxies; high-redshift galaxies; circumgalactic medium
Optical and Near-infrared Continuum Emission Region Size Measurements in the Lensed Quasar FBQ J0951+2635

We present 10 seasons of Sloan Digital Sky Survey r-band monitoring observations and five seasons of H-band observations of the two-image system FBQ J0951+2635 from the Kaj Strand Astrometric Reflector at the United States Naval Observatory, Flagstaff Station. We supplement our light curves with six seasons of monitoring data from the literature to yield a 10 + 6 season combined data set, which we analyzed with our Monte Carlo microlensing analysis routine to generate constraints on the structure of this system's continuum emission source and the properties of the lens galaxy. Complementing our optical light curves with the five-season near-infrared light curves, we ran a joint Monte Carlo analysis to measure the size of the continuum emission region at both wavelengths, yielding log(r 1/2 cm-1) = ${16.24}_{-0.36}^{+0.33}$ in the r band and ${17.04}_{-0.30}^{+0.26}$ in the H band at rest wavelengths of 2744 and 7254 Å, respectively, correcting for an assumed inclination angle of 60°. Modeling the accretion disk temperature profile as a power law T(r) ∝ r -β , we successfully constrain the slope for FBQ J0951+2635 to $\beta ={0.50}_{-0.18}^{+0.50}$ , shallower than, but nominally consistent with, the predictions of standard thin-disk theory, β = 0.75.

Keywords: quasars; gravitational lensing; gravitational microlensing; quasar microlensing
Rocky Planet or Water World? Observability of Low-density Lava World Atmospheres

Super-Earths span a wide range of bulk densities, indicating a diversity in interior conditions beyond that seen in the solar system. In particular, an emerging population of low-density super-Earths may be explained by volatile-rich interiors. Among these, low-density lava worlds have dayside temperatures that are high enough to evaporate their surfaces, providing a unique opportunity to probe their interior compositions and test for the presence of volatiles. In this work, we investigate the atmospheric observability of low-density lava worlds. We use a radiative-convective model to explore the atmospheric structures and emission spectra of these planets, focusing on three case studies with high observability metrics and substellar temperatures spanning ~1900-2800 K: HD 86226 c, HD 3167 b, and 55 Cnc e. Given the possibility of mixed volatile and silicate interior compositions for these planets, we consider a range of mixed volatile and rock-vapor atmospheric compositions. This includes a range of volatile fractions and three volatile compositions: water-rich (100% H2O), water with CO2 (80% H2O+20% CO2), and a desiccated O-rich scenario (67% O2+33% CO2). We find that spectral features due to H2O, CO2, SiO, and SiO2 are present in the infrared emission spectra as either emission or absorption features, depending on dayside temperature, volatile fraction, and volatile composition. We further simulate JWST secondary-eclipse observations for each of the three case studies, finding that H2O and/or CO2 could be detected with as few as ~five eclipses. Detecting volatiles in these atmospheres would provide crucial independent evidence that volatile-rich interiors exist among the super-Earth population.

Keywords: exoplanets; exoplanet atmospheres; exoplanet structure; super earths; exoplanet atmospheric composition; exoplanet atmospheric structure
Tilting Planets during Planet Scattering

Observational constraints on planetary spin axis have recently become possible, and they have revealed a system that favors large spin-axis misalignment, low stellar spin-orbit misalignment, and high eccentricity. To explain the origin of such systems, we propose a mechanism that could tilt the planetary spin axis during planet-planet scattering, which is a natural outcome of in situ formation and disk migration. Specifically, we show that spin-orbit resonances could occur for a short time period during the scattering processes, and excite the misalignment of a planet's spin axis. This typically leads to planets with large spin misalignment and a wide range of eccentricities and inclinations.

Keywords: exoplanet formation; exoplanet astronomy; exoplanet dynamics
Analytical Model of Disk Evaporation and State Transitions in Accreting Black Holes

State transitions in black hole X-ray binaries are likely caused by gas evaporation from a thin accretion disk into a hot corona. We present a height-integrated version of this process, which is suitable for analytical and numerical studies. With radius r scaled to Schwarzschild units and coronal mass accretion rate ${\dot{m}}_{c}$ to Eddington units, the results of the model are independent of black hole mass. State transitions should thus be similar in X-ray binaries and an active galactic nucleus. The corona solution consists of two power-law segments separated at a break radius r b ~ 103(α/0.3)-2, where α is the viscosity parameter. Gas evaporates from the disk to the corona for r > r b , and condenses back for r < r b . At r b , ${\dot{m}}_{c}$ reaches its maximum, ${\dot{m}}_{c,\max }\approx 0.02\,{(\alpha /0.3)}^{3}$ . If at r ≫ r b the thin disk accretes with ${\dot{m}}_{d}\lt {\dot{m}}_{c,\max }$ , then the disk evaporates fully before reaching r b , giving the hard state. Otherwise, the disk survives at all radii, giving the thermal state. While the basic model considers only bremsstrahlung cooling and viscous heating, we also discuss a more realistic model that includes Compton cooling and direct coronal heating by energy transport from the disk. Solutions are again independent of black hole mass, and r b remains unchanged. This model predicts strong coronal winds for r > r b , and a T ~ 5 × 108 K Compton-cooled corona for r < r b . Two-temperature effects are ignored, but may be important at small radii.

Keywords: astrophysical black holes; accretion; black holes; high energy astrophysics; active galactic nuclei; x-ray sources
Simulation for Distributions of Several Geometric Parameters in Nulling Pulsars

We investigate the distributions of the obliquity angle and impact parameters of nulling pulsars of different duty cycles based on the simulation of more than 600,000 samples. We adopt a purely geometric approach for pulsar visibility, in which visible emission is emitted tangentially to the magnetic field line and parallel to the line-of-sight direction. The geometry is incorporated with the model for pulsar magnetospheres of multiple emission states, in which the plasma charge density is dependent on the emission state. We assume that an emission state can only exist between two limiting conditions described by the vacuum and corotation models, respectively. In this model, pulse nulling corresponds to emission switching to a state in which the plasma charge density is zero. The event is detectable only if the switching occurs at source points that lie on a trajectory, whose locus defines the locations of visible emission, within an open-field region. Our results show that detectable nulling is dependent on all three parameters, such that nulling pulsars prefer a small obliquity angle and duty cycle, and tend to have positive impact parameters. We find that the total population of nulling pulsars in our samples is around 23%, of which about 47% possess a duty cycle of 0.1 or smaller. The former implies that there are more nulling pulsars than currently known. Our model predicts that the number of nulling pulsars increases as the obliquity angle decreases, which also implies that the occurrence of nulling in a pulsar should evolve over time.

Keywords: radio pulsars
DirtyGrid II: An Analysis of the Dust and Stellar Properties in Nearby Star-forming Galaxies

We study the dust and stellar properties of the Spitzer Infrared Nearby Galaxies Survey galaxies by fitting the ultraviolet (UV) to far-infrared (FIR) spectral energy distributions using the DIRTYGrid stellar and dust radiative transfer models. We find a minimum of two components of different stellar ages are needed, representing a young and an old stellar population, in order to obtain good fits for most of the galaxies. Our total dust masses agree with literature dust masses to within a factor of 2, and the residuals correlate most strongly with the stellar mass surface density of the old component. The LMC-2 dust grain model best describes the dust found in these normal star-forming galaxies. The derived attenuation curves are steeper than those found previously for starburst galaxies, and possess a weak 2175 Å feature. The relative contribution of the young and old stellar components as a function of wavelength reveals that the young component dominates the far-UV and MIPS24 bands, the old component dominates the optical/near-IR bands, and both components are important for the FIR bands. The DIRTYGrid star formation rates (SFRs) are consistent with a number of literature SFR indicators within a factor of 2. The differences we find are primarily due to the influence of the old stellar population that are accounted for by the DIRTYGrid SFRs fitting on a galaxy-by-galaxy basis using the information present in the full UV-FIR spectral energy distribution.

Keywords: interstellar dust; spectral energy distribution; radiative transfer; galaxies; star formation
A Possible Surviving Companion of the SN Ia in the Galactic SNR G272.2-3.2

We use the Gaia EDR3 to explore the Galactic supernova remnant (SNR) G272.2-3.2, produced by the explosion of a Type Ia supernova (SN Ia) about 7500 yr ago, to search for a surviving companion. From the abundances in the SNR ejecta, G272.2-3.2 is a normal SN Ia. The Gaia parallaxes allow us to select the stars located within the estimated distance range of the SNR, and the Gaia proper motions allow us to study their kinematics. From the Gaia EDR3 photometry, we construct the H-R diagram of the selected sample, which we compare with the theoretical predictions for the evolution of possible star companions of SNe Ia. We can discard several proposed types of companions by combining kinematics and photometry. We can also discard hypervelocity stars. We focus our study on the kinematically most peculiar star, Gaia EDR3 5323900215411075328 (hereafter MV-G272), an 8.9σ outlier in proper motion. It is of M1-M2 stellar type. Its trajectory on the sky locates it at the center of the SNR, 6000-8000 yr ago, a unique characteristic among the sample. Spectra allow a stellar parameter determination and a chemical abundance analysis. In conclusion, we have a candidate to be the surviving companion of the SN Ia that resulted in SNR G272.2-3.2. It is supported by its kinematical characteristics and its trajectory within the SNR. This opens the possibility of a single-degenerate scenario for an SN Ia with an M-type dwarf companion.

Keywords: type ia supernovae