adsabs/SciX_UAT_keywords huggingface dataset:
Ray-tracing Simulations and Spectral Models of X-Ray Radiation in Dusty Media

Dust can play an important role in shaping the X-ray spectra and images of astrophysical sources. In this work we report on the implementation of dust in the ray-tracing platform REFLEX. We illustrate the different effects associated with the interaction between X-ray photons and dust grains, such as dust scattering, near-edge X-ray absorption fine structures, and shielding. We show how the cross sections of the photon-gas interaction change depending on the fraction of metals in dust grains (i.e., the dust depletion factor). We compare REFLEX simulations to the most widely used absorption model that includes dust and show how X-ray spectra are affected by the presence of dust in the absorbing/reprocessing medium for different geometries. We also show how REFLEX can be used to reproduce the dust scattering halos observed in Galactic sources, and we release the first torus X-ray spectral model that considers dust absorption and scattering (RXTORUSD), to reproduce the spectra of active galactic nuclei (AGNs). RXTORUSD also considers other physical processes that are not included in the most widely used AGN torus models, such as Rayleigh scattering and scattering on molecular gas, which can lead to remarkable differences in the predicted X-ray spectra for the same set of geometrical and physical parameters.

Keywords: radiative transfer; x-ray astronomy; interstellar medium; interstellar dust; x-ray active galactic nuclei; x-ray sources; active galaxies
Interferometric Imaging of λ Andromedae: Evidence of Starspots and Rotation

Presented are the first interferometric images of cool starspots on the chromospherically active giant λ Andromedae. Using the Michigan Infra-Red Combiner coupled to the Center for High Angular Resolution Astronomy Array, 26 interferometric observations were made between 2008 August 17 and 2011 September 24. The photometric time series acquired at Fairborn Observatory spanning 2008 September 20 to 2011 January 20 is also presented. The angular diameter and power-law limb-darkening coefficient of this star are 2.759 ± 0.050 mas and 0.229 ± 0.111, respectively. Starspot properties are obtained from both modeled and SQUEEZE reconstructed images. The images from 2010 through 2011 show anywhere from one to four starspots. The cadence in the data for the 2010 and 2011 data sets is sufficient to measure a stellar rotation period based on apparent starspot motion. This leads to estimates of the rotation period (P2010 = 61 ± 4.0 days, P2011 = 54.0 ± 2.4 days) that are consistent with the photometrically determined period of 54.8 days. In addition, the inclination and position angle of the rotation axis are computed for both the 2010 and 2011 data sets; values ( $\bar{{\rm{\Psi }}}$ = 21°5, $\bar{i}$ = 78°0) for each are nearly identical between the two years.

Keywords: starspots; interferometry; photometry; period determination
Response of SDO/HMI Observables to Heating of the Solar Atmosphere by Precipitating High-energy Electrons

We perform an analysis of the line-of-sight (LOS) observables of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) for models of the solar atmosphere heated by precipitating high-energy electrons during solar flares. The radiative hydrodynamic (RADYN) flare models are obtained from the F-CHROMA database. The Stokes profiles for the Fe 6173 Å line observed by SDO/HMI are calculated using the radiative transfer code RH1.5D, assuming statistical equilibrium for atomic level populations, and imposing uniform background vertical magnetic fields of various strengths. The SDO/HMI observing sequence and LOS data processing pipeline algorithm are applied to derive the observables (continuum intensity, line depth, Doppler velocity, LOS magnetic field). Our results reveal that the strongest deviations of the observables from the actual spectroscopic line parameters are found for the model with a total energy deposited of Etotal = 1.0 × 1012 erg cm-2, injected with a power-law spectral index of δ = 3 above a low-energy cutoff of Ec = 25 keV. The magnitudes of the velocity and magnetic field deviations depend on the imposed magnetic field, and can reach 0.35 km s-1 for LOS velocities, 90 G for LOS magnetic field, and 3% for continuum enhancement for the 1000 G imposed LOS magnetic field setup. For Etotal ≥ 3.0 × 1011 erg cm-2 models, the velocity and magnetic field deviations are most strongly correlated with the energy flux carried by ∼50 keV electrons, and the continuum enhancement is correlated with the synthesized ∼55-60 keV hard X-ray photon flux. The relatively low magnitudes of perturbations of the observables and absence of magnetic field sign reversals suggest that the considered RADYN beam heating models augmented with the uniform vertical magnetic field setups cannot explain the strong transient changes found in the SDO/HMI observations.

Keywords: solar flares; solar magnetic fields; solar photosphere; spectropolarimetry
The Equatorial Jet Speed on Tidally Locked Planets. I. Terrestrial Planets

The atmospheric circulation of tidally locked planets is dominated by a superrotating eastward equatorial jet. We develop a predictive theory for the formation of this jet, proposing a mechanism in which the three-dimensional stationary waves induced by the day-night forcing gradient produce an equatorial acceleration. This is balanced in equilibrium by an interaction between the resulting jet and the vertical motion of the atmosphere. The three-dimensional structure of the zonal acceleration is vital to this mechanism. We demonstrate this mechanism in a hierarchy of models. We calculate the three-dimensional stationary waves induced by the forcing on these planets and show the vertical structure of the zonal acceleration produced by these waves, which we use to suggest a mechanism for how the jet forms. General circulation model simulations are used to confirm the equilibrium state predicted by this mechanism, where the acceleration from these waves is balanced by an interaction between the zonal-mean vertical velocity and the jet. We derive a simple model of this using the "Weak Temperature Gradient" approximation, which gives an estimate of the jet speed on a terrestrial tidally locked planet. We conclude that the proposed mechanism is a good description of the formation of an equatorial jet on a terrestrial tidally locked planet and should be useful for interpreting observations and simulations of these planets. The mechanism requires assumptions such as a large equatorial Rossby radius and weak acceleration due to transient waves, and a different mechanism may produce the equatorial jets on gaseous tidally locked planets.

Keywords: exoplanet atmospheres; atmospheric circulation
A Spectroscopic Model of the Type Ia Supernova-Host-galaxy Mass Correlation from SALT3

The unknown cause of the correlation between Type Ia supernova (SN Ia) Hubble residuals and their host-galaxy masses (the "mass step") may bias cosmological parameter measurements. To better understand the mass step, we develop a SALT3 light-curve model for SN cosmology that uses the host-galaxy masses of 296 low-redshift SNe Ia to derive a spectral energy distribution-host-galaxy mass relationship. The resulting model has larger Ca II H and K, Ca II near-infrared triplet, and Si II equivalent widths for SNe in low-mass host galaxies at 2.2-2.7σ significance; this indicates higher explosion energies per unit mass in low-mass-hosted SNe. The model has phase-dependent changes in SN Ia colors as a function of host mass, indicating intrinsic differences in mean broadband light curves. Although the model provides a better fit to the SN data overall, it does not substantially reduce data-model residuals for a typical light curve in our sample nor does it significantly reduce Hubble residual dispersion. This is because we find that previous SALT models parameterized most host-galaxy dependencies with their first principal component, although they failed to model some significant spectral variations. Our new model is luminosity and cosmology independent, and applying it to data reduces the mass step by 0.021 ± 0.002 mag (uncertainty accounts for correlated data sets); these results indicate that ~35% of the mass step can be attributed to luminosity-independent effects. This SALT model version could be trained using alternative host-galaxy properties and at different redshifts, and therefore will be a tool for understanding redshift-dependent correlations between SNe Ia and their host properties as well as their impact on cosmological parameter measurements.

Keywords: type ia supernovae; cosmology; distance measure; dark energy
An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations

Solar radio bursts are strongly affected by radio-wave scattering on density inhomogeneities, changing their observed time characteristics, sizes, and positions. The same turbulence causes angular broadening and scintillation of galactic and extragalactic compact radio sources observed through the solar atmosphere. Using large-scale simulations of radio-wave transport, the characteristics of anisotropic density turbulence from 0.1 R ⊙ to 1 au are explored. For the first time, a profile of heliospheric density fluctuations is deduced that accounts for the properties of extrasolar radio sources, solar radio bursts, and in situ density fluctuation measurements in the solar wind at 1 au. The radial profile of the spectrum-weighted mean wavenumber of density fluctuations (a quantity proportional to the scattering rate of radio waves) is found to have a broad maximum at around (4-7) R ⊙, where the slow solar wind becomes supersonic. The level of density fluctuations at the inner scale (which is consistent with the proton resonance scale) decreases with heliocentric distance as $\langle \delta {{n}_{i}}^{2}\rangle (r)\simeq 2\times {10}^{7}\,{\left(r/{R}_{\odot }-1\right)}^{-3.7}$ cm-6. Due to scattering, the apparent positions of solar burst sources observed at frequencies between 0.1 and 300 MHz are computed to be essentially cospatial and to have comparable sizes, for both fundamental and harmonic emission. Anisotropic scattering is found to account for the shortest solar radio burst decay times observed, and the required wavenumber anisotropy is q ∥/q ⊥ = 0.25-0.4, depending on whether fundamental or harmonic emission is involved. The deduced radio-wave scattering rate paves the way to quantify intrinsic solar radio burst characteristics.

Keywords: radio bursts; interplanetary scintillation; interplanetary turbulence; solar corona; solar wind
Debris Disks in Multiplanet Systems: Are Our Inferences Compromised by Unseen Planets?

Resolved debris disk features (e.g., warps, offsets, edges and gaps, azimuthal asymmetries, radially thickened rings, scale heights) contain valuable information about the underlying planetary systems, such as the posited planet's mass, semimajor axis, and other orbital parameters. Most existing models assume a single planet is sculpting the disk feature, but recent observations of mature planetary systems (e.g., by radial velocity surveys or Kepler) have revealed that many planets reside in multiplanet systems. Here we investigate if/how planet properties inferred from single-planet models are compromised when multiple planets reside in the system. For each disk feature, we build a two-planet model that includes a planet b with fixed parameters and a planet c with a full range of possible parameters. We investigate these two-planet systems and summarize the configurations for which assuming a single planet (I.e., planet b) leads to significantly flawed inferences of that planet's properties. We find that although disk features are usually primarily dominated by a single planet, when using single-planet models, we are at risk of misinterpreting planet properties by orders of magnitude in extreme cases. Specifically, we are at high risk of misinterpreting planet properties from disk warps; at moderate risk from disk edges and gaps, radially thickened rings, and scale height features; and at low risk from host star-disk center offsets and azimuthal asymmetries. We summarize situations where we can infer the need to use a multiplanet model instead of a single-planet one from disk morphology dissimilarities.

Keywords: debris disks; circumstellar matter
Absolute Calibration Strategies for the Hydrogen Epoch of Reionization Array and Their Impact on the 21 cm Power Spectrum

We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA), which aims to measure the cosmological 21 cm signal from the Epoch of Reionization. HERA is a drift-scan array with a 10° wide field of view, meaning bright, well-characterized point-source transits are scarce. This, combined with HERA's redundant sampling of the uv plane and the modest angular resolution of the Phase I instrument, make traditional sky-based and self-calibration techniques difficult to implement with high dynamic range. Nonetheless, in this work, we demonstrate calibration for HERA using point-source catalogs and electromagnetic simulations of its primary beam. We show that unmodeled diffuse flux and instrumental contaminants can corrupt the gain solutions and present a gain-smoothing approach for mitigating their impact on the 21 cm power spectrum. We also demonstrate a hybrid sky and redundant calibration scheme and compare it to pure sky-based calibration, showing only a marginal improvement to the gain solutions at intermediate delay scales. Our work suggests that the HERA Phase I system can be well calibrated for a foreground avoidance power spectrum estimator by applying direction-independent gains with a small set of degrees of freedom across the frequency and time axes.

Keywords: cosmology; reionization; astronomy data analysis
Implications of Different Solar Photospheric Flux-transport Models for Global Coronal and Heliospheric Modeling

The concept of surface-flux transport (SFT) is commonly used in evolving models of the large-scale solar surface magnetic field. These photospheric models are used to determine the large-scale structure of the overlying coronal magnetic field, as well as to make predictions about the fields and flows that structure the solar wind. We compare predictions from two SFT models for the solar wind, open magnetic field footpoints, and the presence of coronal magnetic null points throughout various phases of a solar activity cycle, focusing on the months of April in even-numbered years between 2012 and 2020, inclusively. We find that there is a solar-cycle dependence to each of the metrics considered, but there is not a single phase of the cycle in which all the metrics indicate good agreement between the models. The metrics also reveal large, transient differences between the models when a new active region is rotating into the assimilation window. The evolution of the surface flux is governed by a combination of large-scale flows and comparatively small-scale motions associated with convection. Because the latter flows evolve rapidly, there are intervals during which their impact on the surface flux can only be characterized in a statistical sense, thus their impact is modeled by introducing a random evolution that reproduces the typical surface flux evolution. We find that the differences between the predicted properties are dominated by differences in the model assumptions and implementation, rather than the selection of a particular realization of the random evolution.

Keywords: solar corona; solar magnetic fields; solar wind
Radial Profiles of Non-thermal Emission from Supernova Remnant RX J1713.7-3946

Supernova remnant RX J1713.7-3946 has exhibited the largest surface brightness and a detailed spectral and shell-type morphology, and is one of the brightest TeV sources. The recent H.E.S.S. observation of RX J1713.7-3946 revealed a broken power-law GeV-TeV gamma-ray and a more extended gamma-ray spatial radial profile than in the X-ray band. Based on the diffusion shock acceleration model, we solve spherically symmetric hydrodynamic equations and particle transport equations, and investigate the multi-band non-thermal emission of RX J1713.7-3946 and radial profiles of its surface brightness for two selected zones in the leptonic scenario for gamma-ray emission. We found (1) the diffusion coefficient has a weak energy dependence, and the Kolmogorov type is favored; (2) the magnetic field strength can vary linearly or nonlinearly with radius for different surrounding environments because of possible turbulence in the shock downstream region, and compressional amplification is likely to exist at the shock front; (3) the non-thermal photons from radio to X-ray bands are dominated by synchrotron emission from relativistic electrons if the GeV-TeV gamma-rays are produced by inverse Compton scattering from these electrons interacting with the background photons; then the X-ray and gamma-ray radial profiles can be reproduced except for the more extended gamma-ray emission.

Keywords: theoretical models; radiative processes; non-thermal radiation sources; gamma-rays; supernova remnants
Microphysical Plasma Relations from Special-relativistic Turbulence

The microphysical, kinetic properties of astrophysical plasmas near accreting compact objects are still poorly understood. For instance, in modern general-relativistic magnetohydrodynamic simulations, the relation between the temperature of electrons T e and protons T p is prescribed in terms of simplified phenomenological models where the electron temperature is related to the proton temperature in terms of the ratio between the gas and magnetic pressures, or the β parameter. We here present a very comprehensive campaign of two-dimensional kinetic particle-in-cell simulations of special-relativistic turbulence to investigate systematically the microphysical properties of the plasma in the transrelativistic regime. Using a realistic mass ratio between electrons and protons, we analyze how the index of the electron energy distributions κ, the efficiency of nonthermal particle production ${ \mathcal E }$ , and the temperature ratio ${ \mathcal T }:={T}_{e}/{T}_{p}$ vary over a wide range of values of β and σ. For each of these quantities, we provide two-dimensional fitting functions that describe their behavior in the relevant space of parameters, thus connecting the microphysical properties of the plasma, κ, ${ \mathcal E }$ , and ${ \mathcal T }$ , with the macrophysical ones β and σ. In this way, our results can find application in a wide range of astrophysical scenarios, including the accretion and the jet emission onto supermassive black holes, such as M87* and Sgr A*.

Keywords: plasma astrophysics
What Does the Milky Way Look Like?

In spite of much work, the overall spiral structure morphology of the Milky Way remains somewhat uncertain. In the last two decades, accurate distance measurements have provided us with an opportunity to solve this issue. Using the precise locations of very young objects, for the first time, we propose that our galaxy has a multiple-arm morphology that consists of two-arm symmetry (the Perseus and Norma Arms) in the inner parts and that extends to the outer parts, where there are several long, irregular arms (the Centaurus, Sagittarius, Carina, Outer, and Local Arms).

Keywords: galaxy structure; milky way galaxy; trigonometric parallax
Assessing Spectroscopic Binary Multiplicity Properties Using Robo-AO Imaging

We present higher-order multiplicity results for 60 solar-type spectroscopic binaries based on 0.75 μm imaging data taken by the robotic adaptive optics (Robo-AO) system at the Kitt Peak 2.1 m telescope. Our contrast curves show sensitivity up to ∼5 mag at ∼1″ separation; at very small separations, we identify candidate companions from image deviations relative to the point spread function. We find candidate tertiary companions for 62% of our binaries overall, but we find that this fraction is a strong function of the inner binary orbital period; it ranges from ∼47% for Pbin > 30 days to as high as ∼90% for Pbin ≲ 5 days. We similarly find an increasing tertiary companion frequency for shorter-period binaries in a secondary sample of Kepler eclipsing binaries observed by Robo-AO. Using Gaia distances, we estimate an upper limit orbital period for each tertiary candidate and compare the tertiary-to-binary period ratios for systems in the field versus those in star-forming regions. Taken all together, these results provide further evidence for angular momentum transfer from three-body interactions, resulting in tight binaries with tertiaries that widen from pre-main-sequence to field ages.

Keywords: binary stars; trinary stars; dynamical evolution
The Oceanus Moving Group: A New 500 Myr Old Host for the Nearest Brown Dwarf

We report the discovery of the Oceanus moving group, a ≈500 Myr old group with 50 members and candidate members at distances 2-50 pc from the Sun, using an unsupervised clustering analysis of nearby stars with Gaia DR3 data. This new moving group includes the nearest brown dwarf WISE J104915.57-531906.1 AB (Luhman 16 AB) at a distance of 2 pc, which was previously suspected to be young (600-800 Myr) based on a comparison of its dynamical mass measurements with brown dwarf evolutionary models. We use empirical color-magnitude sequences, stellar activity, and gyrochronology to determine that this new group is roughly coeval with the Coma Ber open cluster, with an isochronal age of 510 ± 95 Myr. This newly discovered group will be useful to refine the age and chemical composition of Luhman 16 AB, which is already one of the best substellar benchmarks known to date. Furthermore, the Oceanus moving group is one of the nearest young moving groups identified to date, making it a valuable laboratory for the study of exoplanets and substellar members, with eight brown dwarf candidate members already identified here.

Keywords: stellar associations; open star clusters; stellar kinematics; brown dwarfs
Exploring the Impact of the Aging Effect on Inferred Properties of Solar Coronal Mass Ejections

In situ measurements of coronal mass ejections (CMEs) when they pass over an interplanetary probe are one of the main ways we directly measure their properties. However, such in situ profiles are subject to several observational constraints that are still poorly understood. This work aims at quantifying one of them, namely, the aging effect, using a CME simulated with a three-dimensional magnetohydrodynamical code. The synthetic in situ profile and the instantaneous profile of the magnetic field strength differ more from each other when taken close to the Sun than far from it. Moreover, out of three properties we compute in this study (i.e., size, distortion parameter, and expansion speed), only the expansion speed shows a dependence of the aging as a function of distance. It is also the property that is the most impacted by the aging effect as it can amount to more than 100 km s‑1 for CMEs observed closer than 0.15 au. This work calls for caution when deducing the expansion speed from CME profiles when they still are that close to the Sun since the aging effect can significantly impact the derived properties.

Keywords: solar coronal mass ejections; heliosphere; magnetohydrodynamical simulations