adsabs/SciX_UAT_keywords huggingface dataset:
LISA and the Existence of a Fast-merging Double Neutron Star Formation Channel

Using a Milky Way (MW) double neutron star (DNS) merger rate of 210 Myr-1, as derived by the Laser Interferometer Gravitational-Wave Observatory (LIGO), we demonstrate that the Laser Interferometer Space Antenna (LISA) will detect on average 240 (330) DNSs within the MW for a 4 yr (8 yr) mission with a signal-to-noise ratio greater than 7. Even adopting a more pessimistic rate of 42 Myr-1, as derived by the population of Galactic DNSs, we find a significant detection of 46 (65) MW DNSs. These DNSs can be leveraged to constrain formation scenarios. In particular, without prior information on a particular system's position and orbital period, traditional NS-discovery methods using radio telescopes alone are insensitive to DNSs with Porb ≲ 1 hr (merger times ≲10 Myr). If a fast-merging channel exists that forms DNSs at these short orbital periods, LISA affords, perhaps, the best opportunity to observationally identify and characterize these systems; we show that toy models for possible formation scenarios leave imprints on DNS orbital eccentricities, which may be measured by LISA for values as small as ∼10-2.

Keywords: neutron stars; gravitational waves; gravitational wave detectors; binary pulsars
Pressure Profiles and Mass Estimates Using High-resolution Sunyaev-Zel'dovich Effect Observations of Zwicky 3146 with MUSTANG-2

The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at z = 0.291 that in X-ray imaging does not appear to exhibit significant pressure substructure in the intracluster medium (ICM). The published M500 values range between 3.88-0.58+0.62 to (22.50 ± 7.58) × 1014 M⊙, where ICM-based estimates with reported errors <20% suggest that we should expect to find a mass between 6.53-0.44+0.44 × 1014 M⊙ (from Planck, with an 8.4σ detection) and 8.52-1.47+1.77 × 1014 M⊙ (from ACT, with a 14σ detection). We investigate the ability to estimate the mass of Zwicky 3146 via the Sunyaev-Zel'dovich (SZ) effect with data taken at 90 GHz by MUSTANG-2 to a noise level better than 15 μK at the center and a cluster detection of 61σ. We derive a pressure profile from our SZ data, which is in excellent agreement with that derived from X-ray data. From our SZ-derived pressure profiles, we infer M500 and M2500 via three methods - Y-M scaling relations, the virial theorem, and hydrostatic equilibrium (HE) - where we employ X-ray constraints from XMM-Newton on the electron density profile when assuming HE. Depending on the model and estimation method, our M500 estimates range from 6.13 ± 0.69 to (10.6 ± 2.0) × 1014 M⊙, where our estimate from HE is 7.69-1.98+2.19 (±27% stat)-0.59+0.63 (±7.9% sys, calibration) × 1014 M⊙. Our fiducial mass, derived from a Y-M relation is 8.06-0.61+0.67 (±7.9% stat)-0.42+0.45 (±5.4% sys, Y-M)-0.54+0.58 (±6.9% sys, cal.) × 1014 M⊙.

Keywords: galaxy clusters; intracluster medium; rich galaxy clusters
Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars

Radial velocity (RV) detection of planets is hampered by astrophysical processes on the surfaces of stars that induce a stochastic signal, or "jitter," which can drown out or even mimic planetary signals. Here, we empirically and carefully measure the RV jitter of more than 600 stars from the California Planet Search sample on a star by star basis. As part of this process, we explore the activity-RV correlation of stellar cycles and include appendices listing every ostensibly companion-induced signal we removed and every activity cycle we noted. We then use precise stellar properties from Brewer et al. to separate the sample into bins of stellar mass and examine trends with activity and with evolutionary state. We find that RV jitter tracks stellar evolution and that in general, stars evolve through different stages of RV jitter: the jitter in younger stars is driven by magnetic activity, while the jitter in older stars is convectively driven and dominated by granulation and oscillations. We identify the "jitter minimum" -- where activity-driven and convectively driven jitter have similar amplitudes -- for stars between 0.7 and 1.7 M⊙ and find that more-massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. Finally, we comment on how these results can inform future RV efforts, from prioritization of follow-up targets from transit surveys like TESS to target selection of future RV surveys.

Keywords: radial velocity; exoplanet astronomy; stellar astronomy; stellar phenomena; exoplanet detection methods
Dependence of Dust Formation on the Supernova Explosion

We investigate the properties, composition, and dynamics of dust formation and growth for a diverse set of core-collapse supernovae (CCSNe), with 15, 20, and 25 M ⊙ progenitor masses, explosion energies ranging from 0.5 to 120 foe, and varied engine type. These explosions are evolved with a 1D Lagrangian hydrodynamics code out to a minimum of 1157 days to model the ejecta as it expands and cools. A multigrain dust nucleation and growth model is applied to these results. We find that higher explosion energies lead to an earlier onset of dust formation, smaller grain sizes, and larger silicate abundances. Further, we see that nuclear burning during the explosion leads to enhanced formation of silicate dust. Finally, we build composite models from our suite to predict the efficiency of CCSN dust production as a function of metallicity.

Keywords: astrophysical dust processes; core-collapse supernovae
Observing the Redshifted 21 cm Signal around a Bright QSO at z ∼ 10

We use hydrodynamics and radiative transfer simulations to study the 21 cm signal around a bright QSO at z ∼ 10. Due to its powerful UV and X-ray radiation, the QSO quickly increases the extent of the fully ionized bubble produced by the pre-existing stellar type sources, in addition to partially ionizing and heating the surrounding gas. As expected, a longer QSO lifetime, tQSO, results in a 21 cm signal in emission located at increasingly larger angular radii, θ, and covering a wider range of θ. Similar features can be obtained with a higher galactic emissivity efficiency, fUV, such that determining the origin of a large ionized bubble (I.e., QSO versus stars) is not straightforward. Such degeneracy could be reduced by taking advantage of the finite light travel time effect, which is expected to affect an H II region produced by a QSO differently from one created by stellar type sources. From an observational point of view, we find that the 21 cm signal around a QSO at various tQSO could be detected by Square Kilometre Array1-low instrument with a high signal-to-noise ratio (S/N). As a reference, for tQSO = 10 Myr, a S/N ∼ 8 is expected assuming that no pre-heating of the intergalactic medium has taken place due to high-z energetic sources, while it can reach values above 10 in cases of pre-heating. Observations of the 21 cm signal from the environment of a high-z bright QSO could then be used to set constraints on its lifetime, as well as to reduce the degeneracy between fUV and tQSO.

Keywords: quasars; high-redshift galaxies; radiative transfer; reionization
On the Effect of Stellar Activity on Low-resolution Transit Spectroscopy and the use of High Resolution as Mitigation

We present models designed to quantify the effects of stellar activity on exoplanet transit spectroscopy and atmospheric characterization at low (R = 100) and high (R = 100,000) spectral resolution. We study three model classes mirroring planetary system archetypes: a hot Jupiter around an early-K star (HD 189733 b); a mini-Neptune around an early-M dwarf (K2-18 b); and terrestrial planets around a late-M dwarf (TRAPPIST-1). We map photospheres with temperatures and radial velocities (RV) and integrate specific intensity stellar models. We obtain transit spectra affected by stellar contamination, the Rossiter-McLaughlin effect (RME), and center-to-limb variations (CLV). We find that, at low resolution, for later-type stars, planetary water features become difficult to distinguish from contamination. Many distributions of unocculted active regions can induce planetary-like features of similar amplitudes in the case of a late-M dwarf. Atmospheric characterization of planets around late-type stars will likely continue to suffer from degeneracy with stellar activity unless active regions' parameters can be constrained using additional information. For the early-K star, stellar contamination mostly manifests itself through a slope at optical wavelengths similar to Rayleigh scattering. In all cases, contamination induces offsets in measured planet radii. At high resolution, we show that we can determine the origin of H2O and CO detection signals and lift the degeneracy observed at low resolution, provided sufficient planet RV variation during transit and adequate correction for the RME and CLV when required. High-resolution spectroscopy may therefore help resolve issues arising from stellar contamination for favorable systems.

Keywords: exoplanets; exoplanet atmospheres; starspots; stellar activity; stellar faculae; transits; transmission spectroscopy
IRIS Observations of the Low-atmosphere Counterparts of Active Region Outflows

Active region (AR) outflows have been studied in detail since the launch of Hinode/EIS and are believed to provide a possible source of mass and energy to the slow solar wind. In this work, we investigate the lower atmospheric counterpart of AR outflows using observations from the Interface Region Imaging Spectrograph (IRIS). We find that the IRIS Si IV, C II> and Mg II transition region (TR) and chromospheric lines exhibit different spectral features in the outflows as compared to neighboring regions at the footpoints ("moss") of hot AR loops. The average redshift of Si IV in the outflow region (≈5.5 km s-1) is smaller than typical moss (≈12-13 km s-1) and quiet Sun (≈7.5 km s-1) values, while the C II line is blueshifted (≈-1.1-1.5 km s-1), in contrast to the moss where it is observed to be redshifted by about ≈2.5 km s-1. Further, we observe that the low atmosphere underneath the coronal outflows is highly structured, with the presence of blueshifts in Si IV and positive Mg II k2 asymmetries (which can be interpreted as signatures of chromospheric upflows) which are mostly not observed in the moss. These observations show a clear correlation between the coronal outflows and the chromosphere and TR underneath, which has not been shown before. Our work strongly suggests that these regions are not separate environments and should be treated together, and that current leading theories of AR outflows, such as the interchange reconnection model, need to take into account the dynamics of the low atmosphere.

Keywords: solar active regions; solar transition region; solar chromosphere
Magnetohydrodynamic Mode Conversion in the Solar Corona: Insights from Fresnel-like Models of Waves at Sharp Interfaces

The solar atmosphere is known to contain many different types of wave-like oscillation. Waves and other fluctuations (e.g., turbulent eddies) are believed to be responsible for at least some of the energy transport and dissipation that heats the corona and accelerates the solar wind. Thus, it is important to understand the behavior of magnetohydrodynamic (MHD) waves as they propagate and evolve in different regions of the Sun's atmosphere. In this paper, we investigate how MHD waves can affect the overall plasma state when they reflect and refract at sharp, planar interfaces in density. First, we correct an error in a foundational paper (Stein) that affects the calculation of wave energy-flux conservation. Second, we apply this model to reflection-driven MHD turbulence in the solar wind, where the presence of density fluctuations can enhance the generation of inward-propagating Alfvén waves. This model reproduces the time-averaged Elsässer imbalance fraction (i.e., the ratio of inward to outward Alfvénic power) from several published numerical simulations. Lastly, we model how the complex magnetic field threading the transition region (TR) between the chromosphere and corona helps convert a fraction of upward-propagating Alfvén waves into fast-mode and slow-mode MHD waves. These magnetosonic waves dissipate in a narrow region around the TR and produce a sharp peak in the heating rate. This newly found source of heating sometimes exceeds the expected heating rate from Alfvénic turbulence by an order of magnitude. It may explain why some earlier models seemed to require an additional ad hoc heat source at this location.

Keywords: alfven waves; interplanetary turbulence; magnetohydrodynamics; solar corona; solar coronal heating; solar wind
An Electric-field-driven Global Coronal Magnetohydrodynamics Simulation Model Using Helioseismic and Magnetic Imager Vector-magnetic-field Synoptic Map Data

We present the simulation methodology and results of our new data-driven global coronal magnetohydrodynamics (MHD) simulation model. In this model, the solar-surface electric field is first calculated such that the curl will satisfy both the induction equation and the given temporal variations of the solar-surface magnetic field. We use the synoptic maps of the Helioseismic and Magnetic Imager three-component vector-magnetic-field data to specify the solar-surface magnetic-field vector for a period from Carrington Rotations (CRs) 2106 to 2110. A set of whole-Sun three-component electric-field maps are obtained for each CR transition interval of about 27.3 days. Using the inverted electric field as the driving variable, our new global coronal MHD model, with the angular resolution of π/64, can trace the evolution of the three-dimensional coronal magnetic field that matches the specified time-dependent solar-surface magnetic-field maps and simultaneously satisfies the divergence-free condition. A set of additional boundary treatments are introduced to control the contribution of the horizontal components of the magnetic field at the weak-field regions. The strength of the solar-surface magnetic field is limited to 20 Gauss for the sake of computational stability in this study. With these numerical treatments, the nonpotential coronal features, such as twisted loop structures, and their eruptive outward motions are obtained. This present model, capable of introducing three-component solar-surface magnetic-field observation data to coronal MHD simulations, is our first step toward a better model framework for the solar corona and hence solar wind.

Keywords: solar corona; solar magnetic fields; magnetohydrodynamical simulations
Formation of Giant Planets by Gas Disk Gravitational Instability on Wide Orbits around Protostars with Varied Masses. II. Quadrupled Spatial Resolution and Beta Cooling

Exoplanet demographics are sufficiently advanced to provide important constraints on theories of planet formation. While core and pebble accretion are preferred for rocky and icy planets, there appears to be a need for gas disk gravitational instability (GDGI) to play a role in the formation of M-dwarf gas giants and those orbiting at large distances. Here we present GDGI models that go beyond those presented by Boss (2011) dealing with the formation of wide-orbit gas giants. The new models use quadrupled spatial resolution, in both the radial and azimuthal directions, to reduce the effects of finite spatial resolution. The new models also employ the β cooling approximation, instead of the diffusion approximation used by Boss (2011), in order to push the models further in time. As in Boss (2011), the central protostars have masses of 0.1, 0.5, 1.0, 1.5, or 2.0 M ⊙, surrounded by disks with masses ranging from 0.019 M ⊙ to 0.21 M ⊙. For each case, two models are computed, one with an initial minimum Toomre Q stability value ranging from 1.1 to 1.7, and one with a higher initial disk temperature, resulting in the initial minimum Q ranging from 2.2 to 3.4. These new models continue to show that GDGI can explain the formation of gas giants at distances of ∼30 to ∼50 au on eccentric orbits (e less than ∼0.2), though the number formed drops to 0 as the protostar mass decreases to 0.1 M ⊙.

Keywords: exoplanet formation; extrasolar gaseous giant planets; gravitational instability; protoplanetary disks
Simultaneous Six-way Observations from the Navy Precision Optical Interferometer

We measured the angular diameters of six stars using the six-element observing mode of the Navy Precision Optical Interferometer (NPOI) for the first time since the early 2000s. Four of the diameters ranged from 1.2 to 1.9 mas, while the two others were much smaller at approximately 0.5 mas to 0.7 mas, which are the two smallest angular diameters measured to date with the NPOI. There is a larger spread in the measurements than data obtained with three-, four-, or five-element modes, which can be attributed in part to the flux imbalance due to the combination of more than two siderostats in a single spectrograph, and also to crosstalk between multiple baselines related to nonlinearities in the fast-delay-line dither strokes. We plan to address this in the future by using the VISION beam combiner.

Keywords: fundamental parameters of stars; high angular resolution; optical interferometry
Satellite Optical Brightness

The apparent brightness of satellites is calculated as a function of satellite position as seen by a ground-based observer in darkness. Both direct illumination of the satellite by the Sun as well as indirect illumination due to reflection from the Earth are included. The reflecting properties of the satellite components and of the Earth must first be estimated (the Bidirectional Reflectance Distribution Function, or BRDF). The reflecting properties of the satellite components can be found directly using lab measurements or accurately inferred from multiple observations of a satellite at various solar angles. Integrating over all scattering surfaces leads to the angular pattern of flux from the satellite. Finally, the apparent brightness of the satellite as seen by an observer at a given location is calculated as a function of satellite position. We develop an improved model for reflection of light from Earth's surface using aircraft data. We find that indirectly reflected light from Earth's surface contributes significant increases in apparent satellite brightness. This effect is particularly strong during civil twilight. We validate our approach by comparing our calculations to multiple observations of selected Starlink satellites and show significant improvement on previous satellite brightness models. Similar methodology for predicting satellite brightness has already informed mitigation strategies for next-generation Starlink satellites. Measurements of satellite brightness over a variety of solar angles widens the effectiveness of our approach to virtually all satellites. We demonstrate that an empirical model in which reflecting functions of the chassis and the solar panels are fit to observed satellite data performs very well. This work finds application in satellite design and operations, and in planning observatory data acquisition and analysis.

Keywords: artificial satellites
Photometric Variability as a Proxy for Magnetic Activity and Its Dependence on Metallicity

Understanding how the magnetic activity of low-mass stars depends on their fundamental parameters is an important goal of stellar astrophysics. Previous studies have shown that activity levels are largely determined by the stellar Rossby number, defined as the rotation period divided by the convective turnover time. However, we currently have little information on the role played by chemical composition. In this work, we investigate how metallicity affects magnetic activity, using photometric variability as an activity proxy. Similarly to other proxies, we demonstrate that the amplitude of photometric variability is well parameterized by the Rossby number, although in a more complex way. We also show that variability amplitude and metallicity are generally positively correlated. This trend can be understood in terms of the effect of metallicity on stellar structure, and hence the convective turnover time (or, equivalently, the Rossby number). Lastly, we demonstrate that the metallicity dependence of photometric variability results in a rotation-period detection bias, whereby the periods of metal-rich stars are more easily recovered for stars of a given mass.

Keywords: low mass stars; stellar activity; metallicity; stellar rotation
Hypervelocity Stars Track Back to the Galactic Center in Gaia DR3

Based on the proper motions and radial velocities from Gaia Data Release 3, we identify two hypervelocity stars (HVSs) that may originate from the Galactic center (GC). We select the candidates by first filtering for all Gaia stars with Galactocentric radial velocities >500 km s-1. We also require the candidates cross the Galactic midplane only once at 80% confidence, as determined by backwards orbit integration in several models of the Galactic potential, given the uncertainties in the Gaia measurables. The final two HVS candidates are the only such stars in our sample whose backwards-integrated trajectories pass within 1 kpc of the GC, suggesting a potential GC origin. We discuss possible ejection scenarios for these HVSs, in particular, by finding that ejection via the Hills mechanism is unlikely unless the HVS trajectories were significantly altered by local or large-scale perturbations to the assumed Galactic potential, e.g., the Large Magellanic Cloud. Interestingly, one of the HVSs ejects in a direction that is curiously aligned with the clockwise stellar disk around Sgr A*, suggesting a possible connection. We also discuss that the two stars may be ejected by other mechanisms.

Keywords: hypervelocity stars; stellar dynamics; stellar kinematics; galactic center; supermassive black holes
The Hubble PanCET Program: Transit and Eclipse Spectroscopy of the Strongly Irradiated Giant Exoplanet WASP-76b

Ultra-hot Jupiters with equilibrium temperatures greater than 2000 K are uniquely interesting targets as they provide us crucial insights into how atmospheres behave under extreme conditions. This class of giant planets receives intense radiation from their host star and usually has strongly irradiated and highly inflated atmospheres. At such a high temperature, cloud formation is expected to be suppressed and thermal dissociation of water vapor could occur. We observed the ultra-hot Jupiter WASP-76b with seven transits and five eclipses using the Hubble Space Telescope and the Spitzer Space Telescope (Spitzer) for a comprehensive study of its atmospheric chemical and physical processes. We detected TiO and H2O absorption in the optical and near-infrared transit spectrum. Additional absorption by a number of neutral and ionized heavy metals like Fe, Ni, Ti, and SiO help explain the short-wavelength transit spectrum. The secondary eclipse spectrum shows muted water feature but a strong CO emission feature in Spitzer's 4.5 μm band indicating an inverted temperature pressure profile. We analyzed both the transit and eclipse spectra with a combination of self-consistent PHOENIX models and atmospheric retrieval. Both spectra were well fitted by the self-consistent PHOENIX forward atmosphere model in chemical and radiative equilibrium at solar metallicity, adding to the growing evidence that both TiO/VO and NUV heavy metals opacity are prominent NUV-optical opacity sources in the stratospheres of ultra-hot Jupiters.

Keywords: exoplanet atmospheres