adsabs/SciX_UAT_keywords huggingface dataset:
Upper Limit on the Dissipation of Gravitational Waves in Gravitationally Bound Systems

It is shown that a gravitationally bound system with a one-dimensional velocity dispersion σ can at most dissipate a fraction $\sim 36{\left(\sigma /c\right)}^{3}$ of the gravitational wave (GW) energy propagating through it, even if their dynamical time is shorter than the wave period. The limit is saturated for low-frequency waves propagating through a system of particles with a mean-free-path equal to the size of the system, such as hot protons in galaxy clusters, strongly interacting dark matter particles in halos, or massive black holes in clusters. For such systems with random motions and no resonances, the dissipated fraction, $\lesssim {10}^{-6}$ , does not degrade the use of GWs as cosmological probes. At high-wave frequencies, the dissipated fraction is additionally suppressed by the square of the ratio between the collision frequency and the wave frequency. The electromagnetic counterparts that result from the dissipation are too faint to be detectable at cosmological distances.

Keywords: gravitational waves
The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities

Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets-such as solar data or data with known injected planetary and/or stellar signals-to better understand method performance and whether planetary signals are preserved.

Keywords: radial velocity; exoplanet detection methods; planet hosting stars; stellar activity; spectrometers
Detectability of Solar Panels as a Technosignature

In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the ultraviolet-to-visible (UV-VIS) and in the near-infrared, within the wavelength range of a space-based flagship mission concept like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide the 2022 human energy needs with a land cover of ∼2.4%, and projecting the future energy demand assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope. Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the UV-VIS (0.34–0.52 μm), we find that several hundreds of hours of observation time are needed to reach a signal-to-noise ratio of 5 for an Earth-like planet around a Sun-like star at 10 pc, even with a solar panel coverage of ∼23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even with much larger populations than today, the total energy use of human civilization would be orders of magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev Type I civilization. Any extraterrestrial civilization that likewise achieves sustainable population levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization as imagined in the Fermi paradox may not exist.

Keywords: technosignatures; exoplanets
Neutron Star Mergers in Active Galactic Nucleus Accretion Disks: Cocoon and Ejecta Shock Breakouts

Neutron star mergers are believed to occur in accretion disks around supermassive black holes. Here we show that a putative jet launched from the merger of a binary neutron star (BNS) or a neutron star-black hole (NSBH) merger occurring at the migration trap in an active galactic nucleus (AGN) disk would be choked. The jet energy is deposited within the disk materials to power a hot cocoon. The cocoon is energetic enough to break out from the AGN disk and produce a bright X-ray shock breakout transient peaking at ∼0.15 days after the merger. The peak luminosity is estimated as $\sim {10}^{46}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , which can be discovered by the Einstein Probe from $z\lesssim 0.5$ . Later on, the nonrelativistic ejecta launched from the merger would break out the disk, powering an X-ray/UV flare peaking at ∼0.5 days after the merger. This second shock breakout signal may be detected by UV transient searches. The cocoon cooling emission and kilonova emission are outshone by the disk emission and are difficult to detect. Future joint observations of gravitational waves from BNS/NSBH mergers and associated two shock breakout signatures can provide strong support for the compact binary coalescence formation channel in AGN disks.

Keywords: neutron stars; black holes; active galactic nuclei; gamma-ray bursts; gravitational waves
Neural Networks for Nuclear Reactions in MAESTROeX

We demonstrate the use of neural networks to accelerate the reaction steps in the MAESTROeX stellar hydrodynamics code. A traditional MAESTROeX simulation uses a stiff ODE integrator for the reactions; here, we employ a ResNet architecture and describe details relating to the architecture, training, and validation of our networks. Our customized approach includes options for the form of the loss functions, a demonstration that the use of parallel neural networks leads to increased accuracy, and a description of a perturbational approach in the training step that robustifies the model. We test our approach on millimeter-scale flames using a single-step, 3-isotope network describing the first stages of carbon fusion occurring in Type Ia supernovae. We train the neural networks using simulation data from a standard MAESTROeX simulation, and show that the resulting model can be effectively applied to different flame configurations. This work lays the groundwork for more complex networks, and iterative time-integration strategies that can leverage the efficiency of the neural networks.

Keywords: neural networks; reaction models; nucleosynthesis; computational methods; hydrodynamical simulations
Nitrogen as a Tracer of Giant Planet Formation. II. Comprehensive Study of Nitrogen Photochemistry and Implications for Observing NH3 and HCN in Transmission and Emission Spectra

Atmospheric nitrogen may provide important constraints on giant planet formation. Following our semianalytical work, we further pursue the relation between observable NH3 and an atmosphere's bulk nitrogen abundance by applying the photochemical kinetics model VULCAN across planetary equilibrium temperature, mass, age, eddy diffusion coefficient, atmospheric composition, and stellar spectral type. We confirm that the quenched NH3 abundance coincides with the bulk nitrogen abundance only at sub-Jupiter-mass (≲1M J) planets and old ages (≳1 Gyr) for solar composition atmospheres, highlighting important caveats for inferring atmospheric nitrogen abundances. Our semianalytical model reproduces the quenched NH3 abundance computed by VULCAN and thus helps to infer the bulk nitrogen abundance from a retrieved NH3 abundance. By computing transmission and emission spectra, we predict that the equilibrium temperature range of 400-1000 K is optimal for detecting NH3 because NH3 depletion by thermochemistry and photochemistry is significant at hotter planets whereas entire spectral features become weak at colder planets. For Jupiter-mass planets around Sun-like stars in this temperature range, NH3 leaves observable signatures of ~50 ppm at 1.5, 2.1, and 11 μm in transmission spectra and >300-100 ppm at 6 and 11 μm in emission spectra. The photodissociation of NH3 leads HCN to replace NH3 at low pressures. However, the low HCN column densities lead to much weaker absorption features than for NH3. The NH3 features are readily accessible to JWST observations to constrain atmospheric nitrogen abundances, which may open a new avenue to understanding the formation processes of giant exoplanets.

Keywords: exoplanet atmospheres; exoplanet atmospheric structure; exoplanet formation; exoplanets; exoplanet atmospheric composition; astrochemistry
Anisotropic Turbulence in Position-Position-Velocity Space: Probing Three-dimensional Magnetic Fields

Direct measurements of three-dimensional magnetic fields in the interstellar medium are not achievable. However, the anisotropic nature of magnetohydrodynamic (MHD) turbulence provides a novel way of tracing the magnetic fields. Guided by the advanced understanding of turbulence's anisotropy in the position-position-velocity (PPV) space, we extend the structure-function analysis to measure both the three-dimensional magnetic field orientation and Alfvén Mach number MA, which provides the information on magnetic field strength. Following the theoretical framework developed in Kandel et al., we find that the anisotropy in a given velocity channel is affected by the inclination angle between the three-dimensional magnetic field direction and the line of sight as well as media magnetization. We analyze the synthetic PPV cubes generated by incompressible and compressible MHD simulations. We confirm that the PPV channel's intensity fluctuations measured in various position angles reveal plane-of-the-sky magnetic field orientation. We show that by varying the channel width, the anisotropies of the intensity fluctuations in PPV space can be used to simultaneously estimate both magnetic field inclination angle and strength of total magnetic fields.

Keywords: interstellar medium; interstellar magnetic fields; interstellar dynamics
Test Particle Energization of Heavy Ions in Magnetohydrodynamic Turbulence

In the present work, we study the energization and displacement of heavy ions through the use of test particles interacting with the electromagnetic fields of magnetohydrodynamic (MHD) turbulence. These fields are obtained from pseudospectral direct numerical solutions of the compressible three-dimensional MHD equations with a strong background magnetic field. We find particle energization to be predominantly perpendicular as the ions become heavier (lower charge-to-mass ratio) and that high displacement is detrimental for perpendicular energization. On the other hand, perpendicular displacement is unaffected by the charge-to-mass ratio, which we explain with a simple guide center model. Using Voronoi tessellation along with this model, we analyze preferential concentration and find that particles behave as tracers in the perpendicular plane, clustering in regions with ∇⊥ · u ⊥ < 0. These regions also have (∇ × E ) z < 0, which is optimal for perpendicular energization, thus providing a mechanism to understand precedent results.

Keywords: magnetohydrodynamics; pickup ions; interplanetary turbulence
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XX. Ages of Single and Multiple Stellar Populations in Seven Bulge Globular Clusters

In the present work we analyzed seven globular clusters (GCs) selected from their location in the Galactic bulge and with metallicity values in the range -1.30 ≲ [Fe/H] ≲ -0.50. The aim of this work is first to derive cluster ages assuming single stellar populations and second to identify the stars from first (1G) and second generations (2G) from the main sequence, subgiant, and red giant branches, and to derive their age differences. Based on a combination of UV and optical filters used in this project, we apply the Gaussian mixture models to distinguish the multiple stellar populations. Applying statistical isochrone fitting, we derive self-consistent ages, distances, metallicities, and reddening values for the sample clusters. An average age of 12.3 ± 0.4 Gyr was obtained both using DSED and BaSTI (accounting atomic diffusion effects) isochrones, without a clear distinction between the moderately metal-poor and the more metal-rich bulge clusters, except for NGC 6717 and the inner halo NGC 6362 with ∼13.5 Gyr. We derived a weighted mean age difference between the multiple populations hosted by each GC of 41 ± 170 Myr adopting canonical He abundances; whereas for higher He in 2G stars, this difference reduces to 17 ± 170 Myr, but with individual uncertainties of 500 Myr.

Keywords: globular star clusters; galactic bulge
Latitude-dependent Atmospheric Waves and Long-period Modulations in Luhman 16 B from the Longest Light Curve of an Extrasolar World

In this work, we present the longest photometric monitoring of up to 1200 hr of the strongly variable brown dwarf binaries Luhman 16 AB and provide evidence of ±5% variability on a timescale of several to hundreds of hours for this object. We show that short-period rotational modulation around 5 hr (k = 1 wavenumber) and 2.5 hr (k = 2 wavenumber) dominate the variability under 10 hr, where the planetary-scale wave model composed of k = 1 and k = 2 waves provides good fits to both the periodograms and light curve. In particular, models consisting of three to four sine waves could explain the variability of the light-curve durations up to 100 hr. We show that the relative range of the k = 2 periods is narrower compared to the k = 1 periods. Using simple models of zonal banding in solar system giants, we suggest that the difference in period range arises from the difference in wind-speed distribution at low and mid-to-high latitudes in the atmosphere. Last, we show that Luhman 16 AB also exhibits long-period ±5% variability, with periods ranging from 15 hr up to 100 hr over the longest monitoring of this object. Our results for the k = 1 and k = 2 waves and long-period evolution are consistent with previous 3D atmosphere simulations, demonstrating that both latitude-dependent waves and slow-varying atmospheric features are potentially present in Luhman 16 AB atmospheres and are a significant contribution to the light-curve modulation over hundreds of rotations.

Keywords: brown dwarfs; exoplanet atmospheres; broad band photometry; atmospheric circulation
A First Chandra View of the Cool Core Cluster A1668: Offset Cooling and AGN Feedback Cycle

We present a multiwavelength analysis of the cluster A1668, performed by means of new EVLA and Chandra observations and archival Hα data. The radio images exhibit a small central source (∼14 kpc at 1.4 GHz) with L1.4GHz ∼ 6 · 1023 W Hz-1. The mean spectral index between 1.4 GHz and 5 GHz is ∼-1, consistent with the usual indices found in BCGs. The cooling region extends for 40 kpc, with bolometric X-ray luminosity Lcool = 1.9 ± 0.1 · 1043 erg s-1. We detect an offset of ∼6 kpc between the cluster BCG and the X-ray peak, and another offset of ∼7.6 kpc between the Hα and the X-ray peaks. We discuss possible causes for these offsets, which suggest that the coolest gas is not condensing directly from the lowest-entropy gas. In particular, we argue that the cool ICM was drawn out from the core by sloshing, whereas the Hα filaments were pushed aside from the expanding radio galaxy lobes. We detect two putative X-ray cavities, spatially associated with the west radio lobe (cavity A) and the east radio lobe (cavity B). The cavity power and age of the system are Pcav ∼ 9 × 1042 erg s-1 and tage ∼ 5.2 Myr, respectively. Evaluating the position of A1668 in the cooling luminosity-cavity power parameter space, we find that the AGN energy injection is currently consistent within the scatter of the relationship, suggesting that offset cooling is likely not breaking the AGN feedback cycle.

Keywords: galaxy clusters; abell clusters; active galactic nuclei; radio lobes; radio sources; cooling flows; intracluster medium
A Brightness Classification Boundary in the Kuiper Belt Population

The Kuiper Belt contains a large number of minor bodies that collectively constrain the dynamical history of the solar system. These bodies are often classified into distinct populations. This note identifies a well-defined boundary (at H-magnitude = 5.65) that separates bright (large) objects from dimmer (smaller) objects. The probability that the two sub-samples are drawn from the same underlying distribution is p ~ 10-15. The larger bodies (estimated radius R ≳ 125 km) are dynamically hot, as measured by their locations in the e- $\sin i$ plane, and likely represent an implanted population. The smaller bodies (R ≲ 125 km) are dynamically colder and are likely to be primordial. The bright/large/hot population currently contains ~200 members, including all ~50 dwarf planet candidates in the Kuiper Belt.

Keywords: kuiper belt; solar system; small solar system bodies
The Structure of Tidal Disruption Event Host Galaxies on Scales of Tens to Thousands of Parsecs

We explore the galaxy structure of four tidal disruption event (TDE) host galaxies on 30 pc to kiloparsec scales using Hubble Space Telescope WFC3 multiband imaging. The star formation histories of these hosts are diverse, including one post-starburst galaxy (ASASSN-14li), two hosts with recent weak starbursts (ASASSN-14ae and iPTF15af), and one early-type galaxy (PTF09ge). Compared to early-type galaxies of similar stellar masses, the TDE hosts have higher central surface brightnesses and stellar mass surface densities on 30-100 pc scales. The TDE hosts do not show the large, kiloparsec-scale tidal disruptions seen in some post-starburst galaxies; the hosts have low morphological asymmetries similar to those of early-type galaxies. The lack of strong asymmetries is inconsistent with a recent major (∼1:1 mass) merger, although minor (≲1:3) mergers are possible. Given the time elapsed since the end of the starbursts in the three post-burst TDE hosts and the constraints on the merger mass ratios, it is unlikely that a bound supermassive black hole binary (SMBHB) has had time to coalesce. The TDE hosts have low central (<140 pc) ellipticities compared to early-type galaxies. The low central ellipticities disfavor a strong radial anisotropy as the cause for the enhanced TDE rate, although we cannot rule out eccentric disks at the scale of the black hole gravitational radius of influence (∼1 pc). These observations suggest that the high central stellar densities are a more important driver than SMBHBs or radial anisotropies in increasing the TDE rate in galaxies with recent starbursts.

Keywords: e+a galaxies; tidal disruption; supermassive black holes
Tidal Evolution of the Earth-Moon System with a High Initial Obliquity

A giant-impact origin for the Moon is generally accepted, but many aspects of lunar formation remain poorly understood and debated. Ćuk et al. proposed that an impact that left the Earth-Moon system with high obliquity and angular momentum could explain the Moon's orbital inclination and isotopic similarity to Earth. In this scenario, instability during the Laplace Plane transition, when the Moon's orbit transitions from the gravitational influence of Earth's figure to that of the Sun, would both lower the system's angular momentum to its present-day value and generate the Moon's orbital inclination. Recently, Tian & Wisdom discovered new dynamical constraints on the Laplace Plane transition and concluded that the Earth-Moon system could not have evolved from an initial state with high obliquity. Here we demonstrate that the Earth-Moon system with an initially high obliquity can evolve into the present state, and we identify a spin-orbit secular resonance as a key dynamical mechanism in the later stages of the Laplace Plane transition. Some of the simulations by Tian & Wisdom did not encounter this late secular resonance, as their model suppressed obliquity tides and the resulting inclination damping. Our results demonstrate that a giant impact that left Earth with high angular momentum and high obliquity (θ > 61°) is a promising scenario for explaining many properties of the Earth-Moon system, including its angular momentum and obliquity, the geochemistry of Earth and the Moon, and the lunar inclination.

Keywords: earth-moon system; orbital resonances; tides
Evidence of Systematic Errors in Spitzer Microlens Parallax Measurements

The microlensing parallax campaign with the Spitzer space telescope aims to measure masses and distances of microlensing events seen toward the Galactic bulge, with a focus on planetary microlensing events. The hope is to measure how the distribution of planets depends on position within the Galaxy. In this paper, we compare 50 microlens parallax measurements from the 2015 Spitzer campaign to three different Galactic models commonly used in microlensing analyses, and we find that ≥74% of these events have microlensing parallax values higher than the medians predicted by Galactic models. The Anderson-Darling tests indicate probabilities of pAD < 6.6 × 10-5 for these three Galactic models, while the binomial probability of such a large fraction of large microlensing parallax values is <4.6 × 10-4. Given that many Spitzer light curves show evidence of large correlated errors, we conclude that this discrepancy is probably due to systematic errors in the Spitzer photometry. We find formally acceptable probabilities of pAD > 0.05 for subsamples of events with bright source stars (IS ≤ 17.75) or Spitzer coverage of the light-curve peak. This indicates that the systematic errors have a more serious influence on faint events, especially when the light-curve peak is not covered by Spitzer. We find that multiplying an error bar renormalization factor of 2.2 by the reported error bars on the Spitzer microlensing parallax measurements provides reasonable agreement with all three Galactic models. However, corrections to the uncertainties in the Spitzer photometry itself are a more effective way to address the systematic errors.

Keywords: gravitational microlensing; microlensing parallax
The Apparent Absence of Forward Scattering in the HD 53143 Debris Disk

HD 53143 is a mature Sun-like star and host to a broad disk of dusty debris, including a cold outer ring of planetesimals near 90 au. Unlike most other inclined debris disks imaged at visible wavelengths, the cold disk around HD 53143 appears as disconnected "arcs" of material, with no forward-scattering side detected to date. We present new, deeper Hubble Space Telescope Imaging Spectrograph coronagraphic observations of the HD 53143 debris disk and show that the forward-scattering side of the disk remains undetected. By fitting our KLIP-reduced observations via forward modeling with an optically thin disk model, we show that fitting the visible wavelength images with an azimuthally symmetric disk with unconstrained orientation results in an unphysical edge-on orientation that is at odds with recent ALMA observations, while constraining the orientation to that observed by ALMA results in nearly isotropically scattering dust. We show that the HD 53143 host star exhibits significant stellar variations due to spot rotation and revisit age estimates for this system.

Keywords: debris disks; circumstellar disks; stellar activity