Sazuna/UAT_keywords huggingface dataset:
Characterizing Continuous Gravitational Waves from Supermassive Black Hole Binaries in Realistic Pulsar Timing Array Data. Pulsar timing arrays recently found evidence for a gravitational-wave background (GWB), likely the stochastic overlap of gravitational waves from many supermassive black hole binaries. Anticipating a continuous gravitational-wave (CW) detection from a single binary soon to follow, we examine how well current Bayesian methods can detect CWs and characterize their binary properties by modeling the response of the NANOGrav 15 yr pulsar timing array to simulated binary populations. We run Markov Chain Monte Carlo searches for CWs in these data sets and compare them to quicker detection statistics including the optimal signal-to-noise ratio (S/N), matched filter detection statistic, and reduced log-likelihood ratio between the signal and noise models calculated at the injected parameters. The latter is the best proxy for Bayesian detection fractions, corresponding to a 50% detection fraction (by Bayes factors &gt;10 favoring a CW detection over noise-only model) at an S/N = 4.6. Source confusion between the GWB and a CW, or between multiple CWs, can cause false detections and unexpected dismissals. Fifty-three percent of realistic binary populations consistent with the recently observed GWB have successful CW detections. Additionally, 82% of these CWs are in the fourth or fifth frequency bin of the 16.03 yr data set (6.9 and 10.8 nHz), with 95th percentile regions spanning 4–12 nHz frequencies, 0.7–20 × 109 M⊙ chirp masses, 60 Mpc–8 Gpc luminosity distances, and 18–13,000 deg2 68% confidence localization areas. These successful detections often poorly recover the chirp mass, with only 29% identifying the chirp mass accurately to within 1 dex with a 68% posterior width also narrower than 1 dex.

Keywords: Supermassive black holes, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Markov chain Monte Carlo
Consequences of Hot Electrons for the Structure of the Outer Heliosphere. The temperature of electrons is largely unknown in the outer heliosphere because there is a gap in Voyager measurements from ∼3 eV to 22 keV. Most models assume that the electrons have the same temperature as the bulk cold thermal solar wind (104 K beyond about 10 au from the Sun), but some studies argue that the electrons could be orders of magnitude hotter. We perform two global, multi-fluid magnetohydrodynamic simulations of the heliosphere: one with cold electrons (∼104 K) and one with hot electrons (∼106 K). The hot-electron case leads to an electron-pressure-dominated heliosheath, which expands the thickness of the heliosheath by 50% in the nose direction relative to the cold-electron case. In the tail, electron impact ionization is important with hot electrons and leads to a runaway ionization cascade that increases the plasma density by an order of magnitude. The cold case produces a short, turbulent, split, croissant-like tail, while the hot case creates a long, laminar, comet-like tail. The expansion of the heliosheath seen with hot electrons is inconsistent with the heliosheath thickness from Voyager measurements, but it is clear that the electron temperature has a strong effect on the heliosphere and must be constrained. We also show that the magnetosonic speed is variable in the heliosheath and not constant, which could affect estimates of the heliosheath thickness with pressure sounding methods.

Keywords: Heliopause, Heliosphere, Termination shock, Plasma astrophysics, Heliosheath, Electron impact ionization, Magnetohydrodynamical simulations
Anomalously Fast Core and Envelope Rotation in Red Giants. Red giants undergo dramatic and complex structural transformations as they evolve. Angular momentum is transported between the core and envelope during this epoch, a poorly understood process. Here, we infer envelope and core rotation rates from Kepler observations of ∼1517 red giants. While many measurements are consistent with the existing studies, our investigation reveals systematic changes in the envelope-to-core rotation ratio and we report the discovery of anomalies such as clump stars with rapidly rotating cores and red giants with envelopes rotating faster than their cores. We propose binary interactions as a possible mechanism by which some of these cores and envelopes are spun up. These results pose challenges to current theoretical expectations and can have major implications for compact remnants born from stellar cores.

Keywords: Stellar rotation, Asteroseismology, Red giant branch, Neural networks
Constraining the Milky Way Halo Accretion History with Simulated Stellar Halos: Designing the HALO7D-X Survey. We present the design for HALO7D-X, a survey of the stellar halo to investigate the accretion history of the Milky Way. The survey will use a combination of Hubble Space Telescope (HST) and Gaia data for sky position and proper motions of faint stars (18 &lt; G &lt; 21.5 mag), while line-of-sight velocity, distance, [Fe/H], and [α/Fe] will be measured using follow-up Keck spectroscopy. The survey will cover 30 lines of sight, made up of multiple HST archival fields and optimized for Keck DEIMOS spectroscopy. We use mock survey observations of the Bullock and Johnston stellar halo simulations to investigate the sensitivity of HALO7D-X to constrain the basic parameters of the accretion history of our Galaxy's stellar halo. We find that we are sensitive to the mass distribution and accretion timeline of the stellar halo progenitors, but not their orbital circularity. We find that the simulated halos fall into three different groups based on the similarities in their distributions of the observable dimensions of our survey. These groups are also distinct from each other in the mass distribution and accretion timeline of their progenitor satellites, showing that by using similarities in our observables among halos, we are able to identify similarities in their accretion histories. With HALO7D-X, we will compare real Milky Way data with simulated halos and use this connection between observables and progenitor mass and accretion timeline to learn about the formation of our Galaxy's stellar halo.

Keywords: Milky Way evolution, Milky Way Galaxy, Astrostatistics
Hydrous Chondrites under Shock. We examine the shock response of a chondrule-like multicomponent silicate melt enriched with 2 wt% H2O, representative of hydrous chondrites, using ab initio molecular dynamics. We calculate Hugoniot equations of state (HEOS) and evaluate how hydration affects transport, structural, and thermodynamic features under shock compression. Under the same initial conditions, our results show that water has a minimal direct effect on HEOS. However, the corresponding decrease in initial density significantly shifts the pressure–temperature trajectory. At constant shock pressures, hydration raises peak temperatures, altering volatile loss and melting behavior. The enhanced heating and melting caused by the presence of water implies that hydrated materials could have played a role in shaping the evolution of planetesimals. This challenges previous assumptions constructed on dry silicate models and suggests that volatile-rich bodies may have differentiated more efficiently. In shocked melts, the fast diffusion of hydrogen, compared to the cations, indicates its weak integration into the silicate network. Accordingly, we find that Si–H forms only transiently. Furthermore, analysis of the electron localization function supports the presence of bonded Si–H and Fe–H species along the HEOS, identified from a geometrical approach. The proportions of hydrides depend on the shock conditions and could affect the redox state of the melt, even when they are rare. Our results suggest that even a small amount of water in silicates influences the thermodynamics and chemical behavior during planetesimal impacts. These transformations should be considered in models of core formation and volatile depletion of early planetary bodies.

Keywords: Impact phenomena, Mineral physics, Planet formation, Planetesimals
Commensal Transient Searches with MeerKAT in Gamma-Ray Burst and Supernova Fields. The sensitivity and field of view of the MeerKAT radio telescope provide excellent opportunities for commensal transient searches. We carry out a commensal transient search in supernova and short gamma-ray burst fields using methodologies established by S. I. Chastain et al. We search for transients in MeerKAT L-band images with integration times of 30 minutes, finding 13 variable sources. We compare these sources to the VLASS and RACS survey data, and examine possible explanations for the variability. Additionally, for one of these sources we examine archival Chandra ACIS data. We find that 12 of these sources are consistent with variability due to interstellar scintillation. The remaining source could possibly have some intrinsic variability. We also split the MeerKAT L band into upper and lower halves, and search for transients in images with an integration time of 8 s. We find a source with a duration of 8–16 s that is highly polarized at the lowest frequencies. This source is spatially coincident with a star detected by the Transiting Exoplanet Survey Satellite. We conclude that this source may be consistent with a stellar flare. Finally, we calculate accurate upper and lower limits on the transient rate using transient simulations.

Keywords: Quasars, Flare stars, Interstellar scintillation, Radio continuum emission, Radio transient sources
The Binary Fraction of B-type Runaway Stars from LAMOST DR8. Runaway stars are defined as stars that depart from their birth clusters at high peculiar velocities. There are two main mechanisms for the formation of runaway stars, i.e., the binary-supernova scenario (BSS) and the dynamical ejection scenario (DES). Investigating the binary fraction of runaway stars is an important step in further exploring the relative significance of the two mechanisms. We analyzed the binary fraction of 203 Galactic B-type runaway stars identified in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Data Release 8 database. Our analysis of radial velocity variations in the runaway star sample reveals an observed spectroscopic binary fraction of 5.4% ± 1.6%, representing the proportion of objects that exhibit statistically significant variations in radial velocity with amplitudes larger than 16 km s‑1. We employed a Monte Carlo method to correct for observational biases and determined an intrinsic binary fraction of 27% ± 8%. The period and mass ratio distributions that best reproduce the observation are f(P) ∝ P‑5.7 for 1 ≤ P ≤ 1000 days, and f(q) ∝ q‑3.6 for 0.1 ≤ q ≤ 1.0, indicating a preference for binaries with shorter periods and less massive companions compared to a uniform distribution. The intrinsic binary fraction, in combination with previous studies on the binary fractions of runaway stars formed by the BSS and the DES, implies that both scenarios contribute comparably to the formation of Galactic B-type runaway stars, where the ratio of the BSS to the DES is 0.86.

Keywords: Spectroscopic binary stars, Early-type stars, Runaway stars
Tracing Dark Matter in the Central Regions of Galaxy Clusters Using Galaxies, Gas, and Intracluster Light in TNG300: Connections to Cluster Dynamical State. Recent studies have highlighted the potential of intracluster light (ICL) as a dark matter tracer. Moreover, ICL coevolves with the brightest cluster galaxy (BCG) and the host cluster, making it a valuable tool for understanding cluster dynamics. In this study, we utilize 426 galaxy clusters (with total mass Mtot &gt; 1014M⊙ at z = 0) simulated in the cosmological hydrodynamical simulation Illustris TNG300 to compare the spatial distributions of dark matter, member galaxies, gas, and ICL and to assess their effectiveness as dark matter tracers in the central regions of clusters at Rvir &lt; 0.3. We apply the Weighted Overlap Coefficient, a methodology for quantifying the similarity of two-dimensional spatial distributions, to various components of the galaxy clusters at different dynamical stages. Our findings reveal that the spatial distributions of ICL combined with the BCG and gas closely resemble the dark matter distribution, with higher fidelity observed in more relaxed galaxy clusters with earlier half-mass epochs. These results demonstrate that the BCG+ICL component serves as an effective tracer of dark matter, consistent with previous observational studies linking cluster light to mass. Moreover, the degree of spatial similarity between the BCG+ICL and dark matter distributions appears to reflect the dynamical state of the cluster.

Keywords: Galaxy clusters, Hydrodynamical simulations, Dark matter distribution, Galactic and extragalactic astronomy, Dark matter
Shockingly Effective: Cluster Winds as Engines of Feedback in Starburst Galaxy VV 114. We present high-resolution Keck Cosmic Web Imager and MUSE integral field unit spectroscopy of VV 114, a local IR-luminous merger undergoing a vigorous starburst and showing evidence of galactic-scale feedback. The high-resolution data allow for spectral deblending of the optical emission lines and reveal a broad emission line component (σbroad ∼ 100─300 km s−1) with line ratios and kinematics consistent with a mixture of ionization by stars and radiative shocks. The shock fraction (percentage of ionization due to shocks) in the high-velocity gas is anticorrelated with the projected surface number density of resolved star clusters, and we find that the radial density profiles around clusters are fit well by models of adiabatically expanding cluster winds driven by massive stellar winds and supernovae (SNe). The total kinetic power estimated from the cluster wind models matches the wind + SN mechanical energy deposition rate estimated from the soft-band X-ray luminosity, indicating that at least 70% of the shock luminosity in the galaxy is driven by the star clusters. Hubble Space Telescope narrowband near-IR imaging reveals embedded shocks in the dust-buried IR nucleus of VV 114E. Most of the shocked gas is blueshifted with respect to the quiescent medium, and there is a close spatial correspondence between the shock map and the Chandra soft-band X-ray image, implying the presence of a galactic superwind. The energy budget of the superwind is in close agreement with the total kinetic power of the cluster winds, confirming the superwind is driven by the starburst.

Keywords: Starburst galaxies, Stellar feedback, Galaxy mergers, Shocks, Luminous infrared galaxies
Secular Resonances in Planet-hosting Binary Stars. II. Application to Terrestrial Planet Formation. Continuing our study of the effects of secular resonances on the formation of terrestrial planets in moderately close binary stars, we present here the results of an extensive numerical simulations of the formation of these objects. Considering a binary with two giant planets and a protoplanetary disk around its primary star, we have simulated the late stage of terrestrial planet formation for different types of the secondary, and different orbital elements of the binary and giant planets. Results demonstrate that terrestrial planet formation can indeed proceed constructively in such systems; however, as predicted by the general theory, secular resonances are suppressed and do not contribute to the formation process. Simulations show that it is in fact the mean-motion resonances of the inner giant planet that drive the dynamics of the protoplanetary disk and the mass and orbital architecture of the final bodies. Simulations also show that in the majority of the cases, the final systems contain only one terrestrial planet with a mass of 0.6–1.7 Earth masses. Multiple planets appear on rare occasions in the form of Earth–Mars analogs with the smaller planet in an exterior orbit. When giant planets are in larger orbits, the number of these double-planet systems increases and their planets become more massive. Results also show that when the orbits of the giant planets carry inclinations, while secular resonances are still suppressed, mean-motion resonances are strongly enhanced, drastically reducing the efficacy of the formation process. We present the results of our simulations and discuss their implications.

Keywords: Binary stars, N-body simulations, Planet formation, Orbital resonances
Validating Solar Atmosphere Models with High-resolution Spectra: The Case of Balmer Lines. Stellar and solar atmosphere models are critical tools for numerous astrophysical applications, including the determination of stellar fundamental parameters, the study of stellar dynamos, and the characterization of exoplanetary atmospheres, habitability, and detectability. In the solar context, these models are indispensable for understanding how solar radiation and its variability influence Earth's atmosphere and climate. High-resolution, spatially resolved observations offer an essential benchmark for assessing and improving the accuracy of existing atmospheric models. In this work, we compare synthetic Balmer line spectra, generated using one-dimensional, static, atmospheric models commonly employed to represent solar quiet regions, with state-of-the-art spectroscopic data obtained at the Institut für Astrophysik und Geophysik and the Göttingen Solar Tower at different positions over the solar disk. Our analysis indicates that, among the investigated models, Model 1001 by J. M. Fontenla et al. overall best reproduces observed properties of Balmer lines.

Keywords: Quiet sun, Solar chromosphere, Radiative transfer, Stellar atmospheres
Measurement of Neutral Atmosphere Density during the Years of Increasing Solar Activity Using Insight-HXMT Data with the Earth Occultation Technique. The density of the Earth's middle and upper atmosphere is an important parameter in Earth science and plays a critical role in the design, operation, and orbital determination of low Earth orbit spacecraft. In this study, we have employed the Earth occultation technique combined with maximum likelihood estimation to estimate the neutral atmospheric density by modeling the attenuation of X-ray photons during the occultation process of Insight-HXMT observations of Crab Nebula. By comparing with blank sky occultation data, we demonstrate that the contribution from cosmic X-ray background can be negligible, which has allowed us to extended our density inversion up to 130 km altitude. This is a significant improvement over earlier work. Based on 83 occultation data sets of the Crab Nebula observed by all three sets of telescopes of Insight-HXMT between 2022 and 2024, we derived the atmospheric densities at altitudes spanning from 55 to 130 km. The results show a general agreement between our results and the predictions from the Navy Research Laboratory Mass Spectrometer Incoherent Scatter Radar Exosphere (NRLMSIS) model within the altitude ranges of 65–90, 95–100, and 120–130 km, particularly during periods of increased solar activity. These retrieved atmospheric density results between 65 and 90 km are consistent with prior studies. However, we also find that the NRLMSIS model overestimates atmospheric density at altitudes 90–95 and 100–120 km by 15%–20%. Furthermore, since the atmospheric density measurements at altitudes of 55–65 km may be subject to selection bias, we do not report the prediction accuracy of the NRLMSIS model at this altitude.

Keywords: Earth atmosphere, Atmospheric composition, Occultation, Pulsar wind nebulae
The Evolutionary Pathway of Low-mass Supermassive Black Holes at Intermediate Redshift: Insights from the JADES Survey. Understanding the relationship between supermassive black holes (SMBHs) and their host galaxies at different redshifts is crucial for unraveling the processes of SMBH–galaxy coevolution. We present the properties of nine type 1 active galactic nuclei (AGNs) at intermediate redshift (2 &lt; z &lt; 4) using the JWST Advanced Deep Extragalactic Survey. All of them show the significant Hα broad line and the AGN contribution in spectral energy distribution. Our sample covers SMBH masses of 106.1‑8.2 M⊙ and stellar masses of 109.3‑11.0 M⊙, comparable to those of the AGNs observed in the local Universe. In the low-mass SMBH regime (&lt;108 M⊙), the black hole (BH)-to-stellar mass ratios in our sample (0.01%–0.1%) differ from those of the AGNs at z &gt; 4 (1%–10%), suggesting that BHs and galaxies may trace different evolutionary pathways at intermediate and high redshifts. We also perform 2D image decomposition using GALFIT to constrain the bulge mass by evaluating the bulge contribution in the rest-frame near-infrared flux. We identify the AGNs with low BH-to-bulge mass ratios compared to those observed in the nearby bulge-dominant galaxies. This finding suggests the existence of a galaxy-first evolutionary path, in which bulge formation occurs before substantial gas is efficiently accreted onto the central engine.

Keywords: Black hole physics, Seyfert galaxies, Active galactic nuclei, A supergiant stars
Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution. The Galactic center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the set of elements measurable in the near-IR, especially neutron-capture elements, improves our ability to trace nucleosynthesis and Galactic chemical evolution. This work aims to identify and characterize a spectral line suitable for determining rubidium (Rb) abundances. Rubidium is produced in roughly equal parts by the r- and s-processes. We analyze high-resolution (R = 45,000) Immersion GRating INfrared Spectrograph (or IGRINS) near-IR spectra of 40 M giants in the solar neighborhood, most observed with Gemini South. We perform spectral synthesis of the Rb I line at 15289.48 Å, using new  loggf  values and including an astrophysical calibration of the blending Fe I lines. The resulting [Rb/Fe] ratios are compared to other neutron-capture elements and interpreted with chemical evolution models. We demonstrate that the used Rb line is a reliable abundance indicator in M giants and the coolest K giants, but becomes too weak at higher temperatures. [Rb/Fe] shows a decreasing trend with metallicity, mirroring that of ytterbium (Yb), another mixed r-/s-process element. Our results agree with optical studies, validating the use of this near-IR line. Comparisons with chemical evolution models confirm that both s- and r-process sources are needed to explain the Rb trend. This work adds Rb to the list of elements measurable in high-resolution H- and K-band spectra, enabling studies of one more neutron-capture element in dust-obscured regions like the Galactic center and inner disk.

Keywords: Chemical abundances, Galaxy chemical evolution, M giant stars, Infrared spectroscopy