Sazuna/UAT_keywords huggingface dataset:
Formation of Massive and Wide First-star Binaries in Radiation Hydrodynamic Simulations. We study the formation of Population III stars by performing radiation hydrodynamic simulations for three different initial clouds extracted from cosmological hydrodynamic simulations. Starting from the cloud collapse stage, we follow the growth of protostars by accretion for ~105 yr until the radiative feedback from the protostars suppresses the accretion and the stellar properties are nearly fixed. We find that Population III stars form in massive and wide binary/small-multiple stellar systems, with masses &gt;30 M ⊙ and separations &gt;2000 au. We also find that the properties of the final stellar system correlate with those of the initial clouds: the total mass increases with the cloud-scale accretion rate, and the angular momentum of the binary orbit matches that of the initial cloud. While the total mass of the system in our simulations is consistent with our previous single-star formation simulations, individual masses are lower due to mass sharing, suggesting potential modification in the extent of feedback from Population III stars in the subsequent evolution of the Universe. We also identify such systems as mini-binaries embedded in a wider outer multiple-star system, which could evolve into progenitors for observed gravitational wave events.

Keywords: Star formation, Early universe, Population III stars
Uncovering Hidden Massive Black Hole Companions with Tidal Disruption Events. Dynamical perturbations from supermassive black hole (SMBH) binaries can increase the rates of tidal disruption events (TDEs). However, most previous work focuses on TDEs from the heavier black hole in the SMBH binary (SMBHB) system. In this work, we focus on the lighter black holes in SMBHB systems and show that they can experience a similarly dramatic increase in their TDE rate due to perturbations from a more massive companion. While the increase in TDEs around the more massive black hole is mostly due to chaotic orbital perturbations, we find that, around the smaller black hole, the eccentric Kozai-Lidov mechanism is dominant and capable of producing a comparably large number of TDEs. In this scenario, the mass derived from the light curve and spectra of TDEs caused by the lighter SMBH companion is expected to be significantly smaller than the SMBH mass estimated from galaxy scaling relations, which are dominated by the more massive companion. This apparent inconsistency can help find SMBHB candidates that are not currently accreting as active galactic nuclei and that are at separations too small for them to be resolved as two distinct sources. In the most extreme cases, these TDEs provide us with the exciting opportunity to study SMBHBs in galaxies where the primary SMBH is too massive to disrupt Sun-like stars.

Keywords: Supermassive black holes, Black holes, High energy astrophysics, Tidal disruption, Active galaxies, Transient sources, Time domain astronomy, Galaxy mergers
Exploring the Origin of Stars on Bound and Unbound Orbits Causing Tidal Disruption Events. Tidal disruption events (TDEs) provide a clue to the properties of a central supermassive black hole (SMBH) and an accretion disk around it, and to the stellar density and velocity distributions in the nuclear star cluster surrounding the SMBH. Deviations of TDE light curves from the standard occurring at a parabolic encounter with the SMBH depend on whether the stellar orbit is hyperbolic or eccentric and the penetration factor (β, the tidal disruption radius to the orbital pericenter ratio). We study the orbital parameters of bound and unbound stars being tidally disrupted by comparison of direct N-body simulation data with an analytical model. Starting from the classical steady-state Fokker-Planck model of Cohn &amp; Kulsrud, we develop an analytical model of the number density distribution of those stars as a function of orbital eccentricity (e) and β. To do so, fittings of the density and velocity distribution of the nuclear star cluster and of the energy distribution of tidally disrupted stars are required and obtained from N-body data. We confirm that most of the stars causing TDEs in a spherical nuclear star cluster originate from the full loss-cone region of phase space, derive analytical boundaries in eccentricity-β space, and find them confirmed by N-body data. Since our limiting eccentricities are much smaller than critical eccentricities for full accretion or the full escape of stellar debris, we conclude that those stars are only very marginally eccentric or hyperbolic, close to parabolic.

Keywords: Accretion, Black hole physics, Supermassive black holes, Intermediate-mass black holes, High energy astrophysics, Tidal disruption, Stellar dynamics, Galaxy nuclei, Galaxy kinematics, Time domain astronomy, N-body simulations, Star clusters
Simultaneous Estimates of Star-cluster Age, Metallicity, Mass, and Extinction (SESAMME). I. Presenting an MCMC Approach to Spectral Stellar Population Fitting. We present the first version release of SESAMME, a public, Python-based full spectrum fitting tool for Simultaneous Estimates of Star-cluster Age, Metallicity, Mass, and Extinction. SESAMME compares an input spectrum of a star cluster to a grid of stellar population models with an added nebular continuum component, using Markov Chain Monte Carlo methods to sample the posterior probability distribution in four dimensions: cluster age, stellar metallicity Z, reddening E(B - V), and a normalization parameter equivalent to a cluster mass. SESAMME is highly flexible in the stellar population models that it can use to model a spectrum; our testing and initial science applications use both BPASS and Starburst99. We illustrate the ability of SESAMME to recover accurate ages and metallicities even at a moderate signal-to-noise ratio (S/N ~ 3-5 per wavelength bin) using synthetic, noise-added model spectra of young star clusters. Finally, we test the consistency of SESAMME with other age and metallicity estimates from the literature using a sample of Hubble Space Telescope/Cosmic Origins Spectrograph far-UV spectra toward young, massive clusters in M83 and NGC 1313. We find that, on the whole, SESAMME infers star cluster properties that are consistent with the literature in both low- and high-metallicity environments.

Keywords: Ultraviolet spectroscopy, Astronomy software, Star clusters
Characterizing the Directionality of Gravitational Wave Emission from Matter Motions within Core-collapse Supernovae. We analyze the directional dependence of the gravitational wave (GW) emission from 15 3D neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Using spin weighted spherical harmonics, we develop a new analytic technique to quantify the evolution of the distribution of GW emission over all angles. We construct a physics-informed toy model that can be used to approximate GW distributions for general ellipsoid-like systems, and use it to provide closed form expressions for the distribution of GWs for different CCSN phases. Using these toy models, we approximate the protoneutron star (PNS) dynamics during multiple CCSN stages and obtain similar GW distributions to simulation outputs. When considering all viewing angles, we apply this new technique to quantify the evolution of preferred directions of GW emission. For nonrotating cases, this dominant viewing angle drifts isotropically throughout the supernova, set by the dynamical timescale of the PNS. For rotating cases, during core bounce and the following tens of milliseconds, the strongest GW signal is observed along the equator. During the accretion phase, comparable-if not stronger-GW amplitudes are generated along the axis of rotation, which can be enhanced by the low T/∣W∣ instability. We show two dominant factors influencing the directionality of GW emission are the degree of initial rotation and explosion morphology. Lastly, looking forward, we note the sensitive interplay between GW detector site and supernova orientation, along with its effect on detecting individual polarization modes.

Keywords: High energy astrophysics, Core-collapse supernovae, General relativity, Gravitational waves, Astronomical simulations
The Detection of Higher-order Millimeter Hydrogen Recombination Lines in the Large Magellanic Cloud. We report the first extragalactic detection of the higher-order millimeter hydrogen recombination lines (Δn &gt; 2). The γ-, ϵ-, and η-transitions have been detected toward the millimeter continuum source N 105-1 A in the star-forming region N 105 in the Large Magellanic Cloud with the Atacama Large Millimeter/submillimeter Array. We use the H40α line, the brightest of the detected recombination lines (H40α, H36β, H50β, H41γ, H57γ, H49ϵ, H53η, and H54η), to determine the electron temperature and study ionized gas kinematics in the region, and the 3 mm free-free continuum emission to determine the physical parameters: the size, emission measure, and electron density. We compare the physical properties of N 105-1 A to a large sample of Galactic compact and ultracompact (UC) H II regions and conclude that N 105-1 A is similar to the most luminous (L &gt; 105 L ⊙) UC H II regions in the Galaxy. N 105-1 A is ionized by an O5.5 V star; it is deeply embedded in its natal molecular clump, and likely associated with a (proto)cluster. We incorporate high-resolution molecular line data including CS, SO, SO2, and CH3OH (~0.12 pc), and HCO+ and CO (~0.087 pc) to explore the molecular environment of N 105-1 A. Based on the CO data, we find evidence for a cloud-cloud collision that likely triggered star formation in the region. We find no clear outflow signatures, but the presence of filaments and streamers indicates ongoing accretion onto the clump hosting the UC H II region. Sulfur chemistry in N 105-1 A is consistent with the accretion shock model predictions.

Keywords: Star forming regions, Molecular clouds, Astrochemistry, Star formation, H II regions, Magellanic Clouds
The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays. We review observations of solar activity, geomagnetic variation, and auroral visibility for the extreme geomagnetic storm on 1872 February 4. The extreme storm (referred to here as the Chapman-Silverman storm) apparently originated from a complex active region of moderate area (≈ 500 μsh) that was favorably situated near disk center (S19° E05°). There is circumstantial evidence for an eruption from this region at 9-10 UT on 1872 February 3, based on the location, complexity, and evolution of the region, and on reports of prominence activations, which yields a plausible transit time of ≈29 hr to Earth. Magnetograms show that the storm began with a sudden commencement at ≈14:27 UT and allow a minimum Dst estimate of ≤ -834 nT. Overhead aurorae were credibly reported at Jacobabad (British India) and Shanghai (China), both at 19.°9 in magnetic latitude (MLAT) and 24.°2 in invariant latitude (ILAT). Auroral visibility was reported from 13 locations with MLAT below ∣20∣° for the 1872 storm (ranging from ∣10.°0∣-∣19.°9∣ MLAT) versus one each for the 1859 storm (∣17.°3∣ MLAT) and the 1921 storm (∣16.°2∣ MLAT). The auroral extension and conservative storm intensity indicate a magnetic storm of comparable strength to the extreme storms of 1859 September (25.°1 ± 0.°5 ILAT and -949 ± 31 nT) and 1921 May (27.°1 ILAT and -907 ± 132 nT), which places the 1872 storm among the three largest magnetic storms yet observed.

Keywords: Geomagnetic fields, Solar flares, Aurorae, Solar active regions, Solar coronal mass ejections, Magnetic storms
The Formation of Blue Large-amplitude Pulsators from White-dwarf Main-sequence Star Mergers. Blue large-amplitude pulsators (BLAPs) are hot low-mass stars that show large-amplitude light variations likely due to radial oscillations driven by iron group opacities. Period changes provide evidence of both secular contraction and expansion among the class. Various formation histories have been proposed, but none are completely satisfactory. Zhang et al. proposed that the merger of a helium-core white dwarf with a low-mass main-sequence star (HeWD+MS) can lead to the formation of some classes of hot subdwarfs. We have analyzed these HeWD+MS merger models in more detail. Between helium-shell ignition and full helium-core burning, the models pass through the volume of luminosity-gravity-temperature space occupied by BLAPs. Periods of expansion and contraction associated with helium-shell flashes can account for the observed rates of period change. We argue that the HeWD+MS merger model provides at least one BLAP formation channel.

Keywords: Binary stars, Stellar mergers, Stellar abundances, White dwarf stars, Stellar evolutionary models, Extreme horizontal branch stars, Blue large-amplitude pulsators, Stellar oscillations, Asteroseismology, Stellar evolution
Velocity-resolved Reverberation Mapping of NGC 3227. We describe the results of a new reverberation mapping program focused on the nearby Seyfert galaxy NGC 3227. Photometric and spectroscopic monitoring was carried out from 2022 December to 2023 June with the Las Cumbres Observatory network of telescopes. We detected time delays in several optical broad emission lines, with Hβ having the longest delay at ${\tau }_{\mathrm{cent}}={4.0}_{-0.9}^{+0.9}$ days and He II having the shortest delay with ${\tau }_{\mathrm{cent}}={0.9}_{-0.8}^{+1.1}$ days. We also detect velocity-resolved behavior of the Hβ emission line, with different line-of-sight velocities corresponding to different observed time delays. Combining the integrated Hβ time delay with the width of the variable component of the emission line and a standard scale factor suggests a black hole mass of ${M}_{\mathrm{BH}}={1.1}_{-0.3}^{+0.2}\times {10}^{7}$ M ☉. Modeling of the full velocity-resolved response of the Hβ emission line with the phenomenological code CARAMEL finds a similar mass of ${M}_{\mathrm{BH}}={1.2}_{-0.7}^{+1.5}\times {10}^{7}$ M ☉ and suggests that the Hβ-emitting broad-line region (BLR) may be represented by a biconical or flared disk structure that we are viewing at an inclination angle of θ  i  ≈ 33° and with gas motions that are dominated by rotation. The new photoionization-based BLR modeling tool BELMAC finds general agreement with the observations when assuming the best-fit CARAMEL results; however, BELMAC prefers a thick-disk geometry and kinematics that are equally composed of rotation and inflow. Both codes infer a radially extended and flattened BLR that is not outflowing.

Keywords: Supermassive black holes, Reverberation mapping, Seyfert galaxies
Investigation of Emission States of PSR J1722-3207. We have conducted a detailed study of single-pulse emission from PSR J1722-3207, which was observed at 1369 MHz using the Parkes 64 m radio telescope. PSR J1722-3207 has an asymmetric two-component mean pulse profile. We find that the brighter leading component exhibits a periodic phase-stationary nondrift amplitude modulation while the trailing component remains unchanged. As a result of this, this pulsar switches between a strong state and a weak emission state periodically. Spectral analysis of the fluctuations showed that the modulation period is very short (~2.0 s or 20P), where P is the rotation period of the pulsar. The polarization properties of the strong and weak states were investigated. The swings in the position angle of the two states are similar, suggesting that their basic emission geometry is the same. At present, it is difficult to explain the periodic mode-changing phenomenon observed in this pulsar with existing subpulse drifting models.

Keywords: Radio pulsars, Pulsars
BASS. XLII. The Relation between the Covering Factor of Dusty Gas and the Eddington Ratio in Nearby Active Galactic Nuclei. Accreting supermassive black holes (SMBHs) located at the centers of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-ray. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z ≲ 0.1) hard X-ray (14-195 keV) selected nonblazar active galactic nuclei (AGN) and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings that showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density-Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs.

Keywords: X-ray astronomy, Quasars, Active galaxies, Seyfert galaxies, Infrared photometry
Energization of Charged Test Particles in Magnetohydrodynamic Fields: Waves versus Turbulence Picture. Direct numerical simulations of three-dimensional compressible magnetohydrodynamic (MHD) turbulence have been performed in order to study the relation between wave modes and coherent structures and the consequent energization of test particles. Moreover, the question of which is the main mechanism of this particle energization is rigorously discussed. In particular, using the same initial conditions, we analyzed the nonlinear and linear evolution of a turbulent state along with the case of randomized phases. Then, the behaviors of the linear and nonlinear simulations were compared through the study of the time evolution of particle kinetic energy and preferential concentration. Also, spatiotemporal spectra were used to identify the presence of wave modes and quantify the fraction of energy around the MHD modes in linear and nonlinear simulations. Finally, the variation of the correlation time of the external forcing is studied in detail along with the effect on the particle energization (and clustering) and the presence of wave modes. More specifically, particle energization tends to decrease when the fraction of linear energy increases, supporting the idea that energization by structures is the dominant mechanism for particle energization instead of resonance with wave modes as suggested by Fermi energization theory.

Keywords: Interplanetary turbulence, Hydrodynamical simulations, Pickup ions
Observations of Multiphase, High-velocity, Shocked Gas in the Vela Supernova Remnant. We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O I, Si II, Si II*, C II, C II*, and Si III. We also detect high-velocity components in the N V doublet and compare these features to observations of high-velocity O VI absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C II and Si II. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N V and O VI absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca II absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR. *Based on observations made with the NASA/ESA Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data collected at the European Southern Observatory under ESO programs 194.C-0833(B) and 099.C-0637(A).

Keywords: Interstellar line absorption, Interstellar abundances, Supernova remnants, Interstellar medium, Diffuse interstellar clouds
Probing Orbital Parameters of Gamma-Ray Binaries with TeV Light Curves. Gamma-ray binaries are binary systems in which the energy flux peaks in the gamma-ray energy band. They harbor a compact object (a neutron star or a black hole) orbiting around a massive star, which provides a strong radiation field. It is believed that the gamma-ray emission from such objects can be strongly attenuated through the electron-positron pair production in gamma-gamma interactions. The importance of gamma-gamma absorption depends on the orbital phase and on the geometry of the system. In this work, we propose a method showing how the orbital parameters of gamma-ray binaries could be probed with TeV light curves that have imprinted features of gamma-gamma absorption.

Keywords: Binary stars, Gamma-ray sources, Pulsars, Non-thermal radiation sources, Companion stars
The Impact of Patchy Reionization on Ultrafaint Dwarf Galaxies. We investigate how patchy reionization affects the star formation history (SFH) and stellar metallicity of ultrafaint dwarf galaxies (UFDs). Patchy reionization refers to varying ultraviolet background strengths depending on a galaxy's environment. Recent observations highlight the significance of this effect on UFDs, as UFDs can have different SFHs depending on their relative position with respect to their host halo during the period of reionization. However, most cosmological hydrodynamic simulations do not consider environmental factors such as patchy reionization, and the effect of reionization is typically applied homogeneously. Using a novel approach to implement patchy reionization, we show how SFHs of simulated UFDs can change. Our cosmological hydrodynamic zoom-in simulations focus on UFD analogs with M vir ~ 109 M ⊙, M * ≲ 105 M ⊙ at z = 0. We find that patchy reionization can weaken the effect of reionization by 2 orders of magnitude up to z = 3, enabling late star formation in half of the simulated UFDs, with quenching times ~460 Myr later than those with homogeneous reionization. We also show that halo merger and mass assembly can affect the SFHs of simulated UFDs, in addition to patchy reionization. The average stellar iron-to-hydrogen ratio, [Fe/H], of the simulated UFDs with patchy reionization increases by 0.22-0.42 dex. Finally, our findings suggest that patchy reionization could be responsible for the extended SFHs of Magellanic UFDs compared to non-Magellanic UFDs.

Keywords: Local Group, Hydrodynamical simulations, Galaxy formation, Population III stars, Dwarf galaxies, Chemical enrichment, Population II stars, Reionization