Sazuna/UAT_keywords huggingface dataset:
Stellar Pulsation and Evolution: A Combined Theoretical Renewal and Updated Models (SPECTRUM). I. Updating Radiative Opacities for Pulsation Models of Classical Cepheid and RR-Lyrae. Pulsating stars are universally recognized as precise distance indicators and tracers of stellar populations. Their variability, combined with well-defined relationships between pulsation properties and intrinsic evolutionary parameters such as luminosity, mass, and age, makes them essential for understanding galactic evolution and retrieving star formation histories. Therefore, accurate modeling of pulsating stars is crucial for using them as standard candles and stellar population tracers. This is the first paper in the "Stellar Pulsation and Evolution: a Combined Theoretical Renewal and Updated Models" project, which aims to present an update of Stellingwerf's hydrodynamical pulsation code, by adopting the latest radiative opacity tables commonly used in stellar evolution community. We assess the impact of this update on pulsation properties, such as periods, instability strip topology, and light-curve shapes, as well as on period–Wesenheit and period–luminosity relations for Classical Cepheids and RR Lyrae stars, comparing the results with those derived using older opacity data. Our results indicate that the opacity update introduces only minor changes: instability strip boundary locations shift by no more than 100 K in effective temperature, and pulsation periods vary within 1σ compared to previous evaluations. Light curves exhibit slight differences in shape and amplitude. Consequently, the theoretical calibration of the Cepheid- or RRL-based extragalactic distance scale remains largely unaffected by the opacity changes. However, achieving consistency in opacity tables between stellar evolution and pulsation codes is a significant step toward a homogeneous and self-consistent stellar evolution and pulsation framework.

Keywords: Pulsating variable stars, Distance indicators, Cepheid variable stars, RR Lyrae variable stars, Stellar evolution
The X-Ray Luminous Type Ibn SN 2022ablq: Estimates of Preexplosion Mass Loss and Constraints on Precursor Emission. Type Ibn supernovae (SNe Ibn) are rare stellar explosions powered primarily by interaction between the SN ejecta and H-poor, He-rich material lost by their progenitor stars. Multiwavelength observations, particularly in the X-rays, of SNe Ibn constrain their poorly understood progenitor channels and mass-loss mechanisms. Here we present Swift X-ray, ultraviolet, and ground-based optical observations of the Type Ibn SN 2022ablq, only the second SN Ibn with X-ray detections to date. While similar to the prototypical Type Ibn SN 2006jc in the optical, SN 2022ablq is roughly an order of magnitude more luminous in the X-rays, reaching unabsorbed luminosities L X ∼ 4 × 1040 erg s‑1 between 0.2–10 keV. From these X-ray observations we infer time-varying mass-loss rates between 0.05 and 0.5 M ⊙ yr‑1 peaking 0.5–2 yr before explosion. This complex mass-loss history and circumstellar environment disfavor steady-state winds as the primary progenitor mass-loss mechanism. We also search for precursor emission from alternative mass-loss mechanisms, such as eruptive outbursts, in forced photometry during the 2 yr before explosion. We find no statistically significant detections brighter than M ≈ ‑14—too shallow to rule out precursor events similar to those observed for other SNe Ibn. Finally, numerical models of the explosion of an ∼15 M ⊙ helium star that undergoes an eruptive outburst ≈1.8 yr before explosion are consistent with the observed bolometric light curve. We conclude that our observations disfavor a Wolf–Rayet star progenitor losing He-rich material via stellar winds and instead favor lower-mass progenitor models, including Roche-lobe overflow in helium stars with compact binary companions or stars that undergo eruptive outbursts during late-stage nucleosynthesis stages.

Keywords: Circumstellar matter, Massive stars, Supernovae, Core-collapse supernovae
Evidence for a Close-in Tertiary Orbiting around the Algol-type System HZ Dra with Tidal Splitting and Spots Activities. We report a cyclic variation of the O ‑ C diagram with a semiamplitude of 0.0033 days and a period of 1.05 yr for the pulsating eclipsing binary HZ Dra. The cyclic variation can be explained by the light travel-time effect via the presence of a close-in third body orbiting around HZ Dra in an elliptical orbit with a maximum semimajor axis of 0.89 au. Based on the Wilson–Devinney code, the contribution of the third light to the total system is determined to be 29.0%, which is in agreement with the estimated value. Our light-curve modeling indicates an evolving hot and cool spot on the surface of the primary and secondary components, respectively. Their positions are roughly symmetrical to the inner Lagrangian point L1, which could be used to explain the variation in the O'Connell effect. Our frequency analysis detects one radial p-mode, seven nonradial p-modes, and one nonradial g-mode. In addition, a total of six multiplets are identified, spaced by the orbital frequency, which can be explained as a tidally split mode caused by the equilibrium tides of the close binary system with a circular orbit. These pulsating features suggest that the primary of HZ Dra is a δ Scuti star, pulsating in both p- and g-mode and influenced by tidal forces.

Keywords: Close binary stars, Eclipsing binary stars, Pulsating variable stars, Eclipsing binary minima timing method
Tracking an Eruptive Prominence Using Multiwavelength and Multiview Observations on 2023 March 7. In this paper, we carry out multiwavelength and multiview observations of the prominence eruption, which generated a C2.3 class flare and a coronal mass ejection (CME) on 2023 March 7. For the first time, we apply the revised cone model to three-dimensional reconstruction and tracking of the eruptive prominence for ∼4 hr. The prominence propagates nonradially and makes a detour around the large-scale coronal loops in active region NOAA 13243. The northward deflection angle increases from ∼36° to ∼47° before returning to ∼36° and keeping up. There is no longitudinal deflection throughout the propagation. The angular width of the cone increases from ∼30° and reaches a plateau at ∼37°. The heliocentric distance of the prominence rises from ∼1.1 to ∼10.0 R ☉, and the prominence experiences continuous acceleration (∼51 m s‑2) over 2 hr, which is probably related to the magnetic reconnection during the C-class flare. The true speed of the CME front is estimated to be ∼829 km s‑1, which is ∼1.2 times larger than that of the CME core (prominence). We conclude that both acceleration and deflection of eruptive prominences in their early lives could be reproduced with the revised cone model.

Keywords: Solar coronal mass ejections, Solar flares, Solar prominences
Monte Carlo Calculation of Electron Energy Degradation in a Pure O<SUB>2</SUB> Atmosphere. Electron degradation serves as a significant energy source in planetary upper atmospheres. In this study, a Monte Carlo model is constructed to investigate the degradation of electrons in a pure O2 atmosphere under the local approximation. Both elastic and inelastic collision processes between electrons and O2 molecules are considered in the model. The yield spectra, characterizing the occurrence of various inelastic collisions for a specified pair of incident and post-collision energies, are obtained from the model. When combined with the information of e-O2 collision cross sections, the yields of each inelastic process are then determined. Furthermore, we derive the mean energy per ion pair and the efficiencies of various inelastic processes, along with the yields of secondary (and higher-order) electrons. The calculations presented here are beneficial for understanding the ionization and heating budgets in planetary atmospheres containing a significant amount of O2 such as Earth and Jovian icy satellites (Europa, Ganymede, and Callisto).

Keywords: Monte Carlo methods, Electron impact ionization, Planetary ionospheres, Electron impact excitation
A Long-duration Superflare on the K Giant HD 251108. Many giant stars are magnetically active, which causes rotational variability, chromospheric emission lines, and X-ray emission. Large outbursts in these emission features can set limits on the magnetic field strength and thus constrain the mechanism of the underlying dynamo. HD 251108 is a Li-rich active K-type giant. We find a rotational period of 21.3 days with color changes and additional long-term photometric variability. Both can be explained with very stable stellar spots. We followed the decay phase of a superflare for 28 days with NICER and from the ground. We track the flare decay in unprecedented detail in several coronal temperature components. With a peak flux around 1034 erg s−1 (0.5─4.0 keV) and an exponential decay time of 2.2 days in the early decay phase, this is one of the strongest flares ever observed, yet it follows trends established from samples of smaller flares, for example, for the relations between Hα and X-ray flux, indicating that the physical process that powers the flare emission is consistent over a large range of flare energies. We estimate a flare loop length about 2─4 times the stellar radius. No evidence is seen for abundance changes during the flare.

Keywords: Stellar x-ray flares, K giant stars, Red giant clump, Stellar flares, Stellar coronae
Dynamics Around Supermassive Black Holes: Extreme-mass-ratio Inspirals as Gravitational-wave Sources. Supermassive black holes and their surrounding dense stellar environments nourish a variety of astrophysical phenomena. We focus on the distribution of stellar-mass black holes around the supermassive black hole and the consequent formation of extreme-mass-ratio inspirals (EMRIs). We derive a steady-state distribution, considering the effects of two-body scattering and gravitational-wave emission, and calculate the EMRI formation rate, eccentricity distribution, and EMRI-to-plunge ratio. Our model predicts: (a) a stronger segregation than previously estimated at the outskirts of the sphere of influence (at ∼0.01–2 pc for a Milky Way–like galaxy); (b) an increased EMRI-to-plunge ratio, favoring EMRIs at galaxies where stellar-mass black holes are scarce; (c) a detection of about 2 × 103 resolvable EMRIs, with a signal-to-noise ratio above 20, along a 4 yr LISA mission time; and (d) a confusion noise, induced by a cosmological population of unresolved EMRIs, reducing the LISA sensitivity in the 1–5 mHz frequency range by up to a factor of ≈2, relative to the instrumental noise.

Keywords: Supermassive black holes, Galactic center, Gravitational wave detectors, Stellar mass black holes, Stellar dynamics, Gravitational wave sources
Extreme-mass-ratio Inspirals in the Strong Segregation Regime—to Inspiral or to Get Ejected?. Extreme-mass-ratio inspirals (EMRIs) of stellar-mass black holes (BHs) are among the main targets for upcoming low-frequency gravitational wave (GW) detectors such as the Laser Interferometer Space Antenna. In the classical scenario, EMRIs are formed when BHs scatter off each other and are driven onto highly eccentric orbits that gradually inspiral due to GW emission. If the cluster is in a state of strong mass segregation, the BHs are expected to reside in a steep cusp around the central massive black hole (MBH), which would facilitate more efficient EMRI formation. However, strong mass segregation may also lead to an increased rate of ejections due to close encounters between the BHs. Here, we test the relevance of such ejections for EMRI formation by numerically solving a two-dimensional Fokker–Planck equation. Our formalism includes the effects of two-body relaxation, GW dissipation, and ejections. We find that the EMRI formation rate can be suppressed due to ejections by more than an order of magnitude for strongly segregated BH cusps with density index γ ≳ 2.25 around central MBHs of mass M • ≲ 106 M ⊙. The EMRI formation rate levels off up to a maximum value of ≃200 Gyr‑1 due to ejections, which is roughly an order of magnitude lower than the usual scenarios ignoring ejections for steep BH cusps around low-mass MBHs. Our analysis reveals the significance of strong scatterings for EMRI formation in galactic nuclei.

Keywords: Supermassive black holes, Galactic center, Stellar mass black holes, Stellar dynamics, Galaxy nuclei, Gravitational wave sources
Constraining the Location of the γ-Ray Emission Region in Radio-loud AGN 3C 380. A detailed broadband spectral and temporal study of a radio-loud active galactic nucleus, 3C 380, is carried out using 14.5 yr of Fermi-LAT data, available Swift observations, and data from other observatories, including AstroSat (2020 August). The source exhibited a GeV outburst on 2020 September 5. Given the sparsity of Swift observations, no useful correlations could be established between γ-ray, X-ray, and UV/optical bands. The source is also a part of the Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments survey and has been monitored at 15 GHz for over a decade. The correlation studies show that radio emission lags γ-rays by ∼150 days. We constrain the location of γ-ray emission by the core shift measurements from the literature and the observed time delays. Using this localization, we constructed and modeled the broadband spectral energy distribution (SED) of the source during its high γ-ray activity states and for the long-term averaged state. The SEDs during the high γ-ray activity states are modeled with two zones: one corresponding to the "steady" or the emission from the source averaged over more than a decade and another corresponding to the "flare" emission. We conclude that the high-energy emission originates within the parsec-scale jet, and moving shocks in the region drive the observed γ-flux variations.

Keywords: Relativistic jets, Radio loud quasars, X-ray active galactic nuclei, Active galactic nuclei, Gamma-rays
GR-RMHD Simulations of Super-Eddington Accretion Flows onto a Neutron Star with Dipole and Quadrupole Magnetic Fields. Although ultraluminous X-ray pulsars (ULXPs) are believed to be powered by super-Eddington accretion onto a magnetized neutron star (NS), the detailed structures of the inflow–outflow and magnetic fields are still not well understood. We perform general relativistic radiation magnetohydrodynamics (GR-RMHD) simulations of super-Eddington accretion flows onto a magnetized NS with dipole and/or quadrupole magnetic fields. Our results show that an accretion disk and optically thick outflows form outside the magnetospheric radius, while inflows aligned with magnetic field lines appear inside. When the dipole field is more prominent than the quadrupole field at the magnetospheric radius, accretion columns form near the magnetic poles, whereas a quadrupole magnetic field stronger than the dipole field results in the formation of a belt-like accretion flow near the equatorial plane. The NS spins up as the angular momentum of the accreting gas is converted into the angular momentum of the electromagnetic field, which then flows into the NS. Even if an accretion column forms near one of the magnetic poles, the observed luminosity is almost the same on both the side with the accretion column and the side without it, because the radiation energy is transported to both sides through scattering. Our model suggests that galactic ULXP Swift J0243.6+6124 has a quadrupole magnetic field of 2 × 1013 G and a dipole magnetic field of less than 4 × 1012 G.

Keywords: Accretion, Neutron stars, Radiative magnetohydrodynamics, High energy astrophysics, Ultraluminous x-ray sources, General relativity
The Star Formation History of Nearby Galaxies: A Machine Learning Approach. Reproducing color–magnitude diagrams (CMDs) of star-resolved galaxies is one of the most precise methods for measuring the star formation history (SFH) of nearby galaxies back to the earliest time. The upcoming big data era poses challenges to the traditional numerical technique in its capacity to deal with vast amounts of data, which motivates us to explore the feasibility of employing machine learning networks in this field. In this study, we refine the synthetic CMD method with a state-of-the-art theoretical stellar evolution model to simulate the properties of stellar populations, incorporate the convolutional neural network in the fitting process to enhance the efficiency, and innovate the initial stellar mass estimation to improve the flexibility. The fine-tuned deep learning network, named SFHNet, has been tested with synthetic data and further validated with photometric data collected from the Hubble Space Telescope. The derived SFHs are largely in accordance with those reported in the literature. Furthermore, the network provides detailed insights into the distribution of stellar density, initial stellar mass, and star formation rate over the age–metallicity map. The application of the deep learning network not only measures the SFH accurately but also enhances the synthetic CMD method's efficiency and flexibility, thereby facilitating a more comprehensive and in-depth understanding of nearby galaxies.

Keywords: Hertzsprung Russell diagram, Convolutional neural networks, Galaxy stellar content
BD+44°493: Chemo-dynamical Analysis and Constraints on Companion Planetary Masses from WIYN/NEID Spectroscopy. In this work, we present high-resolution (R ∼ 100,000), high signal-to-noise ratio (S/N ∼ 800) spectroscopic observations for the well-known, bright, extremely metal-poor, carbon-enhanced star BD+44°493. We determined chemical abundances and upper limits for 17 elements from WIYN/NEID data, complemented with 11 abundances redetermined from Subaru and Hubble data, using the new, more accurate, stellar atmospheric parameters calculated in this work. Our analysis suggests that BD+44°493 is a low-mass (0.83 M ⊙), old (12.1–13.2 Gyr) second-generation star likely formed from a gas cloud enriched by a single metal-free 20.5 M ⊙ Population III star in the early Universe. With a disk-like orbit, BD+44°493 does not appear to be associated with any major merger event in the early history of the Milky Way. From the precision radial-velocity NEID measurements (median absolute deviation = 16 m s‑1), we were able to constrain companion planetary masses around BD+44°493 and rule out the presence of planets as small as   M J out to periods of 100 days. This study opens a new avenue of exploration for the intersection between stellar archaeology and exoplanet science using NEID. *The WIYN Observatory is a joint facility of the University of Wisconsin Madison, Indiana University, NSF NOIRLab, the Pennsylvania State University, Purdue University, and Princeton University. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-12268, GO-12554, and GO-14231.

Keywords: High resolution spectroscopy, Population III stars, Stellar ages, Stellar kinematics, Radial velocity, Chemical abundances, Bayesian information criterion, Stellar masses, Population II stars, CEMP stars, Metallicity, Stellar atmospheres
Toward a Unified Injection Model of Short-lived Radioisotopes in N-body Simulations of Star-forming Regions. Recent research provides compelling evidence that the decay of short-lived radioisotopes (SLRs), such as 26Al, provided the bulk of energy for heating and desiccation of volatile-rich planetesimals in the early solar system. However, it remains unclear whether the early solar system was highly enriched relative to other planetary systems with similar formation characteristics. While the solar system possesses an elevated level of SLR enrichment compared to the interstellar medium, determining SLR enrichment of individual protoplanetary disks observationally has not been performed and is markedly more difficult. We use N-body simulations to estimate enrichment of SLRs in star-forming regions through two likely important SLR sources: stellar winds from massive stars and supernovae (SNae). We vary the number of stars and the radii of the star-forming regions and implement two models of stellar-wind SLR propagation for the radioisotopes 26Al and 60Fe. We find that for 26Al enrichment the solar system is at the upper end of the expected distribution, while for the more SNae-dependent isotope 60Fe we find that the solar system is comparatively very highly enriched. Furthermore, combined with our previous research, these results suggest that the statistical role of 26Al-driven desiccation on exoplanet bulk composition may be underestimated in typical interpretations of the low-mass exoplanet census, and that 60Fe is even less influential as a source of heating than previously assumed.

Keywords: Star forming regions, Protoplanetary disks, Planetesimals, N-body simulations, Planet formation
oMEGACat. IV. Constraining the Ages of Omega Centauri Subgiant Branch Stars with HST and MUSE. We present age estimates for over 8100 subgiant branch (SGB) stars in Omega Centauri (ω Cen) to study its star formation history. Our large data set, which combines multi-wavelength Hubble Space Telescope photometry with MUSE metallicities, provides an unprecedented opportunity to measure individual stellar ages. We do this by fitting each star's photometry and metallicity with theoretical isochrones that are embedded with an empirical [C + N + O]─[Fe/H] relation specific to ω Cen. The bulk of the stars have ages between 13 and 10 Gyr, with the mean stellar age being 12.08 ± 0.01 Gyr and the median age uncertainty being 0.68 Gyr. From these ages we construct the most complete age─metallicity relation for ω Cen to date. We find that the mean age of stars decreases with increasing metallicity and find two distinct streams in the age─metallicity plane, hinting at different star formation pathways. We derive an intrinsic spread in the ages of 0.75 ± 0.01 Gyr for the whole cluster, with the age spread showing a clear increase with metallicity. We verify the robustness of our age estimations by varying isochrone parameters and constraining our systematics. We find the C + N + O relation to be the most critical consideration for constraining the age─metallicity relation. We also present an SGB chromosome map with age information. In the future these stellar ages could be combined with chemical abundances to study age differences in subpopulations and uncover the chemical evolution history of this massive nuclear star cluster.

Keywords: Globular star clusters, Stellar populations, Stellar ages, Star clusters