Sazuna/UAT_keywords huggingface dataset:
Optical Strong Line Ratios Cannot Distinguish between Stellar Populations and Accreting Black Holes at High Ionization Parameters and Low Metallicities. High-redshift observations from JWST indicate that optical strong line ratios do not carry the same constraining power as they do at low redshifts. Critically, this prevents a differentiation between stellar and black hole accretion-driven ionization, thereby obscuring both active galactic nuclei (AGN) demographics and star formation rates. To investigate this, we compute a large suite of photoionization models with Cloudy powered by stellar populations and accreting black holes over a large grid of ages, metallicities, initial mass functions, binarities, ionization parameters, densities, and black hole masses. We use these models to test three rest-frame optical diagnostics designed to separate ionizing sources at low redshifts: the [N II]-BPT, VO87, and OHNO diagrams. We show that these diagnostics are strongly driven by the ionization parameter (log U) and the gas-phase metallicity (Zgas), often more so than the ionizing spectrum itself; there is significant overlap between stellar population and accreting black hole models at high log U and low Zgas. The OHNO diagram is especially contaminated in the AGN region by stellar models with high log U and low Zgas, consistent with high-redshift observations. We show that the [N II]-BPT, VO87, or OHNO diagrams are most sensitive to the shape of the &lt;54 eV ionizing continuum, an energy regime in which stellar populations and black hole accretion disk models can be highly degenerate. Finally, we discuss the potential for emission lines that trace the &gt;54 eV ionizing continuum to differentiate between ionizing sources more effectively than the [N II]-BPT, VO87, or OHNO diagrams alone.

Keywords: Emission line galaxies, Active galactic nuclei, Galaxy evolution, Interstellar medium, High-redshift galaxies
On the Properties of Turbulence in the Remnant of the Tycho Supernova. We investigate the turbulent structures in the Tycho supernova remnant (SNR) by applying two-point autocorrelation and power spectral analyses to high-resolution X-ray and radio images. Using cleaned Chandra and Very Large Array data, we derive two-dimensional (2D) and one-dimensional (1D) autocorrelation functions and power spectra, revealing that the fluctuations in both X-ray brightness (approximately tracing plasma density) and radio brightness (tracing magnetic field strength) follow the power-law distributions consistent with Kolmogorov-type turbulence. Specifically, the power spectra exhibit a slope of 8/3 in 2D and 5/3 in 1D analyses, indicating fully developed turbulence across a broad range of spatial scales. The structure functions and spectral slopes remain robust with and without correction for line-of-sight integration effects, suggesting the presence of Kolmogorov-like turbulence locally throughout the remnant's volume. Anisotropies in the 2D autocorrelation function are aligned with known density and magnetic field gradients. Analysis of the 1D radial properties of turbulence confirms Kolmogorov scaling, and indicates that modes in the power spectra may be related either to periodicity in the fluctuations or to the physical sizes of bright or dim features in the surface brightness. Our results demonstrate that the Tycho SNR hosts a spatially and temporally developed turbulent cascade, providing insight into the physics of turbulence in SNRs.

Keywords: Supernova remnants, Space plasmas, Astrophysical processes
Search for Distant Hypervelocity Star Candidates Using RR Lyrae Stars. Hypervelocity stars (HVSs) are stars with velocities exceeding their local escape velocities. Searching for HVSs and studying their origins can be an important way to study the properties of the Milky Way. In this paper, we utilize precise distances for RR Lyrae stars (RRLs) derived from the period-absolute magnitude─metallicity relation, along with proper motions from Gaia DR3, to conduct a large-volume search for HVSs. Our sample consists of a catalog with 8172 RRLs with metallicity, distance, and radial velocities estimated from the Sloan Digital Sky Survey and LAMOST spectroscopic data and an extended catalog of 135,873 RRLs with metallicity and distance estimated from Gaia photometry. After careful quality cuts, 165 hypervelocity RRL candidates were found. We performed further checks on their light curves and selected the most reliable 87 hypervelocity RRLs. All of them exceed the Milky Way's escape velocity in the tangential component. Among them, seven stars have tangential velocity over 800 km s−1. We identified two spatially distinct distributions of hypervelocity RRLs: one concentrated toward the Galactic center and another localized around the Magellanic Clouds, suggesting that their origins are likely associated with these regions through the Hills or other mechanisms. Furthermore, we detected a significant number of RRLs associated with dwarf galaxies that exceed the Milky Way's escape velocity, likely ejected from their host systems. Future Gaia releases and spectroscopic follow-up observations will provide further insight into their ejection origin.

Keywords: Galaxy structure, Hypervelocity stars, Milky Way dynamics, Distance indicators, RR Lyrae variable stars
Einstein@Home Searches for Gamma-Ray Pulsars in the Inner Galaxy. The Fermi Large Area Telescope (LAT) has revealed a mysterious extended excess of GeV gamma-ray emission around the Galactic Center (GC), which can potentially be explained by unresolved emission from a population of pulsars, particularly millisecond pulsars (MSPs), in the Galactic bulge. We used the distributed volunteer computing system Einstein@Home to search the Fermi-LAT data for gamma-ray pulsations from sources in the inner Galaxy, to try to identify the brightest members of this putative population. We discovered four new pulsars, including one new MSP and one young pulsar whose angular separation to the GC of 0 .° 93 is the smallest of any known gamma-ray pulsar. We demonstrate a phase-resolved difference imaging technique that allows the flux from this pulsar to be disentangled from the diffuse GC emission. No radio pulsations were detected from the four new pulsars in archival radio observations or during the MPIfR-MeerKAT Galactic Plane Survey. While the distances to these pulsars remain uncertain, we find that it is more likely that they are all foreground sources from the Galactic disk, rather than pulsars originating from the predicted bulge population. Nevertheless, our results are not incompatible with an MSP explanation for the GC excess, as only one or two members of this population would have been detectable in our searches.

Keywords: Gamma-ray sources, Pulsars, Rotation powered pulsars, Millisecond pulsars
Probing Starspot Dynamics on the Active M Dwarf TIC 272272592: A Multiyear TESS Study. We present an analysis of temporal starspot evolution and its distribution on an active rapid rotator (Prot = 1.22 days), TIC 272272592, using high-precision time-series photometry from the Transiting Exoplanet Survey Satellite spanning over 3 yr. The primary objective of this work is to study the distribution pattern of starspots across the stellar surface and to investigate the spot evolution over time. This is a fascinating object, being a rapid rotator with a decline flare rate (∼0.5 dex) over 4 yr of Kepler observation. Therefore, we performed starspot modeling on this object using Best rAandom StarSpots Model calculAtioN software, and the analysis indicates the presence of two spots on the stellar surface, with a stable high-latitude spot and occasionally a small midlatitude spot. Over time, the midlatitude spot exhibits a gradual high-latitude migration, suggesting latitudinal evolution. Moreover, our analysis reveals a moderate negative correlation of starspot sizes with time (Spearman ρ = −0.43), suggesting a significant decay across the 3 yr baseline, though no clear cyclic pattern is detected. The spot groups persist for several years, with mean total spot size in sectors 14, 15, 41, 54, and 55 of 5.1%, 5.7%, 5.5%, 4.8%, and 4.4%, respectively. Additionally, we have estimated the peak flare temperature of 36 detected flares between 11,000 ± 1900 K and 24,700 ± 5000 K, and 70% of the flares exhibited peak emitting area of flares within the range from 170 ppm to 563 ppm. Furthermore, no statistically significant correlation was found between stellar flares with rotational phase for this object.

Keywords: M dwarf stars, Starspots, Surface variability, Stellar flares
Spectrotemporal Analysis of X-Ray Reverberation in the Seyfert 1.5 Galaxy 4U 1344─60. The development and implementation of self-consistent spectrotemporal models of X-ray reverberation off of the inner accretion disk have produced several recent X-ray-reverberation-based black hole (BH) mass measurements. We analyze the 2016 simultaneous NuSTAR + Swift observation of the Seyfert 1.5 galaxy 4U 1344−60, presenting the first temporal evidence of X-ray reverberation from the inner disk in this source by using Gaussian process regression to interpolate over gaps in the light curves. We find no such temporal signature in the 2011 Suzaku data, consistent with a previous analysis of that flux spectrum. By performing a joint spectrotemporal fit to the flux and lag spectra of the 2016 data, we show that the lag spectrum requires a boosted reverberation signal and prefers an enhanced coronal height compared to the flux spectrum. These inconsistencies may point toward a coronal and/or inner disk geometry significantly different than the assumed lamppost and razor-thin ones. The best model description prefers radial gradients in disk density and ionization, yielding a BH mass of  MBH=2−1+2×107M⊙ , which is comparable to the range of BH mass estimates in the literature (i.e.,  MBH≍1−8×107M⊙ ). The lack of inner disk reverberation during the 2011 epoch and its emergence during the 2016 epoch may be due to a reduction in the beaming of a vertically extended X-ray corona or the inward migration of the inner disk radius if the disk is "slim" instead of razor-thin.

Keywords: X-ray astronomy, Supermassive black holes, Seyfert galaxies, Active galactic nuclei, Time domain astronomy, Spectroscopy
Have Any LISA Verification Binaries Been Found?. Some electromagnetically observed ultracompact binaries will be strong gravitational wave sources for space-based detectors like the Laser Interferometer Space Antenna (LISA). These sources have historically been referred to as "verification binaries" under the assumption that they will be exploited to assess mission performance. This paper quantitatively interrogates that scenario by considering targeted analyses of known galactic sources in the context of a full simulation of the galactic gravitational wave foreground. We find that the analysis of the best currently known LISA binaries, even making maximal use of the available information about the sources, is susceptible to ambiguity or biases when not simultaneously fitting to the rest of the galactic population. While galactic binaries discovered electromagnetically in advance of, or during, the LISA survey are highly valuable multimessenger systems, the need for a global treatment of the galactic gravitational wave foreground calls into question whether or not they are the best sources for data characterization.

Keywords: Gravitational waves
Asteroseismology and Dynamics Reveal Interior Structure and Coeval Evolution in the Triply Post-main-sequence System DG Leo. δ Scuti stars in binary or multiple systems serve as crucial probes for studying stellar pulsation and evolution. However, many such systems are not ideal for asteroseismology due to uncertainties in mass transfer with close companions and the challenges of dynamically measuring all components' physical properties. The triple system DG Leo, comprising an inner binary and a distant δ Scuti star, is an ideal target due to its well-separated pulsator. By combining new TESS photometry with archival spectroscopy, our dynamical analysis shows that the system's three components share similar masses, radii, and luminosities within errors, occupying coincident Hertzsprung─Russell diagram positions, indicative of coeval evolution. By fitting seven observed δ Scuti frequencies through asteroseismic modeling with dynamically constrained theoretical grids, we simultaneously trace the pulsating star's evolution and constrain the triple system's evolutionary stage, with the derived fundamental parameters showing consistency with the dynamical solutions. Our analysis reveals that all three components of DG Leo are in the post-main-sequence phase, with a system age of  0.7664−0.1258+0.1402  Gyr. Additionally, the δ Scuti component shows multiple nonradial modes with significant mixed-character frequencies, providing precise constraints on its convective core extent ( Rcz/R=0.0562−0.0021+0.0137 ).

Keywords: Stellar oscillations, Trinary stars, Asteroseismology, Delta Scuti variable stars
A Sample of He II λ4686 "Changing-look" Quasars. We present the first systematic search for "changing-look" ("CL") behavior in the broad He II λ4686 emission line in quasars, utilizing repeated spectroscopy from the Sloan Digital Sky Survey. The He II line, originating from high-ionization gas and powered by extreme-ultraviolet photons, serves as a sensitive tracer of changes in the ionizing continuum. After applying strict spectral selection criteria and visual inspection to a parent sample of over 9000 quasars with multiepoch spectra, we identify a sample of 34 He II "CL" quasars that show a significant appearance or disappearance of the broad He II λ4686 line. Compared with previously known Hβ "CL" quasars, the He II "CL" sample exhibits similarly strong continuum variability and broad-line flux changes, yet shows a preference for higher Eddington ratios and lower host-galaxy contamination. These results highlight the value of the He II line in studying the central variable engines of active galactic nuclei and uncovering a more complete census of extreme quasar variability. A comparison with Hβ "CL" further underscores the profound selection biases inherent in "CL" studies, especially those associated with line strength, host-galaxy contamination, and spectral signal-to-noise ratio.

Keywords: Accretion, Supermassive black holes, Catalogs, Quasars
The Survival of Aromatic Molecules in Protoplanetary Disks. Aromaticity is a common chemical functionality in bioactive molecules. In interstellar and circumstellar environments, benzene and other small aromatics are considered the precursors for more complex prebiotic molecules, and they have been shown to potentially have rich ice-phase photochemistry. The availability of small organic molecules in prebiotic networks depends on their photostability in astrophysical environments preceding planet formation, particularly during the protoplanetary disk stage, as the disk composition is linked to the chemical makeup of planets and planetesimals. We study the ultraviolet (UV) photodestruction (120─160 nm) of five aromatic molecules in undiluted ices and, for selected cases, in astrophysically relevant ice matrices (H2O, CO, CO2). For each ice, we measure the destruction cross sections as a function of photon exposure. In undiluted ices, aromatic molecules exhibit substantially lower photodestruction cross sections (σ &lt; 10−19 cm2) than aliphatic hydrocarbons, including cyclohexane (σ = 2.8─4 × 10−18 cm2). Furthermore, neither substituent nature nor size affects the aromatic stability in pure ices, suggesting that the strong intermolecular interactions among aromatic molecules provide protection against vacuum UV exposure, even with small to mid-sized ring substituents. In mixed ices, the photodestruction and reactivity of aromatic molecules (σ = 2.5─6.1 × 10−18 cm2) increase by more than an order of magnitude, but are still lower than in the gas phase. We attribute this to a weaker cage effect and matrix-specific interactions. We use the experimental photodestruction cross sections to estimate the lifetime of aromatic molecules in protoplanetary disks, delineating the disk regions in which aromatic photochemistry is expected to be the most active.

Keywords: Ice destruction, Laboratory astrophysics, Pre-biotic astrochemistry, Astrochemistry
The Gamma-Ray Luminosity Function of Flat-spectrum Radio Quasars. We have utilized the largest sample of gamma-ray-selected Fermi flat-spectrum radio quasars (FSRQs) ever used (519 sources) to construct the luminosity function and its evolution through cosmic history. In addition to spanning large redshift (0 &lt; z ≲ 4) and luminosity ranges (2.9 × 1043 erg s−1─7.3 × 1048 erg s−1), this sample also has a robust calculation of the detection efficiency associated with its observation, making its selection effects and biases well understood. We confirm that the local luminosity function is best explained by a double power law. The evolution of the luminosity function of FSRQs follows a luminosity-dependent density evolution. FSRQs experience positive evolution, with their space density growing with increasing redshift up to a maximum redshift, after which the numbers decrease. This peak in redshift occurs at larger redshifts for higher-luminosity sources and at lower redshifts for lower-luminosity sources. We find an unexpected similarity between the luminosity function of FSRQs and that of BL Lacertae objects (BL Lacs) at intermediate luminosity. This could be a sign of a strong genetic link between the two blazar subclasses or of BL Lac samples being contaminated by large amounts of FSRQs with their jets nearly perfectly aligned with our line of sight.

Keywords: Luminosity function, Cosmological evolution, Gamma-ray sources, Blazars, Flat-spectrum radio quasars, Active galactic nuclei
Ionization Sources of the Local Interstellar Clouds: Two B Stars, Three White Dwarfs, and the Local Hot Bubble. The dominant sources of photoionizing radiation in the extreme-ultraviolet (EUV) incident on the exterior of the local interstellar clouds include two nearby early B-type stars, ϵ CMa (124 ± 2 pc) and β CMa (151 ± 5 pc), three hot dwarfs, and the Local Hot Bubble (LHB). Line emission (170─912 Å) from highly ionized metals (Fe, Ne, Mg) in million-degree LHB plasma may be responsible for the elevated ionization fractions of helium (nHe II/nHe ≍ 0.4) compared to hydrogen (nH II/nH ≍ 0.2) in the local clouds. We update the stellar parameters and ionizing flux for β CMa, after correcting the EUV spectra for intervening H I column density, NH I = (1.9 ± 0.1) × 1018 cm−2, and its hotter effective temperature, Teff ≍ 25,000 K versus 21,000 K for ϵ CMa. These two stars produce a combined H-ionizing photon flux ΦH ≍ 6800 ± 1400 cm−2 s−1 at the external surface of the local clouds. The hot bubble could produce comparable fluxes, ΦH = 2000─9000 cm−2 s−1, depending on the amount of metal depletion into dust grains that survive sputtering. The radial velocities and proper motions of β CMa and ϵ CMa indicate that both stars passed within 10 ± 1 pc of the Sun 4.4 ± 0.1 Myr ago, with 100─200 times higher local ionizing fluxes. At that time, the local clouds were likely farther from the Sun, owing to their transverse motion. Over the past few Myr, EUV radiation from these two stars left a wake of highly ionized gas in a hot, low-density cavity produced by past supernova explosions in the Sco-Cen OB association and connected with the LHB.

Keywords: Interstellar radiation field, OB stars, Diffuse interstellar clouds
Oxygen Isotopes Reveal Low-mass Star Dominance in the Small Magellanic Cloud. Oxygen isotope abundances and their ratios are fingerprints of stellar evolution, and therefore provide a powerful tool in tracing the enrichment history of galaxies. However, their behavior in low-metallicity dwarf galaxies remains largely unexplored. The Small Magellanic Cloud (SMC), a nearby analog of young high-redshift galaxies, offers an ideal laboratory to investigate this regime. Using the Atacama Compact Array, we observed the J = 2 → 1 transitions of 12CO, 13CO, C18O, and C17O from the massive star-forming region LIRS 36 (aka N12A), achieving the first detection of C17O in the SMC. This detection enables the first direct measurement of the 18O/17O abundance ratio of 0.87 ± 0.26 in this galaxy, which is substantially lower than all values in the literature, including molecular clouds in the Milky Way and other galaxies. Such a low ratio of 18O/17O, together with a high 13CO/C18O ratio, indicates chemical enrichment dominated by low-mass stars, consistent with the observed paucity of high-mass stars in the SMC. We suggest that the SMC is governed by a top-light integrated galaxy-wide initial mass function, predicted by the SMC's persistently low star formation activities.

Keywords: Interstellar molecules, Galaxy chemical evolution, Small Magellanic Cloud, Interstellar medium, Galaxies
On the Spatial Distribution of Luminous Blue Variables, B[e] Supergiants, and Wolf─Rayet Stars in the Large Magellanic Cloud. We examine the spatial distributions of luminous blue variables (LBVs), B[e] supergiants, and Wolf─Rayet stars (WR) stars in the Large Magellanic Cloud (LMC) to clarify their relative ages, evolutionary states, and relationships. This survey employs a reference catalog that was not available for previous work, comprising more than 3900 of the LMC's most luminous stars. Our analysis shows that LBVs, B[e] supergiants, and WRs have spatial distributions like normal stars with the same spectral types and luminosities. Most LBVs are not isolated, nor do they require binary or multiple status to explain their spatial relationship to other populations. There are two likely exceptions: one lower-luminosity LBV and one LBV candidate are relatively isolated and may have velocities that require additional acceleration. The B[e] supergiants are spatially and kinematically more dispersed than LBVs, suggesting that they belong to an older population. The most luminous early-type WNs are most closely associated with the evolved late O-type supergiants. The high luminosity late-WNs and WNh stars, however, are highly concentrated in the 30 Dor region, which biases the analysis. The less-luminous WNs and WCs are associated with a mix of evolved late-B, A-type, and yellow supergiants which may be in a post-red-supergiant phase. Spatial distributions of the less-luminous WN, WC, and WN3/O3 stars reinforce proposed evolutionary links among these subtypes. Our analysis also demonstrates the importance of using a comprehensive census, with reference populations clearly defined by spectral type and luminosity, and how small number statistics, especially when combined with spatial clustering, can invalidate some commonly cited statistical tests.

Keywords: B supergiant stars, Massive stars, Luminous blue variable stars, Large Magellanic Cloud, Wolf-Rayet stars