Sazuna/UAT_keywords huggingface dataset:
LZ-STAR Survey: Low-metallicity Star Formation Survey of Sh2-284. I. Ordered Massive Star Formation in the Outer Galaxy. Star formation is a fundamental, yet poorly understood, process of the Universe. It is important to study how star formation occurs in different galactic environments. Thus, here, in the first of a series of papers, we introduce the Low-metallicity Star Formation (LZ-STAR) survey of the Sh2-284 (hereafter S284) region, which, at Z ∼ 0.3–0.5Z⊙, is one of the lowest-metallicity star-forming regions of our Galaxy. LZ-STAR is a multifacility survey, including observations with JWST, the Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope, Chandra, and Gemini. As a starting point, we report JWST and ALMA observations of one of the most massive protostars in the region, S284p1. The observations of shock-excited molecular hydrogen reveal a symmetric, bipolar outflow originating from the protostar, spanning several parsecs, and fully covered by the JWST field of view and ALMA observations of CO(2–1) emission. These allow us to infer that the protostar has maintained a relatively stable orientation of disk accretion over its formation history. The JWST near-infrared continuum observations detect a centrally illuminated bipolar outflow cavity around the protostar, as well as a surrounding cluster of low-mass young stars. We develop new radiative transfer models of massive protostars designed for the low metallicity of S284. Fitting these models to the protostar's spectral energy distribution implies a current protostellar mass of ∼10 M⊙ has formed from an initial ∼100 M⊙ core over the last ∼3 × 105 yr. Overall, these results indicate that massive stars can form in an ordered manner in low-metallicity, protocluster environments.

Keywords: Jets, Massive stars, Young stellar objects, Star formation, Metallicity
Quasar Lifetime Measurements from Extended Lyα Nebulae at z ∼ 6. The existence of billion-solar-mass black holes hosted in luminous quasars within the first gigayear of cosmic history poses a challenge to our understanding of supermassive black hole (SMBH) growth. The problem is further exacerbated by the very short quasar lifetimes of tQ ≲ 106 yr, as derived from the extent of their proximity zone (PZ) sizes observed in the quasars' rest-UV spectra. However, the quasar lifetime estimates based on the extents of the PZs may be underestimated, as time-variable obscuration effects might have limited the quasars' emission along our sightline in the past. In this work, we present independent quasar lifetime measurements for six quasars at z ∼ 6 leveraging the extended nebular emission perpendicular to our line of sight. We use observations from the Very Large Telescope/Multi-Unit Spectroscopic Explorer to search for extended Lyα emission in the circumgalactic medium around quasars with small PZs and estimate their lifetimes as the light travel time between the SMBH and the outer edge of the nebula. We find agreement between the independent lifetime estimates. For one object we find a proximate absorption system prematurely truncating the extent of the quasar's PZ, which thus results in an expected discrepancy between the lifetime estimates. Our results provide further evidence that the quasars' current accretion episode has only recently begun, challenging our models of SMBH growth.

Keywords: Supermassive black holes, Early universe, Quasars, Circumgalactic medium, Nebulae
A Comprehensive Study of the Energy and Redshift Distributions of the Fast Radio Burst Population Based on the First CHIME/FRB Catalog. Fast radio bursts (FRBs) are brief, high-energy bursts of radio waves from extragalactic sources, and their origin remains an open question. In this paper, we perform a comprehensive analysis of the FRB population using the first CHIME/FRB catalog, focusing on their energy and redshift distributions, with careful consideration of selection effects. We investigate a range of models, including the Schechter function and the broken power-law function for the energy distribution, and several redshift evolution models, such as the star formation history (SFH) model, as well as models incorporating time delays relative to the SFH or additional redshift evolution factors. Our results indicate that the energy distribution of FRBs is best described by the Schechter function, with a power-law index of  γ=−1.49−0.27+0.37  and a characteristic cutoff energy of  Ec=2.82−1.47+2.43×1041  erg. Furthermore, we find no evidence for redshift evolution in the energy distribution of FRBs. As for their redshift distribution, our analysis shows that it follows the cosmic SFH, without requiring additional delayed components or redshift evolution factors, suggesting that most FRBs likely originate from young stellar populations. Simultaneously, we infer a local volumetric rate of  Φ0=4.68−2.39+4.66×104Gpc−3yr−1  for E &gt; 1039 erg. These results, robust against CHIME observational biases, may provide new insights into the underlying properties of the FRB population.

Keywords: Radio transient sources
AGN Feedback Efficiency of Narrow Absorption Line Quasars. We consider if outflowing winds that are detected via narrow absorption lines (NALs) with FWHM of &lt;500 km s‑1 (i.e., NAL outflows) in quasar spectra contribute to feedback. As our sample, we choose 11 NAL systems in eight optically luminous quasars from the NAL survey of T. Misawa et al. (2007a), based on the following selection criteria: (i) they exhibit "partial coverage" suggesting quasar origin (i.e., intrinsic NALs), (ii) they have at least one low-ionization absorption line (C II and/or Si II), and (iii) the Lyα absorption line is covered by available spectra. The results depend critically on this selection method, which has caveats and uncertainties associated with it, as we discuss in a dedicated section of this paper. Using the column density ratio of the excited and ground states of C II and Si II, we place upper limits on the electron density as ne &lt; 0.2–18 cm‑3 and lower limits on their radial distance from the flux source R as greater than several hundreds of kpc. We also calculate lower limits on the mass outflow rate and kinetic luminosity of  log(Ṁ/M⊙s‑1)&gt;  1.9–5.5 and  log(Ek̇/ergs‑1)&gt;42.9 –49.8, respectively. Taking the NAL selection and these results at face value, the inferred feedback efficiency can be comparable to or even larger than those of broad absorption line and other outflow classes, and large enough to generate significant active galactic nucleus feedback. However, the question of the connection of quasar-driven outflows to NAL absorbers at large distances from the central engine remains open and should be addressed by future theoretical work.

Keywords: AGN host galaxies, Broad-absorption line quasar, Quasar absorption line spectroscopy, Quasars
The Presolar Heritage of <SUP>50</SUP>Ti and <SUP>26</SUP>Al Heterogeneity in the Protoplanetary Disk. Nucleosynthetic isotope anomalies have been documented within the solar protoplanetary disk for several isotopes, including 48Ca, 50Ti, 54Cr, 94Mo, and 96Zr. However, the existence of isotopic heterogeneities for short-lived radionuclides such as 26Al remains debated. Here, we investigate potential heterogeneity in the 26Al distribution by examining nucleosynthetic 50Ti and 26Al–26Mg isotope systematics in high-temperature early solar system solids—Ca-Al-rich inclusions (CAIs) and hibonites from CM chondrites—and comparing these with presolar grain data. We present high-precision titanium isotope measurements for 13 CAIs, comprising 11 26Al-rich "normal"-type and two 26Al-poor fractionation and unidentified nuclear effect (FUN)-type CAIs. Our data, combined with previously published results, reveal a fundamental decoupling between significant nucleosynthetic 50Ti anomalies and high abundances of 26Al, a pattern also present in presolar grains. We propose that this mutual exclusivity of 50Ti and 26Al observed in CAIs and CM hibonites is inherited directly from protosolar molecular cloud material. Specifically, this isotopic signature reflects the mixing of newly formed, 26Al-rich molecular cloud material with older, Galactically inherited 26Al-poor dust characterized by large nucleosynthetic 50Ti variability. Consequently, solids exhibiting substantial 50Ti anomalies (26Al-poor FUN-type CAIs and CM hibonites) predominantly inherited older, 26Al-poor presolar dust, whereas those with minimal 50Ti anomalies and abundant 26Al (26Al-rich normal CAIs and CM hibonites) incorporated more of the younger, 26Al-rich component. This inherited isotopic signature provides a consistent explanation for disk-scale nucleosynthetic heterogeneity in bulk meteorites, challenging the widely accepted notion that the canonical 26Al/27Al ratio of 5.25 × 10‑5 in 26Al-rich CAIs represents the solar system average.

Keywords: Cosmochronology
Rigidity Dependence of the Long-term Galactic Cosmic Ray Variation by AMS-02. Using measurements from the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station, we have examined the long-term variations in galactic cosmic ray (GCR) proton fluxes in 2011–2018. The AMS-02 data allow for the study of time profiles and the rigidity dependence of the long-term variations observed directly in space in a wide rigidity range from 1 to 100 GV. We have investigated the rigidity dependence of the amplitude of the long-term GCR variations described by the power-law fitting over the solar cycle. For a physical interpretation, we have considered the relationship between long-term GCR variations and heliospheric magnetic field turbulence using power spectral density frequency exponents. The apparent solar cycle variability can be seen in the time profile of the spectral index γ of the power-law rigidity spectrum of long-term GCR variations for 2006–2018 during solar cycle 24. The spectral index γ shows a tendency to be higher for the solar maximum phase compared to the solar minimum phase. Furthermore, we find evidence of the energy-dependent rigidity spectrum of the long-term GCR variations observed by AMS-02. We reveal the soft rigidity spectrum of the GCR isotropic intensity variations for the solar maximum and the hard rigidity spectrum for the solar minimum owing to the essential temporal rearrangements of the structure in the heliospheric magnetic field turbulence from the maxima to minima epoch of solar activity. The long-term GCR variations by AMS-02 show the softening of the spectra toward higher energies.

Keywords: Galactic cosmic rays
Circumgalactic Medium Cloud Sizes from Refractive Fast Radio Burst Scattering. We explore constraints on the size of cool gas clouds in the circumgalactic medium (CGM) obtainable from the presence, or lack thereof, of refractive scattering in fast radio bursts (FRBs). Our refractive analysis sets the most conservative bounds on parsec-scale CGM clumpiness as it does not make assumptions about the turbulent density cascade. We find that the bulk of low-redshift cool CGM gas, constrained to have densities of ne ≲ 10−2 cm−3, likely cannot produce two refractive images and, hence, scattering. It is only for extremely small cloud sizes ≲ 0.1 pc (about 100 times smaller than the so-called shattering scale) that such densities could result in detectable scattering. Dense ne ≳ 0.1 cm−3 gas with shattering-scale cloud sizes is more likely to inhabit the inner several kiloparsecs of the low-redshift CGM; such clouds would result in multiple refractive images and large scattering times ≳ 1−10 ms, but a small fraction of FRB sight lines are likely to be affected. We argue that such large scattering times from an intervening CGM would be a signature of subparsec clouds, even if diffractive scattering from turbulence contributes to the overall scattering. At redshift z ∼ 3, we estimate ∼0.1% of FRBs to intersect massive protoclusters, which may be the most likely place to see scattering owing to their ubiquitous ne ≍ 1 cm−3 cold gas. While much of our discussion assumes a single cloud size, we show similar results hold for a CGM cloud-size distribution motivated by hydrodynamic simulations.

Keywords: Radio transient sources, Radiative processes, Plasma astrophysics, Circumgalactic medium
First Detection of Shock Waves in RRc Stars. Although shock waves have been well documented in fundamental-mode RRab stars, their existence in first-overtone pulsator stars, RRc stars, has remained uncertain. Building upon the spectroscopic frameworks established by M. Chadid et al., we present the first direct detection of multistructured shock phenomena in RRc stars. Using high-resolution phase-resolved spectroscopy, we identify unambiguous shock signatures, including Hα emission, line-doubling, and large-scale variations in radial velocity and line broadening.Our analysis reveals a structured sequence of distinct shock fronts: the main outward shock, ShHe+H, the ballistic shock, ShBall, and a gravitational collapse shock, ShGravity. These phenomena produce measurable dynamical and spectroscopic effects at both photospheric and higher atmospheric layers. We find that RRc stars sustain hypersonic shock regimes despite the absence of He I or He II emission typically used in RRab classification schemes. This discrepancy is attributed to the compact and low-opacity nature of RRc atmospheres, which promotes rapid shock dissipation. These discoveries challenge conventional models of RRc atmospheres and update the classification scheme. We propose an extension to existing classification frameworks to accommodate the unique shock dynamics of RRc stars. These results challenge the long-standing assumption that first-overtone RR Lyrae pulsators lack strong shocks and demonstrate that RRc stars exhibit complex, multiphase atmospheric dynamics. Altogether, our findings reshape the current understanding of RRc atmospheric dynamics.

Keywords: High resolution spectroscopy, A stars, Radial velocity, RRc variable stars, RR Lyrae variable stars, Shocks
Evolution of a Coronal Mass Ejection with an Eruptive Prominence from the Corona to Interplanetary Space. Understanding the location and evolution of the cool dense prominence in relation to the large-scale structure of coronal mass ejections (CMEs) is critical to distinguish between different CME initiation mechanisms and to further deepen our understanding of CME evolution through the heliosphere. Combining remote observations of extreme-ultraviolet images and white-light coronagraphs and heliospheric imagers (HIs) obtained from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, STEREO-A, and Solar Orbiter, we present an analysis of the continuous tracking from the corona to interplanetary space of the substructures of a CME associated with a prominence that erupted on 2022 September 23. The prominence is found to remain bright and compact during the CME propagation for more than three days. We investigate the kinematic evolution of the CME substructures as the CME propagated to around 0.5 au. We find that for the first 0.28 au, both the CME front and prominence propagated coherently, indicating that the prominence was tied to the CME magnetic structure. Beyond 0.28 au, the CME bright front was seen to be distorted. However, the prominence continued to propagate at a nearly constant velocity up to at least 0.5 au. STEREO-A/HI images further show a dark ridge-like feature trailing the CME that passed over the prominence, and the prominence appeared tilted. We deduce that the prominence propagated independently of the CME at larger distances from the Sun. Overall, this study shows that both previously proposed hypotheses—namely, that the prominence is tied to or propagates independently of the CME—are valid but within different distance ranges.

Keywords: Solar coronal mass ejections
Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants. Escape velocity has long been used to constrain the mass of the dark matter (DM) halo in the Milky Way (MW). Here, we present a study of the escape velocity curve using a sample of high-velocity K giants with full 6D phase-space information and of relatively good quality, selected from LAMOST DR8 and cross-matched with Gaia DR3. To expand the high-velocity stars to larger distances, we used radius-dependent criteria of total velocity, i.e., vGC &gt; 300 km s−1 for the solar neighborhood and  vGC&gt;vmin∼0.6×vesc(rGC)  for the outer region. We also selected halo stars based on vϕ − [Fe/H] information to ensure that the sample is isotropic. We modeled the velocity distribution with traditional power-law models to determine the escape velocity in each radial bin. For the first time, we have directly measured a relatively continuous escape velocity curve that can extend to Galactocentric radii of ∼50 kpc, finding a decline in agreement with previous studies. The escape velocity at the solar position yielded by our measurements is  523.74−13.47+12.83kms−1 . Combined with the local circular velocity, we estimated the mass of the MW assuming a Navarro─Frenk─White DM profile, which resulted in a total mass of  M200,total=0.90−0.07+0.06×1012M⊙ , with a concentration of  c200=13.47−1.70+1.85 . The small uncertainty implies that including the escape velocities beyond the solar neighborhood can result in a more precise mass estimate. Our derived MW mass is consistent with some recent studies using the escape velocity as well as other tracers, which may support a lower mass of the DM halo than in the past.

Keywords: Stellar kinematics, Galaxy stellar halos, Milky Way dynamics
Multiwavelength Dust Characterization of the HL Tau Disk and Implications for Planet Formation. We present a comprehensive analysis of the HL Tau dust disk by modeling its intensity profiles across six wavelengths (0.45─7.9 mm) with a resolution of 0 .″ 05 (∼7 au). Using a Markov Chain Monte Carlo (MCMC) approach, we constrain key dust properties, including temperature, surface density, maximum grain size, composition, filling factor, and size distribution. The full fitting, with all parameters free, shows a preference for organics-rich dust with a low filling factor in the outer region (r ≳ 40 au), where the spectral index is ∼3.7, but amorphous-carbon-rich dust also reasonably reproduces the observed intensity profiles. Considering the scattering polarization observed at 0.87 mm, compact, amorphous-carbon-rich dust is unlikely and moderately porous dust is favored. Beyond 40 au, the maximum dust size is likely ∼100 μm if dust is compact or amorphous-carbon rich. However, if the dust is moderately porous and organics-rich, both the predicted dust surface density and dust size can be sufficiently large for the pebble accretion rate to reach ∼10 M⊕ Myr−1 in most regions, suggesting that pebble accretion could be a key mechanism for forming planets in the disk. In contrast, if the dust is amorphous-carbon-rich, forming a giant planet core via pebble accretion is unlikely due to the combined effects of low dust surface density and small dust size required to match the observed emission, suggesting other mechanisms, such as disk fragmentation due to gravitational instability, may be responsible for planet formation in the HL Tau disk.

Keywords: Protoplanetary disks, Planet formation, Circumstellar disks
Dissecting Bar-induced Stellar Kinematics in Disk Galaxies: The Bisymmetric Model and Rotation Curve Modifications. We analyze bars formed in N-body simulations to investigate two key aspects of stellar kinematic structure of barred galaxies: the angular distributions of the radial and azimuthal components of stellar velocities, and the impact of bars on rotation curves. We find that stars on bar-supporting x1-like orbits exhibit characteristic sawtooth-like radial velocity patterns and archlike tangential velocity patterns as a function of azimuth. In contrast, stars on box and disk orbits show little azimuthal variation, effectively smoothing the overall velocity distribution. When averaged over all orbital families, the resulting kinematics are broadly consistent with the bisymmetric model of Sellwood and Spekkens, with the amplitudes of bar-induced velocity perturbations increasing with bar strength. In addition, bars amplify the radial pressure gradient associated with enhanced random stellar motions, leading to a noticeable reduction in the mean rotational velocity. This effect becomes more pronounced with increasing bar strength, resulting in a shallower rotation curve within the bar region. We discuss our results in the context of the kinematic properties of observed barred galaxies.

Keywords: Galaxy bars, Spiral galaxies, Disk galaxies, Stellar kinematics, Galaxy structure, Galaxy disks, Galaxy kinematics, Barred spiral galaxies
Correlation of Burst Behavior with Magnetar Age. We analyze a wide set of historical magnetar burst observations detected with five different instruments, calibrating these to the energy range of Fermi-GBM observations for consistency. We find a striking correlation between a magnetar's characteristic age and both its typical burst energy and its burst activity level. Arguing that this bursting behavior also correlates with true age, we interpret it as the result of a reducing high-stress volume of the crust in an aging magnetar: Previous giant flares cause relaxation of large regions of its crust and inhibit burst clustering, while the reducing burst energy reflects the progressively shallower region of the crust where Hall drift can build stresses effectively, as the field decays through the range ∼1012–1013 G. Low-energy bursts from very young magnetars may represent failures of weak regions of the crust that have only recently solidified.

Keywords: Neutron stars, Magnetars, X-ray bursts, High energy astrophysics
Elemental Abundances in X-Ray Binary Outflows. Line-resolved X-ray spectra of outflows from X-ray binaries are interesting since they provide quantifiable measures of the accreted material onto the compact object (black hole or neutron star), which can not be observed directly in the accretion disk. One such measurement that has been largely overlooked is that of the elemental abundances, which potentially provide insights into the origin of the ejected material. Using the Chandra/HETG grating spectrometer we measure and present elemental abundances in four low-mass X-ray binaries. We compare two measurement methods. One is by fitting line series of individual ions and reconstructing the absorption measure distribution (AMD), and the other is a global fit with one or two individual ionization components. All outflows feature a steep AMD strongly favoring high ionization degrees. The present abundances are consistent with previous works suggesting the abundances in the outflows are nonsolar. We find a tentative trend of increasing abundances with atomic number, which fits some core-collapse supernova models, but there is no exact match to a specific one.

Keywords: High resolution spectroscopy, Low-mass x-ray binary stars, Stellar accretion disks