Sazuna/UAT_keywords huggingface dataset:
The Effect of Rotation on Triggering S Doradus Instabilities in Luminous Blue Variables. Luminous blue variables (LBVs) are an intermediate stage in the evolution of high-mass stars characterized by extreme mass loss and substantial variability. The stars show large irregular episodic variations on timescales of years to decades in their effective temperatures (called "S Dor variations"). Observations show that these variations are triggered when the stars are in a well-defined strip in the H-R diagram that corresponds to the Modified Eddington Limit, where the atmospheric radiation pressure almost balances gravity. In this work we consider the role that rotation plays in the instability that leads to the triggering of S Dor variations in luminous post-main-sequence LBVs. We adopt the existing instability criterion that the effective surface gravity is reduced to 10% of the Newtonian gravity due to radiation pressure in the atmosphere of nonrotating stars. We then specifically describe how rotation impacts this instability. By carrying out numerical simulations of model LBVs at both solar and subsolar metallicities, we confirm that most LBVs should be unstable at both the equator and the poles, and that rotation exacerbates this effect; some models also produce enhanced mass loss at the pole or equator. Our numerical models also predict dense equatorial disks or rings and high-velocity bipolar outflows, in agreement with existing observations of LBV circumstellar nebulae.

Keywords: Late stellar evolution, Luminous blue variable stars, Stellar mass loss, Stellar rotation, S Doradus stars
The Origin Channels of Hierarchical Binary Black Hole Mergers in the LIGO–Virgo–KAGRA O1, O2, and O3 Runs. We infer the origin channels of hierarchical mergers observed in the LIGO–Virgo–KAGRA (LVK) O1, O2, and O3 runs using a hierarchical Bayesian analysis under a parametric population model. By assuming the active galactic nucleus (AGN) disk and nuclear star cluster (NSC) channels, we find that NSCs likely dominate the hierarchical merger rate in the Universe, corresponding to a fraction of   at 90% credible intervals in our fiducial model; AGN disks may contribute up to nearly half of hierarchical mergers detectable with LVK, specifically  . We investigate the impact of the escape speed, along with other population parameters on the branching fraction, suggesting that the mass, mass ratio, and spin of the sources play significant roles in population analysis. We show that hierarchical mergers constitute at least ∼10% of the gravitational-wave events detected by LVK during the O1–O3 runs. Furthermore, we demonstrate that it is challenging to effectively infer detailed information about the host environment based solely on the distribution of black hole merger parameters if multiple formation channels are considered.

Keywords: Active galactic nuclei, Gravitational wave sources, Star clusters
Origin of the Unusual Composition of <SUP>3</SUP>He-rich Solar Energetic Particles. We examine 3He-rich solar energetic particles (SEPs) detected on 2023 October 24–25 by Solar Orbiter at 0.47 au. Measurements reveal that heavy-ion enhancements increase irregularly with mass, peaking at S. C, and especially N, Si, and S, stand out in the enhancement pattern with large abundances. Except for 3He, heavy-ion spectra can only be measured below 0.5 MeV nucleon‑1. At 0.386 MeV nucleon‑1, the event shows a huge 3He/4He ratio of 75.2 ± 33.9, larger than previously observed. Solar Dynamics Observatory extreme-ultraviolet data show a minifilament eruption at the solar source of 3He-rich SEPs that triggered a straight tiny jet. Located at the boundary of a low-latitude coronal hole, the jet base is a bright, small-scale region with a supergranulation scale size. The emission measure (EM) provides relatively cold source temperatures of 1.5–1.7 MK between the filament eruption and nonthermal type III radio burst onset. Analysis suggests that the EM distribution of temperature in the solar source could be a factor that affects the preferential selection of heavy ions for heating or acceleration, thus shaping the observed enhancement pattern. Including previously reported similar events indicates that the eruption of the minifilament is a common feature of events with heavy-ion enhancement not ordered by mass. Surprisingly, sources with weak magnetic fields show extreme 3He enrichment in these events. Moreover, the energy attained by heavy ions seems to be influenced by the size and form of the jets.

Keywords: Solar energetic particles, Solar abundances, Solar active regions, Solar extreme ultraviolet emission
Milky Way Classical Cepheid Distances from Calibrated Infrared Period─Luminosity─Metallicity Relations. Classical Cepheids (DCEPs) serve as fundamental standard candles for measuring cosmic distances and investigating the structure and evolution of the Milky Way disk. However, accurate distance estimation faces challenges due to severe extinction, particularly toward the Galactic center. Although the Gaia Wesenheit magnitude reduces extinction effects, its reliance on a constant optical extinction law introduces significant uncertainties in regions of heavy obscuration. Infrared period─luminosity relations, combined with 3D extinction maps, offer an alternative, but these maps become unreliable beyond approximately 5 kpc. In this work, we calibrate the period─luminosity─metallicity (PLZ) relations for DCEPs across three near-infrared bands (J, H, KS) and four mid-infrared bands (W1, W2, [3.6], and [4.5]). This includes the first calibration of the W1 and W2 bands. To correct for extinction, we employ the infrared multi-passband optimal distance method and the BP─RP method, which complement and validate each other. These homogeneous PLZ relations, combined with reliable extinction corrections, yield the most accurate Galactic DCEP distances to date, covering 3452 DCEPs with an average relative distance error of 3.1%.

Keywords: Cepheid variable stars, Cepheid distance
Photoevaporation from Inner Protoplanetary Disks Confronted with Observations. The decades-long explorations on the dispersal of protoplanetary disks involve many debates about photoevaporation versus magnetized wind launching mechanisms. This work argues that the observed winds originating from the inner disk (R ≲ 0.3 au) cannot be explained by the photoevaporative mechanism. Heating the gas to proper temperatures for the observed forbidden lines (especially [O I] λ6300) will overionize it, suppressing the abundances of species responsible for the emission. Even if adequate emissivity is achieved by fine-tuning the physical parameters, the total cooling power will become unattainable by the radiative heating alone. Energy conservation requires the presumed photoevaporative winds to be heated to ≳105 K when launched from inner disks. However, due to efficient thermal accommodation with dust grains and cooling processes at high densities, X-ray irradiation at energies above 1 keV cannot efficiently launch winds in the first place because of its high penetration. Some studies claiming X-ray wind launching have oversimplified the thermochemical couplings. Confirmed by semianalytic integrations of thermochemical fluid structures, such high ionizations contradict the observed emission of neutral and singly ionized atoms from the winds originating from the inner disks.

Keywords: Stellar accretion disks, Exoplanet formation, Protoplanetary disks, Hydrodynamics
Evaluating Short-warning Mitigation via Intentional Robust Disruption of a Hypothetical Impact of Asteroid 2023 NT1. We investigate various short-warning mitigation scenarios via fragmentation for a hypothetical impact of asteroid 2023 NT1, a near-Earth object (NEO) that was discovered on 2023 July 15, two days after its closest approach to Earth on July 13. The asteroid passed by Earth within ∼0.25 lunar distances, with a closest approach of ∼1 × 105 km and a velocity of 11.27 km s‑1. Its size remains largely uncertain, with an estimated diameter range of 26–58 m and a most probable estimate of 34 m (JPL Sentry, 2023 September 15; weighted by the NEO size frequency distribution). If 2023 NT1 had collided with Earth, it could have caused significant local damage. Assuming a spherical asteroid with a diameter of 34 m, uniform density of 2.6 g cm‑3, and impact velocity of 15.59 km s‑1, a collision would have yielded an estimated impact energy of ∼1.5 Mt, approximately 3 times the energy of the Chelyabinsk airburst in 2013. We analyze the effectiveness of mitigation via intentional robust disruption for objects similar to 2023 NT1. We utilize Pulverize It (PI), a NASA Innovative Advanced Concepts study of planetary defense via fragmentation, to model potential mitigation scenarios through simulations of hypervelocity asteroid disruption and atmospheric ground effects in the case of a terminal defense mode. Simulations suggest that PI is an effective multimodal approach for planetary defense that can operate in extremely short interdiction modes, in addition to long interdiction timescales with extended warning. Our simulations support the proposition that threats like 2023 NT1 can be effectively mitigated with intercepts of 1 day (or less) prior to impact, yielding minimal to no ground damage.

Keywords: Near-Earth objects, Experimental techniques, Asteroids
Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory. We analyzed the 7.92 × 1011 cosmic-ray-induced muon events collected by the IceCube Neutrino Observatory from 2011 May 13, when the fully constructed experiment started to take data, to 2023 May 12. This data set provides an up-to-date cosmic-ray arrival direction distribution in the Southern Hemisphere with unprecedented statistical accuracy covering more than a full period length of a solar cycle. Improvements in Monte Carlo event simulation and better handling of year-to-year differences in data processing significantly reduce systematic uncertainties below the level of statistical fluctuations compared to the previously published results. We confirm the observation of a change in the angular structure of the cosmic-ray anisotropy between 10 TeV and 1 PeV, more specifically in the 100─300 TeV energy range. For the first time, we analyzed the angular power spectrum at different energies. The observed variations of the power spectra with energy suggest relatively reduced large-scale features at high energy compared to those of medium and small scales. The large volume of data enhances the statistical significance at higher energies, up to the PeV scale, and smaller angular scales, down to approximately 6° compared to previous findings.

Keywords: Interstellar magnetic fields, Particle astrophysics, Cosmic rays
On Finding Black Holes in Photometric Microlensing Surveys. There are expected to be millions of isolated black holes in the galaxy resulting from the deaths of massive stars. Measuring the abundance and properties of this remnant population would shed light on the end stages of stellar evolution and the evolution paths of black hole systems. Detecting isolated black holes is currently only possible via gravitational microlensing, which has so far yielded one definitive detection. The difficulty in finding microlensing black holes lies in having to choose a small subset of events, based on characteristics of their light curves, to allocate expensive and scarce follow-up resources to confirm the identity of the lens. Current methods either rely on simple cuts in parameter space without using the full distribution information or are only effective on small subsets of events. In this paper, we present a new lens classification method. The classifier takes in posterior constraints on light-curve parameters and combines them with a Galactic simulation to estimate the lens class probability. This method is flexible and can be used with any set of microlensing light-curve parameters, making it applicable to large samples of events. We make this classification framework available via the popclass Python package. We apply the classifier to ∼10,000 microlensing events from the Optical Gravitational Lensing Experiment survey and find 23 high-probability black hole candidates. Our classifier also suggests that the only known isolated black hole is an observational outlier, according to current Galactic models, and the allocation of astrometric follow-up on this event was a high-risk strategy.

Keywords: Sky surveys, Bayesian statistics, Black holes, Classification, Gravitational microlensing
Multifrequency Radio Observations of the Dissociative Cluster Merger CIZA J0107.7+5408. We present new radio observations of the galaxy cluster merger CIZA J0107.7+5408 (CIZA0107), a large, roughly equal mass, postcore passage, dissociative binary system at z = 0.1066. CIZA0107 is an elongated, disturbed system, hosting two subclusters with optical galaxy number density peaks offset from their associated X-ray density peaks and double-peaked diffuse radio structure. We present new 240–470 MHz and 2.0–4.0 GHz Very Large Array observations of CIZA0107. We image the diffuse emission at high resolution, constrain its integrated spectrum, and map the spectral index distribution. We confirm the presence of steep-spectrum (α ∼ ‑1.3) emission on a scale of ∼0.5 Mpc in both subclusters. We identify two smaller ultrasteep spectrum (α &lt; ‑2) regions, superimposed on larger-scale radio emission associated with the southwestern subcluster. At 340 MHz, we detect a radio edge bounding the emission to the south and show that it is coincident with a weak (M ∼ 1.2) shock identified in the Chandra image. At 3 GHz, the emission does not show any corresponding edgelike feature, and in fact it extends beyond the shock. We investigate the nature of the emission in CIZA0107 and find that, while the system may host a double halo structure, we cannot rule out a scenario in which the emission arises from two relics projected on the central cluster regions.

Keywords: Galaxy clusters, Radio astronomy
Temporal Evolution of a Network Jet's Physical Properties Inferred from FISS/GST and IRIS Observations. Small-scale jets, such as chromospheric and transition region (TR) network jets, are of great interest regarding coronal heating and solar wind acceleration. Spectroscopic analysis based on multiple spectral lines with different formation temperatures is essential for understanding the physical properties and driving mechanisms of jets. Here, we conduct an investigation of the physical properties of a small-scale chromospheric jet in a quiet-Sun network region and its TR counterpart. This jet is recorded from formation to extinction using the Fast Imaging Solar Spectrograph at the Goode Solar Telescope and the Interface Region Imaging Spectrograph. The chromospheric component of the jet exhibits a high line-of-sight speed of up to 45 km s‑1 during its ascending phase, accompanied by spectral profiles akin to rapid blueshifted excursion and downflowing rapid redshifted excursion during the descending phase. Using a cloud model combined with a Multi-Layer Spectral Inversion, we quantify the jet's temperature during its ascending phase, which starts at approximately 11,000 K and increases by only 1000 K over 1 minute, much smaller than a few 104 K, the excess temperature expected in an ideal gas reconnection jet at an outflow speed of 45 km s‑1. The TR counterpart exhibits a Si IV 1394 Å line profile with a non-Gaussian shape, including a blueshifted component and a large nonthermal width. Our results suggest that if the jet is driven by magnetic reconnection in the chromosphere, the heat released by the reconnection may be mostly used to ionize the hydrogen rather than to increase the temperature so that the gas may appear almost isothermal.

Keywords: Solar spicules, Solar chromosphere, Solar activity, Solar transition region
Signature of a Seyfert-like Component in Blazar 3C 273 and Its Reflection-based Explanation. We present the results of blazar 3C 273 from simultaneous observations obtained using the XMM-Newton and NuSTAR satellites during the period 2015–2019 in five epochs. When the spectra are modeled with a power law, significant residuals arise below ∼2 keV and in the energy range of 30–78 keV in NuSTAR data. Residuals in the lower energy band represent soft X-ray excess, while at higher energies it likely represents a Compton reflection hump, which might be a weak component arising from dense and cold material. A faint iron line is present in XMM-Newton observations. We interpret such features as being attributed to the coronal emission plus those produced through reflection from an accretion disk. We model the spectral energy distributions (SEDs) with the single-zone inverse Compton (IC) jet model based on synchrotron self-Compton and external Compton phenomena. It is found that a one-zone synchrotron+IC model explains the SEDs quite well, but the jet component alone fails to fit the multiband X-ray emission for the low flux state of this object in 2018 and 2019, which arises owing to spectral flattening at low-energy X-rays, indicating that an additional Seyfert-like thermal component must be present at X-rays. This is further supported by a big blue bump present in the optical/UV band in all SEDs. Finally, we analyzed all the epochs using the relxill model to incorporate relativistic reflection and to model those residuals of soft excess and Compton hump in the X-ray bands.

Keywords: Active galaxies, X-ray active galactic nuclei
Characterizing the Multiple Protostellar System VLA 1623-2417 with JWST, ALMA, and VLA: Outflow Origins, Dust Growth, and an Unsettled Disk. Utilizing the James Webb Space Telescope (JWST), the Atacama Large Millimeter/submillimeter Array (ALMA), and the Very Large Array (VLA), we present high angular resolution (0 06─0 42), multiwavelength (4 μm─3 cm) observations of the VLA 1623-2417 protostellar system to characterize the origin, morphology and, properties of the continuum emission. JWST observations at 4.4 μm reveal outflow cavities for VLA 1623 A and, for the first time, VLA 1623 B, as well as scattered light from the upper layers of the VLA 1623 W disk. We model the millimeter-centimeter spectral energy distributions to quantify the relative contributions of dust and ionized gas emission, calculate dust masses, and use spectral index maps to determine where optical depth hinders this analysis. In general, all objects appear to be optically thick down to ∼90 GHz, show evidence for significant amounts (tens to hundreds of M⊕) of large (&gt;1 mm) dust grains, and are dominated by ionized gas emission for frequencies ≲15 GHz. In addition, we find evidence of unsettled millimeter dust in the inclined disk of VLA 1623 B possibly attributed to instabilities within the circumstellar disk, adding to the growing catalog of unsettled Class 0/I disks. Our results represent some of the highest-resolution observations possible with current instrumentation, particularly in the case of the VLA. However, our interpretation is still limited at low frequencies (≲22 GHz) and thus motivates the need for next-generation interferometers operating at centimeter wavelengths.

Keywords: Young stellar objects, Star formation, Protoplanetary disks
BATSRUS GPU: Faster-than-real-time Magnetospheric Simulations with a Block-adaptive Grid Code. Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme (BATSRUS), our state-of-the-art extended magnetohydrodynamic code, is the most used and one of the most resource-consuming models in the Space Weather Modeling Framework. It has always been our objective to improve its efficiency and speed with emerging techniques, such as GPU acceleration. To utilize the GPU nodes on modern supercomputers, we port BATSRUS to GPUs with the OpenACC API. Porting the code to a single GPU requires rewriting and optimizing the most used functionalities of the original code into a new solver, which accounts for around 1% of the entire program in length. To port it to multiple GPUs, we implement a new message-passing algorithm to support its unique block-adaptive grid feature. We conduct weak scaling tests on as many as 256 GPUs and find good performance. The program has 50%–60% parallel efficiency on up to 256 GPUs and up to 95% efficiency within a single node (four GPUs). Running large problems on more than one node has reduced efficiency due to hardware bottlenecks. We also demonstrate our ability to run representative magnetospheric simulations on GPUs. The performance for a single A100 GPU is about the same as 270 AMD "Rome" CPU cores (2.1 128-core nodes), and it runs 3.6 times faster than real time. The simulation can run 6.9 times faster than real time on four A100 GPUs.

Keywords: GPU computing, Algorithms, Magnetohydrodynamical simulations
An In-depth Study of Gamma Rays from the Starburst Galaxy M82 with VERITAS. Assuming Galactic cosmic rays originate in supernovae and the winds of massive stars, starburst galaxies should produce very-high-energy (VHE; E &gt; 100 GeV) gamma-ray emission via the interaction of their copious quantities of cosmic rays with the large reservoirs of dense gas within the galaxies. Such VHE emission was detected by VERITAS from the starburst galaxy M82 in 2008–09. An extensive, multiyear campaign followed these initial observations, yielding a total of 254 hr of good-quality VERITAS data on M82. Leveraging modern analysis techniques and the larger exposure, these VERITAS data show a more statistically significant VHE signal (∼6.5 standard deviations, σ). The corresponding photon spectrum is well fit by a power law (Γ = 2.3 ± 0.3stat ± 0.2sys), and the observed integral flux is F (&gt;450 GeV) = (3.2 ± 0.6stat ± 0.6sys) × 10‑13 cm‑2 s‑1, or ∼0.4% of the Crab Nebula flux above the same energy threshold. The improved VERITAS measurements, when combined with various multiwavelength data, enable modeling of the underlying emission and transport processes. A purely leptonic scenario is found to be a poor representation of the gamma-ray spectral energy distribution (SED). A lepto-hadronic scenario with cosmic rays following a power-law spectrum in momentum (index s ≃ 2.25) and with significant bremsstrahlung below 1 GeV provides a good match to the observed SED. The synchrotron emission from the secondary electrons indicates that efficient nonradiative losses of cosmic-ray electrons may be related to advective escape from the starburst core.

Keywords: High energy astrophysics, Gamma-ray sources, Star forming regions, Young massive clusters, Gamma-ray telescopes, Galactic cosmic rays, Non-thermal radiation sources, X-ray sources, Space telescopes, Gamma-ray astronomy, Gamma-rays, Star clusters