bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variabilities of Methanol Maser and Thermal Molecular Lines from an Accretion Burst Source G358.93-0.03
Authors: Zhang Shi-jie , Chen Xi , Zhang Yan-Kun , Miao Dan , Lu Deng-Rong , Ju Bing-Gang 
Published: October 2024

Abstract
From 2019 January to June, the high-mass young stellar object G358.93-0.03 underwent a remarkable accretion burst. Detecting variations in the physical and kinematic environments during episodic accretion is essential for exploring such events. Searching for new maser or molecular lines and monitoring their variability during the accretion burst and postburst stages is feasible for such a study. Using the Purple Mountain Observatory 13.7 m telescope, we carried out monitoring of methanol masers and molecular lines toward G358.93-0.03 in the 3 mm band during the burst (2019 March to June) and postburst stages (2022 October). In addition to the previously abundant detection of the methanol maser lines in the burst stage, eight new methanol maser lines were detected, identified from transitions at 85.57, 93.20, 94.54, 94.82, 99.77, 102.96, 104.35, and 104.41 GHz. Their integrated intensity exhibited an exponential decline during the burst stage, likely associated with the decay process of the accretion burst. None of the eight methanol maser lines were detected in the postburst stage. Besides maser lines, 12 thermal molecular lines were detected in both the burst and postburst stages. Variability of some of them was observed in both stages, but most notably, the ratio of HCO+/N2H+ increased significantly in the burst stage compared to the postburst stage. It is likely caused by the changes of both molecular lines during the burst and postburst stages due to the heating process induced by episodic accretion. Therefore, the comparison of their line intensity ratios might offer a new method for tracing episodic accretion bursts.
Discovery of 118 New Ultracool Dwarf Candidates Using Machine-learning Techniques
Authors: Brooks Hunter , Caselden Dan , Kirkpatrick J. Davy , Raghu Yadukrishna , Elachi Charles A. , Grigorian Jake , Trek Asa , Washburn Andrew , Higashimura 東 Hiro 村滉 , Meisner Aaron M. , Schneider Adam C. , Faherty Jacqueline K. , Marocco Federico , Gelino Christopher R. , Gagné Jonathan , Bickle Thomas P. , Tang Shih-Yun , Rothermich Austin , Burgasser Adam J. , Kuchner Marc J. , Beaulieu Paul , Bell John , Colin Guillaume , Colombo Giovanni , Dereveanco Alexandru , Flores Deiby Pozo , Glebov Konstantin , Gramaize Leopold , Hamlet Les , Hinckley Ken , Kabatnik Martin , Kiwy Frank , Martin David W. , Palma Méndez Raúl F. , Pendrill Billy , Ruiz Lizzeth , Sanchez John , Sainio Arttu , Schümann Jörg , Schonau Manfred , Tanner Christopher , Stevnbak Nikolaj , Stenner Andres , Thévenot Melina , Thakur Vinod , Voloshin Nikita V. , Wȩdracki Zbigniew ,   The Backyard Worlds: Planet 9 Collaboration
Published: October 2024

Abstract
We present the discovery of 118 new ultracool dwarf candidates, discovered using a new machine-learning tool, named SMDET, applied to time-series images from the Wide-field Infrared Survey Explorer. We gathered photometric and astrometric data to estimate each candidate’s spectral type, distance, and tangential velocity. This sample has a photometrically estimated spectral class distribution of 28 M dwarfs, 64 L dwarfs, and 18 T dwarfs. We also identify a T-subdwarf candidate, two extreme T-subdwarf candidates, and two candidate young ultracool dwarfs. Five objects did not have enough photometric data for any estimations to be made. To validate our estimated spectral types, spectra were collected for two objects, yielding confirmed spectral types of T5 (estimated T5) and T3 (estimated T4). Demonstrating the effectiveness of machine-learning tools as a new large-scale discovery technique.
Morphologies of Bright Complex Fast Radio Bursts with CHIME/FRB Voltage Data
Authors: Faber Jakob T. , Michilli Daniele , Mckinven Ryan , Su Jianing , Pearlman Aaron B. , Nimmo Kenzie , Main Robert A. , Kaspi Victoria , Bhardwaj Mohit , Chatterjee Shami , Curtin Alice P. , Dobbs Matt , Eadie Gwendolyn , Gaensler B. M. , Kader Zarif , Leung Calvin , Masui Kiyoshi W. , Pandhi Ayush , Petroff Emily , Pleunis Ziggy , Rafiei-Ravandi Masoud , Sand Ketan R. , Scholz Paul , Shin Kaitlyn , Smith Kendrick , Stairs Ingrid 
Published: October 2024

Abstract
We present the discovery of 12 apparently nonrepeating fast radio burst (FRB) sources, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources, only one of which has been presented previously in the first CHIME/FRB catalog, were selected from a database comprising

O
(

10

3

)

CHIME/FRB full-array raw voltage data recordings, based on their large signal-to-noise ratios and complex morphologies. Our study examines the time-frequency characteristics of these bursts, including drifting, microstructure, and periodicities. The events in this sample display a variety of unique drifting phenomenologies that deviate from the linear negative drifting phenomenon seen in many repeating FRBs, and motivate a possible new framework for classifying drifting archetypes. Additionally, we detect microstructure features of duration ≲50 μs in seven events, with some as narrow as ≃7 μs. We find no evidence of significant periodicities between subburst components. Furthermore, we report the polarization characteristics of seven events, including their polarization fractions and Faraday rotation measures (RMs). The observed ∣RM∣ values span a wide range of 17.24(2)–328.06(2) rad m−2, with apparent linear polarization fractions between 0.340(1) and 0.946(3). The morphological properties of the bursts in our sample appear broadly consistent with predictions from both relativistic shock and magnetospheric models of FRB emission, as well as propagation through discrete ionized plasma structures. We address these models and discuss how they can be tested using our improved understanding of morphological archetypes.
Jets from the Upper Scorpius Variable Young Star System 2MASS J16075796-2040087 via KECK/HIRES Spectro-astrometry
Authors: Whelan Emma T. , Keppler Miriam , Turner Neal J. , Pascucci Ilaria , Hamden Erika , Hoadley Keri , Fang Min 
Published: October 2024

Abstract
2MASS J16075796-2040087 is an ∼5 Myr young star in Upper Sco with evidence for accretion bursts on a timescale of about 15 days and, uncommonly for its age, outflows traced by multicomponent forbidden emission lines (FELs). The accretion bursts may be triggered by a companion at ∼4.6 au. We analyze HIRES spectra optimised for spectro-astrometry to better understand the origin of the several FEL velocity components and determine whether a magnetohydrodynamic (MHD) disk wind is present. The FEL high-velocity component (HVC) traces an asymmetric, bipolar jet ∼700 au long. The jet’s position angle ∼ 277° is not perpendicular to the disk. The lower-velocity emission, classified previously as a disk wind low-velocity component, is found to have more in common with the HVC and overall it is not possible to identify an MHD disk wind component. The spectro-astrometric signal of the low-velocity emission resembles those of jets and its density and ionisation fraction fall into the range of HVCs. We suggest a scenario where the accretion bursts due to the close companion power the jets past the age where such activity ends around most stars. The low-velocity emission here could come from a slow jet launched near the close companion and this emission would be blended with emission from the MHD wind.
Variable Stars in M31 Stellar Clusters from the Panchromatic Hubble Andromeda Treasury
Authors: Smith Richard , Patel Avi , Soraisam Monika D. , Guhathakurta Puragra , Tadepalli Pranav , Zhu Sally , Liu Joseph , Girardi Léo , Johnson L. Clifton , Mukherjee Sagnick , Olsen Knut A. G. , Williams Benjamin F. 
Published: October 2024

Abstract
Variable stars in stellar clusters can offer key constraints on stellar evolution and pulsation models, utilizing estimates of host cluster properties to constrain stellar physical parameters. We present a catalog of 86 luminous (F814W < 19) variable stars in M31 clusters identified by mining the archival Panchromatic Hubble Andromeda Treasury (PHAT) survey using a combination of statistical analysis of sparse PHAT light curves and difference imaging. We determine the evolutionary phases and initial masses of these variable stars by matching them with theoretical isochrones generated using host cluster properties from the literature. We calculate the probability of PHAT photometry being blended due to the highly crowded nature of cluster environments for each cluster-variable star, using these probabilities to inform our level of confidence in the derived properties of each star. Our 86 cluster-variable stars have initial masses between 0.8 and 67 M
⊙. Their evolutionary phases span the main sequence, more evolved hydrogen- and helium-burning phases, and the post–asymptotic giant branch. We identify numerous candidate variable star types: RV Tauri variables, red supergiants, and slowly pulsating B-type supergiants, along with Wolf–Rayet stars, α Cygni and Mira variables, a classical Cepheid, and a possible superasymptotic giant. We characterize 12 cluster-variable stars at higher confidence based on their difference image quality and lower blending probability. Ours is the first systematic study of variable stars in extragalactic stellar clusters leveraging the superior resolution of the Hubble Space Telescope and demonstrating the unique power of stellar clusters in constraining the fundamental properties of variable stars.
Sunyaev–Zeldovich Signals from L* Galaxies: Observations, Analytics, and Simulations
Authors: Oren Yossi , Sternberg Amiel , McKee Christopher F. , Faerman Yakov , Genel Shy 
Published: October 2024

Abstract
We analyze measurements of the thermal Sunyaev–Zeldovich (tSZ) effect arising in the circumgalactic medium (CGM) of L* galaxies, reported by J. N. Bregman et al. (B+22) and S. Das et al. (D+23). In our analysis, we use the Y. Faerman et al. CGM models, a new power-law model (PLM), and the TNG100 simulation. For a given M
vir, our PLM has four parameters: the fraction, f
hCGM, of the halo baryon mass in hot CGM gas, the ratio, ϕ

T
, of the actual gas temperature at the virial radius to the virial temperature, and the power-law indices, a

P,th and a

n
for the thermal electron pressure and the hydrogen nucleon density. The B+22 Compton-y profile implies steep electron pressure slopes (a

P,th ≃ 2). For isothermal conditions, the temperature is at least 1.1 × 106 K, with a hot CGM gas mass of up to 3.5 × 1011
M
⊙ for a virial mass of 2.75 × 1012
M
⊙. However, if isothermal, the gas must be expanding out of the halos. An isentropic equation of state is favored for which hydrostatic equilibrium is possible. The B+22 and D+23 results are consistent with each other and with recent (0.5–2 keV) CGM X-ray observations of Milky Way mass systems. For M
vir ≃ 3 × 1012
M
⊙, the scaled Compton pressure integrals,

E

(
z
)

−
2

/

3

Y

500

/

M

vir
,
12

5

/

3

, lie in the narrow range, 2.5 × 10−4–5.0 × 10−4 kpc2, for all three sets of observations. TNG100 underpredicts the tSZ parameters by factors ∼0.5 dex for the L* galaxies, suggesting that the feedback strengths and CGM gas losses are overestimated in the simulated halos at these mass scales.
Tayler Instability Revisited
Authors: Skoutnev Valentin A. , Beloborodov Andrei M. 
Published: October 2024

Abstract
Tayler instability of toroidal magnetic fields B

ϕ
is broadly invoked as a trigger for turbulence and angular momentum transport in stars. This paper presents a systematic revision of the linear stability analysis for a rotating, magnetized, and stably stratified star. For plausible configurations of B

ϕ
, instability requires diffusive processes: viscosity, magnetic diffusivity, or thermal/compositional diffusion. Our results reveal a new physical picture, demonstrating how different diffusive effects independently trigger instability of two types of waves in the rotating star: magnetostrophic waves and inertial waves. It develops via overstability of the waves, whose growth rate sharply peaks at some characteristic wavenumbers. We determine instability conditions for each wave branch and find the characteristic wavenumbers. The results are qualitatively different for stars with magnetic Prandtl number Pm ≪ 1 (e.g., the Sun) and Pm ≫ 1 (e.g., protoneutron stars). The parameter dependence of unstable modes suggests a nonuniversal scaling of the possible Tayler–Spruit dynamo.
Contactless Manipulation and Raman Analysis of Cometary Analogs and Micrometeorites by Acoustic Levitation
Authors: Ferretti S. , Marrara S. , Bronte Ciriza D. , Magazzù A. , Foti A. , Gucciardi P. G. , Musolino A. , Folco L. , Della Corte V. , Rotundi A. , Saija R. , Mandanici A. , Maragò O. M. , Donato M. G. 
Published: October 2024

Abstract
Extraterrestrial material collected during space missions is highly exposed to contamination issues during on-Earth analysis. Although high-protection-level protocols were developed, to minimize the contamination due to sample manipulation and the substrate contribution an optimal strategy is to perform in situ analysis with contactless techniques. Optical and acoustic trapping represent ideal candidates for contactless manipulation and analysis of nanometer-to-millimeter-sized particles. Here, we show results of the manipulation of cometary analogs and micrometeorite samples using a single-axis acoustic levitator. The investigation of the particle dynamics in the trap allows the calculation of the trap spring constants that are found in the mN/m range. In addition, we collect the Raman spectra of two levitated fragments of Saratov meteorite, demonstrating that acoustic levitation can be effectively used for the contactless and low-contamination characterization of samples of interest in astrophysics.
LMC-driven Anisotropic Boosts in Stream–Subhalo Interactions
Authors: Arora Arpit , Garavito-Camargo Nicolás , Sanderson Robyn E. , Cunningham Emily C. , Wetzel Andrew , Panithanpaisal Nondh , Barry Megan 
Published: October 2024

Abstract
Dark matter subhalos are predicted to perturb stellar streams; stream morphologies and dynamics can, therefore, constrain the mass distribution of subhalos. Using FIRE-2 simulations of Milky Way–mass galaxies, we demonstrate that the presence of an LMC analog significantly changes stream–subhalo encounter rates. The LMC analog brings in many subhalos, increasing encounter rates for streams near the massive satellite by 10%–40%. Additionally, the LMC analog displaces the host from its center of mass (inducing reflex motion), which causes a north–south asymmetry in the density and radial velocity distributions of subhalos. This asymmetry, combined with the presence of LMC-analog subhalos, causes encounter rates at the same distance to vary by 50%–70% across the sky, particularly in regions opposite the LMC analog. Furthermore, the LMC analog induces a density wake in the host's dark matter halo, further boosting the encounter rates near the LMC analog. We also explore how stream orbital properties affect encounter rates, finding up to a 50% increase for streams moving retrograde to the LMC analog’s orbit in the opposite quadrant. Finally, we report the encounter rates for Milky Way streams within the context of our simulations, both with and without the presence of an LMC analog. The dependence of encounter rates on stream location, orbit, and their position relative to the LMC has important implications for where to search for streams with spurs and gaps in the Milky Way.
Instability and Evolution of Shocked Clouds Formed by Orthogonal Collisions between Magnetized Filamentary Molecular Clouds
Authors: Kashiwagi Raiga , Iwasaki Kazunari , Tomisaka Kohji 
Published: October 2024

Abstract
Filamentary molecular clouds are recognized as primary sites for the formation of stars. Specifically, regions characterized by the overlapping point of multiple filaments, known as hub regions, are often associated with active star formation. However, the formation mechanism of this hub structure is not well understood. Therefore, to understand the formation mechanism and star formation in hub structures, as a first step, we investigate the orthogonal collisions between two filaments using three-dimensional ideal magnetohydrodynamical simulations. As a model of initial filaments, we use an infinitely long filament in magnetohydrostatic equilibrium under a global magnetic field running perpendicular to the filament axis. Two identical equilibrium filaments, sharing the same magnetic flux, are arranged with their long axes perpendicular to each other and given an initial velocity perpendicular to their long axes to replicate an orthogonal collision. We find three types of evolution after the shocked cloud is formed: collapse, stable, and expansion modes. The energy balance just after the filaments completely collide explains the future evolution of the shocked cloud. If the magnitude of gravitational energy is larger than the sum of the kinetic, thermal, and magnetic energies, the shocked cloud evolves in collapse mode. If the magnitude of gravitational energy is less than the sum of these energies, the cloud evolves in stable mode when the kinetic energy is relatively small and in expansion mode when the kinetic energy is sufficiently large.
Kinematics of Supernova Remnants Using Multiepoch Maximum Likelihood Estimation: Chandra Observation of Cassiopeia A as an Example
Authors: Sakai Yusuke , Yamada Shinya , Sato Toshiki , Hayakawa Ryota , Kominato Nao 
Published: October 2024

Abstract
Decadal changes in a nearby supernova remnant (SNR) were analyzed using a multiepoch maximum likelihood estimation (MLE) approach. To achieve greater accuracy in capturing the dynamics of SNRs, kinematic features and point-spread function effects were integrated into the MLE framework. Using Cassiopeia A as a representative example, data obtained by the Chandra X-ray Observatory in 2000, 2009, and 2019 were utilized. The proposed multiepoch MLE was qualitatively and quantitatively demonstrated to provide accurate estimates of various motions, including shock waves and faint features, across all regions. To investigate asymmetric structures, such as singular components that deviate from the direction of expansion, the MLE method was extended to combine multiple computational domains and classify kinematic properties using the k-means algorithm. This approach allowed for the mapping of different physical states onto the image, and one classified component was suggested to interact with circumstellar material by comparison with infrared observations from the James Webb Space Telescope. Thus, this technique will help quantify the dynamics of SNRs and discover their unique evolution.
Global Analysis of the Extended Decreases in Cosmic Rays Observed with Worldwide Networks of Neutron Monitors and Muon Detectors: Temporal Variation of the Rigidity Spectrum and Its Implication
Authors: Munakata K. , Hayashi Y. , Kozai M. , Kato C. , Miyashita N. , Kataoka R. , Kadokura A. , Miyake S. , Iwai K. , Echer E. , Dal Lago A. , Rockenbach M. , Schuch N. J. , Bageston J. V. , Braga C. R. , Al Jassar H. K. , Sharma M. M. , Duldig M. L. , Humble J. E. , Sabbah I. , Evenson P. , Kuwabara T. , Kóta J. 
Published: October 2024

Abstract
This paper presents the global analysis of two extended decreases in the galactic cosmic-ray intensity observed by worldwide networks of ground-based detectors in 2012. This analysis is capable of separately deriving the cosmic-ray density (or omnidirectional intensity) and anisotropy, each as a function of time and rigidity. A simple diffusion model along the spiral field line between Earth and a cosmic-ray barrier indicates the long duration of these events, resulting from about 190° eastern extent of a barrier such as an interplanetary shock followed by the sheath region and/or the corotating interaction region (CIR). It is suggested that the coronal mass ejection merging with and compressing the preexisting CIR at its flank can produce such an extended barrier. The derived rigidity spectra of the density and anisotropy both vary in time during each event period. In particular we find that the temporal feature of the “phantom Forbush decrease (FD)” reported in an analyzed period is dependent on rigidity, and looks quite different at different rigidities. From these rigidity spectra of the density and anisotropy, we derive the rigidity spectrum of the average parallel mean free path of pitch angle scattering along the spiral field line and infer the power spectrum of the magnetic fluctuation and its temporal variation. The possible physical cause of the strong rigidity dependence of the phantom FD is also discussed. These results demonstrate the high-energy cosmic rays observed at Earth responding to remote space weather.
AstroSat and Insight-HXMT Observations of the Long-period X-Ray Pulsar 4U 2206+54
Authors: Epili Prahlad R. , Wang Wei 
Published: October 2024

Abstract
We report the timing and spectral studies of the accreting X-ray pulsar 4U 2206+54 using AstroSat and Insight-HXMT observations taken in 2016 and 2020 respectively. X-ray pulsations from the system are detected by both missions. The AstroSat discovered a significant periodic signal at ∼5619 s in 2016, and Insight-HXMT found a pulsation period at ∼5291 s in 2020. A comparison of its spin-period evolution with the present spin-period estimates shows that the neutron star in 4U 2206+54 now has recently been undergoing a spin-up episode after attaining to its slow pulsations of 5750 s around 2015 from its prolonged spin-down phase. The present average spin-up rate of the pulsar is found to be at ∼1.2 × 10−13 Hz s−1. The phase-averaged spectra of the pulsar in 1–60 keV could be explained with a high-energy cutoff power-law continuum model; no evident line features are found with AstroSat. The application of Comptonization models such as comptt and compmag to the phase-averaged spectra of 4U 2206+54 reveals a hotter source photon region near the pulsar with an emission size extending to ∼2–2.8 km. Using the quasi-spherical settling accretion theory, we explain the present spin-up and the possibility of the strong magnetic field of the pulsar.
Broadening the Canonical Picture of EUV-driven Photoevaporation of Accretion Disks
Authors: Nakatani Riouhei , Turner Neal J. , Takasao Shinsuke 
Published: October 2024

Abstract
Photoevaporation driven by hydrogen-ionizing extreme-ultraviolet (EUV) radiation profoundly shapes the lives of diverse astrophysical objects. We construct an analytical model accounting for the finite timescales of photoheating and photoionization and apply it to the dispersal of protoplanetary disks. The model yields improved estimates for the ionization, temperature, and velocity versus distance from the central source when compared to the classical picture of fully ionized and isothermal winds with temperatures ≈104 K and speeds ≈10 km s−1. In contrast to the classical picture, the photoevaporative winds take on several distinct hydrodynamical and thermochemical states depending on the central star’s EUV emission rate and spectral hardness: T Tauri stars with EUV luminosities around 1030 erg s−1 drive nonisothermal ionized disk winds at lower temperatures than the classical value if the spectrum is soft, with an average deposited energy per photoionization less than about 3.7 eV. If, however, the spectrum is hard, the winds tend to be atomic and isothermal at most disk radii. For lower EUV intensities, even with soft spectra, atomic winds can emerge beyond ∼10 au through advection. We show that these predictions are in general agreement with detailed radiation hydrodynamics calculations. The model furthermore illustrates how the energy efficiency of photoevaporation varies with the intensity and spectral hardness of the EUV illumination, as well as addressing discrepancies in the literature around the effectiveness of X-ray photoevaporation. The findings highlight the importance of the photoheating and photoionization timescales both for modeling and for understanding winds’ observed behavior.