Sazuna/UAT_keywords huggingface dataset:
Age Determination of LAMOST Red Giant Branch Stars Based on the Gradient Boosting Decision Tree Method. In this study, we estimate the stellar ages of LAMOST DR8 red giant branch (RGB) stars based on the gradient boosting decision tree (GBDT) algorithm. We used 2643 RGB stars extracted from the APOKASC-2 asteroseismological catalog as the training data set. After selecting the parameters ([α/Fe], [C/Fe], T eff, [N/Fe], [C/H], log g) highly correlated with age using GBDT, we apply the same GBDT method to the new catalog of more than 590,000 stars classified as RGB stars. The test data set shows that the median relative error is around 11.6% for the method. We also compare the predicted ages of RGB stars with other studies (e.g., based on APOGEE) and find some systematic differences. The final uncertainty is about 15%–30% compared to the ages of open clusters. Then, we present the spatial distribution of the RGB sample with an age determination, which could recreate the expected result, and discuss systematic biases. All these diagnostics show that one can apply the GBDT method to other stellar samples to estimate atmospheric parameters and age.

Keywords: Red giant branch, Milky Way disk, Stellar ages, Catalogs
The Impact-driven Atmospheric Loss of Super-Earths around Different Spectral Types of Host Stars. A planet's mass loss is important for the its formation and evolution. The radius valley (RV) is believed to be triggered by evaporation-induced mass loss. As an alternative mechanism for RV, the mass loss of post-impact planets is thoroughly investigated in this work. The impact energy is converted to the planet's internal energy, enhancing its core energy and accelerating mass loss and orbital migration. As the host star changes from K type to F type, the planet's mass loss and orbital migration increase. When the initial gas-to-core-mass ratio is small, the migration efficiency for planets around K-type stars will increase, which helps to suppress mass loss and retain the planet's mass and radius within a specific range. On the contrary, planets around more massive F-type stars experience more substantial mass loss, potentially leading to complete mass loss, and migrate to orbits with longer periods. Our calculation shows that planets around different spectral types of host stars give rise to an RV ranging from 1.3 to 2.0 R ⊕, consistent with the observed range of 1.3–2.6 R ⊕. Despite the presence of uncertain parameters, the planetesimal impact can promote the RV establishment for planets around host stars of different spectral types.

Keywords: Exoplanet migration, Exoplanets, Super Earths, Exoplanet evolution, Exoplanet formation, Exoplanet atmospheres
First Detection in Space of the High-energy Isomer of Cyanomethanimine: H<SUB>2</SUB>CNCN. We report the first detection in the interstellar medium of N-cyanomethanimine (H2CNCN), the stable dimer of HCN of highest energy and the most complex organic molecule identified in space containing the prebiotically relevant NCN backbone. We have identified a plethora of a-type rotational transitions with 3 ≤ J up ≤ 11 and K a ≤ 2 that belong to this species toward the Galactic center G+0.693-0.027 molecular cloud, the only interstellar source showing the three cyanomethanimine isomers (including the Z- and E-isomers of C-cyanomethanimine, HNCHCN). We have derived a total column density for H2CNCN of (2.9 ± 0.1) × 1012 cm‑2, which translates into a total molecular abundance with respect to H2 of (2.1 ± 0.3) × 10‑11. We have also revisited the previous detection of E- and Z-HNCHCN and found a total C/N-cyanomethanimine abundance ratio of 31.8 ± 1.8 and a Z/E-HNCHCN ratio of 4.5 ± 0.2. While the latter can be explained on the basis of thermodynamic equilibrium, chemical kinetics are more likely responsible for the observed C/N-cyanomethanimine abundance ratio, where the gas-phase reaction between methanimine (CH2NH) and the cyanogen radical (CN) arises as the primary formation route.

Keywords: Interstellar molecules, Galactic center, Spectral line identification, Astrochemistry, Interstellar clouds, Pre-biotic astrochemistry
Protoplanetary Disk Polarization at Multiple Wavelengths: Are Dust Populations Diverse?. Millimeter and submillimeter observations of continuum linear dust polarization provide insight into dust grain growth in protoplanetary disks, which are the progenitors of planetary systems. We present the results of the first survey of dust polarization in protoplanetary disks at 870 μm and 3 mm. We find that protoplanetary disks in the same molecular cloud at similar evolutionary stages can exhibit different correlations between observing wavelength and polarization morphology and fraction. We explore possible origins for these differences in polarization, including differences in dust populations and protostar properties. For RY Tau and MWC 480, which are consistent with scattering at both wavelengths, we present models of the scattering polarization from several dust grain size distributions. These models aim to reproduce two features of the observational results for these disks: (1) both disks have an observable degree of polarization at both wavelengths; and (2) the polarization fraction is higher at 3 mm than at 870 μm in the centers of the disks. For both disks, these features can be reproduced by a power-law distribution of spherical dust grains with a maximum radius of 200 μm and high optical depth. In MWC 480, we can also reproduce features (1) and (2) with a model containing large grains (a max = 490 μm) near the disk midplane and small grains (a max = 140 μm) above and below the midplane.

Keywords: Polarimetry, Protoplanetary disks
Gaia23bab: A New EXor. On 2023 March 6, the Gaia telescope alerted a 2 mag burst from Gaia23bab, a young stellar object in the Galactic plane. We observed Gaia23bab with the Large Binocular Telescope obtaining optical and near-infrared spectra close in time to the peak of the burst, and collected all public multiband photometry to reconstruct the historical light curve. The latter shows three bursts in 10 years (2013, 2017, and 2023), whose duration and amplitude are typical of EXor variables. We estimate that, due to the bursts, the mass accumulated on the star is about twice greater than if the source had remained quiescent for the same period of time. Photometric analysis indicates that Gaia23bab is a class II source with age ≲1 Myr, spectral type G3‑K0, stellar luminosity ∼4.0 L ⊙, and mass ∼1.6 M ⊙. The optical/near-infrared spectrum is rich in emission lines. From the analysis of these lines we measured an accretion luminosity and mass accretion rate (L acc burst ∼ 3.7 L ⊙,   ${\dot{M}}_{\mathrm{acc}}$   burst ∼ 2.0 × 10‑7 M ⊙ yr‑1) consistent with those of EXors. More generally, we derived the relationships between accretion and stellar parameters in a sample of EXors. We find that, when in burst, the accretion parameters become almost independent of the stellar parameters and that EXors, even in quiescence, are more efficient than classical T Tauri stars in assembling mass.

Keywords: Pre-main sequence stars, Star formation, Eruptive variable stars, Stellar accretion
Stellar Escape from Globular Clusters. II. Clusters May Eat Their Own Tails. We apply for the first time orbit-averaged Monte Carlo star cluster simulations to study tidal tail and stellar stream formation from globular clusters (GCs), assuming a circular orbit in a time-independent spherical Galactic potential. Treating energetically unbound bodies—potential escapers (PEs)—as collisionless enables this fast but spherically symmetric method to capture asymmetric extratidal phenomena with exquisite detail. Reproducing stream features such as epicyclic overdensities, we show how returning tidal tails can form after the stream fully circumnavigates the Galaxy, enhancing the stream's velocity dispersion by several kilometers per second in our ideal case. While a truly clumpy, asymmetric, and evolving Galactic potential would greatly diffuse such tails, they warrant scrutiny as potentially excellent constraints on the Galaxy's history and substructure. Reexamining the escape timescale Δt of PEs, we find new behavior related to chaotic scattering in the three-body problem; the Δt distribution features sharp plateaus corresponding to distinct locally smooth patches of the chaotic saddle separating the phase-space basins of escape. We study for the first time Δt in an evolving cluster, finding that for PEs with (low, high) Jacobi energy E J, flatter than for a static cluster ( ). Accounting for cluster mass loss and internal evolution lowers the median Δt from ∼10 Gyr to ≲100 Myr. We finally outline potential improvements to escape in the Monte Carlo method intended to enable the first large grids of tidal tail/stellar stream models from full GC simulations and detailed comparison to stream observations.

Keywords: Globular star clusters, Stellar streams, Tidal disruption, Galactic archaeology, Stellar dynamics, Stellar astronomy, Tidal tails, Three-body problem, N-body simulations, Star clusters
Interaction between a Coronal Mass Ejection and Comet 67P/Churyumov–Gerasimenko. The interaction between a coronal mass ejection (CME) and a comet has been observed several times by in situ observations from the Rosetta Plasma Consortium, which is designed to investigate the cometary magnetosphere of comet 67P/Churyumov–Gerasimenko (CG). Goetz et al. reported a magnetic field of up to 300 nT measured in the inner coma, which is among the largest interplanetary magnetic fields observed in the solar system. They suggested the large magnetic field observations in the inner coma come from magnetic field pileup regions, which are generated by the interaction between a CME and/or corotating interaction region and the cometary magnetosphere. However, the detailed interaction between a CME and the cometary magnetosphere of comet CG in the inner coma has not been investigated by numerical simulations yet. In this paper, we will use a numerical model to simulate the interaction between comet CG and a Halloween class CME and investigate its magnetospheric response to the CME. We find that the plasma structures change significantly during the CME event, and the maximum value of the magnetic field strength is more than 500 nT close to the nucleus. Virtual satellites at similar distances as Rosetta show that the magnetic field strength can be as large as 250 nT, which is slightly less than what Goetz et al. reported.

Keywords: Magnetohydrodynamics, Solar coronal mass ejections, Comets
Investigating Mass Segregation of the Binary Stars in the Open Cluster NGC 6819. We search for mass segregation in the intermediate-aged open cluster NGC 6819 within a carefully identified sample of probable cluster members. Using photometry from Gaia, Pan-STARRS, and the Two Micron All Sky Survey as inputs for a Bayesian statistics software suite, BASE-9, we identify a rich population of (photometric) binaries and derive posterior distributions for the cluster age, distance, metallicity, and reddening, as well as star-by-star photometric membership probabilities, masses, and mass ratios (for binaries). Within our entire sample, we identify 2632 cluster members and 777 binaries. We then select a main-sequence "primary sample" with 14.85 &lt;G &lt; 19.5, containing 1342 cluster members and 250 binaries with mass ratios q &gt; 0.5, to investigate mass segregation. Within this primary sample, we find the binary radial distribution is significantly shifted toward the cluster center as compared to the single stars, resulting in a binary fraction that increases significantly toward the cluster core. Furthermore, we find that within the binary sample, more massive binaries have more centrally concentrated radial distributions than less massive binaries. The same is true for the single stars. We verify the expectation of mass segregation for this stellar sample in NGC 6819 through both relaxation time arguments and by investigating a sophisticated N-body model of the cluster. Importantly, this is the first study to investigate mass segregation of the binaries in the open cluster NGC 6819.

Keywords: Bayesian statistics, Binary stars, Relaxation time, Open star clusters, N-body simulations
The Effect of Starspots on Spectroscopic Age and Mass Estimates of Nonaccreting T Tauri Stars in the Taurus–Auriga Star-forming Region. Accurate age and mass determinations for young pre-main-sequence stars are made challenging by the presence of large-scale starspots. We present results from a near-infrared spectroscopic survey of 10 T-Tauri Stars in Taurus-Auriga that characterize spot-filling factors and temperatures, the resulting effects on temperature and luminosity determinations, and the consequences for inferred stellar masses and ages. We constructed composite models of spotted stars by combining BTSettl-CIFIST synthetic spectra of atmospheres to represent the spots and the photosphere along with continuum emission from a warm inner disk. Using a Markov Chain Monte Carlo algorithm, we find the best-fit spot and photospheric temperatures, spot-filling factors, as well as disk-filling factors. This methodology allowed us to reproduce the 0.75–2.40 μm stellar spectra and molecular feature strengths for all of our targets, disentangling the complicated multicomponent emission. For a subset of stars with multiepoch observations spanning an entire stellar rotation, we correlate the spectral variability and changes in the filling factors with rotational periods observed in K2 and AAVSO photometry. Combining spot-corrected effective temperatures and Gaia distances, we calculate luminosities and use the Stellar Parameters of Tracks with Starspots models to infer spot-corrected masses and ages for our sample of stars. Our method of accounting for spots results in an average increase of 60% in mass and a doubling in age with respect to traditional methods using optical spectra that do not account for the effect of spots.

Keywords: Starspots, Early stellar evolution, T Tauri stars, Pre-main sequence stars, Star formation, Stellar evolutionary tracks
Probing Depth Variations of Solar Inertial Modes through Normal Mode Coupling. Recently discovered inertial waves, observed on the solar surface, likely extend to the deeper layers of the Sun. Utilizing helioseismic techniques, we explore these motions, allowing us to discern inertial mode eigenfunctions in both radial and latitudinal orientations. We analyze 8 yr of space-based observations (2010–2017) taken by the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory using normal mode coupling. Couplings between the same and different-degree acoustic modes and different frequency bins are measured in order to capture the various length scales of the inertial modes. We detect inertial modes at high latitude with azimuthal order t = 1 and frequency ∼ ‑80 nHz, measured in a corotating frame with a rotation frequency of 453.1 nHz. This mode is present in the entire convection zone. The presence of Rossby modes may be seen down to a depth of ∼0.83R ⊙, and the Rossby signal is indistinguishable from noise below that depth for high azimuthal order. We find that the amplitudes of these modes increase with depth down to around 0.92R ⊙ and decrease below that depth. We find that the latitudinal eigenfunctions of Rossby modes deviate from sectoral spherical harmonics if we use a similar approach as adopted in earlier studies. We find that spatial leakage and even pure noise in the measurements of nonsectoral components can also explain the abovementioned characteristics of the latitudinal eigenfunctions. This realization underscores the necessity for careful interpretation when considering the latitudinal eigenfunctions of Rossby modes. Exploring the depth-dependent characteristics of these modes will enable us to capture interior dynamics distinctly, separate from p-mode seismology.

Keywords: Helioseismology, Solar convective zone, Solar physics, Solar interior
Bulk Flow Motion Detection in the Local Universe with Pantheon+ Type Ia Supernovae. The bulk flow in the Local Universe is a collective phenomenon due to the peculiar motions of matter structures, which, instead of moving in random directions, appears to follow an approximate dipole velocity flow. We apply a directional analysis to investigate, through the Hubble-Lemaître diagram, the angular dependence of the Hubble constant H 0 of a sample of Type Ia supernovae from the Pantheon+ catalog in the Local Universe (0.015 ≤ z ≤ 0.06). We perform a directional analysis that reveals a statistically significant dipole variation of H 0, at more than 99.9% confidence level, showing that matter structures follow a dipole bulk flow motion toward (l, b) = (326.°1 ± 11.°2, 27.°8 ± 11.°2), close to the Shapley supercluster (l Shapley, b Shapley) = (311.°5, 32.°3), with velocity 132.14 ± 109.3 km s‑1 at the effective distance 102.83 ± 10.2 Mpc. Interestingly, the antipodal direction of this dipole points close to the Dipole Repeller structure. Our analyses confirm that the gravitational dipole system Shapley-Dipole Repeller explains well the observed bulk flow velocity field in the Local Universe. Furthermore, we performed robustness tests that support our results. Additionally, our approach provides a measurement of the Hubble constant H 0 = 70.39 ± 1.4 km s‑1 Mpc‑1, at the effective distance 102.8 Mpc, z ≃ 0.025.

Keywords: Observational cosmology, Type Ia supernovae, Large-scale structure of the universe
All-sky Search for Transient Astrophysical Neutrino Emission with 10 Years of IceCube Cascade Events. Neutrino flares in the sky are searched for in data collected by IceCube between 2011 and 2021 May. This data set contains cascade-like events originating from charged-current electron neutrino and tau neutrino interactions and all-flavor neutral-current interactions. IceCube's previous all-sky searches for neutrino flares used data sets consisting of track-like events originating from charged-current muon neutrino interactions. The cascade data set is statistically independent of the track data sets, and while inferior in angular resolution, the low-background nature makes it competitive and complementary to previous searches. No statistically significant flare of neutrino emission was observed in an all-sky scan. Upper limits are calculated on neutrino flares of varying duration from 1 hr to 100 days. Furthermore, constraints on the contribution of these flares to the diffuse astrophysical neutrino flux are presented, showing that multiple unresolved transient sources may contribute to the diffuse astrophysical neutrino flux.

Keywords: Neutrino astronomy, Transient sources, High energy astrophysics
Properties of the Line-of-sight Velocity Field in the Hot and X-Ray-emitting Circumgalactic Medium of Nearby Simulated Disk Galaxies. The hot, X-ray-emitting phase of the circumgalactic medium of massive galaxies is believed to be the reservoir of baryons from which gas flows onto the central galaxy and into which feedback from active galactic nuclei and stars inject mass, momentum, energy, and metals. These effects shape the velocity fields of the hot gas, which can be observed via the Doppler shifting and broadening of emission lines by X-ray integral field units. In this work, we analyze the gas kinematics of the hot circumgalactic medium of Milky Way–mass disk galaxies from the TNG50 simulation with synthetic observations to determine how future instruments can probe this velocity structure. We find that the hot phase is often characterized by outflows from the disk driven by feedback processes, radial inflows near the galactic plane, and rotation, although in some systems the velocity field is more disorganized and turbulent. With a spectral resolution of ∼1 eV, fast and hot outflows (∼200–500 km s‑1) can be measured, depending on the orientation of the galaxy on the sky. The rotation velocity of the hot phase (∼100–200 km s‑1) can be measured using line shifts in edge-on galaxies, and is slower than that of colder gas phases but similar to stellar rotation velocities. By contrast, the slow inflows (∼50–100 km s‑1) are difficult to measure in projection with these other components, but may be detected in multicomponent spectral fits. We find that the velocity measured is sensitive to which emission lines are used. Measuring these flows will constrain theories of how the gas in these galaxies evolves.

Keywords: AGN host galaxies, X-ray observatories, N-body simulations, Disk galaxies
JWST Photometric Time-delay and Magnification Measurements for the Triply Imaged Type Ia "SN H0pe" at z = 1.78. Supernova (SN) SN H0pe is a gravitationally lensed, triply imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed multiply imaged SNe provide a rare opportunity to constrain the Hubble constant (H 0), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located at z = 1.783 and is the first SN Ia with sufficient light-curve sampling and long enough time delays for an H 0 inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry, we measure time delays of Δt ab =   $-{116.6}_{-9.3}^{+10.8}$   observer-frame days and Δt cb =   $-{48.6}_{-4.0}^{+3.6}$   observer-frame days relative to the last image to arrive (image 2b; all uncertainties are 1σ), which corresponds to a ∼5.6% uncertainty contribution for H 0 assuming 70 km s‑1 Mpc‑1. We also constrain the absolute magnification of each image to μ  a  =   ${4.3}_{-1.8}^{+1.6}$  , μ  b  =   ${7.6}_{-2.6}^{+3.6}$  , μ  c  =   ${6.4}_{-1.5}^{+1.6}$   by comparing the observed peak near-IR magnitude of SN H0pe to the nonlensed population of SNe Ia.

Keywords: Cosmology, Gravitational lensing, Galaxy clusters, Type Ia supernovae
The Intrinsic Sizes of Odd Radio Circles. A new class of sources, the so-called odd radio circles (ORCs), have been discovered by recent sensitive, large-area radio continuum surveys. The distances of these sources have so far relied on photometric redshifts of optical galaxies found at the centers of or near ORCs. Here we present Gemini rest-frame optical spectroscopy of six galaxies at the centers of, or potentially associated with, the first five ORC discoveries. We supplement this with Legacy Survey imaging and Prospector fits to their griz+W1/W2 photometry. Of the three ORCs with central galaxies, all lie at distances (z = 0.27─0.55) that confirm the large intrinsic diameters of the radio circles (300─500 kpc). The central galaxies are massive (M * ∼ 1011 M ☉), red, unobscured ellipticals with old (≳1 Gyr) stellar populations. They have LINER spectral types that are shock-powered or active galactic nucleus (AGN)-powered. All three host low-luminosity, radio-quiet AGN. The similarity of their central galaxies is consistent with a common origin, perhaps as a blast wave from an ancient starburst. The other two ORCs are adjacent and have no prominent central galaxies. However, the z = 0.25 disk galaxy that lies between them hosts a Type 2, moderate-luminosity AGN. They may instead be the lobes of a radio jet from this AGN.

Keywords: Extragalactic radio sources, LINER galaxies, Low-luminosity active galactic nuclei, Galaxy winds, Shocks