Sazuna/UAT_keywords huggingface dataset:
Recurrent Strong Outbursts of an EXor-like Young Eruptive Star Gaia20eae. We present follow-up photometric and spectroscopic observations, and subsequent analysis of Gaia20eae. This source triggered photometric alerts during 2020 after showing a ~3 mag increase in its brightness. Its Gaia Alert light curve showed the shape of a typical eruptive young star. We carried out observations to confirm Gaia20eae as an eruptive young star and classify it. Its pre-outburst spectral energy distribution shows that Gaia20eae is a moderately embedded Class II object with L bol = 7.22 L ⊙. The color-color and color-magnitude diagrams indicate that the evolution in the light curve is mostly gray. Multiple epochs of the Hα line profile suggest an evolution of the accretion rate and winds. The near-infrared spectra display several emission lines, a feature typical of EX Lupi-type (EXor) eruptive young stars. We estimated the mass accretion rate during the dimming phase to be $\dot{M}$ = 3-8 × 10-7 M ⊙ yr-1, higher than typical T Tauri stars of similar mass and comparable to other EXors. We conclude Gaia20eae is a new EXor-type candidate.

Keywords: T Tauri stars, Young stellar objects, Broad band photometry, Spectroscopy
Two New Black Widow Millisecond Pulsars in M28. We report the discovery of two Black Widow millisecond pulsars in the globular cluster (GC) M28 with the MeerKAT telescope. PSR J1824-2452M (M28M) is a 4.78 ms pulsar in a 5.82 hr orbit, and PSR J1824-2452N (M28N) is a 3.35 ms pulsar in a 4.76 hr orbit. Both pulsars have dispersion measures near 119.30 pc cm-3 and have low-mass companion stars (~0.01-0.03 M ⊙) that do not cause strong radio eclipses or orbital variations. Including these systems, there are now five known black widow pulsars in M28. The pulsar searches were conducted as a part of an initial phase of MeerKAT's GC census (within the TRAPUM Large Survey Project). These faint discoveries demonstrate the advantages of MeerKAT's survey sensitivity over previous searches, and we expect to find additional pulsars in continued searches of this cluster.

Keywords: Globular star clusters, Radio astronomy, Radio pulsars, Millisecond pulsars
Another Look at Erupting Minifilaments at the Base of Solar X-Ray Polar Coronal "Standard" and "Blowout" Jets. We examine 21 solar polar coronal jets that we identify in soft X-ray images obtained from the Hinode/X-ray telescope (XRT). We identify 11 of these as blowout jets and four as standard jets (with six uncertain), based on their X-ray-spire widths being respectively wide or narrow (compared to the jet's base) in the XRT images. From corresponding extreme ultraviolet (EUV) images from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA), essentially all (at least 20 of 21) of the jets are made by minifilament eruptions, consistent with other recent studies. Here, we examine the detailed nature of the erupting minifilaments (EMFs) in the jet bases. Wide-spire ("blowout") jets often have ejective EMFs, but sometimes they instead have an EMF that is mostly confined to the jet's base rather than ejected. We also demonstrate that narrow-spire ("standard") jets can have either a confined EMF, or a partially confined EMF where some of the cool minifilament leaks into the jet's spire. Regarding EMF visibility: we find that in some cases the minifilament is apparent in as few as one of the four EUV channels we examined, being essentially invisible in the other channels; thus, it is necessary to examine images from multiple EUV channels before concluding that a jet does not have an EMF at its base. The sizes of the EMFs, measured projected against the sky and early in their eruption, is 14″ ± 7″, which is within a factor of 2 of other measured sizes of coronal-jet EMFs.

Keywords: Solar corona, Solar filament eruptions, Solar extreme ultraviolet emission, Solar x-ray emission
On the Spectral Evolution of Hot White Dwarf Stars. II. Time-dependent Simulations of Element Transport in Evolving White Dwarfs with STELUM. White dwarf stars are subject to various element transport mechanisms that can cause their surface composition to change radically as they cool, a phenomenon known as spectral evolution. In this paper, we undertake a comprehensive theoretical investigation of the spectral evolution of white dwarfs. First, we introduce STELUM, a new implementation of the stellar evolutionary code developed at the Université de Montréal. We provide a thorough description of the physical content and numerical techniques of the code, covering the treatment of both stellar evolution and chemical transport. Then, we present two state-of-the-art numerical simulations of element transport in evolving white dwarfs. Atomic diffusion, convective mixing, and mass loss are considered simultaneously as time-dependent diffusive processes and are fully coupled to the cooling. We first model the PG 1159-DO-DB-DQ evolutionary channel: a helium-, carbon-, and oxygen-rich PG 1159 star transforms into a pure-helium DB white dwarf due to gravitational settling and then into a helium-dominated, carbon-polluted DQ white dwarf through convective dredge-up. We also compute for the first time the full DO-DA-DC evolutionary channel: a helium-rich DO white dwarf harboring residual hydrogen becomes a pure-hydrogen DA star through the float-up process and then a helium-dominated, hydrogen-bearing DC star due to convective mixing. We demonstrate that our results are in excellent agreement with available empirical constraints. In particular, our DO-DA-DC simulation perfectly reproduces the lower branch of the bifurcation observed in the Gaia color-magnitude diagram, which can therefore be interpreted as a signature of spectral evolution.

Keywords: Stellar convection envelopes, White dwarf stars, Stellar evolutionary models, Stellar diffusion, Stellar winds
Performance Enhancement of Tree-based Friends-of-friends Galaxy Finder for High-resolution Simulations of Galaxy Formation. Cosmological simulations are useful tools for studying the evolution of galaxies, and it is critical to accurately identify galaxies and their halos from raw simulation data. The friends-of-friends (FoF) algorithm has been widely adopted for this purpose because of its simplicity and expandability to higher dimensions. However, it is cost-inefficient when applied to high-resolution simulations because standard FoF implementation leads to too many distance calculations in dense regions. We confirm this through our exercise of applying the six-dimensional (6D) FoF galaxy finder code, VELOCIRAPTOR, on the NEWHORIZON simulation. The high particle resolution of NEWHORIZON (M star ~ 104 M ⊙) allows a large central number density (106 kpc-3) for typical galaxies, resulting in a few days to weeks of galaxy searches for just one snapshot. Even worse, we observed a significant decrease in the FoF performance in the high-dimensional 6D searches: "the curse of dimensionality" problem. To overcome these issues, we have developed several implementations that can be readily applied to any tree-based FoF code. They include limiting visits to tree nodes, reordering the list of particles for searching neighbor particles, and altering the tree structure. Compared to the run with the original code, the new run with these implementations results in the identical galaxy detection with the ideal performance, $O(N\mathrm{log}N)$ , N being the number of particles in a galaxy-with a speed gain of a factor of 2700 in 3D or 12 in a 6D FoF search.

Keywords: Astronomy software
Exploring the AGN-Ram Pressure Stripping Connection in Local Clusters. Ram pressure stripping (RPS) by the intracluster medium is one of the most advocated mechanisms that affect the properties of cluster galaxies. A recent study based on a small sample has found that many galaxies showing strong signatures of RPS also possess an active galactic nucleus (AGN), suggesting a possible correlation between the two phenomena. This result has not been confirmed by a subsequent study. Building upon previous findings, here we combine MUSE observations conducted within the GASP program and a general survey of the literature to robustly measure the AGN fraction in ram-pressure-stripped cluster galaxies using Baldwin-Phillips-Terlevich emission line diagrams. Considering a sample of 115 ram-pressure-stripped galaxies with stellar masses ≥ 109 M ☉, we find an AGN fraction of ~27%. This fraction strongly depends on stellar mass: it raises to 51% when only ram-pressure-stripped galaxies of masses M * ≥ 1010 M ☉ are considered. We then investigate whether the AGN incidence is in excess in ram-pressure-stripped galaxies compared to nonstripped galaxies using as a comparison a sample of noncluster galaxies observed by the MaNGA survey. Considering mass-matched samples, we find that the incidence of AGN activity is significantly higher (at a confidence level &gt;99.95%) when RPS is in the act, supporting the hypothesis of an AGN-ram pressure connection.

Keywords: Galaxy clusters, Galaxy properties, Galaxy environments, Active galactic nuclei, Extragalactic astronomy, Galaxy masses
Exploring the Sgr-Milky Way-disk Interaction Using High-resolution N-body Simulations. The ongoing merger of the Sagittarius (Sgr) dwarf galaxy with the Milky Way is believed to strongly affect the dynamics of the Milky Way's disk. We present a suite of 13 N-body simulations, with 500 million-1 billion particles, modeling the interaction between the Sgr dwarf galaxy and the Galactic disk. To quantify the perturbation to the disk's structure and dynamics in the simulation, we compute the number count asymmetry and the mean vertical velocity in a solar-neighborhood-like volume. We find that, overall, the trends in the simulations match those seen in a simple one-dimensional model of the interaction. We explore the effects of changing the mass model of Sgr, the orbital kinematics of Sgr, and the mass of the Milky Way halo. We find that none of the simulations match the observations of the vertical perturbation using Gaia Data Release 2. In the simulation that is the most similar, we find that the final mass of Sgr far exceeds the observed mass of the Sgr remnant, the asymmetry wavelength is too large, and the shape of the asymmetry does not match past z ≈ 0.7 kpc. We therefore conclude that our simulations support the conclusion that Sgr alone could not have caused the observed perturbation to the solar neighborhood.

Keywords: Milky Way formation, Milky Way dynamics, Solar neighborhood, Milky Way disk, Milky Way evolution
Theory of Electron Injection at Oblique Shock of Finite Thickness. A theory of electron injection into diffusive shock acceleration (DSA) for the generation of cosmic-ray electrons at collisionless shocks is presented. We consider a recently proposed particle acceleration mechanism called stochastic shock drift acceleration (SSDA). We find that SSDA may be understood as a diffusive particle acceleration mechanism at an oblique shock of finite thickness. More specifically, it is described by a solution to the diffusion-convection equation for particles with the characteristic diffusion length comparable to the shock thickness. On the other hand, the same equation yields the standard DSA if the diffusion length is much longer than the thickness. Although SSDA predicts, in general, a spectral index steeper than DSA, it is much more efficient for low-energy electron acceleration and is favorable for injection. The injection threshold energy corresponds to the transition energy between the two different regimes. It is of the order of 0.1-1 MeV in typical interstellar and interplanetary conditions if the dissipation scale of turbulence around the shock is determined by the ion inertial length. The electron injection is more efficient at high ${M}_{{\rm{A}}}/\cos {\theta }_{{Bn}}$ , where M A and θ  Bn  are the Alfvén Mach number and the shock obliquity, respectively. The theory suggests that efficient acceleration of electrons to ultrarelativistic energies will be more easily realized at high Mach number, young supernova remnant shocks, but not at weak or moderate shocks in the heliosphere unless the upstream magnetic field is nearly perpendicular to the shock normal.

Keywords: Space plasmas, Interplanetary shocks, High energy astrophysics, Planetary bow shocks, Plasma astrophysics, Shocks
A Model Earth-sized Planet in the Habitable Zone of α Centauri A/B. The bulk chemical composition and interior structure of rocky exoplanets are fundamentally important to understand their long-term evolution and potential habitability. Observations of the chemical compositions of solar system rocky bodies and of other planetary systems have increasingly shown a concordant picture that the chemical composition of rocky planets reflects that of their host stars for refractory elements, whereas this expression breaks down for volatiles. This behavior is explained by devolatilization during planetary formation and early evolution. Here we apply a devolatilization model calibrated with solar system bodies to the chemical composition of our nearest Sun-like stars-α Centauri A and B-to estimate the bulk composition of any habitable-zone rocky planet in this binary system ("α-Cen-Earth"). Through further modeling of likely planetary interiors and early atmospheres, we find that, compared to Earth, such a planet is expected to have (i) a reduced (primitive) mantle that is similarly dominated by silicates, albeit enriched in carbon-bearing species (graphite/diamond); (ii) a slightly larger iron core, with a core mass fraction of ${38.4}_{-5.1}^{+4.7}$ wt% (see Earth's 32.5 ± 0.3 wt%); (iii) an equivalent water-storage capacity; and (iv) a CO2-CH4-H2O-dominated early atmosphere that resembles that of Archean Earth. Further taking into account its ~25% lower intrinsic radiogenic heating from long-lived radionuclides, an ancient α-Cen-Earth (~1.5-2.5 Gyr older than Earth) is expected to have less efficient mantle convection and planetary resurfacing, with a potentially prolonged history of stagnant-lid regimes.

Keywords: Extrasolar rocky planets, Exoplanet dynamics, Theoretical models, Atmospheric composition, Planetary interior
A Star-sized Impact-produced Dust Clump in the Terrestrial Zone of the HD 166191 System. We report on five years of 3-5 μm photometry measurements obtained by warm Spitzer to track the dust debris emission in the terrestrial zone of HD 166191 in combination with simultaneous optical data. We show that the debris production in this young (~10 Myr) system increased significantly in early 2018 and reached a record high level (almost double by mid 2019) by the end of the Spitzer mission (early 2020), suggesting intense collisional activity in its terrestrial zone likely due to either initial assembling of terrestrial planets through giant impacts or dynamical shake-up from unseen planet-mass objects or recent planet migration. This intense activity is further highlighted by detecting a star-size dust clump, passing in front of the star, in the midst of its infrared brightening. We constrain the minimum size and mass of the clump using multiwavelength transit profiles and conclude that the dust clump is most likely created by a large impact involving objects of several hundred kilometers in size with an apparent period of 142 days (i.e., 0.62 au, assuming a circular orbit). The system's evolutionary state (right after the dispersal of its gas-rich disk) makes it extremely valuable to learn about the process of terrestrial-planet formation and planetary architecture through future observations.

Keywords: Extrasolar rocky planets, Exoplanet migration, Infrared excess, Circumstellar matter, Debris disks
A Giant Shell of Ionized Gas Discovered near M82 with the Dragonfly Spectral Line Mapper Pathfinder. We present the discovery of a giant cloud of ionized gas in the field of the starbursting galaxy M82. Emission from the cloud is seen in Hα and [N II] λ6583 in data obtained though a small pathfinder instrument used to test the key ideas that will be implemented in the Dragonfly Spectral Line Mapper, an upcoming ultranarrow-bandpass imaging version of the Dragonfly Telephoto Array. The discovered cloud has a shell-like morphology with a linear extent of 0.°8 and is positioned 0.°6 northwest of M82. At the heliocentric distance of the M81 group, the cloud's longest angular extent corresponds to 55 kpc and its projected distance from the nucleus of M82 is 40 kpc. The cloud has an average Hα surface brightness of 2 × 10-18 $\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}\,{\mathrm{arcsec}}^{-2}$ . The [N II] λ6583/Hα line ratio varies from [N II]/Hα ~ 0.2 to [N II]/Hα ~ 1.0 across the cloud, with higher values found in its eastern end. Follow-up spectra obtained with Keck LRIS confirm the existence of the cloud and yield line ratios of [N II] λ6583/Hα = 0.340 ± 0.003 and [S II] λλ6716, 6731/Hα = 0.64 ± 0.03 in the cloud. This giant cloud of material could be lifted from M82 by tidal interactions or by its powerful starburst. Alternatively, it may be gas infalling from the cosmic web, potentially precipitated by the superwinds of M82. Deeper data are needed to test these ideas further. The upcoming Dragonfly Spectral Line Mapper will have 120 lenses, 40× more than in the pathfinder instrument used to obtain the data presented here.

Keywords: Intergalactic clouds, Intergalactic gas, Circumgalactic medium, Galaxy evolution, Intergalactic medium
Recent Formation of a Spiral Disk Hosting Progenitor Globular Clusters at the Center of the Perseus Brightest Cluster Galaxy. I. Spiral Disk. We address the nature and origin of a spiral disk at the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus cluster, that spans a radius of ~5 kpc. By comparing stellar absorption lines measured in long-slit optical spectra with synthetic spectra for single stellar populations, we find that fitting of these lines requires two stellar populations: (i) a very young population that peaks in radial velocity at ±250 km s-1 of the systemic velocity within a radius of ~720 pc of the nucleus, a 1σ velocity dispersion significantly lower than 140 km s-1, and an age of 0.15 ± 0.05 Gyr; and (ii) a very old population having a constant radial velocity with a radius corresponding to the systemic velocity, a much broader velocity dispersion of ~250 km s-1, and an age of around 10 Gyr. We attribute the former to a post-starburst population associated with the spiral disk, and the latter to the main stellar body of NGC 1275 along the same sight line. If the spiral disk is the remnant of a cannibalized galaxy, then its progenitor would have had to retain an enormous amount of gas in the face of intensive ram-pressure stripping so as to form a total initial mass in stars of ~3 × 109 M ⊙. More likely, the central spiral originally comprised a gaseous body accreted over the distant past from a residual cooling flow, before experiencing a starburst ~0.15 Gyr ago to form its stellar body.

Keywords: Cooling flows, Optical astronomy, Stellar populations, Brightest cluster galaxies, Spectral index, Galaxy spectroscopy, Post-starburst galaxies
Recent Formation of a Spiral Disk Hosting Progenitor Globular Clusters at the Center of the Perseus Brightest Cluster Galaxy. II. Progenitor Globular Clusters. We address the nature and origin of super star clusters (SSCs) discovered by Holtzman et al. within a radius of ~5 kpc from the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus Cluster. We show that, in contrast with the much more numerous population of SSCs subsequently discovered up to ~30 kpc from the center of this galaxy, the central SSC population have maximal masses an order of magnitude higher and a mass function with a shallower power-law slope. Furthermore, whereas the outer SSC population have ages spanning a few Myr to at least ~1 Gyr, the central SSC population have ages strongly concentrated around ~500 Myr with a 1σ dispersion of ~100 Myr. These SSCs share a close spatial and temporal relationship with the "central spiral," which also has a radius ~5 kpc centered on NGC 1275 and a characteristic stellar age of ~150 Myr. We argue that both the central SSC population and the central spiral formed from gas deposited by a residual cooling flow, with the SSCs forming first followed by the formation of the stellar body of the central spiral ~300-400 Myr later. The ages of the central SSC population imply that they are able to withstand very strong tidal fields near the center of NGC 1275, making them genuine progenitor globular clusters. Evidently, a spiral disk hosting progenitor globular clusters has recently formed at the center of a giant elliptical galaxy.

Keywords: Brightest cluster galaxies, Cooling flows, Perseus Cluster, Star clusters
Identification of an X-Ray Pulsar in the BeXRB System IGR J18219-1347. We report on observations of the candidate Be/X-ray binary (BeXRB) IGR J18219-1347 with the Swift/X-ray Telescope, the Nuclear Spectroscopic Telescope ARray, and the Neutron Star Interior Composition Explorer during Type-I outbursts in 2020 March and June. Our timing analysis revealed the spin period of a neutron star with P spin = 52.46 s. This periodicity, combined with the known orbital period of 72.4 days, indicates that the system is a BeXRB. Furthermore, by comparing the spectral energy distribution of the infrared counterpart to that of known BeXRBs, we confirm this classification and set a distance of approximately 10-15 kpc for the source. The broadband X-ray spectrum (1.5-50 keV) of the source is described by an absorbed power law with a photon index Γ ~ 0.5 and a cutoff energy at ~13 keV.

Keywords: X-ray astronomy, Neutron stars, High mass x-ray binary stars, Pulsars
Statistical Analysis of Intermittency and its Association with Proton Heating in the Near-Sun Environment. We use data from the first six encounters of the Parker Solar Probe and employ the partial variance of increments (PVI) method to study the statistical properties of coherent structures in the inner heliosphere with the aim of exploring physical connections between magnetic field intermittency and observable consequences such as plasma heating and turbulence dissipation. Our results support proton heating localized in the vicinity of, and strongly correlated with, magnetic structures characterized by PVI ≥ 1. We show that, on average, such events constitute ≈19% of the data set, though variations may occur depending on the plasma parameters. We show that the waiting time distribution (WT) of identified events is consistent across all six encounters following a power-law scaling at lower WTs. This result indicates that coherent structures are not evenly distributed in the solar wind but rather tend to be tightly correlated and form clusters. We observe that the strongest magnetic discontinuities, PVI ≥ 6, usually associated with reconnection exhausts, are sites where magnetic energy is locally dissipated in proton heating and are associated with the most abrupt changes in proton temperature. However, due to the scarcity of such events, their relative contribution to energy dissipation is minor. Taking clustering effects into consideration, we show that smaller scale, more frequent structures with PVI between 1 ≲ PVI ≲ 6 play a major role in magnetic energy dissipation. The number density of such events is strongly associated with the global solar wind temperature, with denser intervals being associated with higher T  p .

Keywords: Space plasmas, Solar wind, Plasma astrophysics