Sazuna/UAT_keywords huggingface dataset:
GlobULeS. IV. UVIT/AstroSat Detection of Extremely Low Mass White Dwarf Companions to Blue Straggler Stars in NGC 362. We report the discovery of extremely low mass white dwarfs (ELM WDs) as a companion of blue straggler stars (BSSs) in the Galactic globular cluster NGC 362 using images from AstroSat's Ultra Violet Imaging Telescope (UVIT). Spectral energy distributions (SEDs) for 26 far-UV (FUV) bright member BSSs are created using data from the UVIT, the UltraViolet and Optical Telescope (UVOT), Gaia EDR3, and the 2.2 m ESO/MPI telescope. A single SED is fitted to 14 BSSs, whereas double-SED fits revealed ELM WDs as binary companions in 12 of the 26 BSSs studied. The effective temperature, radius, luminosity, and mass of the 12 ELM WDs are found to have a range of T eff = 9750-18,000 K, R = 0.1-0.4 R ☉, L = 0.4-3.3 L ☉, and M = 0.16-0.20 M ☉. These suggest that 12 BSSs are post-mass-transfer systems formed through the case A/B mass transfer pathway. To the best of our knowledge, this is the first finding of ELM WDs as companions to BSSs in globular clusters. This cluster is known to have a binary BSS sequence, and the 12 binary and 14 single BSSs (as classified by the SEDs) follow the mass transfer and collisional sequence of BSSs in the color-magnitude diagram. The cooling ages of nine of the ELM WDs are found to be younger than 500 Myr. Though the binary BSSs may have formed during the core collapse (~200 Myr) or as part of the dynamical evolution of the cluster, they provide new insights on the dynamics of this cluster.

Keywords: Ultraviolet astronomy
Oscillatory Reconnection as a Plasma Diagnostic in the Solar Corona. Oscillatory reconnection is a relaxation process in magnetized plasma, with an inherent periodicity that is exclusively dependent on the properties of the background plasma. This study focuses on the seismological prospects of oscillatory reconnection in the solar corona. We perform three sets of parameter studies (for characteristic coronal values of the background magnetic field, density, and temperature) using the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D magnetic X-point. From each parameter study, we derive the period of the oscillatory reconnection. We find that this period is inversely proportional to the characteristic strength of the background magnetic field and the square root of the initial plasma temperature, while following a square root dependency upon the equilibrium plasma density. These results reveal an inverse proportionality between the magnitude of the Alfvén speed and the period, as well as the background speed of sound and the period. Furthermore, we note that the addition of anisotropic thermal conduction only leads to a small increase in the mean value for the period. Finally, we establish an empirical formula that gives the value for the period in relation to the background magnetic field, density, and temperature. This gives us a quantified relation for oscillatory reconnection, to be used as a plasma diagnostic in the solar corona, opening up the possibility of using oscillatory reconnection for coronal seismology.

Keywords: Magnetohydrodynamics, Solar magnetic reconnection, Solar coronal waves, Solar coronal seismology, Magnetohydrodynamical simulations
The Supersonic Project: The Early Evolutionary Path of Supersonically Induced Gas Objects. Supersonically induced gas objects (SIGOs) are a class of early universe objects that have gained attention as a potential formation route for globular clusters. SIGOs have recently begun to be studied in the context of molecular hydrogen cooling, which is key to characterizing their structure and evolution. Studying the population-level properties of SIGOs with molecular cooling is important for understanding their potential for collapse and star formation, and for addressing whether SIGOs can survive to the present epoch. Here, we investigate the evolution of SIGOs before they form stars, using a combination of numerical and analytical analysis. We study timescales important to the evolution of SIGOs at a population level in the presence of molecular cooling. Revising the previous formulation for the critical density of collapse for SIGOs allows us to show that their prolateness tends to act as an inhibiting factor to collapse. We find that simulated SIGOs are limited by artificial two-body relaxation effects that tend to disperse them. We expect that SIGOs in nature will be longer lived compared to our simulations. Further, the fall-back timescale on which SIGOs fall into nearby dark matter halos, potentially producing a globular-cluster-like system, is frequently longer than their cooling timescale and the collapse timescale on which they shrink through gravity. Therefore, some SIGOs have time to cool and collapse outside of halos despite initially failing to exceed the critical density. From this analysis we conclude that SIGOs should form stars outside of halos in nonnegligible stream velocity patches in the universe.

Keywords: Globular star clusters, Galactic and extragalactic astronomy, Giant molecular clouds, Star formation, High-redshift galaxies
A Preferential Growth Channel for Supermassive Black Holes in Elliptical Galaxies at z ≲ 2. The assembly of stellar and supermassive black hole (SMBH) mass in elliptical galaxies since z ~ 1 can help to diagnose the origins of locally observed correlations between SMBH mass and stellar mass. We therefore construct three samples of elliptical galaxies, one at z ~ 0 and two at 0.7 ≲ z ≲ 2.5, and quantify their relative positions in the M BH-M * plane. Using a Bayesian analysis framework, we find evidence for translational offsets in both stellar mass and SMBH mass between the local sample and both higher-redshift samples. The offsets in stellar mass are small, and consistent with measurement bias, but the offsets in SMBH mass are much larger, reaching a factor of 7 between z ~ 1 and z ~ 0. The magnitude of the SMBH offset may also depend on redshift, reaching a factor of ~20 at z ~ 2. The result is robust against variation in the high- and low-redshift samples and changes in the analysis approach. The magnitude and redshift evolution of the offset are challenging to explain in terms of selection and measurement biases. We conclude that either there is a physical mechanism that preferentially grows SMBHs in elliptical galaxies at z ≲ 2, or that selection and measurement biases are both underestimated, and depend on redshift.

Keywords: Supermassive black holes, Giant elliptical galaxies, Galaxy evolution
Simulation of the Solar Energetic Particle Event on 2020 May 29 Observed by Parker Solar Probe. This paper presents a stochastic three-dimensional focused transport simulation of solar energetic particles (SEPs) produced by a data-driven coronal mass ejection (CME) shock propagating through a data-driven model of coronal and heliospheric magnetic fields. The injection of SEPs at the CME shock is treated using diffusive shock acceleration of post-shock suprathermal solar wind ions. A time-backward stochastic simulation is employed to solve the transport equation to obtain the SEP time-intensity profile at any location, energy, and pitch angle. The model is applied to a SEP event on 2020 May 29, observed by STEREO-A close to ~1 au and by Parker Solar Probe (PSP) when it was about 0.33 au away from the Sun. The SEP event was associated with a very slow CME with a plane-of-sky speed of 337 km s-1 at a height below 6 R  S  as reported in the SOHO/LASCO CME catalog. We compute the time profiles of particle flux at PSP and STEREO-A locations, and estimate both the spectral index of the proton energy spectrum for energies between ~2 and 16 MeV and the equivalent path length of the magnetic field lines experienced by the first arriving SEPs. We find that the simulation results are well correlated with observations. The SEP event could be explained by the acceleration of particles by a weak CME shock in the low solar corona that is not magnetically connected to the observers.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Solar particle emission
Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020. BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ-rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst event during October-November in the g, r, and i bands with the 1.26 m telescope at the Xinglong Observatory, China. We detected significant intranight variations with amplitude rising up to ~30%, where the fastest variability timescale was found to be a few tens of minutes, giving an emitting region size of the order 10-3 pc, which corresponds to ~100 Schwarzschild radius of the central black hole, likely coming from some jet mini-structures. Unlike on the intranight timescale, a clear frequency-dependent pattern along symmetric timescales (~11 days) of flux variation is detected on a long timescale. The spectral evolution was predominated by flattening of the spectra with increasing brightness i.e., a bluer-when-brighter trend in 96% of the cases. On the night before the outburst peak, the color indices shown in a color-magnitude diagram, clustered into two distinct branches, within a period of ~6 hr, which is connected to a hard-soft-hard spectral evolution trend extracted from time-resolved spectra. To the best of our knowledge, such a trend has never been seen in BL Lac or any other blazars before. The results obtained in this study can be explained in the context of shock-induced particle acceleration or magnetic reconnection in the jet where turbulent processes most likely resulted in the asymmetric flux variation on a nightly timescale.

Keywords: Blazars, Active galactic nuclei
The Radio Structure of the γ-Ray Narrow-line Seyfert 1 Galaxy SDSS J211852.96-073227.5. The γ-ray narrow-line Seyfert 1 (NLS1) galaxies can be considered to be the third class of γ-ray active galactic nuclei possessing relativistic jets. In this paper, we present multi-band high-resolution Very Long Baseline Array (VLBA) images of the γ-ray NLS1, SDSS J211852.96-073227.5 (J2118-0732, z = 0.26). We find a core-jet radio morphology and significant flux density variations in the radio core. The high brightness temperature estimated from VLBA images and core variability demonstrate that it exhibits substantial relativistic beaming effects. By considering radio emission in several bands, we find that the source has an inverted spectrum above 1 GHz but a steep spectrum at low frequencies ranging from 74 MHz-1 GHz; these may arise from the present activity and the old diffuse/extended emission, respectively. The core-jet morphology, significant flux density variations, and beaming effect make J2118-0732 resemble a blazar. Considering the low mass of its central black hole and the ongoing merger environment, J2118-0732 may represent a low-mass, low-power counterpart of blazars, and may finally evolve into a blazar.

Keywords: Radio cores, Seyfert galaxies, Active galactic nuclei, Radio jets
Mass Function of a Young Cluster in a Low-metallicity Environment. Sh 2-209. We present deep near-infrared (NIR) imaging of Sh 2-209 (S209), a low-metallicity ([O/H] = -0.5 dex) H II region in the Galaxy. From the NIR images, combined with astrometric data from Gaia EDR3, we estimate the distance to S209 to be 2.5 kpc. This is close enough to enable us to resolve cluster members clearly (≃1000 au separation) down to a mass-detection limit of ≃ 0.1 M ☉, and we have identified two star-forming clusters in S209, with individual cluster scales ~1 pc. We employ a set of model luminosity functions to derive the underlying initial mass functions (IMFs) and ages for both clusters. The IMFs we obtained for both clusters exhibit slightly flat high-mass slopes (Γ ≃ -1.0) compared to the Salpeter IMF (Γ = -1.35), and their break mass of ≃0.1 M ☉ is lower than those generally seen in the solar neighborhood (~0.3 M ☉). In particular, because the S209 main cluster is a star-forming cluster with a larger number of members (~1500) than the number (~100) in regions previously studied in such environments, it is possible for the first time to derive the IMF in a low-metallicity environment with high accuracy over the wide mass range of 0.1-20 M ☉.

Keywords: Luminosity function, Stellar mass functions, Pre-main sequence stars, Star formation, Low mass stars, Infrared sources, Galaxy abundances, Open star clusters, H II regions
Patchy Kinetic Sunyaev-Zel'dovich Effect with Controlled Reionization History and Morphology. Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect by directly specifying the reionization history with the redshift midpoint z mid, duration Δz, and asymmetry A z. We further control the ionizing sources and radiation through the minimum halo mass M h and the radiation mean free path λ mfp. AMBER reproduces the free-electron number density and the patchy kSZ power spectrum of radiation-hydrodynamic simulations at the target resolution (1 Mpc h -1) with matched reionization parameters. With a suite of (2 Gpc/h)3 simulations using AMBER, we first constrain the redshift midpoint 6.0 &lt; z mid &lt; 8.9 using the Planck 2018 Thomson optical depth result (95% CL). Then, assuming z mid = 8, we find that the amplitude of ${D}_{{\ell }=3000}^{\mathrm{pkSZ}}$ scales linearly with the duration of reionization Δ z  and is consistent with the 1σ upper limit from South Pole Telescope (SPT) results up to Δ z  &lt; 5.1 (Δ z  encloses 5%-95% ionization). Moreover, a shorter λ mfp can lead to a ~10% lower ${D}_{{\ell }=3000}^{\mathrm{pkSZ}}$ and a flatter slope in the ${D}_{{\ell }=3000}^{\mathrm{pkSZ}}-{{\rm{\Delta }}}_{z}$ scaling relation, thereby affecting the constraints on Δ z  at ℓ = 3000. Allowing z mid and λ mfp to vary simultaneously, we get spectra consistent with the SPT result (95% CL) up to Δ z  = 12.8 (but A  z  &gt; 8 is needed to ensure the end of reionization before z = 5.5). We show that constraints on the asymmetry require ~0.1 μ k 2 measurement accuracy at multipoles other than ℓ = 3000. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive to M  h  under a fixed reionization history and radiation mean free path.

Keywords: Cosmology, Reionization, Cosmic microwave background radiation, Sunyaev-Zeldovich effect
A Nearby Isolated Dwarf: Star Formation and Structure of ESO 006-001. Observations with the Hubble Space Telescope unexpectedly revealed that the dwarf galaxy ESO 006-001 is a near neighbor to the Local Group at a distance of 2.70 ± 0.11 Mpc. The stellar population in the galaxy is well resolved into individual stars to a limit of M  I  ~ - 0.5 mag. The dominant population is older than 12 Gyr yet displays a significant range in metallicity of -2 &lt; [Fe/H] &lt; - 1, as evidenced by a red giant branch with substantial width. Superimposed on the dominant population are stars on the main sequence with ages less than 100 Myr and helium burning blue loop stars with ages of several hundred Myr. ESO 006-001 is an example of a transition dwarf; a galaxy dominated by old stars but one that has experienced limited recent star formation in a swath near the center. No H I gas is detected at the location of the optical galaxy in spite of the evidence for young stars. Intriguingly, an H I cloud with a similar redshift is detected 9 kpc away in projection. Otherwise, ESO 006-001 is a galaxy in isolation with its nearest known neighbor IC 3104, itself a dwarf, at a distance of ~500 kpc.

Keywords: Dwarf galaxies, Galaxy stellar content
Detection of Solar Filaments Using Suncharts from Kodaikanal Solar Observatory Archive Employing a Clustering Approach. With over 100 yr of solar observations, the Kodaikanal Solar Observatory (KoSO) is a one-of-a-kind solar data repository in the world. Among its many data catalogs, the "suncharts" at KoSO are of particular interest. These suncharts (1904-2020) are colored drawings of different solar features, such as sunspots, plages, filaments, and prominences, made on papers with a Stonyhurst latitude-longitude grid etched on them. In this paper, we analyze this unique data by first digitizing each sunchart using an industry-standard scanner and saving those digital images in a high-resolution ".tif" format. We then examine cycle 19 and cycle 20 data (two of the strongest cycles of the last century) with the aim of detecting filaments. To this end, we employed the "K-means clustering" method, and obtained different filament parameters such as position, tilt angle, length, and area. Our results show that filament length (and area) increases with latitude and the poleward migration is clearly dominated by a particular tilt sign. Lastly, we cross verified our findings with results from KoSO digitized photographic plate database for the overlapping time period and obtained a good agreement between them. This work, acting as a proof-of-the-concept, will kickstart new efforts to effectively use the entire hand-drawn series of multifeature, full-disk solar data and enable researchers to extract new sciences, such as the generation of pseudomagnetograms for the last 100 yr.

Keywords: Solar activity, Solar filaments, Solar cycle
Study of the Effect of Martian Dust Storms on Ionospheric Electron Density Based on Physical-grid Deep Neural Learning Technology. The behavior of the Martian ionosphere during global dust storms has always been a popular topic. Based on many Mars Atmosphere and Volatile Evolution observations, a Martian ionospheric electron density model is constructed herein using a physical-grid deep neural network algorithm. The precision of the model is proved to be high, and the R 2 value of the test set is 0.979. On this basis, the effects of global dust storms on the electron density and peak height of the Martian ionosphere are explored. The results show that the MY34 global dust storm significantly raised the peak height of the Martian electron layer, and its effects mainly ranged from 20°N to 55°N. The periodicity of the global daily average peak electron layer height following this dust storm was more regular than that before the dust storm.

Keywords: Planetary ionospheres, Planetary atmospheres, Neural networks
Unified Relationship between Cold Plasma Ejections and Flare Energies Ranging from Solar Microflares to Giant Stellar Flares. We often find spectral signatures of chromospheric cold plasma ejections accompanied by flares in a wide range of spatial scales in the solar and stellar atmospheres. However, the relationship between physical quantities (such as mass, kinetic energy, and velocity) of cold ejecta and flare energy has not been investigated in a unified manner for the entire range of flare energies to date. This study analyzed the spectra of cold plasma ejections associated with small-scale flares and solar flares (energy 1025-1029 erg) to supply smaller energy samples. We performed Hα imaging spectroscopy observation by the Solar Dynamics Doppler Imager on the Solar Magnetic Activity Research Telescope. We determined the physical quantities of the ejecta by cloud model fitting to the Hα spectrum. We determined the flare energy by differential emission measure analysis using the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory for small-scale flares and by estimating the bolometric energy for large-scale flares. As a result, we found that the ejection mass M and the total flare energy E tot follow a relation of $M\propto {E}_{\mathrm{tot}}^{2/3}$ . We show that the scaling law derived from a simple physical model explains the solar and stellar observations with a coronal magnetic field strength as a free parameter. We also found that the kinetic energy and velocity of the ejecta correlate with the flare energy. These results suggest a common mechanism driven by magnetic fields to cause cold plasma ejections with flares on the Sun and stars.

Keywords: Solar flares, Solar magnetic reconnection, Quiet sun, Solar filaments, Stellar flares, Solar filament eruptions
Principal-component Interferometric Modeling (PRIMO), an Algorithm for EHT Data. I. Reconstructing Images from Simulated EHT Observations. The sparse interferometric coverage of the Event Horizon Telescope (EHT) poses a significant challenge for both reconstruction and model fitting of black hole images. PRIMO is a new principal components analysis-based algorithm for image reconstruction that uses the results of high-fidelity general relativistic, magnetohydrodynamic simulations of low-luminosity accretion flows as a training set. This allows the reconstruction of images that are consistent with the interferometric data and that live in the space of images that is spanned by the simulations. PRIMO follows Monte Carlo Markov Chains to fit a linear combination of principal components derived from an ensemble of simulated images to interferometric data. We show that PRIMO can efficiently and accurately reconstruct synthetic EHT data sets for several simulated images, even when the simulation parameters are significantly different from those of the image ensemble that was used to generate the principal components. The resulting reconstructions achieve resolution that is consistent with the performance of the array and do not introduce significant biases in image features such as the diameter of the ring of emission.

Keywords: Accretion, Black hole physics, Very long baseline interferometry, Principal component analysis, Astronomy image processing, Interferometry
Jets in a Gamma-Ray Burst during Its Prompt Emission: Evolution of the Lorentz Factor. Knowledge about the Lorentz factor and its evolution of relativistic jets in gamma-ray bursts (GRBs) is crucial to understand their physics. An exact value of the bulk Lorentz factor can be estimated based on a high-energy spectral cutoff, which may appear in the GRBs' prompt emission owing to the absorption of photon-photon pair production. In this work, we focus on an investigation of the bulk Lorentz factor evolution of jets in an individual burst. Based on Fermi observations, we search for bursts with multiple GRB pulses characterized by a high-energy spectral cutoff, and nine GRBs are obtained. Together with the estimation of the pulse duration and radiation spectrum, the Lorentz factor of jets corresponding to different pulses in an individual GRB is estimated. It is shown that the Lorentz factor of jets in an individual GRB fluctuates within a certain range and without a general trend in these nine GRBs. In addition, the Lorentz factors of the jets in GRBs 130821A, 160509A, and 160625B seem to increase with time. We also study the relations among L iso, E p,z, and Γ for the pulses in our sample, which are found to be consistent with those found in previous works.

Keywords: Gamma-ray bursts