Sazuna/UAT_keywords huggingface dataset:
2003-2019 Monitoring of the Crab Emission through INTEGRAL SPI, or Vice Versa. The Crab Nebula is used by many instruments as a calibration source, in particular at high energy, where it is one of the brightest celestial objects. The spectrometer INTEGRAL SPI (20 keV-8 MeV), in operation since 2002 October, offers a large data set dedicated to this source, with regular campaigns planned twice per year. We have analyzed the available data to quantify the source behavior on a long-term scale and examine the stability level on timescales from hours to years. As a result, the source flux variability appears to be contained within less than ±5% around an ∼20 yr mean value for broad bands covering the 20-400 keV energy domain, above which statistics limits any firm conclusion. In terms of spectral shape, the Band model provides a good description of the observed emission between 20 keV and 2.2 MeV. The averaged spectrum best-fit parameters correspond to a low-energy slope of 1.99 ± 0.01, a high-energy slope of -2.32 ± 0.02, and a characteristic energy Ec of 531 ± 50 keV to describe the curvature joining both power laws. The spectral parameters have then been determined on the revolution timescale (∼1-2 days), and their steadiness confirms the source emission stability. As a complementary result, this study demonstrates that the SPI instrument efficiency remains within 5% of its initial value after 17 yr of operation.

Keywords: Gamma-ray sources, Space observatories, X-ray sources, Astronomical radiation sources
Adiabatic Mass Loss in Binary Stars. III. From the Base of the Red Giant Branch to the Tip of the Asymptotic Giant Branch. The distinguishing feature of the evolution of close binary stars is the role played by the mass exchange between the component stars. Whether or not the mass transfer is dynamically stable is one of the essential questions in binary evolution. In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We use the adiabatic mass-loss model to systematically survey the thresholds for dynamical timescale mass transfer over the entire span of possible donor star evolutionary states. We also simulate mass-loss process with isentropic envelopes, the specific entropy of which is fixed to be that at the base of the convective envelope, to artificially mimic the effect of such mass loss in superadiabatic surface convection regions, where the adiabatic approximation fails. We illustrate the general adiabatic response of $3.2\,{M}_{\odot }$ donor stars at different evolutionary stages. We extend our study to a grid of donor stars with different masses (from 0.1 to 100 M⊙ with Z = 0.02) and at different evolutionary stages. We proceed to present our criteria for dynamically unstable mass transfer in both tabular and graphical forms. For red giant branch (RGB) and asymptotic giant branch (AGB) donors in systems with such mass ratios, they may have convective envelopes deep enough to evolve into common envelopes on a thermal timescale, if the donor star overfills its outer Lagrangian radius. Our results show that the RGB and AGB stars tend to be more stable than previously believed, and this may be helpful to explain the abundance of observed post-AGB binary stars with an orbital period of around 1000 days.

Keywords: Stellar interiors, Close binary stars, Stellar mass loss, Common envelope evolution, Stellar evolution
Nuclear Structures of <SUP>17</SUP>O and Time-dependent Sensitivity of the Weak s-process to the <SUP>16</SUP>O(n,γ)<SUP>17</SUP>O Rate. We revisit the radiative neutron capture reaction 16O(n,γ)17O of astrophysical interest, based on the new reevaluated cross-section data. Several potentials are proposed to predict direct capture cross sections. The contributions from single-particle resonances to total capture cross section are quantitatively considered in Breit-Wigner formalism, taking into account the interference term between direct capture and resonant cross sections, which is crucial for the description of the behavior around the resonance energies. A new cross section is achieved based upon χ2-fittings for optimized resonance parameters using Minuit code, and it has a largely improved agreement with updated experimental data. Statistical errors are also evaluated for the total and Maxwellian-averaged cross sections. It is confirmed that the direct captures dominate the total cross sections; however, resonant contribution also becomes progressively more important as the energy increases to 100 keV. Resonance contribution can increase the reaction rates for energy region 50 keV &lt; E &lt; 100 keV by 5% ± 5%-25% ± 5%, and around 8% ± 5% in comparison with KADoNiS v0.3 rate and the latest data evaluations, respectively. We show a detailed propagation of the uncertainty in the 16O(n,γ) reaction rate to abundances of nuclei, including s-nuclei during the weak s-process with a multi-zone nuclear network calculation. Although an enhanced rate of 16O(n,γ) diminishes the s-process efficiency in the 25 M⊙ stellar model adopted from the Modules for Experiments in Stellar Astrophysics, it can lead to larger abundances of neutrons as well as 22Ne in the late epoch of C burning.

Keywords: Massive stars, Reaction rates, Helium burning, S-process
CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing. The gas-phase CO abundance (relative to hydrogen) in protoplanetary disks decreases by up to two orders of magnitude from its interstellar medium value of ∼10-4, even after accounting for freeze-out and photodissociation. Previous studies have shown that while local chemical processing of CO and the sequestration of CO ice on solids in the midplane can both contribute, neither of these processes appears capable of consistently reaching the observed depletion factors on the relevant timescale of 1-3 Myr. In this study, we model these processes simultaneously by including a compact chemical network (centered on carbon and oxygen) to 2D (r + z) simulations of the outer (r &gt; 20 au) disk regions that include turbulent diffusion, pebble formation, and pebble dynamics. In general, we find that the CO/H2 abundance is a complex function of time and location. Focusing on CO in the warm molecular layer, we find that only the most complete model (with chemistry and pebble evolution included) can reach depletion factors consistent with observations. In the absence of pressure traps, highly efficient planetesimal formation, or high cosmic-ray ionization rates, this model also predicts a resurgence of CO vapor interior to the CO ice-line. We show the impact of physical and chemical processes on the elemental (C/O) and (C/H) ratios (in the gas and ice phases), discuss the use of CO as a disk mass tracer, and, finally, connect our predicted pebble ice compositions to those of pristine planetesimals as found in the Cold Classical Kuiper Belt and debris disks.

Keywords: Circumstellar matter, Computational methods, Protoplanetary disks, Astrochemistry
Structure and Spectroscopic Properties of Hydrocalcium Isocyanide Isomers: Plausible Astronomical Ca-bearing Molecules. Recently, the first Ca-bearing molecule discovered in space, calcium isocyanide, CaNC, has been detected in the IRC+10216 circumstellar envelope. Related to CaNC are closed-shell stable molecules of [C, Ca, H, N] composition. One of the isomers with this composition is hydrocalcium isocyanide, HCaNC, which belongs to the hydrometal isocyanide/cyanide group of compounds, among which hydromagnesium isocyanide, HMgNC, is, to date, the only one detected in space. In this work, we have performed a study of the [C, Ca, H, N] isomers that are systems of possible interstellar interest by using quantum theoretical methodologies. The analysis of the relative energies predicts three low-lying isomers: c-HCa-NC (1A'), hydrocalcium isocyanide, HCaNC (1Σ), and hydrocalcium cyanide, HCaCN (1Σ). At the composite level, HCaNC (1Σ) and HCaCN (1Σ) were located 0.87 and 4.84 kcal mol-1, respectively, above the c-HCa-NC (1Σ) isomer. Interconversion processes between these isomers have been studied to analyze their stability. Isomer HCaNC is characterized as a transition state and thus directly isomerizes to the c-HCa-NC minimum. The isomerization process of HCaCN → c-HCa-NC shows a small barrier of about 0.76 kcal mol-1 (∼382 K) above HCaCN, at the highest level of theory employed in this work, suggesting that HCaCN could easily isomerize into the most stable isomer, c-HCa-NC. Our results predict two low-lying isomers, namely, c-HCa-NC (1A') and hydrocalcium cyanide, HCaCN (1Σ), as possible candidates for experimental or radioastronomical detection. For these isomers, we provide predictions for their vibrational and rotational spectroscopic parameters that could aid in their eventual characterization in the laboratory or in space.

Keywords: Molecular spectroscopy, Interstellar medium, Astrochemistry
Optical Variability of the Dwarf AGN NGC 4395 from the Transiting Exoplanet Survey Satellite. We present optical light curves from the Transiting Exoplanet Survey Satellite (TESS) for the archetypical dwarf active galactic nucleus (AGN) in the nearby galaxy NGC 4395 hosting a ∼105 M⊙ supermassive black hole (SMBH). Significant variability is detected on timescales from weeks to hours before reaching the background noise level. The ∼month-long, 30 minute-cadence, high-precision TESS light curve can be well fit by a simple damped random walk (DRW) model, with the damping timescale τDRW constrained to be ${2.3}_{-0.7}^{+1.8}$ days (1σ). NGC 4395 lies almost exactly on the extrapolation of the ${\tau }_{\mathrm{DRW}}-{M}_{\mathrm{BH}}$ relation measured for AGNs with BH masses that are more than three orders of magnitude larger. The optical variability periodogram can be well fit by a broken power law with the high-frequency slope (-1.88 ± 0.15) and the characteristic timescale (${\tau }_{\mathrm{br}}\equiv 1/(2\pi {f}_{\mathrm{br}})={1.4}_{-0.5}^{+1.9}$ days) consistent with the DRW model within 1σ. This work demonstrates the power of TESS light curves in identifying low-mass accreting SMBHs with optical variability, and a potential global ${\tau }_{\mathrm{DRW}}-{M}_{\mathrm{BH}}$ relation that can be used to estimate SMBH masses with optical variability measurements.

Keywords: Surveys, Black hole physics, Seyfert galaxies, Active galactic nuclei
Cosmic Reionization On Computers: The Galaxy-Halo Connection between 5 ≤ z ≤ 10. We explore the connection between the stellar component of galaxies and their host halos during the epoch of reionization (5 ≤ z ≤ 10) using the CROC (Cosmic Reionization on Computers) simulations. We compare simulated galaxies with observations and find that CROC underpredicts the abundance of luminous galaxies when compared to observed UV luminosity functions, and analogously the most massive galaxies when compared to observed stellar mass functions. We can trace the deficit of star formation to high redshifts, where the slope of the star formation rate to stellar mass relation is consistent with observations, but the normalization is systematically low. This results in a star formation rate density and stellar mass density that are systematically offset from observations. However, the less luminous or lower stellar mass objects have luminosities and stellar masses that agree fairly well with observational data. We explore the stellar-to-halo mass ratio (SHMR), a key quantity that is difficult to measure at high redshifts and that models do not consistently predict. In CROC, the SHMR decreases with redshift, a trend opposite to some abundance-matching studies. These discrepancies uncover where future effort should be focused in order to improve the fidelity of modeling cosmic reionization. We also compare the CROC galaxy bias with observational measurements using Lyman-break galaxy samples, finding reasonable consistency.

Keywords: Hydrodynamical simulations, Reionization, Galaxies
The Proper Motion of the Central Compact Object RX J0822-4300 in the Supernova Remnant Puppis A, Revisited. We present an improved proper-motion measurement of the central compact object RX J0822-4300, located in the supernova remnant Puppis A. By employing a new data set taken in 2019 February by the High Resolution Camera on board the Chandra X-ray Observatory, we approximately double the available temporal baseline for our analysis to slightly more than 19 yr (7000 days). We correct for the astrometric inaccuracy of Chandra using calibrator stars with known optical positions that are detected in all observations. Thereby, we obtain absolute positions of RX J0822-4300 accurate to around $0\buildrel{\prime\prime}\over{.} 1$ and from these a new best estimate for its total proper motion of ${\mu }_{\mathrm{tot}}=(80.4\pm 7.7)\,\mathrm{mas}\,{\mathrm{yr}}^{-1}$. For a remnant distance of 2 kpc, this corresponds to a projected kick velocity of $(763\pm 73)\ \,\mathrm{km}\,{{\rm{s}}}^{-1}$ at a position angle of ${\phi }_{0}={(247.8\pm 4.4)}^{\circ }$. The proper-motion measurement of RX J0822-4300 is used for discussing the kinematic age of Puppis A.

Keywords: Neutron stars, X-ray astronomy, X-ray point sources, Pulsars, Supernova remnants, Proper motions, Compact objects
A New Method to Constrain Neutron Star Structure from Quasi-periodic Oscillations. We develop a new method to measure neutron star (NS) parameters and derive constraints on the equation of state (EoS) of dense matter by fitting the frequencies of simultaneous quasi-periodic oscillation (QPO) modes observed in the X-ray flux of accreting NSs in low-mass X-ray binaries. To this aim, we calculate the fundamental frequencies of geodesic motion around rotating NSs based on an accurate general-relativistic approximation for their external spacetime. Once the fundamental frequencies are related to the observed frequencies through a QPO model, they can be fit to the data to obtain estimates of the three parameters describing the spacetime, namely the NS mass, angular momentum and quadrupole moment. From these parameters we derive information on the NS structure and EoS. We present a proof of principle of our method applied to pairs of kHz QPO frequencies observed from three systems (4U1608-52, 4U0614+09, and 4U1728-34). We identify the kHz QPOs with the azimuthal and the periastron precession frequencies of matter orbiting the NS, and via our Bayesian inference technique we derive constraints on the neutrons stars' masses and radii. This method is applicable to other geodesic-frequency-based QPO models.

Keywords: Neutron stars, Low-mass x-ray binary stars, Gravitation
A Gaia-based Catalog of Candidate Stripped Nuclei and Luminous Globular Clusters in the Halo of Centaurus A. Tidally stripped galaxy nuclei and luminous globular clusters (GCs) are important tracers of the halos and assembly histories of nearby galaxies, but are difficult to reliably identify with typical ground-based imaging data. In this paper we present a new method to find these massive star clusters using Gaia DR2, focusing on the massive elliptical galaxy Centaurus A (Cen A). We show that stripped nuclei and GCs are partially resolved by Gaia at the distance of Cen A, showing characteristic astrometric and photometric signatures. We use this selection method to produce a list of 632 new candidate luminous clusters in the halo of Cen A out to a projected radius of 150 kpc. Adding in broadband photometry and visual examination improves the accuracy of our classification. In a spectroscopic pilot program we have confirmed five new luminous clusters, which includes the 7th and 10th most luminous GC in Cen A. Three of the newly discovered GCs are further away from Cen A than all previously known GCs. Several of these are compelling candidates for stripped nuclei. We show that our novel Gaia selection method retains at least partial utility out to distances of ∼25 Mpc and hence is a powerful tool for finding and studying star clusters in the sparse outskirts of galaxies in the local universe.

Keywords: Globular star clusters, Galaxy nuclei, Galaxy kinematics, Ultracompact dwarf galaxies, Elliptical galaxies, Star clusters
TXS 0128+554: A Young Gamma-Ray-emitting Active Galactic Nucleus with Episodic Jet Activity. We have carried out a Chandra X-ray and multifrequency radio Very Long Baseline Array study of the active galactic nucleus (AGN) TXS 0128+554, which is associated with the Fermi γ-ray source 4FGL J0131.2+5547. The AGN is unresolved in a target 19.3 ks Chandra image, and its spectrum is well fit by a simple absorbed power-law model, with no distinguishable spectral features. Its relatively soft X-ray spectrum compared to other compact symmetric objects (CSOs) may be indicative of a thermal emission component, for which we were able to obtain an upper temperature limit of kT = 0.08 keV. The compact radio morphology and measured advance speed of 0.32 c ± 0.07 c indicate a kinematic age of only 82 yr ± 17 yr, placing TXS 0128+554 among the youngest members of the CSO class. The lack of compact, inverted spectrum hotspots and an emission gap between the bright inner jet and outer radio lobe structure indicate that the jets have undergone episodic activity, and were relaunched a decade ago. The predicted γ-ray emission from the lobes, based on an inverse Compton-emitting cocoon model, is three orders of magnitude below the observed Fermi-LAT flux. A comparison to other Fermi-detected and non-Fermi-detected CSOs with redshift z &lt; 0.1 indicates that the γ-ray emission likely originates in the inner jet/core region, and that nearby, recently launched AGN jets are primary candidates for detection by the Fermi-LAT instrument.

Keywords: Jets, Radio jets, Extragalactic radio sources, Very long baseline interferometry, Relativistic jets, Radio lobes, Radio galaxies, Active galactic nuclei, X-ray active galactic nuclei, Gamma-ray astronomy
Uncovering Magnetic Turbulence in Young Supernova Remnants with Polarized X-Ray Imaging. Observations of young supernova remnants (SNRs) in X-rays and γ-rays have provided conclusive evidence for particle acceleration to at least TeV energies. Analysis of high-spatial-resolution X-ray maps of young SNRs has indicated that the particle acceleration process is accompanied by strong nonadiabatic amplification of magnetic fields. If Fermi acceleration is the mechanism producing the energetic cosmic rays (CRs), the amplified magnetic field must be turbulent, and CR-driven instabilities are among the most probable mechanisms for converting the shock ram pressure into magnetic turbulence. The development and evolution of strong magnetic turbulence in collisionless plasmas forming SNR shells are complicated phenomena which include the amplification of magnetic modes, anisotropic mode transformations at shocks, as well as the nonlinear physics of turbulent cascades. Polarized X-ray synchrotron radiation from ultrarelativistic electrons accelerated in the SNR shock is produced in a thin layer immediately behind the shock and is not subject to the Faraday depolarization effect. These factors open up possibilities to study some properties of magnetic turbulence, and here we present polarized X-ray synchrotron maps of SNR shells assuming different models of magnetic turbulence cascades. It is shown that different models of anisotropic turbulence can be distinguished by measuring the predominant polarization angle direction. We discuss the detection of these features in Tycho's SNR with the coming generation of X-ray polarimeters such as the Imaging X-ray Polarimetry Explorer.

Keywords: Space plasmas, High energy astrophysics, Plasma astrophysics, Supernova remnants, Starlight polarization, Interstellar synchrotron emission, Shocks, Particle astrophysics, Cosmic rays
Using the "Ghost Front" to Predict the Arrival Time and Speed of CMEs at Venus and Earth. Using in situ measurements and remote-sensing observations, we study two coronal mass ejections (CMEs) that left the Sun on 2012 June 13-14 and impacted both Venus and Earth while the planets were in close radial alignment. The two CMEs generate multiple fronts in Solar Terrestrial Relations Observatory (STEREO)/Heliospheric Imager (HI) images, which can also be observed in the "J-map" as bifurcated features. We present the "ghost front" model to combine remote observations from STEREO/SECCHI and in situ observations from the Wind and Venus Express (VEX) spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the observations of multiple fronts to a kinematically evolving flux rope model and assuming the CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson scattered light returned from the flank and nose of a single front for each CME. An interaction takes place between CME-1 and CME-2 that can be observed in the HI-1 field of view (FOV) before CME-1 encounters Venus. The multipoint in situ observations of the shock-CME interaction event serve as further evidence of the interaction between CMEs. The arrival times calculated from the ghost front model are within 2.5 hr of those observed at VEX and Wind. Our analysis indicates that ghost fronts could provide information about the longitudinally extended shape of the CME in the FOV of HI-1, which can be used to improve the forecast of interplanetary CME arrival time at Earth.

Keywords: Space weather, Solar coronal mass ejections, Heliosphere
Unveiling the Hierarchical Structure of Open Star Clusters: The Perseus Double Cluster. We introduce a new kinematic method to investigate the structure of open star clusters. We adopt a hierarchical clustering algorithm that uses the celestial coordinates and the proper motions of the stars in the field of view of the cluster to estimate a proxy of the pairwise binding energy of the stars and arrange them in a binary tree. The cluster substructures and their members are identified by trimming the tree at two thresholds, according to the σ-plateau method. Testing the algorithm on 100 mock catalogs shows that, on average, the membership of the identified clusters is (91.5 ± 3.5)% complete and the fraction of unrelated stars is (10.4 ± 2.0)%. We apply the algorithm to the stars in the field of view of the Perseus double cluster from the Data Release 2 of Gaia. This approach identifies a single structure, Sub1, that separates into two substructures, Sub1-1 and Sub1-2. These substructures coincide with h Per and χ Per: the distributions of the proper motions and the color-magnitude diagrams of the members of Sub1-1 and Sub1-2 are fully consistent with those of h Per and χ Per reported in the literature. These results suggest that our hierarchical clustering algorithm can be a powerful tool to unveil the complex kinematic information of star clusters.

Keywords: Stellar kinematics, Astronomy data analysis, Open star clusters, Astronomy data visualization, Single-linkage hierarchical clustering