Sazuna/UAT_keywords huggingface dataset:
Particle Acceleration and Heating in Regions of Magnetic Flux Emergence. The interaction between emerging and pre-existing magnetic fields in the solar atmosphere can trigger several dynamic phenomena, such as eruptions and jets. A key element during this interaction is the formation of large-scale current sheets, and eventually their fragmentation that leads to the creation of a strongly turbulent environment. In this paper, we study the kinetic aspects of the interaction (reconnection) between emerging and ambient magnetic fields. We show that the statistical properties of the spontaneously fragmented and fractal electric fields are responsible for the efficient heating and acceleration of charged particles, which form a power-law tail at high energies on sub-second timescales. A fraction of the energized particles escapes from the acceleration volume, with a super-hot component with a temperature close to 150 MK, and with a power-law high-energy tail with an index between -2 and -3. We estimate the transport coefficients in energy space from the dynamics of the charged particles inside the fragmented and fractal electric fields, and the solution of a fractional transport equation, as appropriate for a strongly turbulent plasma, agrees with the test-particle simulations. We also show that the acceleration mechanism is not related to Fermi acceleration, and the Fokker-Planck equation is inconsistent and not adequate as a transport model. Finally, we address the problem of correlations between spatial transport and transport in energy space. Our results confirm the observations reported for high-energy particles (hard X-rays, type III bursts, and solar energetic particles) during the emission of solar jets.

Keywords: Solar energetic particles, Magnetohydrodynamics, Solar magnetic flux emergence, Solar magnetic reconnection
Density Conversion between 1D and 3D Stellar Models with <SUP>1D</SUP>MESA2HYDRO<SUP>3D</SUP>. We present 1DMESA2HYDRO3D, an open-source, Python-based software tool that provides an accessible means of generating physically motivated initial conditions (ICs) for hydrodynamical simulations from 1D stellar structure models. We test 1DMESA2HYDRO3D on five stellar models generated with the MESA stellar evolution code and verify its capacity as an IC generator with the Phantom smoothed particle hydrodynamics code. Consistency between the input density profiles, the 1DMESA2HYDRO3D-rendered particle distributions, and the state of the distributions after evolution over 10 dynamical timescales is found for model stars ranging in structure and density from a radially extended supergiant to a white dwarf.

Keywords: Stellar structures, Stellar evolutionary models, Astronomy software
New Star Observations with NuSTAR: Flares from Young Stellar Objects in the ρ Ophiuchi Cloud Complex in Hard X-Rays. We study the structure and dynamics of extreme flaring events on young stellar objects (YSOs) observed in hard X-rays by the Nuclear Spectroscopic Telescope Array (NuSTAR). During 2015 and 2016, NuSTAR made three observations of the star-forming region ρ Ophiuchi, each with an exposure ∼50 ks. NuSTAR offers unprecedented sensitivity above ∼7 keV, making this data set the first of its kind. Through improved coverage of hard X-rays, it is finally possible to directly measure the high-energy thermal continuum for hot plasmas and to sensitively search for evidence of nonthermal emission from YSO flares. During these observations, multiple flares were observed, and spectral and timing analyses were performed on three of the brightest flares. By fitting an optically thin thermal plasma model to each of these events, we found flare plasma heated to high temperatures (∼40-80 MK) and determined that these events are ∼1000 times brighter than the brightest flares observed on the Sun. Two of the studied flares showed excess emission at 6.4 keV, and this excess may be attributable to iron fluorescence in the circumstellar disk. No clear evidence for a nonthermal component was observed, but upper limits on nonthermal emission allow for enough nonthermal energy to account for the estimated thermal energy in the flare on protostar IRS 43, which is consistent with the standard model for solar and stellar flares.

Keywords: Stellar x-ray flares, Star forming regions, Stellar activity, Young stellar objects, Pre-main sequence stars, Stellar flares
Galactic Gas Flows from Halo to Disk: Tomography and Kinematics at the Milky Way’s Disk-Halo Interface. We present a novel absorption-line survey using 54 blue horizontal branch stars in the Milky Way halo as background sources for detecting gas flows at the disk-halo interface. Distance measurements to high-latitude (b &gt; 60°) background stars at 3.1-13.4 kpc, combined with unprecedented spatial sampling and spectral resolution, allow us to examine the 3D spatial distribution and kinematics of gas flows near the disk. We detect absorption signatures of extraplanar Ca II and Na I in Keck HIRES spectra and find that their column densities exhibit no trend with distance to the background sources, indicating that these clouds lie within 3.1 kpc of the disk. We calculate covering fractions of f Ca II  = 63%, f Na I  = 26%, and f H I  = 52%, consistent with a picture of the circumgalactic medium (CGM) that includes multiphase clouds containing small clumps of cool gas within hotter, more diffuse gas. Our measurements constrain the scale of any substructure within these cool clouds to &lt;0.5 kpc. Ca II and Na I absorption features exhibit an intermediate-velocity (IV) component inflowing at velocities of -75 km s-1 &lt;v &lt; -25 km s-1 relative to the local standard of rest, consistent with previously studied H I structures in this region. We report the new detection of an inflow velocity gradient Δv  z  ∼ 6-9 km s-1 kpc-1 across the Galactic plane. These findings place constraints on the physical and kinematic properties of CGM gas flows through the disk-halo interface and support a galactic fountain model in which cold gas rains back onto the disk.

Keywords: Galaxy fountains, Galaxy kinematics, Circumgalactic medium, Milky Way Galaxy fountains, Milky Way Galaxy, Galaxy processes
Mimetic DBI Inflation in Confrontation with Planck2018 Data. We study mimetic gravity in the presence of a Dirac-Born-Infeld (DBI)-like term, which is a non-canonical setup of the scalar field’s derivatives. We consider two general cases with varying and constant sound speeds and construct the potentials for both the DBI and mimetic DBI (MDBI) models. By considering the power-law scale factor as a = a 0 t  n , we search for the observational viability of these models. We show that the MDBI model in some ranges of the parameter space is free from ghost and gradient instabilities. By studying the behavior of r-n  s  and α  s -n  s  in confrontation with Planck2018 data, we find some constraints on the model’s parameters. We show that, for the case with varying sound speed, power-law DBI inflation is not consistent with Planck2018 TT, TE, EE+lowE+lensing data, but the MDBI inflation is consistent with the same data at 95% confidence level, in some ranges of the model’s parameter space such as 40 ≤ n ≤ 55 the model is also free from instabilities in these ranges of parameters. For a constant sound speed, we study both DBI and MDBI models numerically by adopting some sample values of c  s , and find n ∼ 102 for the DBI model and n ∼ 10 for the MDBI model. We also compare the results with Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO data and see that the DBI and MDBI models with varying sound speed are ruled out by these joint data. However, these models with constant sound speed are consistent with the same data, with n ∼ 102 for the DBI model and n ∼ 10 for the MDBI model. In this case, we find some tighter constraints on the corresponding sound speed.

Keywords: Early universe, Cosmological models, Inflationary universe
Relativistic Sweet-Parker Current Sheet and Its Macroscopic Evolution. The problem of the relativistic Sweet-Parker current sheet is investigated, incorporating the effects of resistivity and thermal inertia. The scaling laws of the steady-state current sheet are obtained, and generalizations are carried out to include pair processes. We study the macroscopic evolutions of the spontaneous current sheet, including thinning, stretching, and both at the same time, which are critical for understanding the processes in an evolving current sheet.

Keywords: Relativity, Plasma astrophysics, Magnetic fields
The Impact of Pair-instability Mass Loss on the Binary Black Hole Mass Distribution. A population of binary black hole mergers has now been observed in gravitational waves by Advanced LIGO and Virgo. The masses of these black holes appear to show evidence for a pileup between 30 and 45 M ⊙ and a cutoff above ∼45 M ⊙. One possible explanation for such a pileup and subsequent cutoff are pulsational pair-instability supernovae (PPISNe) and pair-instability supernovae (PISNe) in massive stars. We investigate the plausibility of this explanation in the context of isolated massive binaries. We study a population of massive binaries using the rapid population synthesis software COMPAS, incorporating models for PPISNe and PISNe. Our models predict a maximum black hole mass of 40 M ⊙. We expect ∼10% of all binary black hole mergers at redshift z = 0 will include at least one component that went through a PPISN (with mass 30-40 M ⊙), constituting ∼20%-50% of binary black hole mergers observed during the first two observing runs of Advanced LIGO and Virgo. Empirical models based on fitting the gravitational-wave mass measurements to a combination of a power law and a Gaussian find a fraction too large to be associated with PPISNe in our models. The rates of PPISNe and PISNe track the low metallicity star formation rate, increasing out to redshift z = 2. These predictions may be tested both with future gravitational-wave observations and with observations of superluminous supernovae.

Keywords: Gravitational wave astronomy, Supernovae, Gravitational waves, Black holes
Quantifying the Propagation of Fast Coronal Mass Ejections from the Sun to Interplanetary Space by Combining Remote Sensing and Multi-point In Situ Observations. In order to have a comprehensive view of the propagation and evolution of coronal mass ejections (CMEs) from the Sun to deep interplanetary space beyond 1 au, we carry out a kinematic analysis of seven CMEs in solar cycle 23. The events are required to have coordinated coronagraph observations, interplanetary type II radio bursts, and multi-point in situ measurements at the Earth and Ulysses. A graduated cylindrical shell model, an analytical model without free parameters, and a magnetohydrodynamic model are used to derive CME kinematics near the Sun, to quantify the CME/shock propagation in the Sun-Earth space, and to connect in situ signatures at the Earth and Ulysses, respectively. We find that each of the seven CME-driven shocks experienced a major deceleration before reaching 1 au and thereafter propagated with a gradual deceleration from the Earth to larger distances. The resulting CME/shock propagation profile for each case is roughly consistent with all the data, which verifies the usefulness of the simple analytical model for CME/shock propagation in the heliosphere. The statistical analysis of CME kinematics indicates a tendency that the faster the CME, the larger the deceleration, and the shorter the deceleration time period within 1 au. For several of these events, the associated geomagnetic storms were mainly caused by the southward magnetic fields in the sheath region. In particular, the interaction between a CME-driven shock and a preceding ejecta significantly enhanced the pre-existing southward magnetic fields and gave rise to a severe complex geomagnetic storm.

Keywords: Interplanetary shocks, Heliosphere, Solar wind, Solar radio emission, Solar coronal mass ejections
Magnetic Structures at the Boundary of the Closed Corona: A Semi-automated Study of S-Web Morphology. Interchange reconnection is thought to play an important role in driving the dynamics of the slow solar wind. To understand the details of this process, it is important to catalog the various magnetic structures that are present at the boundary between open and closed magnetic flux. To this end we have developed a numerical method for partitioning the coronal volume into individual flux domains using volume segmentation along layers of high magnetic squashing degree (Q). Our publicly available implementation of this method is able to identify the different magnetic structures within a coronal magnetic field model that define the open-closed boundary and comprise the so-called Separatrix-Web (S-Web). With this we test previous predictions of how different configurations of high-Q arcs within the S-Web are related to coronal magnetic field structures. Here we present our findings from a survey of 11 different potential field source surface models, spanning from 2008 to 2017, which offer a representative sample of the coronal magnetic field across nearly a complete solar cycle. Two key findings of our analysis are that (i) “vertex” structures—where arcs of the S-Web meet away from the heliospheric current sheet—are associated with underlying magnetic dome structures, and (ii) that any given arc of the S-Web is almost equally as likely to be formed by a narrow corridor of open flux (corresponding to a hyperbolic flux tube) as by the separatrix surface of a magnetic null. Together, these findings highlight the importance of a variety of topological configurations for future studies of interchange reconnection and the acceleration of the solar wind.

Keywords: Slow solar wind, Solar magnetic reconnection, Space weather, Solar corona, Magnetic fields
Jellyfish: Ram Pressure Stripping As a Diagnostic Tool in Studies of Cluster Collisions. Prompted by the discovery of A1758N_JFG1, a spectacular case of ram pressure stripping (RPS) in the galaxy cluster A1758N, we investigate the properties of other galaxies suspected to undergo RPS in this equal-mass, post-collision merger. Exploiting constraints derived from Hubble Space Telescope images and Keck longslit spectroscopy, our finding of apparent debris trails and dramatically enhanced star formation rates in an additional seven RPS candidates support the hypothesis that RPS, and hence rapid galaxy evolution in high-density environments, is intricately linked to cluster collisions. Unexpectedly, we find the vast majority of RPS candidates in A1758N to be moving toward us, and in a shared direction as projected on the plane of the sky. We hypothesize that this directional bias is the result of two successive events: (1) the quenching, during and after the first core passage, of star formation in galaxies with an approximately isotropic velocity distribution within the central region of the merger, and (2) RPS events triggered in late-type galaxies falling into the merging system along a filament, possibly enhanced by a shock front expanding into the outskirts of the southeastern subcluster. Since this explanation implies that the merger axis of A1758N must be significantly inclined with respect to the plane of the sky, our findings open the possibility of RPS events becoming important diagnostic tools to constrain the geometry of cluster collisions that, due to the orientation of the merger axis, lack the classic observational signatures of face-on mergers.

Keywords: Large-scale structure of the universe, Galaxy structure, Rich galaxy clusters, Star formation, Galaxy evolution, Intracluster medium
Probing CO and N<SUB>2</SUB> Snow Surfaces in Protoplanetary Disks with N<SUB>2</SUB>H<SUP>+</SUP> Emission. Snowlines of major volatiles regulate the gas and solid C/N/O ratios in the planet-forming midplanes of protoplanetary disks. Snow surfaces are the 2D extensions of snowlines in the outer disk regions, where radiative heating results in an increasing temperature with disk height. CO and N2 are two of the most abundant carriers of C, N, and O. N2H+ can be used to probe the snow surfaces of both molecules, because it is destroyed by CO and formed from N2. Here we present Atacama Large Millimeter/submillimeter Array (ALMA) observations of N2H+ at ∼0.″2-0.″4 resolution in the disks around LkCa 15, GM Aur, DM Tau, V4046 Sgr, AS 209, and IM Lup. We find two distinctive emission morphologies: N2H+ is either present in a bright, narrow ring surrounded by extended tenuous emission, or in a broad ring. These emission patterns can be explained by two different kinds of vertical temperature structures. Bright, narrow N2H+ rings are expected in disks with a thick Vertically Isothermal Region above the Midplane (VIRaM) layer (LkCa 15, GM Aur, DM Tau) where the N2H+ emission peaks between the CO and N2 snowlines. Broad N2H+ rings come from disks with a thin VIRaM layer (V4046 Sgr, AS 209, IM Lup). We use a simple model to extract the first sets of CO and N2 snowline pairs and corresponding freeze-out temperatures toward the disks with a thick VIRaM layer. The results reveal a range of N2 and CO snowline radii toward stars of similar spectral type, demonstrating the need for empirically determined snowlines in disks.

Keywords: Interstellar molecules, Protoplanetary disks, Astrochemistry
Hunting Young White Dwarfs at the Center of Planetary Nebulae. We present Gemini-South observations of nine faint and extended planetary nebulae (PNe). Using direct images taken with the spectrograph Gemini-South multi-object spectrograph (GMOS), we built the (u\prime -g\prime ) versus (g\prime -r\prime ) diagrams of the stars in the observed areas which allowed us to consider their geometrical positions and identify the probable central stars of the nebulae. Our stellar spectra of seven stars, also taken with GMOS, indicate that four (and probably two more) objects are white dwarfs of the DAO subtype. Moreover, the white dwarf status of the four stars is confirmed by the parameters T eff and log g derived with the help of theoretical stellar spectra. Given this evidence, we propose that these hot stars are the central ionizing sources of the nebulae. With this work we hope to help improve the current scarce statistics on central white dwarfs in PNe.

Keywords: Planetary nebulae nuclei, White dwarf stars, Planetary nebulae, Subdwarf stars
X-Ray Monitoring of the Magnetar CXOU J171405.7-381031 in Supernova Remnant CTB 37B. We present the results of our 8 yr X-ray monitoring campaign on CXOU J171405.7-381031, the magnetar associated with the faint supernova remnant (SNR) CTB 37B. It is among the youngest by inferred spin-down age, and most energetic in spin-down power of magnetars, and may contribute, at least partially, to the GeV and TeV emission coincident with the SNR. We use a series of Chandra, XMM-Newton, and NuSTAR observations to characterize the timing and spectral properties of the magnetar. The spin-down rate of the pulsar almost doubled in &lt;1 yr and then decreased slowly to a more stable value. Its X-ray flux varied by ≈50%, possibly correlated with the spin-down rate. The 1-79 keV spectrum is well-characterized by an absorbed blackbody plus power-law model with an average temperature of kT = 0.62 ± 0.04 keV and photon index Γ = 0.92 ± 0.16, or by a Comptonized blackbody with kT = 0.55 ± 0.04 keV and an additional hard power law with Γ = 0.70 ± 0.20. In contrast with most magnetars, the pulsed signal is found to decrease with energy up to 6 keV, which is apparently caused by mixing with the hard spectral component that is pulse-phase shifted by ≈0.43 cycles from the soft X-rays. We also analyze the spectrum of the nearby, diffuse nonthermal source XMMU J171410.8-381442, whose relation to the SNR is uncertain.

Keywords: Neutron stars, Magnetars, Compact objects, Pulsars
Detailed Chemical Composition and Orbit of the Newly Discovered Globular Cluster FSR 1758: Implications for the Accretion of the Sequoia Dwarf Galaxy onto the Milky Way. We present detailed chemical abundances, radial velocity, and orbital parameters for FSR 1758, a recently discovered massive cluster in the direction of the Galactic bulge. High-resolution (R ∼ 42,000) spectra were obtained for nine members using the Magellan/Clay telescope instrumented with the MIKE echelle spectrogragh in the wavelength range of ∼4900-8700 Å. Cluster membership was determined using Gaia DR2 proper motions and confirmed with our radial velocity measurements. We find a metallicity of [Fe/H] = -1.58 ± 0.03, consistent with previous photometric estimates, and no significant iron spread. While other studies have suggested that this massive object could be the remnant of a captured dwarf galaxy, our results are consistent with a globular cluster (GC) nature, given its lack of any intrinsic metallicity spread and the Na-O anticorrelation similar to those of other GC. In addition, the small velocity dispersion of 4.9 ± 1.2 km s-1 we find is that typical of a GC. We also confirm a retrograde orbit that appears to be highly eccentric suggesting it is a halo interloper currently in the bulge. We support the hypothesis that FSR 1758 was part of a disrupted dwarf galaxy named Sequoia. Based on observations carried out at the Magellan/Clay telescope under program CN2018B-71.

Keywords: Globular star clusters
Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy. We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in r-process elements, i.e., they have &lt; [{Eu}/{Fe}]&gt; ≈ +0.4 dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in α-elements, i.e., the lower metallicity stars have higher Ca and Ti abundances. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by r-process enhanced stars, Reticulum II, Tucana III’s stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different r-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of r-process enhancement. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Chemically peculiar stars, Dwarf galaxies, Chemical abundances