Sazuna/UAT_keywords huggingface dataset:
A New Space Weather Tool for Identifying Eruptive Active Regions. One of the main goals of solar physics is the timely identification of eruptive active regions. Space missions such as Solar Orbiter or future space weather forecasting missions would largely benefit from this achievement. Our aim is to produce a relatively simple technique that can provide real-time indications or predictions that an active region will produce an eruption. We expand on the theoretical work of Pagano et al. that was able to distinguish eruptive from non-eruptive active regions. From this, we introduce a new operational metric that uses a combination of observed line-of-sight magnetograms, 3D data-driven simulations, and the projection of the 3D simulations forward in time. Results show that the new metric correctly distinguishes active regions as eruptive when observable signatures of eruption have been identified and as non-eruptive when there are no observable signatures of eruption. After successfully distinguishing eruptive from non-eruptive active regions we illustrate how this metric may be used in a “real-time” operational sense were three levels of warning are categorized. These categories are: high risk (red), medium risk (amber), and low risk (green) of eruption. Through considering individual cases, we find that the separation into eruptive and non-eruptive active regions is more robust the longer the time series of observed magnetograms used to simulate the build up of magnetic stress and free magnetic energy within the active region. Finally, we conclude that this proof of concept study delivers promising results where the ability to categorize the risk of an eruption is a major achievement.

Keywords: Solar active region magnetic fields, Space weather, Solar active regions, Solar coronal mass ejections, Solar magnetic fields
Abundance Ratios in GALAH DR2 and Their Implications for Nucleosynthesis. Using a sample of 70,924 stars from the second data release of the GALAH optical spectroscopic survey, we construct median sequences of [X/Mg] versus [Mg/H] for 21 elements, separating the high-α/“low-Ia” and low-α/“high-Ia” stellar populations through cuts in [Mg/Fe]. Previous work with the near-IR APOGEE survey has shown that such sequences are nearly independent of location in the Galactic disk, implying that they are determined by stellar nucleosynthesis yields with little sensitivity to other chemical evolution aspects. The separation between the two [X/Mg] sequences indicates the relative importance of prompt and delayed enrichment mechanisms, while the sequences’ slopes indicate metallicity dependence of the yields. GALAH and APOGEE measurements agree for some of their common elements, but differ in sequence separation or metallicity trends for others. GALAH offers access to nine new elements. We infer that about 75% of solar C comes from core-collapse supernovae and 25% from delayed mechanisms. We find core-collapse fractions of 60%-80% for the Fe-peak elements Sc, Ti, Cu, and Zn, with strong metallicity dependence of the core-collapse Cu yield. For the neutron capture elements Y, Ba, and La, we infer large delayed contributions with non-monotonic metallicity dependence. The separation of the [Eu/Mg] sequences implies that at least ∼30% of Eu enrichment is delayed with respect to star formation. We compare our results to predictions of several supernova and asymptotic giant branch yield models; C, Na, K, Mn, and Ca all show discrepancies with models that could make them useful diagnostics of nucleosynthesis physics.

Keywords: Stellar abundances, Galaxy abundances, Nucleosynthesis, Stellar nucleosynthesis
The Role of C/O in Nitrile Astrochemistry in PDRs and Planet-forming Disks. Complex nitriles, such as HC3N, and CH3CN, are observed in a wide variety of astrophysical environments, including at relatively high abundances in photon-dominated regions (PDRs) and the ultraviolet exposed atmospheres of planet-forming disks. The latter have been inferred to be oxygen-poor, suggesting that these observations may be explained by organic chemistry in C-rich environments. In this study we first explore if the PDR complex nitrile observations can be explained by gas-phase PDR chemistry alone if the elemental C/O ratio is elevated. In the case of the Horsehead PDR, we find that gas-phase chemistry with C/O ≳ 0.9 can indeed explain the observed nitrile abundances, increasing predicted abundances by several orders of magnitude compared to standard C/O assumptions. We also find that the nitrile abundances are sensitive to the cosmic-ray ionization treatment, and provide constraints on the branching ratios between CH3CN and CH3NC productions. In a fiducial disk model, an elevated C/O ratio increases the CH3CN and HC3N productions by more than an order of magnitude, bringing abundance predictions within an order of magnitude to what has been inferred from observations. The C/O ratio appears to be a key variable in predicting and interpreting complex organic molecule abundances in PDRs across a range of scales.

Keywords: Interstellar molecules, Photodissociation regions, Astrochemistry, Computational methods, Protoplanetary disks
Constraining the Equation of State of Neutron Stars through GRB X-Ray Plateaus. The unknown equation of state (EoS) of neutron stars (NSs) is puzzling because of rich non-perturbative effects of strong interaction there. A method to constrain the EoS using the detected X-ray plateaus of gamma-ray bursts (GRBs) is proposed in this paper. Observations show some GRB X-ray plateaus may be powered by strongly magnetized millisecond NSs. The properties of these NSs should then satisfy: (i) the spin-down luminosity of these NSs should be brighter than the observed luminosity of the X-ray plateaus; and (ii) the total rotational energy of these NSs should be larger than the total energy of the X-ray plateaus. Through the case study of GRB 170714A, the moment of inertia of NSs is constrained as I&gt; 1.0× {10}45{≤ft(\tfrac{{P}cri}}{1{ms}}\right)}2 {{g}} {cm}}2, where P cri is the critical rotational period that an NS can achieve. The constraint of the radii of NSs according to GRB 080607 is shown in Table 1.

Keywords: Neutron stars, Gamma-ray bursts, Particle astrophysics
The Diffusion Coefficient with Displacement Variance of Energetic Particles Caused by Adiabatic Focusing. The equation κ  zz  = dσ 2/(2dt) describing the relation of the parallel diffusion coefficient κ  zz  with the displacement variance σ 2 (hereafter DCDV) is a well-known formula. In this study, we find that DCDV is only applicable to two kinds of transport equations of the isotropic distribution function, one without cross-terms and the other without a convection term. Here, by employing the more general transport equation, i.e., the variable coefficient differential equation derived from the Fokker-Planck equation, a new equation of κ  zz  as a function of σ 2 is obtained. We find that DCDV is the special case of the new equation. In addition, another equation of κ  zz  as a function of σ 2 corresponding to the telegraph equation is also investigated preliminarily.

Keywords: Interplanetary turbulence, Magnetic fields, Solar energetic particles
Growth of Massive Black Holes at High-z via Accretion Predominantly Driven by Magnetic Outflows. Luminous quasars powered by accreting supermassive black holes (SMBHs) have been found in the early universe at z≳ 7.5, which set a strong constraint on both the seed black hole (BH) mass and the rapid growth of the SMBHs. In this work, we explore how the SMBHs grow through Eddington-limited accretion driven predominantly by magnetic outflows. Most angular momentum and the released gravitational energy in the disk can be removed by magnetic outflows, therefore the mass-accretion rate of the BH can be high even if the disk is radiating at sub-Eddington luminosity. It is found that the SMBH with several billion solar masses discovered at z≳ 7 may be grown through chaotic accretion predominantly driven by magnetic outflows from a stellar mass BH, when the disks are radiating at moderate luminosity (∼0.5 Eddington luminosity) with mild outflows. We find that most SMBHs are spinning at moderate values of spin parameter a *, which implies only a small fraction of quasars may have radio jets.

Keywords: Accretion, Supermassive black holes, Jets, Quasars, Magnetic fields
Mining for Candidates of Galactic Stellar-mass Black Hole Binaries with LAMOST. We study the prospects of searching for black hole (BH) binary systems with a stellar-mass BH and a non-compact visible companion, by utilizing the spectroscopic data of the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST). We simulate the Galactic BH binary population and determine its optical visibility by considering the stellar synthetic population model and the distributions of binary orbital parameters. By convolving the visibility of BH binaries with the LAMOST detection sensitivity, we predict that ≳400 candidate BH binaries can be found by the low-resolution, non-time-domain survey, and ∼50-350 candidates by the LAMOST ongoing medium-resolution, time-domain spectroscopic survey. Most of the candidates are short-period (0.2-2 days) binaries with M-, K-, G-, or F-type companions, in which ∼47% have a mass function (the lower limit of the BH mass) larger than 3 M ⊙. By complementing the LAMOST spectroscopic data with other photometric/spectroscopic surveys or follow-up observations, these candidates could be confirmed. Therefore, by exploring the LAMOST data, we can enlarge the sample of dynamically confirmed BH binaries significantly, which can improve our understanding of the mass distribution of BHs and the stellar evolution model.

Keywords: Compact binary stars, Stellar mass black holes, Stellar dynamics, Spectroscopic binary stars, Radial velocity
Search for Surviving Companions of Progenitors of Young LMC SN Ia Remnants. We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs) and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main-sequence or helium star companions. No obvious candidates of surviving companions are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi Unit Spectroscopic Explorer observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182 ± 0 km s-1 and 213 ± 0 km s-1, respectively, more than 2.5σ from the mean radial velocity of the underlying stellar population, 264 and 270 km s-1, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the supernova progenitors.

Keywords: Large Magellanic Cloud, Supernova remnants, Type Ia supernovae, Companion stars, Interstellar medium
A Cooling Anomaly of High-mass White Dwarfs. Recently, the power of Gaia data has revealed an enhancement of high-mass white dwarfs (WDs) on the Hertzsprung-Russell diagram, called the Q branch. This branch is located at the high-mass end of the recently identified crystallization branch. Investigating its properties, we find that the number density and velocity distribution on the Q branch cannot be explained by the cooling delay of crystallization alone, suggesting the existence of an extra cooling delay. To quantify this delay, we statistically compare two age indicators—the dynamical age inferred from transverse velocity, and the photometric isochrone age—for more than one thousand high-mass WDs (1.08-1.23 M ⊙) selected from Gaia Data Release 2. We show that about 6% of the high-mass WDs must experience an 8 Gyr extra cooling delay on the Q branch, in addition to the crystallization and merger delays. This cooling anomaly is a challenge for WD cooling models. We point out that 22Ne settling in C/O-core WDs could account for this extra cooling delay.

Keywords: Bayesian statistics, Stellar ages, Stellar kinematics, White dwarf stars, Milky Way disk, Hertzsprung Russell diagram
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation. The ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive (&gt;500 {M}☉ ), cold (≤15 K), 3.6-70 μm dark prestellar clump candidates, embedded in infrared dark clouds, were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We have mosaicked each clump (∼1 arcmin2) in continuum and line emission with the 12 m, 7 m, and Total Power (TP) arrays at 224 GHz (1.34 mm), resulting in ∼1.″2 resolution (∼4800 au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or “warm core” line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass (&lt;1 {M}☉ ) cores and no high-mass (&gt;30 {M}☉ ) prestellar cores (maximum mass 11 {M}☉ ). From the prestellar core mass function, we derive a power-law index of 1.17 ± 0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.

Keywords: Infrared dark clouds, Massive stars, Star forming regions, Dust continuum emission, Star formation
Radial Variations in Grain Sizes and Dust Scale Heights in the Protoplanetary Disk around HD 163296 Revealed by ALMA Polarization Observations. The disk of HD 163296 shows ring and gap substructures in observations with the Atacama Large Millimeter/submillimeter Array. In addition, this is the only disk where the rings and gaps are spatially resolved in millimeter-wave polarization measurements. In this paper, we conduct radiative transfer modeling that includes self-scattering polarization to constrain the grain size and its distribution. We found that the grain size and dust scale height are the key parameters for reproducing the radial and azimuthal distributions of the observed polarization signature. Radial variation is mainly determined by grain size. The polarization fraction is high if the particle size is ∼λ/2π it is low if the particle size is larger or smaller than this. In contrast, azimuthal variation in polarization is enhanced if the dust scale height is increased. Based on detailed modeling of the polarization of HD 163296, we found the following radial variations in the grain size and dust scale height. The maximum grain size was 140 μm in the gaps and significantly larger or smaller in the rings. The dust scale height is less than one-third of the gas scale height inside the 70 au ring, and two-thirds of it outside. Furthermore, we constrained the gas turbulence to be α ≲ 1.5 × 10-3 in the 50 au gap and α ∼ 0.015-0.3 in the 90 au gap. The transition in the turbulence strength at the boundary of the 70 au ring indicates the existence of a dead zone.

Keywords: Scattered disk objects, Polarimetry, Protoplanetary disks, Planet formation
A Comprehensive Chandra Study of the Disk Wind in the Black Hole Candidate 4U 1630-472. The mechanisms that drive disk winds are a window into the physical processes that underlie the disk. Stellar-mass black holes are an ideal setting in which to explore these mechanisms, in part because their outbursts span a broad range in mass accretion rate. We performed a spectral analysis of the disk wind found in six Chandra/HETG observations of the black hole candidate 4U 1630-472, covering a range of luminosities over two distinct spectral states. We modeled both wind absorption and extended wind re-emission components using PION, a self-consistent photoionized absorption model. In all but one case, two photoionization zones were required in order to obtain acceptable fits. Two independent constraints on launching radii, obtained via the ionization parameter formalism and the dynamical broadening of the re-emission, helped characterize the geometry of the wind. The innermost wind components (r≃ {10}2-3{GM}/{c}2) tend toward small volume filling factors, high ionization, densities up to n≃ {10}15-16 {cm}}-3, and outflow velocities of ∼0.003c. These small launching radii and large densities require magnetic driving, as they are inconsistent with numerical and analytical treatments of thermally driven winds. Outer wind components (r≃ {10}5{GM}/{c}2) are significantly less ionized and have filling factors near unity. Their larger launching radii, lower densities (n≃ {10}12 {cm}}-3), and outflow velocities (∼0.0007c) are nominally consistent with thermally driven winds. The overall wind structure suggests that these components may also be part of a broader MHD outflow and perhaps better described as magneto-thermal hybrid winds.

Keywords: Accretion, Black hole physics
Improved Coupling of Hydrodynamics and Nuclear Reactions via Spectral Deferred Corrections. Simulations in stellar astrophysics involve the coupling of hydrodynamics and nuclear reactions under a wide variety of conditions, from simmering convective flows to explosive nucleosynthesis. Numerical techniques such as operator splitting (most notably Strang splitting) are usually employed to couple the physical processes, but this can affect the accuracy of the simulation, particularly when the burning is vigorous. Furthermore, Strang splitting does not have a straightforward extension to higher-order integration in time. We present a new temporal integration strategy based on spectral deferred corrections, and describe the second- and fourth-order implementations in the open source, finite-volume, compressible hydrodynamics code Castro. One notable advantage to these schemes is that they combine standard low-order discretizations for individual physical processes in a way that achieves an arbitrarily high order of accuracy. We demonstrate the improved accuracy of the new methods on several test problems of increasing complexity.

Keywords: Computational astronomy, Astronomy software, Hydrodynamics, Nucleosynthesis, Computational methods, Nuclear astrophysics, Stellar nucleosynthesis, Astrophysical fluid dynamics
Adiabatic and Radiative Cooling of Relativistic Electrons Applied to Synchrotron Spectra and Light Curves of Gamma-Ray Burst Pulses. We investigate the adiabatic and radiative (synchrotron and inverse-Compton) cooling of relativistic electrons whose injected or initial distribution with energy is a power law. Analytical and numerical results are presented for the cooling-tail and the cooled-injected distribution that develop below and above the typical energy of injected electrons, for the evolution of the peak energy E  p  of the synchrotron emission spectrum. The pulse shape resulting from an episode of electron injection is also analyzed. The synchrotron emission calculated numerically is compared with the spectrum and shape of Gamma-ray burst (GRB) pulses. Both adiabatic and radiative cooling processes lead to a softening of the pulse spectrum, and both types of cooling processes lead to pulses peaking earlier and lasting shorter at higher energy, quantitatively consistent with observations. For adiabatic-dominated electron cooling, a power-law injection rate R  i  suffices to explain the observed power-law GRB low-energy spectra. Synchrotron-dominated cooling leads to power-law cooling-tails that yield the synchrotron standard slope α = -3/2 provided that R  i  ∼ B 2, which is exactly the expectation if the magnetic field is a constant fraction of the post-shock energy density. Increasing (decreasing) R  i  and decreasing (increasing) B(t) lead to harder (softer, respectively) slopes α than the standard value and to nonpower-law (curved) cooling-tails. Inverse-Compton cooling yields four values for the slope α but, as for synchrotron, other R  i  or B histories yield a wider range of slopes and curved low-energy spectra. Feedback between the power-law segments that develop below and above the typical injected electron leads to a synchrotron spectrum with many breaks.

Keywords: Gamma-ray bursts, Non-thermal radiation sources
Planet Formation around Supermassive Black Holes in the Active Galactic Nuclei. As a natural consequence of the elementary processes of dust growth, we discovered that a new class of planets can be formed around supermassive black holes (SMBHs). We investigated a growth path from submicron sized icy dust monomers to Earth-sized bodies outside the “snow line,” located several parsecs from SMBHs in low luminosity active galactic nuclei (AGNs). In contrast to protoplanetary disks, the “radial drift barrier” does not prevent the formation of planetesimals. In the early phase of the evolution, low collision velocity between dust particles promotes sticking; therefore, the internal density of the dust aggregates decreases with growth. When the porous aggregate’s size reaches 0.1-1 cm, the collisional compression becomes effective, and the decrease in internal density stops. Once 10-100 m sized aggregates are formed, they are decoupled from gas turbulence, and the aggregate layer becomes gravitationally unstable, leading to the formation of planets by the fragmentation of the layer, with 10 times the mass of the Earth. The growth timescale depends on the turbulent strength of the circumnuclear disk and the black hole mass M BH, and it is comparable to the AGN’s lifetime (∼108 yr) for low mass (M BH ∼ 106 M ⊙) SMBHs.

Keywords: Interstellar dust, Supermassive black holes, Planetary system formation, Active galactic nuclei, Exoplanet formation