adsabs/SciX_UAT_keywords huggingface dataset:
An Investigation of Open Clusters Berkeley 68 and Stock 20 Using CCD UBV and Gaia DR3 Data

We performed detailed photometric and astrometric analyses of the open star clusters Berkeley 68 and Stock 20. This was based on ground-based CCD UBV photometric data complemented by space-based Gaia Data Release 3 (DR3) photometry and astrometry. A total of 198 and 51 stars were identified as likely cluster members for Berkeley 68 and Stock 20, respectively. Two-color diagrams were used to derive the reddening and photometric metallicity for each cluster. The reddening for Berkeley 68 and Stock 20 is E(B - V) = 0.520 ± 0.032 mag and 0.400 ± 0.048 mag, respectively. Photometric metallicity [Fe/H] is -0.13 ± 0.08 dex for Berkeley 68 and -0.01 ± 0.06 dex for Stock 20. Keeping as constant reddening and metallicity, we determined the distance moduli and ages of the clusters through fitting isochrones to the UBV and Gaia-based color-magnitude diagrams. Photometric distances are d = 3003 ± 165 pc for Berkeley 68 and 2911 ± 216 pc for Stock 20. The cluster ages are 2.4 ± 0.2 Gyr and 50 ± 10 Myr for Berkeley 68 and Stock 20, respectively. Present-day mass function slopes were found to be Γ = 1.38 ± 0.71 and Γ = 1.53 ± 0.39 for Berkeley 68 and Stock 20, respectively. These values are compatible with the value of Salpeter. The relaxation times were estimated as 32.55 and 23.17 Myr for Berkeley 68 and Stock 20, respectively. These times are less than the estimated cluster ages, indicating that both clusters are dynamically relaxed. Orbit integration was carried out only for Berkeley 68 since radial velocity data were not available for Stock 20. Analysis indicated that Berkeley 68 was born outside the solar circle and belongs to the thin-disk component of the Milky Way.

Keywords: open star clusters
Complementary Mass Spectral Analysis of Isomeric O-bearing Organic Compounds and Fragmentation Differences through Analog Techniques for Spaceborne Mass Spectrometers

Mass spectrometers on board spacecraft typically use either impact ionization or electron ionization (EI) as ion sources. Understanding the similarities and differences in the spectral signatures and fragmentation patterns produced by different techniques in mass spectrometry could elucidate the composition of organic compounds. Here we present a comparison between the mass spectra obtained through laser-induced liquid beam ion desorption (LILBID; proven to simulate the impact ionization mass spectra of ice grains) and EI mass spectra of pairs of low-mass, isomeric aldehydes and ketones. Our comparison confirms that EI produces more fragmentation of carbonyl compounds, particularly aldehydes, than LILBID. We find protonated molecular ions [M+H]+ in LILBID but molecular ions [M]+ in EI spectra. From the evaluated species, LILBID generally produces oxygen-carrying fragment ions (e.g., [CHO]+ and [C2H3O]+) in the mass ranges 26-30 and 39-44 u, while in EI, most ions in these ranges correspond to hydrocarbon fragments. The LILBID spectra additionally show mostly protonated oxygen-bearing fragments [CH3O]+ and [C2H5O]+ at m/z 31 and 45, less commonly observed in EI spectra. We observe a decrease in the relative intensities of cation fragment mass lines between m/z 26 and 33 and an increase between m/z 39 and 45, with an increasing carbon number for ketones and aldehydes with LILBID and EI, respectively. Our study provides a basis for complementary compositional analysis to identify the structural properties of organic species in a space environment using different spaceborne mass spectrometers (e.g., SUrface Dust Analyzer and MAss Spectrometer for Planetary EXploration) on board NASA's future Europa Clipper space mission.

Keywords: planetary science; europa; enceladus; mass spectrometry; astrobiology
A 60 kpc Galactic Wind Cone in NGC 3079

Galactic winds are associated with intense star formation and active galactic nuclei. Depending on their formation mechanism and velocity, they may remove a significant fraction of gas from their host galaxies, thus suppressing star formation, enriching the intergalactic medium, and shaping the circumgalactic gas. However, the long-term evolution of these winds remains mostly unknown. We report the detection of a wind from NGC 3079 to at least 60 kpc from the galaxy. We detect the wind in far-ultraviolet (FUV) line emission to 60 kpc (as inferred from the broad FUV filter in the Galaxy Evolution Explorer) and X-rays to at least 30 kpc. The morphology, luminosities, temperatures, and densities indicate that the emission comes from shocked material, and the O/Fe ratio implies that the X-ray-emitting gas is enriched by Type II supernovae. If so, the speed inferred from simple shock models is about 500 km s-1, which is sufficient to escape the galaxy. However, the inferred kinetic energy in the wind from visible components is substantially smaller than canonical hot superwind models.

Keywords: galactic winds; starburst galaxies; late-type galaxies
Exploring the Evolution of Stellar Rotation Using Galactic Kinematics

The rotational evolution of cool dwarfs is poorly constrained after ∼1-2 Gyr due to a lack of precise ages and rotation periods for old main-sequence stars. In this work, we use velocity dispersion as an age proxy to reveal the temperature-dependent rotational evolution of low-mass Kepler dwarfs and demonstrate that kinematic ages could be a useful tool for calibrating gyrochronology in the future. We find that a linear gyrochronology model, calibrated to fit the period- ${T}_{\mathrm{eff}}$ relationship of the Praesepe cluster, does not apply to stars older than around 1 Gyr. Although late K dwarfs spin more slowly than early-K dwarfs when they are young, at old ages, we find that late K dwarfs rotate at the same rate or faster than early-K dwarfs of the same age. This result agrees qualitatively with semiempirical models that vary the rate of surface-to-core angular momentum transport as a function of time and mass. It also aligns with recent observations of stars in the NGC 6811 cluster, which indicate that the surface rotation rates of K dwarfs go through an epoch of inhibited evolution. We find that the oldest Kepler stars with measured rotation periods are late K and early M dwarfs, indicating that these stars maintain spotted surfaces and stay magnetically active longer than more massive stars. Finally, based on their kinematics, we confirm that many rapidly rotating GKM dwarfs are likely to be synchronized binaries.

Keywords: stellar evolution; low mass stars; late-type stars; stellar phenomena; solar analogs; stellar activity; milky way disk; milky way dynamics; stellar magnetic fields
Cometary Activity Begins at Kuiper Belt Distances: Evidence from C/2017 K2

We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 ≲ rH ≲ 16 au. The comet continues to be characterized by a coma of submillimeter-sized and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross section of the coma, C, is related to the heliocentric distance by a power law, $C\propto {r}_{H}^{-s}$ <!-- --> ,with heliocentric index s = 1.14 ± 0.05. This dependence is significantly weaker than the rH-2 variation of the insolation as a result of two effects. These are, first, the heliocentric dependence of the dust velocity and, second, a lag effect due to very slow-moving particles ejected long before the observations were taken. A Monte Carlo model of the photometry shows that dust production beginning at rH ∼ 35 au is needed to match the measured heliocentric index, with only a slight dependence on the particle size distribution. Mass-loss rates in dust at 10 au are of order 103 kg s-1, while loss rates in gas may be much smaller, depending on the unknown dust to gas ratio. Consequently, the ratio of the nongravitational acceleration to the local solar gravity, α', may, depending on the nucleus size, attain values of ∼10-7 ≲ α' ≲ 10-5, comparable to values found in short-period comets at much smaller distances. Nongravitational acceleration in C/2017 K2 and similarly distant comets, while presently unmeasured, may limit the accuracy with which we can infer the properties of the Oort cloud from the orbits of long-period comets.

Keywords: small solar system bodies; long period comets; comet nuclei; comae
Rapid Evolution of Volatile CO from the Protostellar Disk Stage to the Protoplanetary Disk Stage

Recent observations show that the CO gas abundance, relative to H2, in many 1-10 Myr old protoplanetary disks may be heavily depleted by a factor of 10-100 compared to the canonical interstellar medium (ISM) value of 10-4. When and how this depletion happens can significantly affect compositions of planetesimals and atmospheres of giant planets. It is therefore important to constrain whether the depletion occurs already at the earliest protostellar disk stage. Here we present spatially resolved observations of C18O, C17O, and 13C18O J = 2-1 lines in three protostellar disks. We show that the C18O line emits from both the disk and the inner envelope, while C17O and 13C18O lines are consistent with a disk origin. The line ratios indicate that both C18O and C17O lines are optically thick in the disk region, and only the 13C18O line is optically thin. The line profiles of the 13C18O emissions are best reproduced by Keplerian gaseous disks at similar sizes as their mm-continuum emissions, suggesting small radial separations between the gas and mm-sized grains in these disks, in contrast to the large separation commonly seen in protoplanetary disks. Assuming a gas-to-dust ratio of 100, we find that the CO gas abundances in these protostellar disks are consistent with the ISM abundance within a factor of 2, nearly one order of magnitude higher than the average value of 1-10 Myr old disks. These results suggest that there is a fast, ∼1 Myr, evolution of the abundance of CO gas from the protostellar disk stage to the protoplanetary disk stage.

Keywords: protoplanetary disks; circumstellar disks; astrochemistry; molecular gas; protostars
An Equation of State for Magnetized Neutron Star Matter and Tidal Deformation in Neutron Star Mergers

We derive an equation of state (EOS) for magnetized charge-neutral nuclear matter relevant for a neutron star (NS). The calculations are performed within an effective chiral model based on the generalization of the σ model with nonlinear self-interactions of the σ mesons along with the ρ-σ cross-coupling term. This model is extended by introducing the contributions of a strong magnetic field on the charged particles. The contributions arising from the effects of the magnetic field on the Dirac sea of charged baryons are also included. The resulting EOS for the magnetized dense matter is used to investigate the NS properties like its mass, radius, and tidal deformability. The magnitude of the magnetic field at the core of the NS considered here is in the range of 1015-1018 G, for which the relative deformation from spherical symmetry turns out to be less than 1%, giving a post facto justification for the spherically symmetric treatment of the NS structure. The dimensionless tidal deformability Λ1.4 is 526 for an NS with mass 1.4 M⊙, which is consistent with the recent observation of GW 170817. The maximum mass of the NS in the presence of a strong magnetic field is consistent with the observational constraints on the mass of the pulsar PSR J0348-0432, and its radius at a mass of 1.4 M⊙ is also in agreement with the empirical bounds.

Keywords: neutron stars
An Implicit Finite Volume Scheme to Solve the Time-dependent Radiation Transport Equation Based on Discrete Ordinates

We describe a new algorithm to implicitly solve the time-dependent, frequency-integrated radiation transport (RT) equation, which is coupled to an explicit solver for equations of magnetohydrodynamics (MHD) using Athena++. The radiation field is represented by specific intensities along discrete rays, which are evolved using a conservative finite volume approach for both Cartesian and curvilinear coordinate systems. All terms for spatial transport of photons and interactions between gas and radiation are calculated implicitly together. An efficient Jacobi-like iteration scheme is used to solve the implicit equations. This removes any time-step constraint due to the speed of light in RT. We evolve the specific intensities in the lab frame to simplify the transport step. The lab frame specific intensities are transformed to the comoving frame via Lorentz transformation when the source term is calculated. Therefore, the scheme does not need any expansion in terms of v/c. The radiation energy and momentum source terms for the gas are calculated via direct quadrature in the angular space. The time step for the whole scheme is determined by the normal Courant-Friedrichs-Lewy condition in the MHD module. We provide a variety of test problems for this algorithm, including both optically thick and thin regimes, and for both gas and radiation pressure-dominated flows to demonstrate its accuracy and efficiency.

Keywords: computational methods; radiative transfer
Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey

We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules N2H+, HC3N, and CCS at 82-94 GHz using the Nobeyama 45 m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N2H+ and HC3N line emissions are approximately similar to the distribution of the 850 μm dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850 μm dust continuum emission. Occasionally (12%), we observe CCS emission, which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect the nonthermal velocity dispersion.

Keywords: interstellar clouds
Revisiting the Relationship between the Long GRB Rate and Cosmic Star Formation History Based on a Large Swift Sample

The exact relationship between the long gamma-ray burst (LGRB) rate and the cosmic star formation rate (CSFR) is essential for using LGRBs as cosmological probes. In this work, we collect a large sample composed of 371 Swift LGRBs with known redshifts and prompt emission properties. We first compare the rest-frame prompt properties of these bursts in different redshift bins, finding negligible redshift evolution of the luminosity of LGRBs with ${L}_{\mathrm{iso}}\gtrsim {10}^{51}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ between z ∼ 1 and z ∼ 4. Then, by utilizing the CSFR obtained from the large-scale cosmological hydrodynamical simulation, the Illustris simulation, we calculate the cumulative redshift distribution of LGRBs under different metallicity thresholds. After comparing with our sample, we find that the predictions with a moderate threshold between $0.3\,{Z}_{\odot }\leqslant {Z}_{\mathrm{th}}\leqslant 1.0\,{Z}_{\odot }$ are consistent with the sample between redshift 0 < z < 3, while at higher redshifts, between 3 < z < 5, all metallicity thresholds fit the data well. When changing to an empirical model based on observations, the predictions show similar results as well. After comparing with the metallicity distribution of the observed LGRB host galaxies between 0 < z < 1, we confirm that the production of LGRBs in galaxies with super-solar metallicity is suppressed. Nevertheless, considering that a significant fraction of stars are born in sub-solar metallicity environments at z ≳ 3, we suggest that, as a first approximation, LGRBs can be used as direct tracers of the CSFR in this redshift range.

Keywords: gamma-ray bursts; star formation; galaxy chemical evolution
The Formation and Eruption of a Sigmoidal Filament Driven by Rotating Network Magnetic Fields

We present the formation and eruption of a sigmoidal filament driven by rotating network magnetic fields (RNFs) near the center of the solar disk, which was observed by the 1 m aperture New Vacuum Solar Telescope at the Fuxian Solar Observatory on 2018 July 12. Counterclockwise RNFs twist two small-scale filaments at their northeastern foot-point region, giving a rotation of nearly 200° within about 140 minutes. The motion of the RNF has a tendency to accelerate at first and then decelerate obviously, as the average rotation speed increased from 10 to 150° hr-1, and then slowed down to 50° hr-1. Coalescence then occurs between filaments F1 and F2. Meanwhile the fine structures in the southwestern region of the filament was involved in another interaction of coalescence. The subsequent EUV brightening due to plasma heating is observed in the two interaction regions. These interacting structures, including F1, F2 and the fine structures in the southwestern region, eventually evolve into a larger-scale sigmoidal filament twisted in the same direction as the RNFs gave. The twist of the sigmoidal filament has exceeded 4π and the filament finally erupted. The motion of the sigmoidal filament remains uniform until a nearby jet collides, causing the filament to erupt faster. These results provide evidence that RNF plays an important role in the formation and eruption of the sigmoidal filament. The phenomena also suggests that the kink instability is the trigger mechanism for the filament eruption.

Keywords: solar chromosphere; solar filaments; solar magnetic fields; solar rotation; quiescent solar prominence; solar activity; solar filament eruptions
SPECULATOR: Emulating Stellar Population Synthesis for Fast and Accurate Galaxy Spectra and Photometry

We present SPECULATOR -- a fast, accurate, and flexible framework for emulating stellar population synthesis (SPS) models for predicting galaxy spectra and photometry. For emulating spectra, we use a principal component analysis to construct a set of basis functions and neural networks to learn the basis coefficients as a function of the SPS model parameters. For photometry, we parameterize the magnitudes (for the filters of interest) as a function of SPS parameters by a neural network. The resulting emulators are able to predict spectra and photometry under both simple and complicated SPS model parameterizations to percent-level accuracy, giving a factor of 103-104 speedup over direct SPS computation. They have readily computable derivatives, making them amenable to gradient-based inference and optimization methods. The emulators are also straightforward to call from a GPU, giving an additional order of magnitude speedup. Rapid SPS computations delivered by emulation offers a massive reduction in the computational resources required to infer the physical properties of galaxies from observed spectra or photometry and simulate galaxy populations under SPS models, while maintaining the accuracy required for a range of applications.

Keywords: galaxies; neural networks; galaxy photometry
Statistical Properties of Superflares on Solar-type Stars: Results Using All of the Kepler Primary Mission Data

We report the latest statistical analyses of superflares on solar-type (G-type main-sequence; effective temperature is 5100-6000 K) stars using all of the Kepler primary mission data and Gaia Data Release 2 catalog. We updated the flare detection method from our previous studies by using a high-pass filter to remove rotational variations caused by starspots. We also examined the sample biases on the frequency of superflares, taking into account gyrochronology and flare detection completeness. The sample sizes of solar-type and Sun-like stars (effective temperature is 5600-6000 K and rotation period is over 20 days in solar-type stars) are ∼4 and ∼12 times, respectively, compared with Notsu et al. As a result, we found 2341 superflares on 265 solar-type stars and 26 superflares on 15 Sun-like stars; the former increased from 527 to 2341 and the latter from three to 26 events compared with our previous study. This enabled us to have a more well-established view on the statistical properties of superflares. The observed upper limit of the flare energy decreases as the rotation period increases in solar-type stars. The frequency of superflares decreases as the stellar rotation period increases. The maximum energy we found on Sun-like stars is 4 × 1034 erg. Our analysis of Sun-like stars suggests that the Sun can cause superflares with energies of ∼7 × 1033 erg (∼X700-class flares) and ∼1 × 1034 erg (∼X1000-class flares) once every ∼3000 and ∼6000 yr, respectively.

Keywords: flare stars; optical flares; stellar flares; g dwarf stars; g stars
These are not the Stars You are Looking for: On the Detection of X-Ray Emission from HD 143352

As part of a search for X-ray emission from RV Tau variable stars, we discovered a serendipitous X-ray detection of the closest RV Tau variable star, HD 143352. X-rays were detected in the 0.2-2.0 keV energy band, with most counts detected in the 0.5-1.0 keV band. The emission is consistent with a 106 K plasma and LX ∼ 2 × 1028 erg s-1. This would be the second RV Tau star detected in X-ray emission. However, after estimating the temperature (Teff ∼ 6000 K) and bolometric luminosity (Lbol ∼ 4L⊙) from the spectral energy distribution, we place HD 143352 on the main sequence. These stellar parameters suggest HD 143352 is neither an RV Tau variable nor a post-asymptotic giant branch star nor a super giant, but rather an early F-type main sequence star. The X-ray emission detected from HD 143352 is consistent with coronal-like emission with LX/Lbol ∼ 10-6.

Keywords: rv tauri variable stars; x-ray surveys; f stars; dc stars; stellar activity; stellar classification; henry draper catalog
Estimating the Evolution of Sparks in the Partially Screened Gap of Pulsars from Subpulse Drifting

A novel scheme has been developed to show that the observed phase behavior associated with subpulse drifting from two pulsars, J1034-3224 and J1720-2933, can be used to obtain the magnetic field configuration in the partially screened gap (PSG). The outflowing plasma along the open magnetic field line region of pulsars is generated as a result of spark discharges in an inner acceleration region (IAR) above the polar cap. The IAR has been modeled as a PSG with a steady supply of positively charged ions emitted from the heated polar cap surface dominated by strong non-dipolar magnetic fields. In a PSG the sparks are tightly packed and constrained to be present along the polar cap boundary. The sparks lag behind the rotation of the star during their lifetimes. As a result, the sparking pattern evolves along two different directions in a clockwise and counterclockwise manner around a stationary central spark and can be associated with the observed phenomenon of subpulse drifting. PSR J1034-3224 has four prominent components and exhibits bi-drifting where alternate components show the opposite sense of drifting, while PSR J1720-2933 has a single component profile and shows systematically coherent drift bands. We show that the differences in their drifting behavior can be directly linked to different natures of the non-dipolar surface magnetic field configurations.

Keywords: pulsars; radio pulsars