Sazuna/UAT_keywords huggingface dataset:
The Contour Method: a New Approach to Finding Modes of Nonadiabatic Stellar Pulsations. The contour method is a new approach to calculating the nonadiabatic pulsation frequencies of stars. These frequencies can be found by solving for the complex roots of a characteristic equation constructed from the linear nonadiabatic stellar pulsation equations. A complex-root solver requires an initial trial frequency for each nonadiabatic root. A standard method for obtaining initial trial frequencies is to use a star's adiabatic pulsation frequencies, but this method can fail to converge to nonadiabatic roots, especially as the growth and/or damping rate of the pulsations becomes large. The contour method provides an alternative way to obtain initial trial frequencies that robustly converges to nonadiabatic roots, even for stellar models with extremely nonadiabatic pulsations and thus high growth/damping rates. We describe the contour method implemented in the GYRE stellar pulsation code and use it to calculate the nonadiabatic pulsation frequencies of $10\,{M}_{\odot }$ and $20\,{M}_{\odot }$ β Cephei star models, and of a $0.9\,{M}_{\odot }$ extreme helium star model.

Keywords: Stellar oscillations, Computational methods, Asteroseismology, Astronomy software
The MOSDEF Survey: The Variation of the Dust Attenuation Curve with Metallicity. We derive a UV-optical stellar dust attenuation curve of galaxies at z = 1.4-2.6 as a function of gas-phase metallicity. We use a sample of 218 star-forming galaxies, excluding those with very young or heavily obscured star formation, from the MOSFIRE Deep Evolution Field survey with Hα, Hβ, and [N II]λ 6585 spectroscopic measurements. We constrain the shape of the attenuation curve by comparing the average flux densities of galaxies sorted into bins of dust obscuration using Balmer decrements, i.e., Hα-to-Hβ luminosities. The average attenuation curve for the high-metallicity sample ( $12+\mathrm{log}({\rm{O}}/{\rm{H}})\gt 8.5$ , corresponding to ${M}_{* }\gtrsim {10}^{10.4}$ ${M}_{\odot }$ ) has a shallow slope, identical to that of the Calzetti local starburst curve, and a significant UV 2175 Å extinction bump that is ∼0.5× the strength of the Milky Way bump. On the other hand, the average attenuation curve of the low-metallicity sample ( $12+\mathrm{log}({\rm{O}}/{\rm{H}})\sim 8.2-8.5$ ) has a steeper slope similar to that of the SMC curve, only consistent with the Calzetti slope at the 3σ level. The UV bump is not detected in the low-metallicity curve, indicating the relative lack of the small dust grains causing the bump at low metallicities. Furthermore, we find that on average the nebular reddening (E(B - V)) is a factor of 2 times larger than that of the stellar continuum for galaxies with low metallicities, while the nebular and stellar reddening are similar for galaxies with higher metallicities. The latter is likely due to a high surface density of dusty clouds embedding the star-forming regions but also reddening the continuum in the high-metallicity galaxies.

Keywords: Interstellar dust, Galaxy properties, Interstellar abundances, Chemical abundances, Interstellar dust extinction, Galaxy abundances, Galaxy evolution, High-redshift galaxies, Galaxies
Giant Micropulse Emission in the Vela Pulsar at the C Band. We present here the analysis of giant micropulses from the Vela pulsar. A total of 4187 giant micropulses with peak flux density &gt;2.5 Jy were detected during almost 4 hr of observations carried out with the Yunnan 40 m radio telescope at 6800 MHz. Nine of the giant micropulses arrived approximately 3-4 ms earlier than the peak of average pulse profile, longer than that at lower frequencies. The remaining giant micropulses were clustered into three distributions that correspond to three main emission regions, including four giant micropulses occurring on the trailing edge of the averaged profile. We find that the peak flux density distribution follows a power law with index α ≈ -4. Furthermore, a certain amount of memory is present from the giant micropulse waiting time distribution. Possible emission mechanisms are discussed.

Keywords: Radio pulsars
Inconsistencies Between Local and Global Measures of CME Radial Expansion as Revealed by Spacecraft Conjunctions. The radial expansion of coronal mass ejections (CMEs) is known to occur from remote observations, from the variation of their properties with radial distance, and from local in situ plasma measurements showing a decreasing speed profile throughout the magnetic ejecta (ME). However, little is known on how local measurements compare to global measurements of expansion. Here, we present results from the analysis of 42 CMEs measured in the inner heliosphere by two spacecraft in radial conjunction. The magnetic-field decrease with distance provides a measure of their global expansion. Near 1 au, the decrease in their bulk speed provides a measure of their local expansion. We find that these two measures have little relation with each other. We also investigate the relation between characteristics of CME expansion and CME properties. We find that the expansion depends on the initial magnetic-field strength inside the ME, but not significantly on the magnetic field inside the ME measured near 1 au. This is indirect evidence that CME expansion in the innermost heliosphere is driven by the high magnetic pressure inside the ME, while by the time the MEs reach 1 au, they are expanding due to the decrease in the solar-wind dynamic pressure with distance. We also determine the evolution of the ME tangential and normal magnetic-field components with distance, revealing significant deviations as compared to the expectations from force-free field configurations as well as some evidence that the front half of MEs expand at a faster rate than the back half.

Keywords: Interplanetary magnetic fields, Solar coronal mass ejections
Updated Spin and Orbital Parameters and Energy Dependent Pulse Behaviors of the Accreting Millisecond X-Ray Pulsar IGR J17591-2342. We present our work in updating the spin and orbital parameters for the newly discovered accreting millisecond X-ray pulsar (AMXP) IGR J17591-2342 through pulsar timing and analyzing its energy dependent pulse behaviors. The data being analyzed were collected by Neutron Star Interior Composition ExploreR, which observed this AMXP from 2018 August to October. Using the pulse arrival time delay technique, more accurate spin and orbital parameters were evaluated. From the measured spin frequency derivative, it is estimated that the magnetic field of the neutron star in IGR J17591-2342 is approximately 4 × 108 G. Precise pulse profiles can be made using the updated spin and orbital parameters. The soft phase lag phenomenon that is usually seen in other AMXPs is also observed from ∼4 to 12 keV with a value of 0.06 cycles (1.14 μs). Additionally, the pulsed fractional amplitude increases from 1 to ∼5 keV and then decreases for higher energy bands. We found that these phenomena, as well as the energy spectrum, can be explained by the two-component model with a relatively strong blackbody component and an additional unpulsed disk blackbody component.

Keywords: Accretion, Neutron stars, Millisecond pulsars, Close binary stars, Stellar accretion disks
The Origin of a Distributed Stellar Population in the Star-forming Region W4. Stellar kinematics provides the key to understanding the formation process and dynamical evolution of stellar systems. Here, we present a kinematic study of the massive star-forming region (SFR) W4 in the Cassiopeia OB6 association using the Gaia Data Release 2 and high-resolution optical spectra. This SFR is composed of a core cluster (IC 1805) and a stellar population distributed over 20 pc, which is a typical structural feature found in many OB associations. According to a classical model, this structural feature can be understood in the context of the dynamical evolution of a star cluster. The core-extended structure exhibits internally different kinematic properties. Stars in the core have an almost isotropic motion, and they appear to reach virial equilibrium given their velocity dispersion (0.9 ± 0.3 km s-1) comparable to that in a virial state (∼0.8 km s-1). On the other hand, the distributed population shows a clear pattern of radial expansion. From the N-body simulation for the dynamical evolution of a model cluster in subvirial state, we reproduce the observed structure and kinematics of stars. This model cluster experiences collapse for the first 2 Myr. Some members begin to radially escape from the cluster after the initial collapse, eventually forming a distributed population. The internal structure and kinematics of the model cluster appear similar to those of W4. Our results support the idea that the stellar population distributed over 20 pc in W4 originate from the dynamical evolution of IC 1805.

Keywords: Stellar kinematics, Stellar dynamics, Star formation, Open star clusters, Stellar associations
Faraday Dispersion Function of Disk Galaxies with Axisymmetric Global Magnetic Fields. I.. Faraday tomography is a novel method to probe the three-dimensional structure of magnetic fields of polarized radio sources. In this paper, we investigate the intrinsic Faraday dispersion function (FDF) of disk galaxies extending a simple analytic model of galactic magnetic fields developed in Ideguchi et al. The model consists of axisymmetric coherent fields and turbulent fields, and we consider the effects of inclination, the relative amplitude of coherent and turbulent magnetic fields, and the pitch angle of coherent fields. Our simple model makes it easy to obtain a physical interpretation of FDFs and helps us understand observational results. We find that FDFs generally have two peaks when galaxies are observed with nonzero inclination and the gap between the two peaks, their relative heights, and their widths are dependent on the model parameters. In particular, the gap is strongly dependent on the inclination angle and typically varies by a factor of two when we consider the inclination of 10°-60°, while the relative height varies by less than 20%. These findings provide us with the important lesson that the presence of two peaks in intrinsic FDFs does not necessarily imply the presence of two separate radio sources within a beam and they allow us to estimate the galactic parameters.

Keywords: Galaxy magnetic fields, Galaxy properties, Milky Way magnetic fields
Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project. We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]-[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1″ yr-1; our fastest-moving discovery is WISEA J155349.96+693355.2 (μ ≍ 2"15 yr-1), a possible T-type subdwarf. We also report a newly discovered wide-separation (∼400 au) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5'5 projected separation (∼8700 au if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf.

Keywords: Brown dwarfs, Y dwarfs, Solar neighborhood, Infrared astronomy, Proper motions, Visual binary stars, T dwarfs
Population Modeling of Fast Radio Bursts from Source Properties. We present a method to estimate the source properties of Fast Radio Bursts (FRBs) from observations by assuming a fixed dispersion measure contribution from a Milky Way-like host galaxy, pulse temporal broadening models for turbulent plasma, and a flat FRB energy spectrum. Then we perform Monte Carlo simulations to constrain the properties of the FRB source, its host galaxy, and scattering in the intervening plasma from the observational data of FRBs detected with Parkes. The typical scatter broadening of the intrinsic pulse is found to be considerably small, ≲ 10-2 - 1 ms, from physical models, with the interstellar medium contribution suppressed significantly relative to that of the intergalactic medium. The intrinsic width for nonrepeating FRBs is broadened by a factor of ∼2-3 on average, primarily due to dispersive smearing. From the simulations, we find that the host galaxy dispersion measure contribution is likely to be comparable to the Galactic contribution and the FRB energy decreases significantly at high frequencies with a negative spectral index. The FRB spatial density is found to increase up to redshift ∼2.0 and then drops significantly at larger distances. We obtain the energy distribution for FRB 121102 with repetition rate ∼0.1-0.3 hr-1 and exponential energy cutoff that is significantly smaller compared to typical FRB energies. We find that the probability of observing none of the other FRBs to be repeating at Parkes is ∼0.8-0.9 with the current follow-up data insufficient to suggest more than one class of FRB progenitors.

Keywords: Neutron stars, Cosmological models, Intergalactic medium, Interstellar scattering, Radio astronomy, Astronomical simulations, Radio transient sources
Magnetospheric Multiscale Observations of the Off-equatorial Dipolarization Front Dynamics in the Terrestrial Magnetotail. We report the Magnetospheric Multiscale observations of dynamics at an off-equatorial dipolarization front (DF) in the Terrestrial Magnetotail. Three different plasma waves, namely electromagnetic ion cyclotron (EMIC) waves, lower hybrid drift waves, and electrostatic solitary waves (ESWs), associated with different electron pitch angle distributions were detected at different subregions of a single DF. It is interesting to note that the EMIC wave was linearly polarized, associating with a parallel current as a result of the antiparallel drift of electrons in the energy range of about 0.3-2 keV. These suggest that the wave was most likely to be locally generated. This generation could be explained by the current-driven kink-like instability due to the electron drift. The current-driven instabilities may dissipate the energy of the field-aligned current at the DF and thus play important roles in the magnetosphere-ionosphere coupling. On the other hand, the detected ESWs are interpreted as multidimensional electromagnetic electron holes (EHs) which are manifestations of several distinguishing features in electric and magnetic field perturbation. The EHs with a strong positive central potential suggested the likelihood of nonlinear behavior.

Keywords: Space plasmas, Plasma astrophysics
The Erratic Path to Coalescence of LISA Massive Black Hole Binaries in Subparsec-resolution Simulations of Smooth Circumnuclear Gas Disks. We perform high-resolution simulations to follow the orbital decay of 5 × 105 and 107 M⊙ massive black hole (MBH) pairs embedded in a circumnuclear gas disk (CND), from the CND scale (100 pc) down to 0.1-0.01 pc, the scale at which a circumbinary disk (CBD) could form. The MBHs' erratic orbital evolution is characterized by three stages: (i) a slow initial decay that leads to some circularization; (ii) a fast-migration phase, analogous to type III migration for massive planets in protoplanetary disks, in which angular momentum is efficiently drained by disk-driven torques arising from the co-orbital region of the secondary MBH, at a distance of 1-3 Hill radii; and (iii) a very slow decay phase, in which orbital angular momentum can even increase. In this last stage, a CBD forms when the parsec-scale decay rate becomes small enough to allow sufficient time for a cavity to be carved. When this happens, the MBH separation nearly stalls in our higher-resolution run. We suggest an empirically modified gap-opening criterion that takes into account such timescale effects, as well as other deviations from standard assumptions. Interestingly, a CBD does not form in the lower-resolution runs, resulting in a faster subparsec decay. Our findings show that the subparsec MBH pairing in gaseous disks is a stochastic and fragile process. Additional mechanisms, such as the stellar-driven hardening, may be necessary to guarantee that the gravitational wave emission phase is entered and the MBHs become accessible to future detectors such as the Laser Interferometer Space Antenna.

Keywords: Galaxy circumnuclear disk, Supermassive black holes, Black hole thermodynamics, Galaxy nuclei
X-Ray Properties of Young Radio Quasars at z &gt; 4.5. We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts 4.5 &lt; z &lt; 5.0. All sources are detected in the 0.5-7.0 keV energy band. Emission spectra are extracted, and the average photon index for the sample is measured to be 1.5 ± 0.1. Unabsorbed rest-frame 2-10 keV luminosities are found to range between (0.5-23.2) × 1045 erg s-1. The optical-X-ray power-law spectral index ${\alpha }_{\mathrm{ox}}$ is calculated for each source using optical/UV data available in the literature. The ${\alpha }_{\mathrm{ox}}$ -UV relationship is compared with other quasar surveys, and an anticorrelation is observed that agrees with independent estimates. Rest-frame radio and X-ray luminosities are established for the sample, and a correlation between the luminosities is detected. These multiwavelength results reinforce a lack of spectral evolution for quasars over a broad redshift range. We additionally identify three quasars from our multiwavelength analysis that are statistically significant outliers, with one source being a Compton-thick candidate in the early universe, and discuss each in detail.

Keywords: Active galactic nuclei, Active galaxies, High-redshift galaxies, High energy astrophysics
The Formation of a Stellar Association in the NGC 7000/IC 5070 Complex: Results from Kinematic Analysis of Stars and Gas. We examine the clustering and kinematics of young stellar objects (YSOs) in the North America/Pelican Nebulae, as revealed by Gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular-line maps. The Gaia parallaxes and proper motions allow us to significantly refine previously published lists of YSOs, demonstrating that many of the objects previously thought to form a distributed population turn out to be nonmembers. The members are subdivided into at least six spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. Three of the groups are expanding, with velocity gradients of 0.3-0.5 km s-1 pc-1, up to maximum velocities of ∼8 km s-1 away from the groups' centers. The two known O-type stars associated with the region, 2MASS J20555125+4352246 and HD 199579, are rapidly escaping one of these groups, following the same position-velocity relation as the low-mass stars. We calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. However, on a global scale, the relative motions of the groups do not appear either divergent or convergent. The velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. Most of the stellar population has ages similar to the freefall timescales for the natal clouds. Thus, we suggest the nearly freefall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex.

Keywords: Stellar kinematics, Millimeter astronomy, Star forming regions, T Tauri stars, Young stellar objects, Giant molecular clouds, Star formation, Space astrometry, OB stars, Stellar associations
Restoring Process of Sunspot Penumbra. We describe the disappearance of a sector of sunspot penumbra and its restoring process observed in the preceding sunspot of active region NOAA 12348. The evolution of the magnetic field and the plasma flows supports the idea that the penumbra forms due to a change of inclination of the magnetic field of the canopy. Moving magnetic features have been observed during the disintegration phase of that sector of sunspot penumbra. During the restoring phase we have not observed any magnetic flux emergence around the sunspot. The restoring process of the penumbra sector completed in about 72 hr and it was accompanied by the transition from the counter-Evershed flow to the classical Evershed flow. The inversion of photospheric spectropolarimetric measurements taken by the Interferometric Bidimensional Spectroscopic Instrument (IBIS) allowed us to reconstruct how the uncombed configuration of the magnetic field forms during the new settlement of the penumbra, i.e., the vertical component of the magnetic field seems to be progressively replaced by some horizontal field lines, corresponding to the intraspines.

Keywords: Sunspots, Solar photosphere, Solar chromosphere, Solar magnetic fields
Gaia 18dvy: A New FUor in the Cygnus OB3 Association. We present optical-infrared photometric and spectroscopic observations of Gaia 18dvy, located in the Cygnus OB3 association at a distance of 1.88 kpc. Gaia 18dvy was noted by the Gaia alerts system when its light curve exhibited a ≳4 mag rise in 2018-2019. The brightening was also observable at mid-infared wavelengths. The infrared colors of Gaia 18dvy became bluer as the outburst progressed. Its optical and near-infrared spectroscopic characteristics in the outburst phase are consistent with those of bona fide FU Orionis-type young eruptive stars. The progenitor of the outburst is probably a low-mass K-type star with an optical extinction of ∼3 mag. A radiative transfer modeling of the circumstellar structure, based on the quiescent spectral energy distribution, indicates a disk with a mass of 4 × 10-3 M☉. Our simple accretion disk modeling implies that the accretion rate had been exponentially increasing for more than 3 yr until mid-2019, when it reached a peak value of 6.9 × 10-6 M☉ yr-1. In many respects, Gaia 18dvy is similar to the FU Ori-type object HBC 722.

Keywords: Accretion, Eruptive variable stars, Star formation, Protoplanetary disks