Sazuna/UAT_keywords huggingface dataset:
Nonlinear Mechanisms that Regulate the Solar Cycle Amplitude. The solar magnetic activity cycle has an amplitude that varies within a wide but limited range of values. This implies that there are nonlinear mechanisms that prevent runaway solutions. The purpose of this paper is to propose observable nonlinear mechanisms in the framework of the Babcock-Leighton-type dynamo. Sunspot emergences show systematic properties that strong cycles tend to have higher mean latitudes and lower tilt angle coefficients. We use the surface flux transport model to investigate the effect of these systematic properties on the expected final total dipolar moment, i.e., cancellation plus generation of dipole moment by a whole solar cycle. We demonstrate that the systematic change in latitude has similar nonlinear feedback on the solar cycle (latitudinal quenching) as tilt does (tilt quenching). Both forms of quenching lead to the expected final total dipolar moment being enhanced for weak cycles and saturated to a nearly constant value for normal and strong cycles. This explains observed long-term solar cycle variability, e.g., the Gnevyshev-Ohl rule, which, in turn, justifies the nonlinear mechanisms inherent in the Babcock-Leighton-type dynamo.

Keywords: Solar cycle, Solar magnetic fields, Sunspots, Solar dynamo
Distortion of Magnetic Fields in the Dense Core SL 42 (CrA-E) in the Corona Australis Molecular Cloud Complex. The detailed magnetic field structure of the dense core SL 42 (CrA-E) in the Corona Australis molecular cloud complex was investigated based on near-infrared polarimetric observations of background stars to measure dichroically polarized light produced by magnetically aligned dust grains. The magnetic fields in and around SL 42 were mapped using 206 stars, and curved magnetic fields were identified. On the basis of simple hourglass (parabolic) magnetic field modeling, the magnetic axis of the core on the plane of the sky was estimated to be 40° ± 3°. The plane-of-sky magnetic field strength of SL 42 was found to be 22.4 ± 13.9 μG. Taking into account the effects of thermal/turbulent pressure and the plane-of-sky magnetic field component, the critical mass of SL 42 was obtained to be Mcr = 21.2 ± 6.6 M⊙, which is close to the observed core mass of Mcore ≈ 20 M⊙. We thus conclude that SL 42 is in a condition close to the critical state if the magnetic fields lie near the plane of the sky. Because there is a very low-luminosity object toward the center of SL 42, it is unlikely that this core is in a highly subcritical condition (i.e., the magnetic inclination angle is significantly deviated from the plane of the sky). The core probably started to collapse from a nearly kinematically critical state. In addition to the hourglass magnetic field modeling, the Inoue &amp; Fukui mechanism may explain the origin of the curved magnetic fields in the SL 42 region.

Keywords: Interstellar dust, Dense interstellar clouds, Infrared astronomy, Interstellar magnetic fields, Starlight polarization
Limits to Rest-frame Ultraviolet Emission from Far-infrared-luminous z ≃ 6 Quasar Hosts. We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z ≃ 6 quasars and the z = 5.85 hot-dust-free quasar SDSS J0005-0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of mJ &gt; 22.7 mag and mH &gt; 22.4 mag, corresponding to stellar masses of M* &lt; 2 × 1011M⊙. These stellar mass limits are consistent with the local MBH - M* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z ≃ 6 host galaxies, but likely in the presence of significant dust ($\langle {A}_{\mathrm{UV}}\rangle \simeq 2.6$ mag). We also detect a total of up to nine potential z ≃ 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1"4-3"2, or 8.4-19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of -22.1 to -19.9 mag and UV spectral slopes β of -2.0 to -0.2, consistent with luminous star-forming galaxies at z ≃ 6. These results suggest that the quasars are in dense environments typical of luminous z ≃ 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z ≃ 6 quasar host galaxies and better constrain their stellar mass and dust content.

Keywords: AGN host galaxies, Barred spiral galaxies, High-redshift galaxies, Quasars
Dust-scattering Halo and Giant Hard X-Ray Flare from the Supergiant Fast X-Ray Transient IGR J16479-4514 Investigated with XMM-Newton and INTEGRAL. We report results from the analysis of XMM-Newton and INTEGRAL data of IGR J16479-4514. The unpublished XMM-Newton observation, performed in 2012, occurred during the source eclipse. No pointlike X-ray emission was detected from the source; conversely, extended X-ray emission was clearly detected up to a size distance compatible with a dust-scattering halo produced by the source X-ray emission before being eclipsed by its companion donor star. The diffuse emission of the dust-scattering halo could be observed without any contamination from the central point X-ray source, compared to a previous XMM-Newton observation published in 2008. Our comprehensive analysis of the 2012 unpublished spectrum of the diffuse emission, as well as the 2008 reanalyzed spectra extracted from three adjacent time intervals and different extraction regions (optimized for pointlike and extended emission), allowed us to clearly disentangle the scattering halo spectrum from the residual pointlike emission during the 2008 eclipse. Moreover, the pointlike emission detected in 2008 could be separated into two components attributed to the direct emission from the source and scattering in the stellar wind, respectively. From archival unpublished INTEGRAL data, we identified a very strong (∼3 × 10-8 erg cm-2 s-1) and fast (∼25 minute duration) flare that was classified as a giant hard X-ray flare, since the measured peak luminosity is ∼7 × 1037 erg s-1. Giant X-ray flares from supergiant fast X-ray transients are very rare; to date, only one has been reported from a different source. We propose a physical scenario to explain the origin in the case of IGR J16479-4514.

Keywords: Accretion, X-ray transient sources, High mass x-ray binary stars
Eruptive-Impulsive Homologous M-class Flares Associated with Double-decker Flux Rope Configuration in Minisigmoid of NOAA 12673. We present a multiwavelength analysis of two homologous, short-lived, impulsive flares of GOES class M1.4 and M7.3 that occurred from a very localized minisigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jetlike plasma ejection that for a brief amount of time moved toward the east in a collimated manner before drastically changing direction toward the southwest. Nonlinear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the minisigmoid region prior to the flares. A set of open field lines originating near the active region that were most likely responsible for the anomalous dynamics of the erupted plasma gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultraviolet brightening beneath the filament, along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.

Keywords: Solar activity, Solar corona, Solar x-ray flares, Solar active region filaments
Thermal and Orbital Evolution of Low-mass Exoplanets. The thermal, orbital, and rotational dynamics of tidally loaded exoplanets are interconnected by intricate feedback. The rheological structure of the planet determines its susceptibility to tidal deformation and, as a consequence, participates in shaping its orbit. The orbital parameters and the spin state, conversely, control the rate of tidal dissipation and may lead to substantial changes in the interior. We investigate the coupled thermal-orbital evolution of differentiated rocky exoplanets governed by the Andrade viscoelastic rheology. The coupled evolution is treated by a semianalytical model, 1D parameterized heat transfer, and self-consistently calculated tidal dissipation. First, we conduct several parametric studies, exploring the effect of the rheological properties, the planet size, and the orbital eccentricity on tidal locking and dissipation. These tests show that the role of tidal locking into high spin-orbit resonances is most prominent on low eccentric orbits, where it results in substantially higher tidal heating than synchronous rotation. Second, we calculate the long-term evolution of three currently known low-mass exoplanets with nonzero orbital eccentricity and absent or yet-unknown eccentricity forcing (namely GJ 625 b, GJ 411 b, and Proxima Centauri b). The tidal model incorporates the formation of a stable magma ocean and a consistently evolving spin rate. We find that the thermal state is strongly affected by the evolution of eccentricity and spin state and proceeds as a sequence of thermal equilibria. Final despinning into synchronous rotation slows down the orbital evolution and helps to maintain long-term stable orbital eccentricity.

Keywords: Exoplanet dynamics, Extrasolar rocky planets, Tidal friction, Exoplanets, Orbital evolution, Exoplanet tides, Tidal interaction
Opacity-driven Convection and Variability in Accretion Disks around Supermassive Black Holes. We study the structure of accretion disks around supermassive black holes in the radial range of -100 gravitational radii, using a three-dimensional radiation magnetohydrodynamic simulation. For typical conditions in this region of active galactic nuclei (AGNs), the Rosseland mean opacity is expected to be larger than the electron scattering value. We show that the iron opacity bump causes the disk to be convectively unstable. Turbulence generated by convection puffs up the disk due to additional turbulent pressure support and enhances the local angular momentum transport. This also results in strong fluctuations in surface density and heating of the disk. The opacity drops with increasing temperature and convection is suppressed. The disk cools down and the whole process repeats again. This causes strong oscillations of the disk scale height and luminosity variations by more than a factor of ≈3-6 over a few years' timescale. Since the iron opacity bump will move to different locations of the disk for black holes with different masses and accretion rates, we suggest that this is a physical mechanism that can explain the variability of AGN with a wide range of amplitudes over a timescale of years to decades.

Keywords: Accretion, Supermassive black holes, Radiative magnetohydrodynamics, Black holes, Quasars, Active galactic nuclei, Radiative transfer simulations, Magnetohydrodynamical simulations
Torsional Oscillations in Dynamo Models with Fluctuations and Potential for Helioseismic Predictions of the Solar Cycles. Using a nonlinear mean-field solar dynamo model, we study relationships between the amplitude of the "extended" mode of migrating zonal flows ("torsional oscillations") and magnetic cycles, and investigate whether properties the torsional oscillations in subsurface layers and in the deep convection zone can provide information about the future solar cycles. We consider two types of dynamo models: models with regular variations of the α-effect, and models with stochastic fluctuations, simulating "long-memory" and "short-memory" types of magnetic activity variations. It is found that torsional oscillation parameters, such the zonal acceleration, show a considerable correlation with the magnitude of the subsequent cycles with a time lag of 11-20 yr. The sign of the correlation and the time-lag parameters can depend on the depth and latitude of the torsional oscillations as well as on the properties of long-term ("centennial") variations of the dynamo cycles. The strongest correlations are found for the zonal acceleration at high latitudes at the base of the convection zone. The model results demonstrate that helioseismic observations of the torsional oscillations can be useful for advanced prediction of the solar cycles, 1-2 sunspot cycles ahead.

Keywords: Solar cycle, Solar rotation, Solar dynamo
Evryscope and K2 Constraints on TRAPPIST-1 Superflare Occurrence and Planetary Habitability. The nearby ultracool dwarf TRAPPIST-1 possesses several Earth-sized terrestrial planets, three of which have equilibrium temperatures that may support liquid surface water, making it a compelling target for exoplanet characterization. TRAPPIST-1 is an active star with frequent flaring, with implications for the habitability of its planets. Superflares (stellar flares whose energy exceeds 1033 erg) can completely destroy the atmospheres of a cool star's planets, allowing ultraviolet radiation and high-energy particles to bombard their surfaces. However, ultracool dwarfs emit little ultraviolet flux when quiescent, raising the possibility of frequent flares being necessary for prebiotic chemistry that requires ultraviolet light. We combine Evryscope and Kepler observations to characterize the high-energy flare rate of TRAPPIST-1. The Evryscope is an array of 22 small telescopes imaging the entire Southern sky in g' every two minutes. Evryscope observations, spanning 170 nights over 2 yr, complement the 80 day continuous short-cadence K2 observations by sampling TRAPPIST-1's long-term flare activity. We update TRAPPIST-1's superflare rate, finding a cumulative rate of ${4.2}_{-0.2}^{+1.9}$ superflares per year. We calculate the flare rate necessary to deplete ozone in the habitable-zone planets' atmospheres, and find that TRAPPIST-1's flare rate is insufficient to deplete ozone if present on its planets. In addition, we calculate the flare rate needed to provide enough ultraviolet flux to power prebiotic chemistry. We find TRAPPIST-1's flare rate is likely insufficient to catalyze some of the Earthlike chemical pathways thought to lead to ribonucleic acid synthesis, and flux due to flares in the biologically relevant UV-B band is orders of magnitude less for any TRAPPIST-1 planet than has been experienced by Earth at any time in its history.

Keywords: M dwarf stars, Extrasolar rocky planets, Exoplanets, Red dwarf flare stars, Flare stars, Astrobiology, Stellar flares, Pre-biotic astrochemistry
MINESweeper: Spectrophotometric Modeling of Stars in the Gaia Era. We present MINESweeper, a tool to measure stellar parameters by jointly fitting observed spectra and broadband photometry to model isochrones and spectral libraries. This approach enables the measurement of spectrophotometric distances, in addition to stellar parameters such as Teff, $\mathrm{log}g$, [Fe/H], [α/Fe], and radial velocity. MINESweeper employs a Bayesian framework and can easily incorporate a variety of priors, including Gaia parallaxes. Mock data are fit in order to demonstrate how the precision of derived parameters depends on evolutionary phase and signal-to-noise ratio. We then fit a selection of data in order to validate the model outputs. Fits to a variety of benchmark stars including Procyon, Arcturus, and the Sun result in derived stellar parameters that are in good agreement with the literature. We then fit combined spectra and photometry of stars in the open and globular clusters M92, M13, M3, M107, M71, and M67. Derived distances, [Fe/H], [α/Fe], and $\mathrm{log}g$-Teff relations are in overall good agreement with literature values, although there are trends between metallicity and $\mathrm{log}g$ within clusters that point to systematic uncertainties at the ≈0.1 dex level. Finally, we fit a large sample of stars from the H3 Spectroscopic Survey in which high-quality Gaia parallaxes are also available. These stars are fit without the Gaia parallaxes so that the geometric parallaxes can serve as an independent test of the spectrophotometric distances. Comparison between the two reveals good agreement within their formal uncertainties after accounting for the Gaia zero-point uncertainties.

Keywords: Stellar luminosities, Stellar properties, Stellar ages, Stellar abundances, Stellar effective temperatures, Stellar radii, Stellar evolutionary models, Stellar physics, Stellar colors, Stellar masses, Stellar distance, Stellar spectral lines
A Priori Validation of Subgrid-scale Models for Astrophysical Turbulence. We perform a priori validation tests of subgrid-scale (SGS) models for the turbulent transport of momentum, energy, and passive scalars. To this end, we conduct two sets of high-resolution hydrodynamical simulations with a Lagrangian code: an isothermal turbulent box with rms Mach numbers of 0.3, 2, and 8, and the classical wind tunnel where a cold cloud traveling through a hot medium gradually dissolves due to fluid instabilities. Two SGS models are examined: the eddy diffusivity (ED) model widely adopted in astrophysical simulations and the "gradient model" due to Clark et al. We find that both models predict the magnitude of the SGS terms equally well (correlation coefficient &gt;0.8). However, the gradient model provides excellent predictions for the orientation and shape of the SGS terms while the ED model predicts both poorly, indicating that isotropic diffusion is a poor approximation to the instantaneous turbulent transport. The best-fit coefficient of the gradient model is in the range of [0.16, 0.21] for the momentum transport, and the turbulent Schmidt number and Prandtl number are both close to unity, in the range of [0.92, 1.15].

Keywords: Hydrodynamical simulations, Computational methods, Hydrodynamics
First Structure Formation under the Influence of Gas-Dark Matter Streaming Velocity and Density: Impact of the "Baryons Trace Dark Matter" Approximation. The impact of streaming between baryons and dark matter on the first structures has been actively explored by recent studies. We investigate how the key results are affected by two popular approximations. One is to implement the streaming by accounting for only the relative motion while assuming "baryons trace dark matter" spatially at the initialization of simulation. This neglects the smoothing on the gas density taking place before the initialization. In our simulation initialized at zi = 200, it overestimates the gas density power spectrum by up to 40% at k ≈ 102 h Mpc-1 at z = 20. Halo mass (Mh) and baryonic fraction in halos (${f}_{b,h}$) are also overestimated, but the relation between the two remains unchanged. The other approximation tested is to artificially amplify the density/velocity fluctuations in the cosmic mean density to simulate the first minihalos that form in overdense regions. This gives a head start to the halo growth while the subsequent growth is similar to that in the mean density. The growth in a true overdense region, on the other hand, is accelerated gradually in time. For example, raising σ8 by 50% effectively transforms $z\to \sqrt{1.5}z$ in the halo mass growth history while, at 2σ overdensity, the growth is accelerated by a constant in redshift: $z\to z+4.8$. As a result, halos have grown more massive in the former than in the latter before z ≈ 27 and vice versa after. The ${f}_{b,h}$-Mh relation is unchanged in those cases as well, suggesting that the Population III formation rate for a given Mh is insensitive to the tested approximations.

Keywords: Cosmology, Early universe, Reionization, Primordial galaxies
Testing the Weak Equivalence Principle with the Binary Neutron Star Merger GW 170817: The Gravitational Contribution of the Host Galaxy. The successful detection of the binary neutron star merger GW 170817 and its electromagnetic counterparts has provided an opportunity to explore the joint effect of the host galaxy and the Milky Way (MW) on the weak equivalence principle (WEP) test. In this paper, using the Navarro-Frenk-White profile and the Hernquist profile, we present an analytic model to calculate the galactic potential, in which the possible locations of the source from the observed angle offset and the second supernova kick are accounted for. We show that the upper limit of Δγ is 10-9 for the comparison between GW 170817 and a gamma-ray burst (GRB 170817A), and it is 10-4 for the comparison between GW 170817 and a bright optical transient (SSS 17a, now with the IAU identification of AT 2017gfo). These limits are more stringent by one to two orders of magnitude than those determined solely using the measured MW potential in the literature. We demonstrate that the WEP test is strengthened by the contribution from the host galaxy to the Shapiro time delay. Meanwhile, we also find that large natal kicks produce a maximum deviation of about 20% from the results with a typical kick velocity of 400 to ∼500 km s-1. Finally, we analyze the impact from the halo mass of NGC 4993 with a typical 0.2 dex uncertainty and find that the upper limit of Δγ, with a maximum mass ${10}^{12.4}{h}^{-1}\,{M}_{\odot }$ , is nearly two times more stringent than that of the minimum mass ${10}^{12.0}{h}^{-1}\,{M}_{\odot }$ .

Keywords: Black hole physics, Gamma-ray bursts, Binary stars, Gravitational waves
Luminosity Models and Density Profiles for Nuclear Star Clusters for a Nearby Volume-limited Sample of 29 Galaxies. Nuclear star clusters (NSCs) are dense stellar clusters that are found at the centers of a majority of galaxies. In this paper, we study the density profiles for 29 galaxies in a volume-limited survey within 10 Mpc to characterize their NSCs. These galaxies span a 3 × 108-8 × 1010 M⊙ and a wide range of Hubble types. We use high-resolution Hubble Space Telescope archival data to create luminosity models for the galaxies using Sérsic profiles to parameterize the NSCs. We also provide estimates for photometric masses of NSCs and their host galaxies using color-M/L relationships and examine their correlation. We use the multi-Gaussian expansion to derive the NSC densities and their 3D mass-density profiles. The 3D density profiles characterize the NSC densities on scales as small as ∼1 pc, approaching the likely spheres of influence for BHs in these objects. We find that these densities correlate with galaxy mass, with NSC density profiles becoming both denser and flatter at higher galaxy masses. Most galaxy NSCs are denser than typical globular clusters. We parameterize the 3D NSC density profiles and their scatter and slope as a function of galaxy stellar mass to enable the construction of realistic nuclear mass profiles. Our fitted profiles and the derived relations are useful in predicting the rate of tidal disruption events in galaxies. We will verify the results of this paper in a follow-up paper that presents the dynamical modeling of the same sample of NSCs.

Keywords: Globular star clusters, Late-type galaxies, Tidal disruption, Young star clusters, Galaxy nuclei, Early-type galaxies