adsabs/SciX_UAT_keywords huggingface dataset:
Influences of Internal Forcing on Atmospheric Circulations of Irradiated Giant Planets

Close-in giant planets with strong stellar irradiation show atmospheric circulation patterns with strong equatorial jets and global-scale stationary waves. So far, almost all modeling works on atmospheric circulations of such giant planets have mainly considered external radiation alone, without taking into account the role of internal heat fluxes or just treating it in very simplified ways. Here, we study atmospheric circulations of strongly irradiated giant planets by considering the effect of internal forcing, which is characterized by small-scale stochastic interior thermal perturbations, using a three-dimensional atmospheric general circulation model. We show that the perturbation-excited waves can largely modify atmospheric circulation patterns in the presence of relatively strong internal forcing. Specifically, our simulations demonstrate three circulation regimes: a superrotation regime, a midlatitude-jet regime, and a quasi-periodic oscillation regime, depending on the relative importance of external and internal forcings. It is also found that strong internal forcing can cause noticeable modifications of the thermal phase curves.

Keywords: exoplanet atmospheres; atmospheric circulation; brown dwarfs; hot jupiters
How Complete Are Surveys for Nearby Transiting Hot Jupiters?

Hot Jupiters are a rare and interesting outcome of planet formation. Although more than 500 hot Jupiters (HJs) are known, most of them were discovered by a heterogeneous collection of surveys with selection biases that are difficult to quantify. Currently, our best knowledge of HJ demographics around FGK stars comes from the sample of ≈40 objects detected by the Kepler mission, which have a well-quantified selection function. Using the Kepler results, we simulate the characteristics of the population of nearby transiting HJs. A comparison between the known sample of nearby HJs and simulated magnitude-limited samples leads to four conclusions. (1) The known sample of HJs appears to be ≈75% complete for stars brighter than Gaia G ≤ 10.5, falling to ≲50% for G ≤ 12. (2) There are probably a few undiscovered HJs with host stars brighter than G ≈ 10 located within 10° of the Galactic plane. (3) The period and radius distributions of HJs may differ for F-type hosts (which dominate the nearby sample) and G-type hosts (which dominate the Kepler sample). (4) To obtain a magnitude-limited sample of HJs that is larger than the Kepler sample by an order of magnitude, the limiting magnitude should be approximately G ≈ 12.5. This magnitude limit is within the range for which NASA's Transiting Exoplanet Survey Satellite can easily detect HJs, presenting the opportunity to greatly expand our knowledge of hot-Jupiter demographics.

Keywords: exoplanets; hot jupiters
Finding Peas in the Early Universe with JWST

The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. We analyze the Near Infrared Spectrograph ERO spectra of three z ~ 8 galaxies to determine their metallicities, gas temperatures, and ionization. These galaxies offer the first opportunity to understand the physical properties of Epoch-of-Reionization galaxies through detailed rest-optical emission-line spectroscopy. We show that these objects have metal abundances $12+\mathrm{log}[{\rm{O}}/{\rm{H}}]\,\approx $ 6.9-8.3, based on both the T e method and on a recent calibration of the R 23 metallicity indicator. Since the spectra are some of the earliest science data from JWST, we compare several line ratios with values expected from robust physics, to validate our measurement procedures. We compare the abundances and emission-line ratios to a nearby sample of Green Pea galaxies-a population of nearby emission-line galaxies whose UV properties resemble Epoch-of-Reionization galaxies, and which often have large Lyman continuum escape fractions. The JWST data show striking further similarities between these high-redshift galaxies and nearby Green Peas. The z ~ 8 galaxies span the metallicity range covered by Green Peas. They also show the compact morphology that is typical of emission-line-dominated galaxies at all redshifts. Based on these similarities with Green Peas, it is likely that these are the first rest-optical spectra of galaxies that are actively driving cosmological reionization.

Keywords: galaxy evolution; reionization; emission line galaxies; high-redshift galaxies; starburst galaxies; metallicity; james webb space telescope; gravitational lensing; blue compact dwarf galaxies
The UV Luminosity Function of Protocluster Galaxies at z ∼ 4: The Bright-end Excess and the Enhanced Star Formation Rate Density

We report the rest-frame ultraviolet luminosity function of g-dropout galaxies in 177 protocluster candidates (PC UVLF) at z ∼ 4 selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing it with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess toward the bright end. This excess cannot be explained by the contribution of only active galactic nuclei, and we also find that this excess is more significant in higher density regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at z ∼ 4. We also estimate the star formation rate density (SFRD) in protocluster regions as ≃6%-20% of the cosmic SFRD, based on the measured PC UVLF after correction for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a nonnegligible contribution to the cosmic SFRD at z ∼ 4, as previously suggested by simulations. Our results suggest that protoclusters are essential components for galaxy evolution at z ∼ 4.

Keywords: galaxy evolution; protoclusters; high-redshift galaxies
Long-term Spectra of the Blazars Mrk 421 and Mrk 501 at TeV Energies Seen by HAWC

The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high-energy sky in the 300 GeV to >100 TeV energy range. HAWC has detected two blazars above 11σ, Markarian 421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between 2015 June and 2018 July, resulting in ~1038 days of exposure. In this work, we report the time-averaged spectral analyses for both sources, above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light, the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cutoff with index $\alpha =2.26\pm {\left(0.12\right)}_{\mathrm{stat}}{\left({}_{-0.2}^{+0.17}\right)}_{\mathrm{sys}}$ and energy cutoff ${E}_{c}=5.1\pm {\left(1.6\right)}_{\mathrm{stat}}{\left({}_{-2.5}^{+1.4}\right)}_{\mathrm{sys}}$ TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index $\alpha =2.61\pm {\left(0.11\right)}_{\mathrm{stat}}{\left({}_{-0.07}^{+0.01}\right)}_{\mathrm{sys}}$ . The maximum energies at which the Mrk 421 and Mrk 501 signals are detected are 9 and 12 TeV, respectively. This makes these some of the highest energy detections to date for spectra averaged over years-long timescales. Since the observation of gamma radiation from blazars provides information about the physical processes that take place in their relativistic jets, it is important to study the broadband spectral energy distributions (SEDs) of these objects. For this purpose, contemporaneous data in the gamma-ray band to the X-ray range, and literature data in the radio to UV range, were used to build time-averaged SEDs that were modeled within a synchrotron-self Compton leptonic scenario.

Keywords: active galactic nuclei; bl lacertae objects; gamma-ray sources
Reliable Probability Forecast of Solar Flares: Deep Flare Net-Reliable (DeFN-R)

We developed a reliable probabilistic solar-flare forecasting model using a deep neural network, named Deep Flare Net-Reliable (DeFN-R). The model can predict the maximum classes of flares that occur in the following 24 hr after observing images, along with the event occurrence probability. We detected active regions from 3 × 105 solar images taken during 2010-2015 by Solar Dynamic Observatory and extracted 79 features for each region, which we annotated with flare occurrence labels of X-, M-, and C-classes. The extracted features are the same as used by Nishizuka et al.; for example, line-of-sight/vector magnetograms in the photosphere, brightening in the corona, and the X-ray emissivity 1 and 2 hr before an image. We adopted a chronological split of the database into two for training and testing in an operational setting: the data set in 2010-2014 for training and the one in 2015 for testing. DeFN-R is composed of multilayer perceptrons formed by batch normalizations and skip connections. By tuning optimization methods, DeFN-R was trained to optimize the Brier skill score (BSS). As a result, we achieved BSS = 0.41 for ≥C-class flare predictions and 0.30 for ≥M-class flare predictions by improving the reliability diagram while keeping the relative operating characteristic curve almost the same. Note that DeFN is optimized for deterministic prediction, which is determined with a normalized threshold of 50%. On the other hand, DeFN-R is optimized for a probability forecast based on the observation event rate, whose probability threshold can be selected according to users' purposes.

Keywords: solar magnetic fields; solar activity; solar x-ray flares; solar active regions; space weather; neural networks; classification; time series analysis; magnetic fields; astrostatistics techniques
N-body Interactions will be Detectable in the HR-8799 System within 5 yr with VLTI-GRAVITY

While Keplerian orbits account for the majority of the astrometric motion of directly-imaged planets, perturbations due to N-body interactions allow us to directly constrain exoplanet masses in multiplanet systems. This has the potential to improve our understanding of massive directly-imaged planets, which nearly all currently have only model-dependent masses. The VLTI-GRAVITY instrument has demonstrated that interferometry can achieve 100x better astrometric precision than existing methods, a level of precision that makes detection of planet-planet interactions possible. In this study, we show that in the HR-8799 system, planet-planet deviations from currently used Keplerian approximations are expected to be up to one-quarter of a milliarcsecond within five years, which will make them detectable with VLTI-GRAVITY. Modeling of this system to directly constrain exoplanet masses will be crucial in order to make precise predictions.

Keywords: astrometric exoplanet detection; exoplanet dynamics; exoplanet systems
Systematic Research of Low-redshift Optically Selected SDSS Type 2 AGNs but with Apparent Long-term Optical Variabilities from Catalina Sky Survey. I. Data Sample and Basic Results

The main objective of this article, the first in a dedicated series, is to report basic results on systematic research of low-redshift optically selected SDSS Type 2 active galactic nuclei (AGNs) but with apparent optical variabilities. For all the pipeline-classified Type 2 AGNs in SDSS DR16 with z < 0.3 and signal-to-noise ratio > 10, long-term optical V-band light curves are collected from the Catalina Sky Survey. Through all light curves described by a damped random walk process with process parameters of σ/(mag/days0.5) and τ/days, 156 Type 2 AGNs have apparent variabilities with process parameters at least 3 times larger than corresponding uncertainties and with ln(σ/(mag/days0.5)) > -4, indicating central AGN activity regions directly in the line of sight, leading the 156 Type 2 AGNs as misclassified Type 2 AGNs. Furthermore, based on spectroscopic emission features around Hα, 31 out of the 156 AGNs have broad Hα, indicating the 31 Type 2 AGNs are actually Type 1.8 and/or 1.9 AGNs. Meanwhile, 14 out of the 156 AGNs have multiepoch SDSS spectra. After checking multiepoch spectra of the 14 objects, no clues for appearance and/or disappearance of broad lines indicates true Type 2 AGNs rather than changing-look AGNs are preferred in the collected Type 2 AGNs with long-term variabilities. Moreover, a small sample of Type 2 AGNs have long-term variabilities with features roughly described by theoretical tidal disruption events (TDEs) expected t -5/3, indicating probable central TDEs as further and strong evidence to support true Type 2 AGNs.

Keywords: active galactic nuclei; active galaxies; emission line galaxies; seyfert galaxies
A Bright First Day for Tidal Disruption Events

Stream-stream collision may be an important prepeak energy dissipation mechanism in tidal disruption events (TDEs). We perform local three-dimensional radiation hydrodynamic simulations in a wedge geometry including the gravity to study stream self-crossing with an emphasis on resolving the collision and following the subsequent outflow. We find that the collision can contribute to prepeak optical emissions by converting ≳5% of the stream kinetic energy to radiation, yielding prompt emission of ~1042-44 erg s-1. The radiative efficiency is sensitive to stream mass fallback rates and strongly depends on the downstream gas optical depth. Even for a sub-Eddington (10%) mass fallback rate, the strong radiation pressure produced in the collision can form a local super-Eddington region near the collision site, where a fast, aspherical outflow is launched. A higher mass fallback rate usually leads to more optically thick outflow and lower net radiative efficiency. For $\dot{M}\gtrsim 0.1{\dot{M}}_{\mathrm{Edd}}$ , the estimated photosphere size of the outflow can expand by 1-2 orders of magnitude, reaching ~1014 cm. The average gas temperature at this photospheric surface is a few × 104 K, roughly consistent with inferred prepeak photosphere properties for some optical TDEs. We find that the dynamics is sensitive to the collision angle and radius, but the radiative efficiency or outflow properties show more complex dependency than is often assumed in ballistic models.

Keywords: astrophysical black holes; tidal disruption; accretion; astronomical radiation sources
Population Synthesis of Helium White Dwarf-Red Giant Star Mergers and the Formation of Lithium-rich Giants and Carbon Stars

The formation histories of lithium-rich and carbon-rich red giants are not yet understood. It has been proposed that the merger of a helium-core white dwarf with a red giant branch (RGB) star might provide a solution. We have computed an extended grid of post-merger evolution models and combined these with predictions of binary-star population synthesis. The results strongly support the proposal that the merger of a helium white dwarf with an RGB star can provide the progenitors of both lithium-rich red clump stars and early-R carbon stars. The distribution of post-merger models in Teff, log g, log L, the surface abundances of lithium and carbon, and the predicted space densities agree well with the observed distributions of these parameters for Li-rich and early-R stars in the Galaxy.

Keywords: red giant stars; stellar physics; asteroseismology; stellar abundances; red giant clump; stellar evolutionary models; stellar evolution; binary stars; white dwarf stars; lithium stars; chemically peculiar stars; carbon stars
High-latitude Observations of Inertial-range Turbulence by the Ulysses Spacecraft During the Solar Minimum of 1993-96

We have examined Ulysses magnetic field measurements for the years 1993 through 1996 as the spacecraft moved sunward from 5 au at high southern latitudes, passing through perihelion during the first fast-latitude scan to achieve high northern latitudes, and finally returning to 5 au. These years represent near-solar-minimum activity, providing a clear measure of high-latitude solar-wind turbulence. We apply a series of tests to the data, examining both the magnetic variance anisotropy and the underlying wavevector anisotropy, finding them to be consistent with past 1 au observations. The variance anisotropy depends upon both the thermal proton temperature parameter and the amplitude of the magnetic power spectrum, while the underlying wavevector anisotropy is dominated by the component perpendicular to the mean magnetic field. We also examine the amplitude of the magnetic power spectrum as well as the associated turbulent transport of energy to small scales that results in the heating of the thermal plasma. The measured turbulence is found to be stronger than that seen at low latitudes by the Voyager spacecraft as it traverses the distance from 1 to 5 au during the years approaching solar maximum. If the high- and low-latitude sources are comparable, this would indicate that while the heating processes are active in both regions, the turbulence has had less decay time in the transport of energy to small scales. Alternatively, it may also be that the high-latitude source is stronger.

Keywords: solar wind; interplanetary turbulence; interplanetary magnetic fields; magnetohydrodynamics; space plasmas
Magnetogenesis in a Collisionless Plasma: From Weibel Instability to Turbulent Dynamo

We report on a first-principles numerical and theoretical study of plasma dynamo in a fully kinetic framework. By applying an external mechanical force to an initially unmagnetized plasma, we develop a self-consistent treatment of the generation of "seed" magnetic fields, the formation of turbulence, and the inductive amplification of fields by the fluctuation dynamo. Driven large-scale motions in an unmagnetized, weakly collisional plasma are subject to strong phase mixing, which leads to the development of thermal pressure anisotropy. This anisotropy triggers the Weibel instability, which produces filamentary "seed" magnetic fields on plasma-kinetic scales. The plasma is thereby magnetized, enabling efficient stretching and folding of the fields by the plasma motions and the development of Larmor-scale kinetic instabilities such as the firehose and mirror. The scattering of particles off the associated microscale magnetic fluctuations provides an effective viscosity, regulating the field morphology and turbulence. During this process, the seed field is further amplified by the fluctuation dynamo until energy equipartition with the turbulent flow is reached. By demonstrating that equipartition magnetic fields can be generated from an initially unmagnetized plasma through large-scale turbulent flows, this work has important implications for the origin and amplification of magnetic fields in the intracluster and intergalactic mediums.

Keywords: extragalactic magnetic fields; cosmic magnetic fields theory; plasma astrophysics; intracluster medium; intergalactic medium
RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz

We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ~11 Gλ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013-2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ~25 Gλ. For all of these measurements, fringes are detected only up to ~2.8 Earth diameter or ~3 Gλ baseline lengths, resulting in a new image with angular resolution of ~150 μas or ~20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds ${T}_{{\rm{B}},\min }\sim {10}^{12}\,$ K. It is challenging to explain the origin of this record-high ${T}_{{\rm{B}},\min }$ value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.

Keywords: relativistic jets; active galactic nuclei; radio galaxies; very long baseline interferometry
CCD UBV and Gaia DR3 Analyses of the Open Clusters King 6 and NGC 1605

A detailed analysis of ground-based CCD UBV photometry and space-based Gaia Data Release 3 (DR3) data for the open clusters King 6 and NGC 1605 was performed. Using the PYUPMASK algorithm on Gaia astrometric data to estimate cluster membership probabilities, we have identified 112 stars in King 6 and 160 stars in NGC 1605 as the statistically most likely members of each cluster. We calculated reddening and metallicity separately using UBV two-color diagrams to estimate parameter values via independent methods. The color excess E(B - V) and photometric metallicity [Fe/H] for King 6 are 0.515 ± 0.030 mag and 0.02 ± 0.20 dex, respectively. For NGC 1605, they are 0.840 ± 0.054 mag and 0.01 ± 0.20 dex, respectively. With reddening and metallicity kept constant, we have estimated the distances and cluster ages by fitting PARSEC isochrones to color-magnitude diagrams based on the Gaia and UBV data. The photometric distances are 723 ± 34 pc for King 6 and 3054 ± 243 pc for NGC 1605. The cluster ages are 200 ± 20 Myr and 400 ± 50 Myr for King 6 and NGC 1605, respectively. The mass function slopes were found to be 1.29 ± 0.18 and 1.63 ± 0.36 for King 6 and NGC 1605, respectively. These values are in good agreement with the value of Salpeter. The relaxation times were estimated as 5.8 Myr for King 6 and 60 Myr for NGC 1605. These indicate that both clusters are dynamically relaxed since these times are less than the estimated cluster ages. A Galactic orbit analysis shows that both clusters formed outside the solar circle and are members of the young thin-disk population.

Keywords: open star clusters; stellar kinematics; hertzsprung russell diagram
A Coronagraph with a Sub-λ/D Inner Working Angle and a Moderate Spectral Bandwidth

Future high-contrast imaging spectroscopy with a large segmented telescope will be able to detect atmospheric molecules of Earth-like planets around G- or K-type main-sequence stars. Increasing the number of target planets will require a coronagraph with a small inner working angle (IWA), and wide spectral bandwidth is required if we enhance a variety of detectable atmospheric molecules. To satisfy these requirements, in this paper, we present a coronagraphic system that provides an IWA less than 1λ 0/D over a moderate wavelength band, where λ 0 is the design-center wavelength and D denotes the full width of the rectangular aperture included in the telescope aperture. A performance simulation shows that the proposed system approximately achieves a contrast below 10-10 at 1λ 0/D over the wavelengths of 650-750 nm. In addition, this system has a core throughput ≥10% at input separation angles of ~0.7-1.4λ 0/D; to reduce telescope time, we need prior information on the target's orbit by other observational methods to a precision higher than the width of the field of view. For some types of aberration including tilt aberration, the proposed system has a sensitivity less than ever-proposed coronagraphs that have IWAs of approximately 1λ 0/D. In future observations of Earth-like planets, the proposed coronagraphic system may serve as a supplementary coronagraphic system dedicated to achieving an extremely small IWA.

Keywords: astrobiology; coronagraphic imaging; direct imaging; exoplanets