Sazuna/UAT_keywords huggingface dataset:
The Bimodal Distribution in Exoplanet Radii: Considering Varying Core Compositions and H<SUB>2</SUB> Envelope's Sizes. Several models have been introduced in order to explain the radius distribution in exoplanet radii observed by Fulton et al. with one peak at ∼ 1.3{R}\oplus, the other at ∼ 2.4{R}\oplus, and the minimum at ∼ 1.75{R}\oplus . In this paper we focus on the hypothesis that the exoplanet size distribution is caused by stellar X-ray and ultraviolet (XUV)-induced atmospheric loss. We evolve 106 synthetic exoplanets by exposing them to XUV irradiation from synthetic zero-age main-sequence stars. For each planet we set a different interior composition, which ranged from 100 wt% Fe (very dense), through to 100 wt% MgSiO3 (average density), and to 100 wt% {H}2O ice (low density), with varying hydrogen envelope sizes that varied from 0 wt% (a negligible envelope) to 100 wt% (a negligible core). Our simulations were able to replicate the bimodal distribution in exoplanet radii. We argue that in order to reproduce the distribution by Fulton et al. it is mandatory for there to be a paucity of exoplanets with masses above ∼ 8{M}\oplus . Furthermore, our best-fit result predicts an initial flat distribution in exoplanet occurrence for {M}P≲ 8{M}\oplus with a strong deficiency for planets with ≲ 3{M}\oplus . Our results are consistent with the ∼ 1.3{R}\oplus radius peak mostly encompassing denuded exoplanets, while the ∼ 2.4{R}\oplus radius peak is mainly comprised of exoplanets with large hydrogen envelopes.

Keywords: Mini Neptunes, Super Earths, Exoplanets
Analysis of Turbulence Properties in the Mercury Plasma Environment Using MESSENGER Observations. Turbulence is ubiquitous in space and astrophysical plasmas, such as the solar wind, planetary magnetospheres, and the interstellar medium. It plays a key role in converting electric and magnetic energies into kinetic energy of the plasma particles. Here, the properties of MHD and kinetic-scale magnetic fluctuations in the Mercury environment are investigated using data collected by the MESSENGER spacecraft from 2011 March 23 to 2015 April 28. It is found that spectral indices at MHD scales vary from ∼-5/3 in the near-Planet solar wind (possibly the foreshock) to ∼-1.3 within the magnetosheath close to bow shock. The spectra steepen further in the magnetosheath close to magnetopause, and reach ∼-2.2 within the magnetosphere. Only 15% of events were found to have the Kolmogorov scaling ∼-5/3 in the magnetosheath. The high variability of the spectral indices implies that the scaling of turbulent fluctuations in the magnetosheath is not universal, and it emphasizes the role of the bow shock on the turbulence dynamics, at least at the largest scales. Analysis of the magnetic compressibility shows that only ∼30% of events with Kolmogorov inertial range in the magnetosheath are dominated by (shear) Alfvénic fluctuations, which contrasts with well-known features of solar wind turbulence. At kinetic scales, the steepest spectra (slopes ∼-2.8) occur in the solar wind, before flattening to ∼-2 near the bow shock, then steepening again to ∼-2.8 in the magnetosheath. The spectral indices at kinetic scales are close to the ones at large scales in the magnetosphere, which may be caused by the presence of heavy ions in the latter. The statistical results are compared with previous observations reported in other planetary plasma environments.

Keywords: Space plasmas, Magnetohydrodynamics, Interplanetary shocks, Plasma astrophysics, Megamasers, Interplanetary particle acceleration
Double White Dwarf Merger Products among High-mass White Dwarfs. Double white dwarf (double-WD) binaries may merge within a Hubble time and produce high-mass WDs. Compared to other high-mass WDs, the double-WD merger products have higher velocity dispersion because they are older. With the power of Gaia data, we show strong evidence for double-WD merger products among high-mass WDs by analyzing the transverse-velocity distribution of more than 1000 high-mass WDs (0.8-1.3 M⊙). We estimate that the fraction of double-WD merger products in our sample is about 20%. We also obtain a precise double-WD merger rate and its mass dependence. Our merger rate estimates are close to binary population synthesis results and support the idea that double-WD mergers may contribute to a significant fraction of type Ia supernovae.

Keywords: Bayesian statistics, Stellar ages, Stellar kinematics, White dwarf stars, Type Ia supernovae
Detection of Strong Epicyclic Density Spikes in the GD-1 Stellar Stream: An Absence of Evidence for the Influence of Dark Matter Subhalos?. The density variations in thin stellar streams may encode important information on the nature of dark matter. For instance, if dark matter aggregates into massive subhalos, these perturbers are expected to scatter stars out of dynamically cold stellar streams, possibly leading to detectable gaps in those structures. Here, we reexamine the density variations in the GD-1 stream, using Gaia Data Release 2 (DR2) astrometry and Panoramic Survey Telescope and Rapid Response System photometry, together with high-precision radial velocities measured with the Canada-France-Hawaii Telescope/ESPaDOnS and Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph instruments and complemented with public radial velocity catalogs. We show that after correcting for projection effects, the density profile exhibits high contrast periodic peaks, separated by 2.64 ± 0.18 kpc. An N-body simulation is presented that reproduces this striking morphology with simple epicyclic motion in a smooth Galactic potential. We also discuss the reliability of measuring density variations using ground-based photometric surveys, and for the particular case of GD-1 we highlight some of the artifacts present in the Gaia DR2 catalog along its track. Massive dark subhalos do not appear to be required to explain the density clumping along GD-1.

Keywords: Milky Way dark matter halo, Hydrodynamics, Milky Way dynamics, Stellar dynamics, Dark matter, Milky Way Galaxy
A New Way for Walén Test of Alfvénic Fluctuations in Solar Wind Streams via EEMD. Pure Alfvén waves at 1 au can be effectively identified by a Walén test of plasma and magnetic field observations. In this study, a new method, based on the Ensemble Empirical Mode Decomposition (EEMD) technique, is proposed for analyzing Alfvén fluctuations in two ways: (1) the Walén test relied on a time-dependent frame, which is extracted from the trend of differences between plasma and Alfvén velocity; and (2) a modified Walén test of the reconstructed Alfvénic and plasma velocity fluctuations by EEMD, after removing the high/low-frequency components irrelevant to Alfvénicity. Referencing the three validated methods mentioned in Chao et al., the same four cases in high-speed solar wind steams are tested by the EEMD method, considering Alfvénic parameters such as the Walén slope, the standard deviation ratio, the Alfvén ratio, the normalized cross helicity, the normalized residual energy, and the mean deviation relative to 1. The test results indicate that the first EEMD method can improve most Alfvénic parameters, since a time-varying velocity of the De Hoffmann-Teller frame is obtained from the process of self-adaptive data analysis, especially for complex cases with nonstationary and multiple background frames. The second EEMD method provides a kind of flexible testing to reconstruct the optimal fluctuations satisfied for the Walén relation, which achieves similar or even better results than normal prior methods based on bandpass filtering. We suggest that the EEMD method can be an alternative way to identify large-amplitude Alfvén waves in solar wind streams with single-satellite data.

Keywords: Space plasmas, Magnetohydrodynamics, Solar wind, Alfven waves, Interplanetary magnetic fields
Searching for Quasiperiodic Modulations in γ-Ray Active Galactic Nuclei. We perform a systematic search of quasiperiodic variabilities in γ-ray active galactic nuclei in the third Fermi Large Area Telescope source catalog (3FGL). We employ two techniques, Lomb-Scargle Periodogram and Weighted Wavelet Z-transform, to obtain power spectra of γ-ray light curves covering from 2008 August to 2016 December. The results show that besides several objects that have been reported in previous works, an additional source, the flat spectrum radio quasars PKS 0601-70 has a possible quasiperiodic variability of 450 days in its γ-ray light curves with the significance of &gt;3σ. The physical implications of our findings are discussed.

Keywords: Blazars, Active galactic nuclei, Jets, Gamma-rays
Chemistry and Physics of a Low-metallicity Hot Core in the Large Magellanic Cloud. We here present the results of 0.1 pc scale observations in 250 and 350 GHz toward a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected toward the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO2 and 34SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be 32S/34S = 17 and 32S/33S = 53 based on SO, SO2, and CS isotopologues, suggesting that both 34S and 33S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (&gt;100 K) traced by high-excitation lines of CH3OH and SO2, as well as warm gas (∼50 K) traced by CH3OH, SO2, 34SO, OCS, and CH3CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH3OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperatures during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO2 shows similar abundances within all of the known LMC hot cores, and the typical abundance roughly scales with the LMC's metallicity. Nitrogen-bearing molecules are generally less abundant in the LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity.

Keywords: Interstellar molecules, Isotopic abundances, Submillimeter astronomy, Interstellar line emission, Large Magellanic Cloud, Astrochemistry, Dust continuum emission, Star formation, Protostars, Metallicity
Forecasting the Ambient Solar Wind with Numerical Models. II. An Adaptive Prediction System for Specifying Solar Wind Speed near the Sun. The ambient solar wind flows and fields influence the complex propagation dynamics of coronal mass ejections in the interplanetary medium and play an essential role in shaping Earth's space weather environment. A critical scientific goal in the space weather research and prediction community is to develop, implement, and optimize numerical models for specifying the large-scale properties of solar wind conditions at the inner boundary of the heliospheric model domain. Here we present an adaptive prediction system that fuses information from in situ measurements of the solar wind into numerical models to better match the global solar wind model solutions near the Sun with prevailing physical conditions in the vicinity of Earth. In this way, we attempt to advance the predictive capabilities of well-established solar wind models for specifying solar wind speed, including the Wang-Sheeley-Arge model. In particular, we use the Heliospheric Upwind eXtrapolation (HUX) model for mapping the solar wind solutions from the near-Sun environment to the vicinity of Earth. In addition, we present the newly developed Tunable HUX (THUX) model, which solves the viscous form of the underlying Burgers equation. We perform a statistical analysis of the resulting solar wind predictions for the period 2006-2015. The proposed prediction scheme improves all the investigated coronal/heliospheric model combinations and produces better estimates of the solar wind state at Earth than our reference baseline model. We discuss why this is the case and conclude that our findings have important implications for future practice in applied space weather research and prediction.

Keywords: Solar photosphere, Heliosphere, Solar wind, Solar corona, Solar coronal holes, Corotating streams
Architecture of Three-planet Systems Predicted from the Observed Protoplanetary Disk of HL Tau. A number of protoplanetary disks (PPDs) observed with the Atacama Large Millimeter/submillimeter Array potentially provide direct examples of initial conditions for planetary systems. In particular, the HL Tau disk has been intensively studied, and its rings/gaps are conventionally interpreted to be a result of unseen massive planets embedded in the gaps. Based on this interpretation, we carried out N-body simulations to investigate the orbital evolution of planets within the PPD and after disk dispersal. Before disk dispersal, our N-body simulations include both migration and mass growth of the planet coupled with the evolution of the disk. By varying the disk parameters, we produce a variety of widely separated planetary systems consisting of three super-Jupiters at the end of disk dispersal. We found that the outer planet is more massive than the inner one, and the migration of the innermost planet is inefficient due to the accretion of outer planet(s). We also showed how the final configuration and the final planetary mass depend on disk parameters. The migration is found to be convergent, and no planet pair has a period ratio less than 2. After disk dispersal, we switch to purely gravitational N-body simulations and integrate the orbits up to 10 Gyr. Most simulated systems remain stable for at least 10 Gyr. We discuss the implications of our result in terms of the observed widely separated planetary systems HR 8799 and PDS 70.

Keywords: Protoplanetary disks, Planet formation
The Not So Simple Stellar System ω Cen. II. Evidence in Support of a Merging Scenario. We present multiband photometry covering ∼5° × 5° across ω Cen collected with the Dark Energy Camera on the 4 m Blanco telescope, combined with Hubble Space Telescope and Wide Field Imager data for the central regions. The unprecedented photometric accuracy and field coverage allows us to confirm the different spatial distribution of blue and red main-sequence stars, and of red giant branch (RGB) stars with different metallicities. The ratio of the number of blue to red main-sequence stars shows that the blue main-sequence stellar subpopulation has a more extended spatial distribution compared to the red main-sequence one, with the frequency of blue main-sequence stars increasing at a distance of ∼20' from ω Cen's center. Similarly, the more metal-rich RGB stars show a more extended spatial distribution compared to the more metal-poor ones in the outskirts of the cluster. Moreover, the centers of the distributions of metal-rich and metal-poor RGB stars are shifted in different directions with respect to the geometrical center of ω Cen. We constructed stellar density profiles for the blue and red main-sequence stars; they show that the blue main-sequence stellar subpopulation has a more extended spatial distribution compared to the red main-sequence one in the outskirts of ω Cen, confirming the results based on the number ratio. We also computed the ellipticity profile of ω Cen, which has a maximum value of 0.16 at a distance of ∼8' from the center, and a minimum of 0.05 at ∼30'; the average ellipticity is ∼0.10. The circumstantial evidence presented in this work suggests a merging scenario for the formation of the peculiar stellar system ω Cen.

Keywords: Globular star clusters, Stellar populations, Dwarf galaxies, Galaxy stellar content, Hertzsprung Russell diagram, Stellar evolution
GMC Collisions as Triggers of Star Formation. VII. The Effect of Magnetic Field Strength on Star Formation. We investigate the formation of stars within giant molecular clouds (GMCs) evolving in environments of different global magnetic field strength and large-scale dynamics. Building upon a series of magnetohydrodynamic simulations of noncolliding and colliding GMCs, we employ density- and magnetically regulated star formation subgrid models in clouds that range from moderately magnetically supercritical to near critical. We examine gas and star cluster morphologies, magnetic field strengths and relative orientations, prestellar core densities, temperatures, mass-to-flux ratios and velocities, star formation rates and efficiencies over time, spatial clustering of stars, and kinematics of the stars and natal gas. The large-scale magnetic criticality of the region greatly affects the overall gas evolution and star formation properties. GMC collisions enhance star formation rates and efficiencies in magnetically supercritical conditions, but may actually inhibit them in the magnetically critical case. This may have implications for star formation in different Galactic environments such as the Galactic Center and the main Galactic disk.

Keywords: Interstellar magnetic fields, Star formation, Molecular clouds, Interstellar medium
CS Depletion in Prestellar Cores. The CS molecule is known to be adsorbed onto dust in cold and dense conditions, causing it to be significantly depleted in the central region of cores. This study is aimed to investigate the depletion of the CS molecule using the optically thin {C}34{S} molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197, using two molecular lines, {C}34S (J = 2 - 1) and {N}2{H}+ (J = 1 - 0) with the NRO 45 m telescope, doubling the number of cores where the CS depletion was probed using {C}34S . In most of our targets, the distribution of {C}34S emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to {H}2 directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of ∼3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced, by an order of magnitude, when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line of sight is removed. Except for L1197—which is classified as relatively the least evolved core in our targets, based on its observed physical parameters—we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region, regardless of the relative difference in their evolutionary status.

Keywords: Interstellar molecules, Abundance ratios, Star forming regions, Dense interstellar clouds, Interstellar medium, Meridian circles
A Decade of Multiwavelength Observations of the TeV Blazar 1ES 1215+303: Extreme Shift of the Synchrotron Peak Frequency and Long-term Optical-Gamma-Ray Flux Increase. Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z = 0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.

Keywords: Jets, BL Lacertae objects, Blazars, Active galaxies, Gamma-rays
COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition. We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a comoving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855+45.4184; d = 31.5 pc) and a T4 companion (PSO J058.9869+45.4296) at a 40"6 (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf's age ({7.3}-1.6+2.8 Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters ({T}eff={1255}-8+6 K, log g={5.44}-0.03+0.02 dex, R={0.789}-0.005+0.011 {R}Jup), we find that cloudless model atmospheres have brighter Y- and J-band fluxes than the data, suggesting that condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 μm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6-T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is well known, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈200-300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.

Keywords: White dwarf stars, Brown dwarfs, Substellar companion stars