Sazuna/UAT_keywords huggingface dataset:
Sun-like Stars Shed Light on Solar Climate Forcing. Recently published precise stellar photometry of 72 Sun-like stars obtained at the Fairborn Observatory between 1993 and 2017 is used to set limits on the solar forcing of Earth's atmosphere of ±4.5 W m-2 since 1750. This compares with the +2.2 ± 1.1 W m-2 IPCC estimate for anthropogenic forcing. Three critical assumptions are made. In decreasing order of importance they are: (a) most of the brightness variations occur within the average time series length of ≈17 yr; (b) the Sun seen from the ecliptic behaves as an ensemble of middle-aged solar-like stars; and (c) narrowband photometry in the Strömgren b and y bands are linearly proportional to the total solar irradiance. Assumption (a) can best be relaxed and tested by obtaining more photometric data of Sun-like stars, especially those already observed. Eight stars with near-solar parameters have been observed from 1999, and two since 1993. Our work reveals the importance of continuing and expanding ground-based photometry, to complement expensive solar irradiance measurements from space.

Keywords: The Sun, Solar spectral irradiance, Solar analogs
A Word to the WISE: Confusion is Unavoidable for WISE-selected Infrared Excesses. Stars with excess infrared radiation from circumstellar dust are invaluable for studies of exoplanetary systems, informing our understanding of processes of planet formation and destruction alike. All-sky photometric surveys have made the identification of dusty infrared excess candidates trivial, however, samples that rely on data from Wise Infrared Survey Explorer (WISE) are plagued with source confusion, leading to high false-positive rates. Techniques to limit its contribution to WISE-selected samples have been developed, and their effectiveness is even more important as we near the end-of-life of Spitzer, the only facility capable of confirming the excess. Here, we present a Spitzer follow-up of a sample of 22 WISE-selected infrared excess candidates near the faint-end of the WISE detection limits. Eight of the 22 excesses are deemed the result of source confusion, with the remaining candidates all confirmed by the Spitzer data. We consider the efficacy of ground-based near-infrared imaging and astrometric filtering of samples to limit confusion among the sample. We find that both techniques are worthwhile for vetting candidates, but fail to identify all of the confused excesses, indicating that they cannot be used to confirm WISE-selected infrared excess candidates, but only to rule them out. This result confirms the expectation that WISE-selected infrared excess samples will always suffer from appreciable levels of contamination, and that care should be taken in their interpretation regardless of the filters applied.

Keywords: Infrared excess, White dwarf stars, Circumstellar dust
The Energy Sources of Double-peaked Superluminous Supernova PS1-12cil and Luminous Supernova SN 2012aa. In this paper, we present the study of the energy reservoir powering the light curves (LCs) of PS1-12cil and SN 2012aa, which are superluminous and luminous supernovae (SNe), respectively. The multiband and bolometric LCs of these two SNe show unusual secondary bumps after the main peaks. The two-peaked LCs cannot be explained by any simple energy-source models (e.g., the 56Ni cascade decay model, the magnetar spindown model, or the ejecta-circumstellar medium interaction model). Therefore, we employ the 56Ni plus ejecta-circumstellar medium (CSM) interaction (CSI) model, the magnetar plus CSI model, and the double CSI model to fit their bolometric LCs, and find that both these two SNe can be explained by the double CSI model and the magnetar plus CSI model. Based on the modeling, we calculate the the time when the shells were expelled by the progenitors: provided that they were powered by double ejecta-shell CSI, the inner and outer shells might be expelled ∼0.2-3.6 and ∼2-25 yr before the explosions of the SNe, respectively; the shells were expelled ∼2-20 yr before the explosions of the SNe if they were powered by magnetars plus CSI.

Keywords: Magnetars, Circumstellar matter, Supernovae, Stellar mass loss
Torsional Alfvénic Oscillations Discovered in the Magnetic Free Energy during Solar Flares. We report the discovery of torsional Alfvénic oscillations in solar flares, which modulate the time evolution of the magnetic free energy Ef(t), while the magnetic potential energy Ep(t) is uncorrelated, and the nonpotential energy varies as Enp(t) = Ep + Ef(t). The mean observed time period of the torsional oscillations is Pobs = 15.1 ± 3.9 minutes, the mean field line length is L = 135 ± 35 Mm, and the mean phase speed is Vphase = 315 ± 120 km s-1, which we interpret as torsional Alfvénic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the free energy, indicating new emerging flux (if positive), magnetic cancellation, or flare energy dissipation (if negative). The time evolution of the free energy has been calculated in this study with the Vertical-current Approximation (Version 4) Non-linear Force-free Field code, which incorporates automatically detected coronal loops in the solution and bypasses the non-force-freeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.

Keywords: Solar coronal loops, Solar flares, Magnetic fields
Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions. Pyroxenes ((Ca, Mg, Fe, Mn)2Si2O6) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO3) by He2+ ions was investigated. Thin films of CaSiO3 deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He2+ ions show a significant increase in sputtering, as compared to equally fast He+ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar8+ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.

Keywords: Lunar composition, Exosphere, The Moon, Solar wind, Laboratory astrophysics, Mercury (planet)
Pathways to Dissipation in Weakly Collisional Plasmas. Observed turbulence in space and astrophysics is expected to involve cascade and subsequent dissipation and heating. Contrary to standard collisional fluid turbulence, the weakly collisional magnetized plasma cascade may involve several channels of energy conversion, interchange, and spatial transport, leading eventually to the production of internal energy. This paper describes these channels of transfer and conversion, collectively amounting to a complex generalization of the Kolmogorov cascade. Channels may be described using compressible magnetohydrodynamic (MHD) and multispecies Vlasov-Maxwell formulations. Key steps are conservative transport of energy in space, parallel incompressible and compressible cascades in scale, electromagnetic work on particles driving macroscopic and microscopic flows, and pressure-strain interactions, both compressive and shear-like, that produce internal energy. A significant contrast with the collisional case is that the steps leading to the disappearance of large-scale energy in favor of internal energy are formally reversible. This property motivates a discussion of entropy, reversibility, and the relationship between dissipation with collisions and in the Vlasov system without collisions. Where feasible, examples are given from MHD and Particle in Cell simulations and from MMS observations.

Keywords: Space plasmas, Plasma physics, Interplanetary turbulence, Solar coronal heating, Plasma astrophysics, Solar wind
Temporal Evolution of Spatially Resolved Individual Star Spots on a Planet-hosting Solar-type Star: Kepler-17. Star spot evolution is visible evidence of the emergence/decay of the magnetic field on a stellar surface, and it is therefore important for the understanding of the underlying stellar dynamo and consequential stellar flares. In this paper, we report the temporal evolution of individual star spot areas on the hot-Jupiter-hosting, active solar-type star Kepler-17, whose transits occur every 1.5 days. The spot longitude and area evolution are estimated (1) from the stellar rotational modulations of Kepler data and (2) from the brightness enhancements during the exoplanet transits caused by existence of large star spots. As a result of the comparison, the number of spots, spot locations, and the temporal evolution derived from the rotational modulations are largely different from those of in-transit spots. We confirm that, although only two light-curve minima appear per rotation, there are clearly many spots present on the star. We find that the observed differential intensity changes are sometimes consistent with the spot pattern detected by transits, but at other times they do not match with each other. Although the temporal evolution derived from the rotational modulation differs from those of in-transit spots to a certain degree, the emergence/decay rates of in-transit spots are within an order of magnitude of those derived for sunspots as well as our previous research based only on rotational modulations. This supports the hypothesis that the emergence/decay of sunspots and extremely large star spots on solar-type stars occur through the same underlying processes.

Keywords: Starspots, Sunspots, Stellar magnetic fields, Solar magnetic fields, Magnetic variable stars
Unraveling the Nature of the Deeply Embedded Wolf-Rayet Star WR 121a. An X-ray study of the deeply embedded Wolf-Rayet star WR 121a has been carried out using long-term (spanning over ∼12 yr) archival observations from Chandra and XMM-Newton. For the first time, a periodic variation of 4.1 days has been detected in the X-ray light curve of WR 121a. No companion is seen in a merged and exposure-corrected Chandra X-ray image of WR 121a, as found in other previous observations in the J band. The X-ray spectrum of WR 121a is well explained by a thermal plasma emission model with temperatures of 0.98 ± 0.34 keV and 3.55 ± 0.69 keV for the cool and hot components, respectively, and nonsolar abundances. The present study indicates that WR 121a is an X-ray-bright massive binary with an X-ray luminosity of ∼1034 erg s-1, which can be explained by active wind collision between its components. Phase-locked modulations have been seen in the flux variation of WR 121a where the flux increases by a factor of ∼1.6 from minimum to maximum in the 0.3-10.0 keV energy band. These variations could be caused by the wind collision region being eclipsed by the secondary star in a binary orbit. The winds of both components of WR 121a appear to be radiative. Radiative inhibition and radiative braking are the most likely processes that are severely affecting the wind collision in this short-period massive binary system.

Keywords: Early-type stars, Binary stars, WN stars, Stellar winds, Wolf-Rayet stars, X-ray stars
Diffuse Lyα Halos around 300 Spectroscopically Confirmed Lyα Emitters at z ∼ 5.7. We report the detection of diffuse Lyα halos (LAHs) around star-forming galaxies at z ∼ 5.7 by stacking 310 spectroscopically confirmed Lyα emitters (LAEs). The majority of the LAEs are identified from our spectroscopic survey of galaxies at z &gt; 5.5. They are all located in well-studied fields with deep narrowband and broadband imaging data. We combine the LAE sample and its subsamples in the narrowband NB816 (I.e., the Lyα band) and z band (I.e., the continuum band). By comparing the stacked objects with their corresponding point-spread functions, we clearly detect extended LAHs around these LAEs. We perform sophisticated simulations and analyses on statistical and systematic errors, and confirm that the detected halos are not caused by errors. The scale lengths of the LAHs, when described by a double-component model, range from 1.2 to 5.3 kpc with a typical value of ∼2 kpc. The LAH sizes from our sample are in agreement with those of individual LAEs at the similar redshift measured by Very Large Telescope/MUSE but are relatively smaller than those of photometrically selected LAEs in previous studies. We also find that LAEs with higher Lyα luminosities, higher UV-continuum luminosities, or smaller Lyα equivalent widths tend to have larger LAH sizes. Our results are consistent with a scenario that LAHs originate from the scattered light of the central galaxies by H I gas in the circumgalactic medium.

Keywords: Lyman-alpha galaxies, High-redshift galaxies, Galaxy properties, Circumgalactic medium
Physical Origin of GeV Emission in the Early Phase of GRB 170405A: Clues from Emission Onsets with Multiwavelength Observations. The origin of GeV emission from the early epoch of gamma-ray bursts (GRBs) is a widely discussed issue. The long gamma-ray burst GRB 170405A, observed by the Fermi Gamma-ray Space Telescope, showed high-energy emission delayed by ∼20 s with respect to the X-ray emission, followed by temporally fading gamma-ray emission lasting for ∼1000 s, as commonly observed in high-energy GRBs. In addition, a high-energy spectral cutoff at ∼50 MeV was detected in the prompt-emission phase. If this feature is caused by pair-production opacity, the bulk Lorentz factor of the GRB ejecta can be estimated to be Γbulk = 170-420. Simultaneously with Fermi, GRB 170405A was observed by the Swift/Burst Alert Telescope and X-ray telescope, and a clear optical onset was detected ∼200 s after the burst by the Swift/Ultraviolet Optical Telescope. By coupling the deceleration time to the derived bulk Lorentz factor, the deceleration time was found to correspond to the delayed onset in the optical band. While the delayed onset in the optical band is evidence that this emission had an external shock origin, the temporally extended emission in the GeV band before the optical onset is hard to reconcile with the standard synchrotron emission from the same external shock. This may imply that the common feature of GeV emission with a power-law decay does not necessarily have the same origin as the optical afterglow in all GRBs detected by the Fermi/Large Area Telescope, particularly in their early epoch. Another mechanism to explain the GeV emission in GRB 170405A may be required, such as an internal shock or inverse Compton emission.

Keywords: Gamma-ray bursts, Astronomy data analysis
Massive Stars in the SDSS-IV-APOGEE Survey: Wolf-Rayet Stars of the WN Type. In this paper, we describe the results obtained in our study of Galactic Wolf-Rayet stars of the WN type, using the APOGEE2 spectrographs. The APOGEE2 WN star near-infrared spectra presented here were selected through a careful examination of the APOGEE2 DR16 sample, being compound of at least one exemplar of each Wolf-Rayet star from WN4 to WN11 types. Besides the APOGEE2 WN sample, we also identified three new Galactic exemplars of the WN type. The first is WR 147-1, a narrow-lined Wolf-Rayet star of the WN4-5 type located in the direction of the Cygnus-X North complex. The two remaining objects, WR 48-11 and WR 48-12, are found at projected angular distances of several arcminutes southwest from the Danks 1 cluster. WR 48-12 has an estimated heliocentric distance of {7.0}-3.0+5.0 kpc, which is not compatible (within the quoted uncertainties) with that of about 3.8 ± 0.6 kpc for the G305 complex. On the other hand, WR 48-11 has a probable heliocentric distance of {19.0}-4.7+6.5 kpc, which is about three times that of the former, implying that it is probably placed well behind the G305 complex, perhaps at the outermost portion of the Perseus arm.

Keywords: Stellar types, O stars
Pileups and Migration Rates for Planets in Low-mass Disks. We investigate how planets interact with viscous accretion disks, in the limit that the disk is sufficiently low mass that the planet migrates more slowly than the disk material. In that case, the disk's surface density profile is determined by the disk being in viscous steady state (VSS) while overflowing the planet's orbit. We compute the VSS profiles with 2D hydrodynamical simulations, and show that disk material piles up behind the planet, with the planet effectively acting as a leaky dam. Previous 2D hydrodynamical simulations missed the pileup effect because of incorrect boundary conditions, while previous 1D models greatly overpredicted the pileup due to the neglect of nonlocal deposition. Our simulations quantify the magnitude of the pileup for a variety of planet masses and disk viscosities. We also calculate theoretically the magnitude of the pileup for moderately deep gaps, showing good agreement with simulations. For very deep gaps, current theory is inadequate, and we show why and what must be understood better. The pileup is important for two reasons. First, it is observable in directly imaged protoplanetary disks, and hence can be used to diagnose the mass of a planet that causes it or the viscosity within the disk. Second, it determines the planet's migration rate. Our simulations determine a new Type-II migration rate (valid for low-mass disks), and show how it connects continuously with the well-verified Type-I rate.

Keywords: Protoplanetary disks, Planet formation, Circumstellar disks
Saturn's Probable Interior: An Exploration of Saturn's Potential Interior Density Structures. The gravity field of a giant planet is typically our best window into its interior structure and composition. Through comparison of a model planet's calculated gravitational potential with the observed potential, inferences can be made about interior quantities, including possible composition and the existence of a core. Necessarily, a host of assumptions go into such calculations, making every inference about a giant planet's structure strongly model dependent. In this work, we present a more general picture by setting Saturn's gravity field, as measured during the Cassini Grand Finale, as a likelihood function driving a Markov Chain Monte Carlo exploration of the possible interior density profiles. The result is a posterior distribution of the interior structure that is not tied to assumed composition, thermal state, or material equations of state. Constraints on interior structure derived in this Bayesian framework are necessarily less informative, but are also less biased and more general. These empirical and probabilistic constraints on the density structure are our main data product, which we archive for continued analysis. We find that the outer half of Saturn's radius is relatively well constrained, and we interpret our findings as suggesting a significant metal enrichment, in line with atmospheric abundances from remote sensing. As expected, the inner half of Saturn's radius is less well constrained by gravity, but we generally find solutions that include a significant density enhancement, which can be interpreted as a core, although this core is often lower in density and larger in radial extent than typically found by standard models. This is consistent with a dilute core and/or composition gradients.

Keywords: Planet formation, Saturn, Planetary interior, Planetary structure
Simulation of Alfvén Wave Propagation in the Magnetic Chromosphere with Radiative Loss: Effects of Nonlinear Mode Coupling on Chromospheric Heating. We perform magnetohydrodynamic simulations to investigate the propagation of Alfvén waves in the magnetic chromosphere. We use the 1.5D expanding flux tube geometry setting and transverse perturbation at the bottom to generate the Alfvén wave. Compared with previous studies, our expansion is that we include the radiative loss term introduced by Carlsson &amp; Leenaarts. We find that when an observation-based transverse wave generator is applied, the spatial distribution of the time-averaged radiative loss profile in our simulation is consistent with that in the classic atmospheric model. In addition, the energy flux in the corona is larger than the required value for coronal heating in the quiet region. Our study shows that the Alfvén wave-driven model has the potential to simultaneously explain chromospheric heating and how energy is transported to the corona.

Keywords: Solar chromospheric heating, Solar chromosphere
Atmosphere Origins for Exoplanet Sub-Neptunes. Planets with 2 R⊕ &lt; R &lt; 3 R⊕ and orbital period &lt;100 days are abundant; these sub-Neptune exoplanets are not well understood. For example, Kepler sub-Neptunes are likely to have deep magma oceans in contact with their atmospheres, but little is known about the effect of the magma on the atmosphere. Here we study this effect using a basic model, assuming that volatiles equilibrate with magma at T ∼ 3000 K. For our Fe-Mg-Si-O-H model system, we find that chemical reactions between the magma and the atmosphere and dissolution of volatiles into the magma are both important. Thus, magma matters. For H, most moles go into the magma, so the mass target for both H2 accretion and H2 loss models is weightier than is usually assumed. The known span of magma oxidation states can produce sub-Neptunes that have identical radius but with total volatile masses varying by 20-fold. Thus, planet radius is a proxy for atmospheric composition but not for total volatile content. This redox diversity degeneracy can be broken by measurements of atmosphere mean molecular weight. We emphasize H2 supply by nebula gas, but also consider solid-derived H2O. We find that adding H2O to Fe probably cannot make enough H2 to explain sub-Neptune radii because &gt;103 km thick outgassed atmospheres have high mean molecular weight. The hypothesis of magma-atmosphere equilibration links observables such as atmosphere H2O/H2 ratio to magma FeO content and planet formation processes. Our model's accuracy is limited by the lack of experiments (lab and/or numerical) that are specific to sub-Neptunes; we advocate for such experiments.

Keywords: Extrasolar rocky planets, Exoplanet evolution, Exoplanet formation, Exoplanet atmospheres