adsabs/SciX_UAT_keywords huggingface dataset:
The Relationships among Solar Flare Impulsiveness, Energy Release, and Ribbon Development

We develop the impulsiveness index, a new classification system for solar flares using the Solar Dynamics Observatory/Extreme Ultraviolet Experiment 304 Å Sun-as-a-star light curves. Impulsiveness classifies events based on the duration and intensity of the initial high-energy deposition of energy into the chromosphere. In stellar flare U-band light curves, Kowalski et al. found that impulsiveness is related to quantities such as a proxy for the Balmer jump ratio. However, the lack of direct spatial resolution in stellar flares limits our ability to explain this phenomenon. We calculate impulsiveness for 1368 solar flares between 2010 April and 2014 May. We divide events into categories of low, mid, and high impulsiveness. We find, in a sample of 480 flares, that events with high maximum reconnection rate tend to also have high impulsiveness. For six case studies, we compare impulsiveness to magnetic shear, ribbon evolution, and energy release. We find that the end of the 304 Å light-curve rise phase in these case studies corresponds to the cessation of polarity inversion line (PIL)-parallel ribbon motion, while PIL-perpendicular motion persists afterward in most cases. The measured guide-field ratio for low- and mid-impulsiveness case-study flares decreases about an order of magnitude during the impulsive flare phase. Finally, we find that, in four of the six case studies, flares with higher, more persistent shear tend to have low impulsiveness. Our study suggests that impulsiveness may be related to other properties of the impulsive phase, though more work is needed to verify this relationship and apply our findings to stellar flare physics.

Keywords: active solar chromosphere; active sun; solar activity; solar active region magnetic fields; solar active regions; solar chromospheric heating; solar chromosphere; solar electromagnetic emission; solar flares; solar magnetic reconnection; solar x-ray flares
The Runaway Greenhouse Effect on Hycean Worlds

Hycean worlds are a proposed subset of sub-Neptune exoplanets with substantial water inventories, liquid surface oceans, and extended hydrogen-dominated atmospheres favorable for habitability. We aim to quantitatively define the inner edge of the Hycean habitable zone (HZ) using a 1D radiative-convective model. As a limiting case, we model a dry hydrogen-helium envelope above a surface ocean. For a 1 bar (10,100 bar) atmosphere, the hydrogen greenhouse effect alone sets the inner edge of the HZ at 0.216 au (0.58, 3.71 au) for a Sun-like G star and at 0.0364 au (0.110, 0.774 au) for an 3500 K M star. Introducing water vapor into the atmosphere, the runaway greenhouse instellation limit is greatly reduced due to the presence of superadiabatic layers where convection is inhibited. This moves the inner edge of the HZ from ≈1 au for a G star to 1.6 au (3.85 au) for a Hycean world with a H2-He inventory of 1 bar (10 bar). For an M star, the inner edge is equivalently moved from 0.17-0.28 au (0.54 au). Our results suggest that most of the current Hycean world observational targets are not likely to sustain a liquid water ocean. We present an analytical framework for interpreting our results, finding that the maximum possible outgoing longwave radiation scales approximately inversely with the dry mass inventory of the atmosphere. We discuss the possible limitations of our 1D modeling and recommend the use of 3D convection-resolving models to explore the robustness of superadiabatic layers.

Keywords: exoplanet atmospheres; exoplanet atmospheric structure; exoplanet atmospheric composition; habitable planets; habitable zone; exoplanet atmospheric dynamics
Energetic Proton Propagation and Acceleration Simulated for the Bastille Day Event of 2000 July 14

This work presents results from simulations of the 2000 July 14 ("Bastille Day") solar proton event. We used the Energetic Particle Radiation Environment Model (EPREM) and the CORona-HELiosphere (CORHEL) software suite within the SPE Threat Assessment Tool (STAT) framework to model proton acceleration to GeV energies due to the passage of a CME through the low solar corona, and we compared the model results to GOES-08 observations. The coupled simulation models particle acceleration from 1 to 20 R⊙, after which it models only particle transport. The simulation roughly reproduces the peak event fluxes and the timing and spatial location of the energetic particle event. While peak fluxes and overall variation within the first few hours of the simulation agree well with observations, the modeled CME moves beyond the inner simulation boundary after several hours. The model therefore accurately describes the acceleration processes in the low corona and resolves the sites of most rapid acceleration close to the Sun. Plots of integral flux envelopes from multiple simulated observers near Earth further improve the comparison to observations and increase potential for predicting solar particle events. Broken power-law fits to fluence spectra agree with diffusive acceleration theory over the low energy range. Over the high energy range, they demonstrate the variability in acceleration rate and mirror the interevent variability observed in solar cycle 23 ground-level enhancements. We discuss ways to improve STAT predictions, including using corrected GOES energy bins and computing fits to the seed spectrum. This paper demonstrates a predictive tool for simulating low-coronal solar energetic particle acceleration.

Keywords: solar energetic particles; solar activity; solar coronal mass ejections; solar storm
Magellan/M2FS and MMT/Hectochelle Spectroscopy of Dwarf Galaxies and Faint Star Clusters within the Galactic Halo

We present spectroscopic data for 16,369 stellar targets within and/or toward 38 dwarf spheroidal galaxies and faint star clusters within the Milky Way halo environment. All spectra come from observations with the multiobject, fiber-fed echelle spectrographs M2FS at the Magellan/Clay telescope or Hectochelle at the MMT, reaching a typical limiting magnitude G ≲ 21. Data products include processed spectra from all observations and catalogs listing estimates-derived from template model fitting-of line-of-sight velocity (median uncertainty 1.4 km s-1) effective temperature (255 K), (base-10 logarithm of) surface gravity (0.59 dex in cgs units), [Fe/H] (0.4 dex) and [Mg/Fe] (0.27 dex) abundance ratios. The sample contains multiepoch measurements for 3720 sources, with up to 15 epochs per source, enabling studies of intrinsic spectroscopic variability. The sample contains 6087 likely red giant stars (based on surface gravity), and 4492 likely members (based on line-of-sight velocity and Gaia-measured proper motion) of the target systems. The number of member stars per individual target system ranges from a few, for the faintest systems, to ~850 for the most luminous. For most systems, our new samples extend over wider fields than have previously been observed; of the likely members in our samples, 820 lie beyond 2 times the projected half-light radius of their host system, and 42 lie beyond 5 R half. * This paper presents data gathered with the Magellan Telescopes at Las Campanas Observatory, Chile, and the MMT Observatory, a joint facility of the Smithsonian Institution, and the University of Arizona.

Keywords: dark matter; milky way dark matter halo; galaxy dark matter halos; dark matter distribution; dwarf galaxies; dwarf spheroidal galaxies; milky way stellar halo; spectroscopy; radial velocity; metallicity; chemical abundances
Observed Polarized Scattered Light Phase Functions of Planet-forming Disks

Dust particles are the building blocks from which planetary bodies are made. A major goal of studies of planet-forming disks is to constrain the properties of dust particles and aggregates in order to trace their origin, structure, and the associated growth and mixing processes in the disk. Observations of the scattering and/or emission of dust in a location of the disk often lead to degenerate information about the kinds of particles involved, such as the size, porosity, or fractal dimensions of aggregates. Progress can be made by deriving the full (polarizing) scattering phase function of such particles at multiple wavelengths. This has now become possible by careful extraction from scattered light images. Such an extraction requires knowledge about the shape of the scattering surface in the disk, and we discuss how to obtain such knowledge as well as the associated uncertainties. We use a sample of disk images from observations with the Very Large Telescope/SPHERE to, for the first time, extract the phase functions of a whole sample of disks with broad phase-angle coverage. We find that polarized phase functions come in two categories. Comparing the extracted functions with theoretical predictions from rigorous T-Matrix computations of aggregates, we show that one category can be linked back to fractal, porous aggregates, while the other is consistent with more compact, less porous aggregates. We speculate that the more compact particles become visible in disks where embedded planets trigger enhanced vertical mixing.

Keywords: exoplanets; planet formation; protoplanetary disks; circumstellar disks; high contrast techniques; direct imaging; polarimetry
Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

The Imaging X-ray Polarimetry Explorer measured with high significance the X-ray polarization of the brightest Z-source, Sco X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0% ± 0.2% and a polarization angle of 8° ± 6° at a 90% confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broadband spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasiperiodic oscillations. From a spectropolarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% confidence level, compatible with expectations for an electron scattering dominated optically thick atmosphere at the Sco X-1 inclination of ~44°; for the higher-energy Comptonized component, we obtain a polarization of 1.3% ± 0.4%, in agreement with expectations for a slab of Thomson optical depth of ~7 and an electron temperature of ~3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or a change in the corona geometry with the accretion flow.

Keywords: polarimetry; spectropolarimetry; neutron stars; accretion; stellar accretion disks; low-mass x-ray binary stars; x-ray telescopes
Planetary Refractory Composition and Volatile Accretion into Gas Giants in the Protoplanetary Disks of the Sun and WASP-12

We present a detailed theoretical exploration of the refractory compositions and volatile enrichments of planets forming in protoplanetary disks with solar-like conditions. The two cases of the Sun and WASP-12 are studied due to the availability of spectral measurements and their known planets. The distribution throughout their disks of solid compounds with a wide range of volatilities is computed by a comprehensive chemical thermodynamics code. After the calculation of refractory compounds down to the water snowline, the compositional distributions are documented for planets generated in certain locations of protoplanetary disks depending on thermodynamic conditions. These results are referred to proposed bulk compositions for solar terrestrial planets, and for the core of the hot Jupiter WASP-12b. The material left over after the formation of rocky components is collected and treated in calculations to determine the abundances of fundamental volatile molecules in the outer regions of the disks. The distributions of planetesimal volatile composition are then altered for four different cases of the carbon-to-oxygen ratios, and for oxidizing and reducing conditions, in order to adjust the best fit for the accretion zone of Jupiter and WASP-12b. We compare the Jovian results to in situ atmospheric measurements from Jupiter's atmosphere. Overall, this study proposes a holistic approach to estimate possible planetary interior and envelope compositions from hot toward cold disk zones, along with the mass of planetesimals accreted into the envelopes of gas giants.

Keywords: exoplanets; hot jupiters; solar system planets; atmospheric composition; solar system terrestrial planets; cosmochemistry; extrasolar rocky planets; extrasolar gaseous giant planets; protoplanetary disks; astrochemistry
Manifestation of Rossby Waves in the Global Magnetic Field of the Sun during Cycles 21-24

The evolution of the solar global magnetic field (GMF) was investigated and compared with oscillations of different periods during cycles 21-24. The data from the Wilcox Solar Observatory were used. The results indicate that GMF structures were associated with certain oscillations. Oscillations of 81.83-163.65 days were associated with structures lasting 10-20 CRs. They occurred as some pulses during solar maxima. Oscillations of 163.652-463.680 days were associated with GMF structures lasting ≈20-50 CRs. They match two peaks in the magnetic-field cycle. Oscillations of 1.270-5.231 yr were formed during the dominance of the sectorial GMF structure. Oscillations of 5.231-13.451 yr were the most intense. From cycle 22 to 24, their intensity decreased, and the range of periods narrowed and shifted to longer periods, determining the corresponding changes in the oscillations of 81.83 days-5.231 yr and associated GMF structures. They match well the evolution of the zonal GMF structure. They are assumed to be a descending part of a period of ≈≥60 yr. A decrease in the magnetic field from cycle 22 to 24 may be due to a decrease in the intensity of these oscillations. Some periodicities of the revealed oscillations are in good agreement with the estimates of the periods for fast magnetic Rossby waves. The GMF structure connection with Rossby waves is discussed.

Keywords: wavelet analysis; solar photosphere; solar cycle; solar oscillations; solar magnetic fields
CUTE Reveals Escaping Metals in the Upper Atmosphere of the Ultrahot Jupiter WASP-189b

Ultraviolet observations of ultrahot Jupiters, exoplanets with temperatures over 2000 K, provide us with an opportunity to investigate if and how atmospheric escape shapes their upper atmosphere. Near-ultraviolet transit spectroscopy offers a unique tool to study this process owing to the presence of strong metal lines and a bright photospheric continuum as the light source against which the absorbing gas is observed. WASP-189b is one of the hottest planets discovered to date, with a dayside temperature of about 3400 K orbiting a bright A-type star. We present the first near-ultraviolet observations of WASP-189b, acquired with the Colorado Ultraviolet Transit Experiment (CUTE). CUTE is a 6U NASA-funded ultraviolet spectroscopy mission, dedicated to monitoring short-period transiting planets. WASP-189b was one of the CUTE early science targets and was observed during three consecutive transits in 2022 March. We present an analysis of the CUTE observations and results demonstrating near-ultraviolet (2500-3300 Å) broadband transit depth ( ${1.08}_{-0.08}^{+0.08} \% $ ) of about twice the visual transit depth indicating that the planet has an extended, hot upper atmosphere with a temperature of about 15,000 K and a moderate mass-loss rate of about 4 × 108 kg s-1. We observe absorption by Mg II lines (R p /R s of ${0.212}_{-0.061}^{+0.038}$ ) beyond the Roche lobe at >4σ significance in the transmission spectrum at a resolution of 10 Å, while at lower resolution (100 Å), we observe a quasi-continuous absorption signal consistent with a "forest" of low-ionization metal absorption dominated by Fe II. The results suggest an upper atmospheric temperature (~15,000 K), higher than that predicted by current state-of-the-art hydrodynamic models.

Keywords: exoplanets; near ultraviolet astronomy; astronomical techniques; spectroscopy; exoplanet atmospheres; transits; exoplanet atmospheric composition; space observatories
Zwicky Transient Facility Observations of Trojan Asteroids: A Thousand Colors, Rotation Amplitudes, and Phase Functions

We introduce a new method for analyzing sparse photometric data of asteroids and apply it to Zwicky Transient Facility observations of the Jupiter Trojan asteroids. This method relies on the creation of a likelihood model that includes the probability distribution of rotational brightness variations at an unknown rotation phase. The likelihood model is analyzed via a Markov Chain Monte Carlo to quantify the uncertainty in our parameter estimates. Using this method, we provide color, phase parameter, absolute magnitude, and amplitude of rotation measurements for 1049 Jupiter Trojans. We find that phase parameter is correlated with color and the distribution of Trojan asteroid rotational amplitudes is indistinguishable from that of main-belt asteroids.

Keywords: light curves; multi-color photometry; jupiter trojans; sky surveys
Free-floating Planets, Survivor Planets, Captured Planets, and Binary Planets from Stellar Flybys

In star clusters, close stellar encounters can strongly impact the architecture of a planetary system or even destroy it. We present a systematic study of the effects of stellar flybys on two-planet systems. When such a system experiences flybys, one or both planets can be ejected, forming free-floating planets (FFPs), captured planets (CPs) around the flyby star, and free-floating binary planets (BPs); the remaining single-surviving planets (SSPs) can have their orbital radii and eccentricities greatly changed. Through numerical experiments, we calculate the formation fractions (or branching ratios) of FFPs, SSPs, CPs, and BPs as a function of the pericenter distance of the flyby, and use them to derive analytical expressions for the formation rates of FFPs, SSPs, CPs and BPs in general cluster environments. We find that the production rates of FFPs and SSPs are similar (for the initial planet semimajor axis ratio a 1/a 2 = 0.6–0.8), while the rate for CPs is a few times smaller. The formation fraction of BPs depends strongly on a 1/a 2 and on the planet masses. For Jupiter-mass planets, the formation fraction of BPs is always less than 1% (for a 1/a 2 = 0.8) and typically much smaller (≲0.2% for a 1/a 2 ≲ 0.7). The fraction remains less than 1% when considering 4M J planets. Overall, when averaging over all flybys, the production rate of BPs is less than 0.1% of that of FFPs. We also derive the velocity distribution of FFPs produced by stellar flybys, and the orbital parameter distributions of SSPs, CPs, and BPs. These results can be used in future studies of exotic planets (including FFPs) and planetary systems.

Keywords: planetary dynamics; extrasolar gaseous giant planets; free floating planets; star clusters
Standing Sausage Perturbations in Solar Coronal Slabs with Continuous Transverse Density Profiles: Cutoff Wavenumbers, Evanescent Eigenmodes, and Oscillatory Continuum

The lack of observed sausage perturbations in solar active region loops is customarily attributed to the relevance of cutoff axial wavenumbers and the consequent absence of trapped modes (called "evanescent eigenmodes" here). However, some recent eigenvalue problem studies suggest that cutoff wavenumbers may disappear for those equilibria where the external density varies sufficiently slowly, thereby casting doubt on the rarity of candidate sausage perturbations. We examine the responses of straight, transversely structured coronal slabs to small-amplitude sausage-type perturbations that excite axial fundamentals, by solving the pertinent initial value problem with eigensolutions for a closed domain. The density variation in the slab exterior is dictated by some steepness parameter μ, and cutoff wavenumbers are theoretically expected to be present (absent) when μ ≥ 2 (μ < 2). However, our numerical results show no qualitative difference in the system evolution when μ varies, despite the differences in the modal behavior. Only oscillatory eigenmodes are permitted when μ ≥ 2. Our discrete eigenspectrum becomes increasingly closely spaced when the domain broadens, and an oscillatory continuum results for a truly open system. Oscillatory eigenmodes remain allowed and dominate the system evolution when μ < 2. We show that the irrelevance of cutoff wavenumbers does not mean that all fast waves are evanescent. Rather, it means that an increasing number of evanescent eigenmodes emerge when the domain size increases. We conclude that sausage perturbations remain difficult to detect, even for the waveguide formulated here.

Keywords: magnetohydrodynamics; solar coronal waves; solar coronal seismology
Examining Uranus' ζ Ring in Voyager 2 Wide-angle Camera Observations: Quantifying the Ring's Structure in 1986 and Its Modifications Prior to the Year 2007

The ζ ring is the innermost component of the Uranian ring system. It is of scientific interest because its morphology changed significantly between the Voyager 2 encounter in 1986 and subsequent Earth-based observations around 2007. It is also of practical interest because some Uranus mission concepts have the spacecraft pass through the inner flank of this ring. Recent reexaminations of the Voyager 2 images have revealed additional information about this ring that provide a more complete picture of the ring's radial brightness profile and phase function. These data reveal that this ring's brightness varies with phase angle in a manner similar to other tenuous rings, consistent with it being composed primarily of submillimeter-sized particles. The total cross section of particles within this ring can also be estimated from these data, but translating that number into the actual risk to a spacecraft flying through this region depends on a number of model-dependent parameters. Fortunately, comparisons with Saturn's G and D rings allows the ζ ring's particle number density to be compared with regions previously encountered by the Voyager and Cassini spacecraft. Finally, these data indicate that the observed changes in the ζ ring's structure between 1986 and 2007 are primarily due to a substantial increase in the amount of dust at distances between 38,000 and 40,000 km from Uranus' center.

Keywords: planetary rings; uranus; dust physics