adsabs/SciX_UAT_keywords huggingface dataset:
Nekhoroshev Estimates for the Survival Time of Tightly Packed Planetary Systems

N-body simulations of nonresonant, tightly packed planetary systems have found that their survival time (I.e., time to first close encounter) grows exponentially with their interplanetary spacing and planetary masses. Although this result has important consequences for the assembly of planetary systems by giant collisions and their long-term evolution, this underlying exponential dependence is not understood from first principles, and previous attempts based on orbital diffusion have only yielded power-law scalings. We propose a different picture, where large deviations of the system from its initial conditions is due to a few slowly developing high-order resonances. Thus, we show that the survival time of the system T can be estimated using a heuristic motivated by Nekhoroshev's theorem, and obtain a formula for systems away from overlapping two-body mean-motion resonances as T/P={c1 a/Δa \exp (c2 Δa/a/μ,SUP>1/4), where P is the average Keplerian period, a is the average semimajor axis, Δa ≪ a is the difference between the semimajor axes of neighboring planets, μ is the planet-to-star mass ratio, and c1 and c2 are dimensionless constants. We show that this formula is in good agreement with numerical N-body experiments for c1 = 5 × 10-4 and c2 = 8.

Keywords: exoplanet dynamics; few-body systems; planetary system formation
The Early Ultraviolet Light Curves of Type II Supernovae and the Radii of Their Progenitor Stars

We present a sample of 34 normal Type II supernovae (SNe II) detected with the Zwicky Transient Facility, with multiband UV light curves starting at t ≤ 4 days after explosion, and X-ray observations. We characterize the early UV-optical color, provide empirical host-extinction corrections, and show that the t > 2 day UV-optical colors and the blackbody evolution of the sample are consistent with shock cooling (SC) regardless of the presence of "flash ionization" features. We present a framework for fitting SC models that can reproduce the parameters of a set of multigroup simulations up to 20% in radius and velocity. Observations of 15 SNe II are well fit by models with breakout radii <1014 cm. Eighteen SNe are typically more luminous, with observations at t ≥ 1 day that are better fit by a model with a large >1014 cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest that these large-breakout events are explosions of stars with an inflated envelope or with confined circumstellar material (CSM). Using the X-ray data, we derive constraints on the extended (∼1015 cm) CSM density independent of spectral modeling and find that most SN II progenitors lose up to a few years before explosion. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the of red supergiants (RSGs) explode as SNe II with breakout radii consistent with the observed distribution of RSGs, with a tail extending to large radii, likely due to the presence of CSM.

Keywords: type ii supernovae; core-collapse supernovae; shocks; plasma astrophysics; ultraviolet astronomy; ultraviolet transient sources; transient sources
The State of the Heliosphere Revealed by Limb-halo Coronal Mass Ejections in Solar Cycles 23 and 24

We compare the properties of halo coronal mass ejections (CMEs) that originate close to the limb (within a central meridian distance range of 60°-∼90°) during solar cycles 23 and 24 to quantify the effect of the heliospheric state on CME properties. There are 44 and 38 limb halos in cycles 23 and 24, respectively. Normalized to the cycle-averaged total sunspot number, there are 42% more limb halos in cycle 24. Although the limb halos as a population are very fast (average speed ∼1464 km s-1), cycle-24 halos are slower by ∼26% than the cycle-23 halos. We introduce a new parameter, the heliocentric distance of the CME leading edge at the time a CME becomes a full halo; this height is significantly shorter in cycle 24 (by ∼20%) and has a lower cutoff at ∼6 Rs. These results show that cycle-24 CMEs become halos sooner and at a lower speed than the cycle-23 ones. On the other hand, the flare sizes are very similar in the two cycles, ruling out the possibility of eruption characteristics contributing to the differing CME properties. In summary, this study reveals the effect of the reduced total pressure in the heliosphere that allows cycle-24 CMEs to expand more and become halos sooner than in cycle 23. Our findings have important implications for the space-weather consequences of CMEs in cycle 25 (predicted to be similar to cycle 24) and for understanding the disparity in halo counts reported by automatic and manual catalogs.

Keywords: heliosphere; radio bursts; solar coronal mass ejections; solar energetic particles; solar flares
The Origin of Inequality: Isolated Formation of a 30+10 M⊙ Binary Black Hole Merger

The LIGO/Virgo Collaboration has reported the detection of GW190412, a black hole-black hole (BH-BH) merger with the most unequal masses to date. (Another system, with even more unequal-mass components, was recently published by LIGO/Virgo: GW190814 (m1 = 23 $\,{M}_{\odot }$ , m2 = 2.6 $\,{M}_{\odot }$ ); however, it is not known whether it is a BH-BH or BH-NS merger (Abbott et al. 2020).) They are m1 = 24.4-34.7 $\,{M}_{\odot }$ and m2 = 7.4-10.1 $\,{M}_{\odot }$ , corresponding to a mass ratio of q = 0.21-0.41 (90% probability range). Additionally, GW190412's effective spin was estimated to be χeff = 0.14-0.34, with the spin of the primary BH in the range aspin = 0.17-0.59. Based on this and prior detections, ≳10% of BH-BH mergers have q ≲ 0.4. Major BH-BH formation channels (i.e., dynamics in dense stellar systems, classical isolated binary evolution, or chemically homogeneous evolution) tend to produce BH-BH mergers with comparable masses (typically with q ≳ 0.5). Here we test whether the classical isolated binary evolution channel can produce mergers resembling GW190412. We show that our standard binary evolution scenario, with the typical assumptions on input physics that we have used in the past, produces such mergers. For this particular model of the input physics the overall BH-BH merger rate density in the local universe (z ∼ 0) is $73.5\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ , while for systems with $q\lt 0.41$ the rate density is $6.8\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ . The results from our standard model are consistent with the masses and spins of the black holes in GW190412, as well as with the LIGO/Virgo estimate of the fraction of unequal-mass BH-BH mergers. As GW190412 shows some weak evidence for misaligned spins, we provide distribution of the precession parameter in our models and conclude that if among the new LIGO/Virgo detections the evidence of system precession is strong and more than 10% of BH-BH mergers have large in-plane spin components (χp > 0.5), then the common envelope isolated binary BH-BH formation channel can be excluded as their origin.

Keywords: black hole physics; high energy astrophysics; black holes; stellar evolution; stellar evolutionary models; compact objects; common envelope binary stars; gravitational wave sources
The Role of Far-ultraviolet Pumping in Exciting the [O I] Lines in Protostellar Disks and Winds

We use Cloudy to re-examine excitation of [O I] 6300 Å and [O I] 5577 Å in the X-ray driven photoevaporative wind models of Owen and collaborators, and in more recent magnetothermal models by Wang et al. We find that, at the measured accretion luminosities, the far-ultraviolet (FUV) radiation would populate the upper levels of the oxygen, which would eventually contribute to the [O I] lines. FUV pumping competes with collisions as an excitation mechanism of the [O I] lines, and they each originate from a distinct region in the protostellar disk environment. Consequently, the line strengths and shapes of [O I] 6300 Å and [O I] 5577 Å would be affected by the inclusion of FUV pumping in the radiation transport simulations.

Keywords: protoplanetary disks; atomic physics; atomic spectroscopy
Morphological Evolution of Ordinary Chondrite Microstructure during Heating: Implications for Atmospheric Entry

Meteoroid entry physics remain poorly understood, owing to the extreme conditions experienced by the meteoroid during hypervelocity atmospheric passage, which are not reproducible in ground-test facilities. Therefore, much of our knowledge of fundamental processes is based on bolide lightcurve inference and a posteriori analysis of recovered meteorites. Here, novel in situ microtomography experiments at entry-relevant temperatures were performed on samples of two ordinary chondrites: Tamdakht (H5) and Tenham (L6). The two meteorites were imaged while undergoing a temperature ramp from room temperature to 1200°C. A machine-learning mediated analysis of the microstructural evolution reveals incongruent melting of the meteorite, initiated by the meteoritic iron and iron sulfide grains, and subsequent flow through microcracks that leads to the evolution of large voids. This behavior is correlated to a broad, high-temperature endotherm, noted from differential scanning calorimetry analysis, indicative of the heat of fusion of the melting grains. Correspondingly, a surface elemental analysis indicates that the sulfur species in iron sulfide are highly mobile, which can result in the formation of nonstoichiometric iron-sulfur compounds with melting points that span the temperature range of the observed endotherm. The implications for entry phenomena, in particular meteoroid ablation, are discussed.

Keywords: meteoroids; meteorites; chondrites; impact phenomena
The Magnetic Field of the Active Planet-hosting M Dwarf AU Mic

AU Mic is a young, very active M dwarf star with a debris disk and at least one transiting Neptune-size planet. Here we present a detailed analysis of the magnetic field of AU Mic based on previously unpublished high-resolution optical and near-infrared spectropolarimetric observations. We report a systematic detection of circular and linear polarization signatures in the stellar photospheric lines. Tentative Zeeman Doppler imaging modeling of the former data suggests a nonaxisymmetric global field with a surface-averaged strength of about 90 G. At the same time, linear polarization observations indicate the presence of a much stronger ≈2 kG axisymmetric dipolar field, which contributes no circular polarization signal due to the equator-on orientation of AU Mic. A separate Zeeman broadening and intensification analysis allowed us to determine a mean field modulus of 2.3 and 2.1 kG from the Y- and K-band atomic lines, respectively. These magnetic field measurements are essential for understanding environmental conditions within the AU Mic planetary system.

Keywords: stellar activity; stellar magnetic fields; m dwarf stars
The Sixth Data Release of the Radial Velocity Experiment (RAVE). II. Stellar Atmospheric Parameters, Chemical Abundances, and Distances

We present part 2 of the sixth and final Data Release (DR6) of the Radial Velocity Experiment (RAVE), a magnitude-limited ( $9\lt I\lt 12$ ) spectroscopic survey of Galactic stars randomly selected in Earth's southern hemisphere. The RAVE medium-resolution spectra (R ∼ 7500) cover the Ca triplet region (8410-8795 Å) and span the complete time frame from the start of RAVE observations on 2003 April 12 to their completion on 2013 April 4. In the second of two publications, we present the data products derived from 518,387 observations of 451,783 unique stars using a suite of advanced reduction pipelines focusing on stellar atmospheric parameters, in particular purely spectroscopically derived stellar atmospheric parameters ( ${T}_{\mathrm{eff}}$ , $\mathrm{log}g$ , and the overall metallicity), enhanced stellar atmospheric parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar atmospheric parameters for giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [α/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios. The RAVE DR6 catalogs are cross-matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the RAVE website (http://rave-survey.org) or the Vizier database.

Keywords: surveys; sky surveys; milky way galaxy; milky way dynamics; galaxy stellar content; stellar populations; catalogs
BreakBRD Galaxies. I. Global Properties of Spiral Galaxies with Central Star Formation in Red Disks

We introduce a collection of primarily centrally star-forming galaxies that are selected by disk color to have truncated disk star formation. We show that common explanations for centrally concentrated star formation—low stellar mass, bars, and high-density environments—do not universally apply to this sample. To gain insight into our sample, we compare these galaxies to a parent sample of strongly star-forming galaxies and to a parent sample of galaxies with low specific star formation rates. We find that in star formation and color space from ultraviolet to the infrared these galaxies either fall between the two samples or agree more closely with galaxies with high specific star formation rates. Their morphological characteristics also lie between high and low specific star formation rate galaxies, although their Petrosian radii agree well with that of the low specific star formation rate parent sample. We discuss whether this sample is likely to be quenching or showing an unusual star formation distribution while continuing to grow through star formation. Future detailed studies of these galaxies will give us insights into how the local conditions within a galaxy balance environmental influence to govern the distribution of star formation. In this first paper in a series, we describe the global properties that identify this sample as separate from more average spiral galaxies, and we identify paths forward to explore the underlying causes of their differences.

Keywords: galaxy evolution; galaxy processes; galaxy physics; spiral galaxies; galaxy environments; extragalactic astronomy; galaxy quenching; quenched galaxies
Gas Density Perturbations in the Cool Cores of CLASH Galaxy Clusters

We present a systematic study of gas density perturbations in cool cores of high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool-core features observed with the Chandra X-ray Observatory. Here, we focus on the X-ray residual image characteristics after subtracting their global profile of the X-ray surface brightness distribution. We find that all of the galaxy clusters in our sample have, at least, both one positive and one negative excess regions in the X-ray residual image, indicating the presence of gas density perturbations. We identify and characterize the locally perturbed regions using our detection algorithm, and extract X-ray spectra of the intracluster medium (ICM). The ICM temperature in the positive excess region is lower than that in the negative excess region, whereas the ICM in both regions is in pressure equilibrium in a systematic manner. These results indicate that gas sloshing in cool cores takes place in more than 80% of relaxed clusters (95% CL). We confirm this physical picture by analyzing synthetic X-ray observations of a cool-core cluster from a hydrodynamic simulation, finding that our detection algorithm can accurately extract both the positive and negative excess regions and can reproduce the temperature difference between them. Our findings support the picture that the gas density perturbations are induced by gas sloshing, and a large fraction of cool-core clusters have undergone gas sloshing, indicating that gas sloshing may be capable of suppressing runaway cooling of the ICM.

Keywords: galaxy clusters; hydrodynamical simulations; intracluster medium; x-ray astronomy
Splitting and Reconstruction of a Solar Filament Caused by Magnetic Emergence and Reconnection

We present observations and interpretation of a nonerupting filament in NOAA active region (AR) 12827 that undergoes splitting and restructuring on 2021 June 4, using the high-resolution data obtained by the New Vacuum Solar Telescope, the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. At the beginning, the right footpoint of the filament is rooted in the AR positive polarity, and its right leg has a spread-out structure, which is confirmed by the extrapolated 3D magnetic structure. Many small positive and negative magnetic polarities connected by EUV-emitting loops gradually appear between two extensions of the right footpoint polarity as the extensions separate. The right leg of the filament is then observed to split into two parts, which continue to separate, while the left part of the filament still maintains a whole structure. As the newly emerged magnetic loops rise between the two parts of the right leg, magnetic reconnection occurs between the newly emerged magnetic loops and the magnetic fields supporting the southeastern splitting part. The longer magnetic loops resulting from this reconnection merge with the magnetic fields of the other part of the split filament leg, thus reforming an entire filament with a displaced right footpoint. We conclude that magnetic emergence is responsible for the splitting of the filament leg, while magnetic reconnection leads to the reconstruction of the filament.

Keywords: solar magnetic flux emergence; solar magnetic reconnection; solar magnetic fields
PHANGS-JWST First Results: The Dust Filament Network of NGC 628 and Its Relation to Star Formation Activity

PHANGS-JWST mid-infrared (MIR) imaging of nearby spiral galaxies has revealed ubiquitous filaments of dust emission in intricate detail. We present a pilot study to systematically map the dust filament network (DFN) at multiple scales between 25 and 400 pc in NGC 628. MIRI images at 7.7, 10, 11.3, and 21 μm of NGC 628 are used to generate maps of the filaments in emission, while PHANGS-HST B-band imaging yields maps of dust attenuation features. We quantify the correspondence between filaments traced by MIR thermal continuum/polycyclic aromatic hydrocarbon (PAH) emission and filaments detected via extinction/scattering of visible light; the fraction of MIR flux contained in the DFN; and the fraction of H II regions, young star clusters, and associations within the DFN. We examine the dependence of these quantities on the physical scale at which the DFN is extracted. With our highest-resolution DFN maps (25 pc filament width), we find that filaments in emission and attenuation are cospatial in 40% of sight lines, often exhibiting detailed morphological agreement; that ~30% of the MIR flux is associated with the DFN; and that 75%-80% of the star formation in H II regions and 60% of the mass in star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anticorrelated with looser associations of stars younger than 5 Myr identified using PHANGS-HST near-UV imaging. We discuss the impact of these findings on studies of star formation and the interstellar medium, and the broad range of new investigations enabled by multiscale maps of the DFN.

Keywords: interstellar medium; interstellar filaments; interstellar dust; dust continuum emission; extinction; star formation; star forming regions
A "Hyperburst" in the MAXI J0556-332 Neutron Star: Evidence for a New Type of Thermonuclear Explosion

The study of transiently accreting neutron stars provides a powerful means to elucidate the properties of neutron star crusts. We present extensive numerical simulations of the evolution of the neutron star in the transient low-mass X-ray binary MAXI J0556-332. We model nearly 20 observations obtained during the quiescence phases after four different outbursts of the source in the past decade, considering the heating of the star during accretion by the deep crustal heating mechanism complemented by some shallow heating source. We show that cooling data are consistent with a single source of shallow heating acting during the last three outbursts, while a very different and powerful energy source is required to explain the extremely high effective temperature of the neutron star, ~350 eV, when it exited the first observed outburst. We propose that a gigantic thermonuclear explosion, a "hyperburst" from unstable burning of neutron-rich isotopes of oxygen or neon, occurred a few weeks before the end of the first outburst, releasing ~1044 ergs at densities of the order of 1011 g cm-3. This would be the first observation of a hyperburst, and these would be extremely rare events, as the buildup of the exploding layer requires about a millennium of accretion history. Despite its large energy output, the hyperburst did not produce, due to its depth, any noticeable increase in luminosity during the accretion phase and is only identifiable by its imprint on the later cooling of the neutron star.

Keywords: neutron stars; accretion; low-mass x-ray binary stars; astrophysical explosive burning
Extensive Pollution of Uranus and Neptune's Atmospheres by Upsweep of Icy Material during the Nice Model Migration

In the Nice model of Solar System formation, Uranus and Neptune undergo an orbital upheaval, sweeping through a planetesimal disk. The region of the disk from which material is accreted by the ice giants during this phase of their evolution has not previously been identified. We perform direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment event, with collision rates as high as ∼3 per hour assuming km-sized planetesimals, increasing the total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the largest total enhancement. We determine that, for some plausible planetesimal properties, the resulting atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling timescale according to existing models. Our findings suggest that substantial accretion during this phase of planetary evolution may have been sufficient to impact the atmospheric composition and thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.

Keywords: solar system formation; uranus; neptune; planetesimals
Scattering Polarization of 3 μm Water-ice Feature by Large Icy Grains

Water ice has a strong spectral feature at a wavelength of approximately 3 μm, which plays a vital role in our understanding of the icy universe. In this study, we investigate the scattering polarization of this water-ice feature. The linear polarization degree of light scattered by micron-sized icy grains is known to be enhanced at the ice band; however, the dependence of this polarization enhancement on various grain properties is unclear. We find that the enhanced polarization at the ice band is sensitive to the presence of micron-sized grains as well as their ice abundance. We demonstrate that this enhancement is caused by the high absorbency of the water-ice feature, which attenuates internal scattering and renders the surface reflection dominant over internal scattering. Additionally, we compare our models with polarimetric observations of the low-mass protostar L1551 IRS 5. Our results show that scattering by a maximum grain radius of a few microns with a low water-ice abundance is consistent with observations. Thus, scattering polarization of the water-ice feature is a useful tool for characterizing ice properties in various astronomical environments.

Keywords: circumstellar dust; spectropolarimetry; ice destruction; near infrared astronomy