adsabs/SciX_UAT_keywords huggingface dataset:
Heating and Eruption of a Solar Circular-ribbon Flare

We studied a circular-ribbon flare, SOL2014-12-17T04:51, with emphasis on its thermal evolution as determined by the differential emission measure (DEM) inversion analysis of the extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. Both temperature and emission measure start to rise much earlier than the flare, along with an eruption and formation of a hot halo over the fan structure. In the main flare phase, another set of ribbons forms inside the circular ribbon, and expands as expected for ribbons at the footpoints of a postflare arcade. An additional heating event further extends the decay phase, which is also characteristic of some eruptive flares. The basic magnetic configuration appears to be a fan-spine topology, rooted in a minority-polarity patch surrounded by majority-polarity flux. We suggest that reconnection at the null point begins well before the impulsive phase, when the null is distorted into a breakout current sheet, and that both flare and breakout reconnection are necessary in order to explain the subsequent local thermal evolution and the eruptive activities in this confined magnetic structure. Using local DEMs, we found a postflare temperature increase inside the fan surface, indicating that the so-called EUV late phase is due to continued heating in the flare loops.

Keywords: the sun; solar physics
Structure and Rotation of Young Massive Star Clusters in a Simulated Dwarf Starburst

We analyze the three-dimensional shapes and kinematics of the young star cluster population forming in a high-resolution GRIFFIN project simulation of a metal-poor dwarf galaxy starburst. The star clusters, which follow a power-law mass distribution, form from the cold phase interstellar medium with an initial mass function sampled with individual stars down to four solar masses at sub-parsec spatial resolution. Massive stars and their important feedback mechanisms are modeled in detail. The simulated clusters follow a surprisingly tight relation between the specific angular momentum and mass with indications of two sub-populations. Massive clusters (Mcl ≳ 3 × 104 M⊙) have the highest specific angular momenta at low ellipticities (ɛ ∼ 0.2) and show alignment between their shapes and rotation. Lower mass clusters have lower specific angular momenta with larger scatter, show a broader range of elongations, and are typically misaligned indicating that they are not shaped by rotation. The most massive clusters (M ≳ 105 M⊙) accrete gas and protoclusters from a ≲100 pc scale local galactic environment on a t ≲ 10 Myr timescale, inheriting the ambient angular momentum properties. Their two-dimensional kinematic maps show ordered rotation at formation, up to v ∼ 8.5 km s-1, consistent with observed young massive clusters and old globular clusters, which they might evolve into. The massive clusters have angular momentum parameters λR ≲ 0.5 and show Gauss-Hermite coefficients h3 that are anti-correlated with the velocity, indicating asymmetric line-of-sight velocity distributions as a signature of a dissipative formation process.

Keywords: young star clusters; computational astronomy; stellar kinematics; star formation
ALMA 0.5 kpc Resolution Spatially Resolved Investigations of Nuclear Dense Molecular Gas Properties in Nearby Ultraluminous Infrared Galaxies Based on HCN and HCO+ Three Transition Line Data

We present the results of our ALMA ≲0.5 kpc resolution dense molecular line (HCN and HCO+ J = 2-1, J = 3-2, and J = 4-3) observations of 12 nearby (ultra)luminous infrared galaxies ([U]LIRGs). After matching beam sizes of all molecular line data to the same values in all (U)LIRGs, we derive molecular line flux ratios by extracting spectra in the central 0.5, 1, and 2 kpc circular regions and in 0.5-1 and 1-2 kpc annular regions. Based on non-local thermal equilibrium model calculations, we quantitatively confirm that the innermost (≲0.5 kpc) molecular gas is very dense (≳105 cm-3) and warm (≳300 K) in ULIRGs, and that in one LIRG, it is also modestly dense (104-5 cm-3) and warm (~100 K). We then investigate the spatial variation of the HCN-to-HCO+ flux ratios and high-J to low-J flux ratios of HCN and HCO+. A subtle sign of a decreasing trend in these ratios from the innermost (≲0.5 kpc) to the outer nuclear (0.5-2 kpc) region is discernible in a significant fraction of the observed ULIRGs. For two ULIRGS hosting an active galactic nucleus (AGN), which display the trend most clearly, we find based on a Bayesian approach that the HCN-to-HCO+ abundance ratio and gas kinetic temperature systematically increase from the outer nuclear to the innermost region. We suggest that this trend comes from potential AGN effects because no such spatial variation is found in a starburst-dominated LIRG.

Keywords: ultraluminous infrared galaxies; luminous infrared galaxies; supermassive black holes; active galactic nuclei; galaxy mergers; starburst galaxies; molecular spectroscopy; molecular gas; millimeter astronomy; submillimeter astronomy; radio interferometers; active galaxies
Core States of Neutron Stars from Anatomizing Their Scaled Structure Equations

Given an Equation of State (EOS) for neutron star (NS) matter, there is a unique mass-radius sequence characterized by a maximum mass ${M}_{\mathrm{NS}}^{\max }$ at radius R max. We first show analytically that the ${M}_{\mathrm{NS}}^{\max }$ and R max scale linearly with two different combinations of the NS central pressure P c and energy density ɛ c, by dissecting perturbatively the dimensionless Tolman-Oppenheimer-Volkoff (TOV) equations governing NS internal variables. The scaling relations are then verified via 87 widely used and rather diverse phenomenological as well as 17 microscopic NS EOSs with/without considering hadron-quark phase transitions and hyperons, by solving numerically the original TOV equations. The EOS of the densest NS matter allowed before it collapses into a black hole is then obtained. Using the universal ${M}_{\mathrm{NS}}^{\max }$ and R max scalings and Neutron Star Interior Composition Explorer and XMM-Newton mass-radius observational data for PSR J0740+6620, a very narrow constraining band on the NS central EOS is extracted directly from the data for the first time, without using any specific input EOS model.

Keywords: neutron star cores
Insight-HXMT Discovery of the Highest-energy CRSF from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

The detection of cyclotron resonance scattering features (CRSFs) is the only way to directly and reliably measure the magnetic field near the surface of a neutron star (NS). The broad energy coverage and large collection area of Insight-HXMT in the hard X-ray band allowed us to detect the CRSF with the highest energy known to date, reaching about 146 keV during the 2017 outburst of the first galactic pulsing ultraluminous X-ray source (pULX) Swift J0243.6+6124. During this outburst, the CRSF was only prominent close to the peak luminosity of ~2 × 1039 erg s-1, the highest to date in any of the Galactic pulsars. The CRSF is most significant in the spin-phase region corresponding to the main pulse of the pulse profile, and its centroid energy evolves with phase from 120 to 146 keV. We identify this feature as the fundamental CRSF because no spectral feature exists at 60-70 keV. This is the first unambiguous detection of an electron CRSF from an ULX. We also estimate a surface magnetic field of ~1.6 × 1013 G for Swift J0243.6+6124. Considering that the dipole magnetic field strengths, inferred from several independent estimates of magnetosphere radius, are at least an order of magnitude lower than our measurement, we argue that the detection of the highest-energy CRSF reported here unambiguously proves the presence of multipole field components close to the surface of the neutron star. Such a scenario has previously been suggested for several pulsating ULXs, including Swift J0243.6+6124, and our result represents the first direct confirmation of this scenario.

Keywords: binary pulsars; high mass x-ray binary stars; accretion; ultraluminous x-ray sources; magnetic fields; neutron stars
Morpheus Reveals Distant Disk Galaxy Morphologies with JWST: The First AI/ML Analysis of JWST Images

The dramatic first images with JWST demonstrated its power to provide unprecedented spatial detail for galaxies in the high-redshift universe. Here, we leverage the resolution and depth of the JWST Cosmic Evolution Early Release Science Survey data in the Extended Groth Strip to perform pixel-level morphological classifications of galaxies in JWST F150W imaging using the Morpheus deep-learning framework for astronomical image analysis. By cross-referencing with existing photometric redshift catalogs from the Hubble Space Telescope (HST) CANDELS survey, we show that JWST images indicate the emergence of disk morphologies before z ~ 2 and with candidates appearing as early as z ~ 5. By modeling the light profile of each object and accounting for the JWST point-spread function, we find the high-redshift disk candidates have exponential surface brightness profiles with an average Sérsic index <n> = 1.04 and >90% displaying "disky" profiles (n < 2). Comparing with prior Morpheus classifications in CANDELS we find that a plurality of JWST disk galaxy candidates were previously classified as compact based on the shallower HST imagery, indicating that the improved optical quality and depth of the JWST helps to reveal disk morphologies that were hiding in the noise. We discuss the implications of these early disk candidates on theories for cosmological disk galaxy formation.

Keywords: galaxy classification systems; neural networks; disk galaxies; galaxies; james webb space telescope
The Physical Properties of Low-redshift FeLoBAL Quasars. II. The Rest-frame Optical Emission Line Properties

We report the results of an analysis of the Hβ emission line region of a sample of 30 low-redshift (z < 1) iron low-ionization broad absorption line quasars (FeLoBALQs). Eleven of these objects are newly classified as FeLoBALQs. A matched sample of 132 unabsorbed quasars was analyzed in parallel. The emission lines showed the well-known anticorrelation between the [O III] and Fe II emission. Using a summary statistic called E1 to quantify this anticorrelation, we found that while the distribution of E1 for the unabsorbed quasars has a single peak, the FeLoBALQs have a bimodal shape in this parameter. Previous studies have shown that the line emission properties of BAL and non-BALQs are consistent; therefore, the difference in the Hβ region emission between FeLoBALQs and unabsorbed quasars is a new result. The two populations of FeLoBALQs are characterized by low and high bolometric luminosities and Eddington ratios. Some previous studies have suggested that BALQs are high accretion rate objects and therefore the discovery of the low accretion rate branch of FeLoBAL quasars was unexpected. We also found that the Hβ FWHM is systematically broader among the FeLoBALQs, implying a higher inclination viewing angle or a dearth of low velocity line emitting gas.

Keywords: broad-absorption line quasar; quasars
Statistical Mechanics of Collisionless Orbits. V. The Approach to Equilibrium for Idealized Self-gravitating Systems

Self-gravitating Newtonian systems consisting of a very large number of particles have generally defied attempts to describe them using statistical mechanics. This is paradoxical since many astronomical systems, or simulations thereof, appear to have universal, equilibrium structures for which no physical basis exists. A decade ago we showed that extremizing the number of microstates with a given energy per unit mass, under the constraints of conserved total energy and mass, leads to the maximum entropy state, $n(E)\propto \exp (-\beta (E-{{\rm{\Phi }}}_{0}))-1$ , known as DARKexp. This differential energy distribution, and the resulting density structures, closely approximate those of dark matter halos with central cusps, ρ ~ r -1, and outer parts, ρ ~ r -4. Here we define a nonequilibrium functional, S D , which is maximized for DARKexp and increases monotonically during the evolution toward equilibrium of idealized collisionless systems of the extended spherical infall model. Systems that undergo more mixing more closely approach DARKexp.

Keywords: dark matter; navarro-frenk-white profile; gravitation; newtonian gravitation; galaxy structure; galaxy dark matter halos; galaxy physics
High-resolution CARMA Observation of Molecular Gas in the North America and Pelican Nebulae

In this paper, we present the first results from a CARMA high-resolution 12CO(1-0), 13CO(1-0), and C18O(1-0) molecular line survey of the North America and Pelican (NAP) Nebulae. CARMA observations have been combined with single-dish data from the Purple Mountain 13.7 m telescope, to add short spacings and to produce high-dynamic-range images. We find that the molecular gas is predominantly shaped by the W80 H II bubble, driven by an O star. Several bright rims noted in the observation are probably remnant molecular clouds, heated and stripped by the massive star. Matching these rims in molecular lines and optical images, we construct a model of the three-dimensional structure of the NAP complex. Two groups of molecular clumps/filaments are on the near side of the bubble: one is being pushed toward us, whereas the other is moving toward the bubble. Another group is on the far side of the bubble, and moving away. The young stellar objects in the Gulf region reside in three different clusters, each hosted by a cloud from one of the three molecular clump groups. Although all gas content in the NAP is impacted by feedback from the central O star, some regions show no signs of star formation, while other areas clearly exhibit star formation activity. Additional molecular gas being carved by feedback includes cometary structures in the Pelican Head region, and the boomerang features at the boundary of the Gulf region. The results show that the NAP complex is an ideal place for the study of feedback effects on star formation.

Keywords: stellar feedback; molecular clouds; photodissociation regions; h ii regions; star formation; star forming regions; massive stars; radio interferometers; radio telescopes; dust continuum emission; interstellar emissions; young stellar objects
Characterizing Compact 15-33 GHz Radio Continuum Sources in Local U/LIRGs

We present the analysis of ~100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs; L IR ≥ 1011 L ⊙), using FWHM ≲ 0.″1-0.″2 resolution 15 and 33 GHz observations with the Karl G. Jansky Very Large Array. We identify a total of 133 compact radio sources with effective radii of 8-170 pc, which are classified into four main categories-"AGN" (active galactic nuclei), "AGN/SBnuc" (AGN-starburst composite nucleus), "SBnuc" (starburst nucleus), and "SF" (star-forming clumps)-based on ancillary data sets and the literature. We find that "AGN" and "AGN/SBnuc" more frequently occur in late-stage mergers and have up to 3 dex higher 33 GHz luminosities and surface densities compared with "SBnuc" and "SF," which may be attributed to extreme nuclear starburst and/or AGN activity in the former. Star formation rates (SFRs) and surface densities (ΣSFR) are measured for "SF" and "SBnuc" using both the total 33 GHz continuum emission (SFR ~ 0.14-13 M ⊙ yr-1, ΣSFR ~ 13-1600 M ⊙ yr-1 kpc-2) and the thermal free-free emission from H II regions (median SFRth ~ 0.4 M ⊙ yr-1, ${{\rm{\Sigma }}}_{{\mathrm{SFR}}_{\mathrm{th}}}\sim 44\,{M}_{\odot }$ yr-1 kpc-2). These values are 1-2 dex higher than those measured for similar-sized clumps in nearby normal (non-U/LIRGs). The latter also have a much flatter median 15-33 GHz spectral index (~-0.08) compared with "SBnuc" and "SF" (~-0.46), which may reflect higher nonthermal contribution from supernovae and/or interstellar medium densities in local U/LIRGs that directly result from and/or lead to their extreme star-forming activities on 100 pc scales.

Keywords: luminous infrared galaxies; radio continuum emission; galaxy nuclei; very large array; star forming regions
Phase Diagram for the Methane-Ethane System and Its Implications for Titan's Lakes

On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in the lakes and seas. In this study, we have combined laboratory work and modeling to refine the methane-ethane binary phase diagram at low temperatures and probe how the molecules interact at these conditions. We used visual inspection for the liquidus and Raman spectroscopy for the solidus. Through these methods, we determined a eutectic point of 71.15 ± 0.5 K at a composition of 0.644 ± 0.018 methane-0.356 ± 0.018 ethane mole fraction from the liquidus data. Using the solidus data, we found a eutectic isotherm temperature of 72.2 K with a standard deviation of 0.4 K. In addition to mapping the binary system, we looked at the solid-solid transitions of pure ethane and found that, when cooling, the transition of solid I-III occurred at 89.45 ± 0.2 K. The warming sequence showed transitions of solid III-II occurring at 89.85 ± 0.2 K and solid II-I at 89.65 ± 0.2 K. Ideal predictions were compared with molecular dynamics simulations to reveal that the methane-ethane system behaves almost ideally, and the largest deviations occur as the mixing ratio approaches the eutectic composition.

Keywords: saturnian satellites
Oblique Quasi-kink Modes in Solar Coronal Slabs Embedded in an Asymmetric Magnetic Environment: Resonant Damping, Phase and Group Diagrams

There has been considerable interest in magnetoacoustic waves in static, straight, field-aligned, 1D equilibria where the exteriors of a magnetic slab are different between the two sides. We focus on trapped, transverse fundamental, oblique quasi-kink modes in pressureless setups, where the density varies continuously from a uniform interior (with density ρ i) to a uniform exterior on either side (with density ρ L or ρ R), assuming ρ L ≤ ρ R ≤ ρ i. The continuous structuring and oblique propagation make our study new, relative to pertinent studies, and lead to wave damping via the Alfvén resonance. We compute resonantly damped quasi-kink modes as resistive eigenmodes, and isolate the effects of system asymmetry by varying ρ i/ρ R from the "Fully Symmetric" (ρ i/ρ R = ρ i/ρ L) to the "Fully Asymmetric" limit (ρ i/ρ R = 1). We find that the damping rates possess a nonmonotonic ρ i/ρ R-dependence as a result of the difference between the two Alfvén continua, and resonant absorption occurs only in one continuum when ρ i/ρ R is below some threshold. We also find that the system asymmetry results in two qualitatively different regimes for the phase and group diagrams. The phase and group trajectories lie essentially on the same side (different sides) relative to the equilibrium magnetic field when the configuration is not far from a "Fully Asymmetric" ("Fully Symmetric") one. Our numerical results are understood by making analytical progress in the thin-boundary limit, and discussed for imaging observations of axial standing modes and impulsively excited wavetrains.

Keywords: solar coronal seismology; solar coronal waves; magnetohydrodynamics
Dynamics of Laterally Propagating Flames in X-Ray Bursts. II. Realistic Burning and Rotation

We continue to investigate two-dimensional laterally propagating flames in type I X-ray bursts using fully compressible hydrodynamics simulations. In the current study we relax previous approximations where we artificially boosted the flames. We now use more physically realistic reaction rates, thermal conductivities, and rotation rates, exploring the effects of neutron star rotation rate and thermal structure on the flame. We find that at lower rotation rates the flame becomes harder to ignite, whereas at higher rotation rates the nuclear burning is enhanced by increased confinement from the Coriolis force and the flame propagates steadily. At higher crustal temperatures, the flame moves more quickly and accelerates as it propagates through the atmosphere. If the temperature is too high, instead of a flame propagating across the surface the entire atmosphere burns uniformly. Our findings could have implications for the relationship between observed burst rise times and neutron star rotation and accretion rates. All of the software used for these simulations is freely available.

Keywords: x-ray bursts; nucleosynthesis; open source software; hydrodynamics; hydrodynamical simulations; neutron stars; computational methods
Structure and Color Gradients of Ultradiffuse Galaxies in Distant Massive Galaxy Clusters

We have measured structural parameters and radial color profiles of 108 ultradiffuse galaxies (UDGs), carefully selected from six distant massive galaxy clusters in the Hubble Frontier Fields (HFF) in a redshift range from 0.308 to 0.545. Our best-fitting GALFIT models show that the HFF UDGs have a median Sérsic index of 1.09, which is close to 0.86 for local UDGs in the Coma cluster. The median axis-ratio value is 0.68 for HFF UDGs and 0.74 for Coma UDGs, respectively. The structural similarity between HFF and Coma UDGs suggests that they are the same kind of galaxies seen at different times, and that the structures of UDGs do not change at least for several billion years. By checking the distribution of HFF UDGs in the rest-frame UVJ and UVI diagrams, we find a large fraction of them are star forming. Furthermore, a majority of HFF UDGs show small U - V color gradients within the 1 ∗ R e,SMA region, and the fluctuation of the median radial color profile of HFF UDGs is smaller than 0.1 mag, which is compatible to Coma UDGs. Our results indicate that cluster UDGs may fade or quench in a self-similar way, irrespective of the radial distance, in less than ~4 Gyr.

Keywords: low surface brightness galaxies
The Yarkovsky Effect in REBOUNDx

To more thoroughly study the effects of radiative forces on the orbits of small, astronomical bodies, we introduce the Yarkovsky effect into REBOUNDX, an extensional library for the N-body integrator REBOUND. Two different versions of the Yarkovsky effect (the "Full Version" and the "Simple Version") are available for use, depending on the needs of the user. We provide demonstrations for both versions of the effect and compare their computational efficiency with another previously implemented radiative force. In addition, we show how this effect can be used in tandem with other features in REBOUNDX by simulating the orbits of asteroids during the asymptotic giant branch phase of a 2 M ⊙ star. This effect is made freely available for use with the latest release of REBOUNDX.

Keywords: astronomy data modeling; astronomy software; n-body simulations; radiative processes; asteroid dynamics; orbital evolution
A Second Earth-sized Planet in the Habitable Zone of the M Dwarf, TOI-700

We report the discovery of TOI-700 e, a 0.95 R ⊕ planet residing in the Optimistic Habitable Zone (HZ) of its host star. This discovery was enabled by multiple years of monitoring from NASA's Transiting Exoplanet Survey Satellite (TESS) mission. The host star, TOI-700 (TIC 150428135), is a nearby (31.1 pc), inactive, M2.5 dwarf (V mag = 13.15). TOI-700 is already known to host three planets, including the small, HZ planet, TOI-700 d. The new planet has an orbital period of 27.8 days, and based on its radius (0.95 R ⊕), it is likely rocky. TOI-700 was observed for 21 sectors over Years 1 and 3 of the TESS mission, including 10 sectors at 20 s cadence in Year 3. Using this full set of TESS data and additional follow-up observations, we identify, validate, and characterize TOI-700 e. This discovery adds another world to the short list of small, HZ planets transiting nearby and bright host stars. Such systems, where the stars are bright enough that follow-up observations are possible to constrain planet masses and atmospheres using current and future facilities, are incredibly valuable. The presence of multiple small, HZ planets makes this system even more enticing for follow-up observations.

Keywords: exoplanet systems; transit photometry; low mass stars; m dwarf stars; astronomy data analysis