adsabs/SciX_UAT_keywords huggingface dataset:
Generalized Coronal Loop Scaling Laws and Their Implication for Turbulence in Solar Active Region Loops

Recent coronal loop modeling has emphasized the importance of combining both Coulomb collisions and turbulent scattering to characterize field-aligned thermal conduction, which invokes a hybrid loop model. In this work, we generalize the hybrid model by incorporating a nonuniform heating and cross section that are both formulated by a power-law function of temperature. Based on the hybrid model solutions, we construct scaling laws that relate loop-top temperature (T a ) and heating rate (H a ) to other loop parameters. It is found that the loop-top properties for turbulent loops are additionally power-law functions of the turbulent mean free path (λ T ), with the functional forms varying from situation to situation, depending on the specification of the heating and/or areal parameters. More importantly, both a sufficiently footpoint-concentrated heating and a cross-sectional expansion with height can effectively weaken (strengthen) the negative (positive) power-law dependence of T a (H a ) on λ T . The reason lies in a notable reduction of heat flux by footpoint heating and/or cross-sectional expansion in the turbulence-dominated coronal part, where turbulent scattering introduces a much weaker dependence of the conduction coefficient on temperature. In this region, therefore, the reduction of the heat flux predominately relies on a backward flattening of the temperature gradient. Through numerical modeling that incorporates more realistic conditions, this scenario is further consolidated. Our results have important implications for solar active region (AR) loops. With the factors of nonuniform heating and cross section taken into account, AR loops can bear relatively stronger turbulence while still keeping a physically reasonable temperature for nonflaring loops.

Keywords: solar active regions; solar corona; solar coronal loops; hydrodynamics
Outbursting Quasi-Hilda Asteroid P/2010 H2 (Vales)

Quasi-Hilda asteroid P/2010 H2 (Vales) underwent a spectacular photometric outburst by ≥7.5 mag (factor of ≥103) in 2010. Here, we present our optical observations of this event in the four month period from April 20 to August 10. The outburst, starting UT 2010 April 15.70, released dust particles of total cross-section 17,600 km2 (albedo 0.1 assumed) and mass ∼1.2 × 109 kg, this being about 10-4 of the mass of the nucleus, taken as a sphere of radius 1.5 km and density 500 kg m-3. While the rising phase of the outburst was very steep (brightness doubling time of hours), subsequent fading occurred slowly (fading timescales increasing from weeks to months), as large, low velocity particles drifted away from the nucleus. A simple model of the fading lightcurve indicates that the ejected particles occupied a broad range of sizes, from ∼1 μm to 6 cm, and followed a differential power-law distribution with index 3.6 ± 0.1 (similar to that in other comets). The fastest particles had speeds ≥210 m s-1, indicating gas-drag acceleration of small grains well coupled to the flow. Low-energy processes known to drive mass loss in active asteroids, including rotational disruption; thermal and desiccation stress cracking; and electrostatic repulsion, cannot generate the high particles speeds measured in P/Vales, and are discounted. Impact origin is unlikely given the short dynamical lifetimes of the quasi-Hildas and the low collision probabilities of these objects. The specific energy of the ejecta is estimated at 220 J kg-1. The outburst follows a series of encounters with Jupiter in the previous century, consistent with the delayed activation of buried supervolatiles (and/or the crystallization of subsurface amorphous ice) by conducted heat following an inward displacement of the perihelion. A potential origin in the debris cloud produced by avalanche is also considered.

Keywords: comets; small solar system bodies; asteroids; hilda group; minor planets; short period comets
SAUNAS. I. Searching for Low Surface Brightness X-Ray Emission with Chandra/ACIS

We present Selective Amplification of Ultra Noisy Astronomical Signal (SAUNAS), a pipeline designed for detecting diffuse X-ray emission in the data obtained with the Advanced CCD Imaging Spectrometer (ACIS) of the Chandra X-ray Observatory. SAUNAS queries the available observations in the Chandra archive and performs photometric calibration, point-spread function modeling and deconvolution, point-source removal, adaptive smoothing, and background correction. This pipeline builds on existing and well-tested software including CIAO, VorBin, and LIRA. We characterize the performance of SAUNAS through several quality performance tests and demonstrate the broad applications and capabilities of SAUNAS using two galaxies already known to show X-ray-emitting structures. SAUNAS successfully detects the 30 kpc X-ray superwind of NGC 3079 using Chandra/ACIS data sets, matching the spatial distribution detected with more sensitive XMM-Newton observations. The analysis performed by SAUNAS reveals an extended low surface brightness source in the field of UGC 5101 in the 0.3–1.0 keV and 1.0–2.0 keV bands. This source is potentially a background galaxy cluster or a hot gas plume associated with UGC 5101. SAUNAS demonstrates its ability to recover previously undetected structures in archival data, expanding exploration into the low surface brightness X-ray Universe with Chandra/ACIS.

Keywords: x-ray astronomy; astronomical methods; x-ray photometry; x-ray observatories; space telescopes; circumgalactic medium
Deciphering the 3D Orion Nebula. II. A Low Ionization Region of Multiple Velocity Components Southwest of θ1 Ori C Confounds Interpretation of Low Velocity Resolution Studies of Temperature, Density, and Abundance

We establish that there are two velocity systems along lines of sight that contribute to the emission-line spectrum of the brightest parts of the Orion Nebula. These overlie the Orion-S embedded molecular cloud southwest of the dominant ionizing star (θ1 Ori C). Examination of 10 × 10″ samples of high spectral resolution emission-line spectra of this region reveals it to be of low ionization, with velocities and ionization different from the central part of the nebula. These properties jeopardize earlier determinations of abundance and physical conditions since they indicate that this region is much more complex than has been assumed in analyzing earlier spectroscopic studies and argue for use of very high spectral resolution or known simple regions in future studies.

Keywords: h ii regions
Similar Scale-invariant Behaviors between Soft Gamma-Ray Repeaters and an Extreme Epoch from FRB 121102

The recent discovery of a Galactic fast radio burst (FRB) associated with a hard X-ray burst from the soft gamma-ray repeater (SGR) J1935+2154 has established the magnetar origin of at least some FRBs. In this work, we study the statistical properties of soft gamma-ray/hard X-ray bursts from SGRs 1806-20 and J1935+2154 and of radio bursts from the repeating FRB 121102. For SGRs, we show that the probability density functions for the differences of fluences, fluxes, and durations at different times have fat tails with a q-Gaussian form. The q values in the q-Gaussian distributions are approximately steady and independent of the temporal interval scale adopted, implying a scale-invariant structure of SGRs. These features indicate that SGR bursts may be governed by a self-organizing criticality (SOC) process, confirming previous findings. Very recently, 1652 independent bursts from FRB 121102 have been detected by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here we also investigate the scale-invariant structure of FRB 121102 based on the latest observations of FAST, and show that FRB 121102 and SGRs share similar statistical properties. Given the bimodal energy distribution of FRB 121102 bursts, we separately explore the scale-invariant behaviors of low- and high-energy bursts of FRB 121102. We find that the q values of low- and high-energy bursts are different, which further strengthens the evidence of the bimodality of the energy distribution. Scale invariance in both the high-energy component of FRB 121102 and SGRs can be well explained within the same physical framework of fractal-diffusive SOC systems.

Keywords: magnetars; soft gamma-ray repeaters; radio transient sources; radio bursts
First High-resolution Spectroscopy of X-Ray Absorption Lines in the Obscured State of NGC 5548

Multiwavelength spectroscopy of NGC 5548 revealed remarkable changes due to the presence of an obscuring wind from the accretion disk. This broadened our understanding of obscuration and outflows in active galactic nuclei. Swift monitoring of NGC 5548 shows that over the last 10 yr, the obscuration has gradually declined. This provides a valuable opportunity for analyses that have not been feasible before because of too much obscuration. The lowered obscuration, together with the high-energy spectral coverage of Chandra HETG, facilitates the first study of X-ray absorption lines in the obscured state. The comparison of the lines (Mg XI, Mg XII, Si XIII, and Si XIV) between the new and historical spectra reveals interesting changes, most notably the He-like absorption being significantly diminished in 2022. Our study finds that the changes are caused by an increase in both the ionization parameter and the column density of the warm-absorber outflow in the obscured state. This is contrary to the shielding scenario that is evident in the appearance of the UV lines, where the inner obscuring wind shields outflows that are farther out, thus lowering their ionization. The X-ray absorption lines in the HETG spectra appear to be unaffected by the obscuration. The results suggest that the shielding is complex because various components of the ionized outflow are affected differently. We explore various possibilities for the variability behavior of the X-ray absorption lines and find that the orbital motion of a clumpy ionized outflow traversing our line of sight is the most likely explanation.

Keywords: x-ray active galactic nuclei; seyfert galaxies; quasar absorption line spectroscopy; high resolution spectroscopy
Modeling the Light Curve of HD 222925's Progenitor Kilonova

The leading theory for heavy element nucleosynthesis is that a majority of isotopes heavier than iron are formed in neutron star mergers (NSMs), visible through the kilonovae that proceed them. In this work, we derive the potential kilonova light curve associated with the elemental abundances of the "gold standard" metal-poor star HD 222925, which is thought to be enriched by a single NSM. Previous work explores which initial kilonova conditions best match the elemental abundances in HD 222925 and finds two main solutions: either the ejecta is highly constrained, or the underlying nuclear microphysics model is incomplete. We construct the light curves for these two cases in hopes of using kilonova to break this degeneracy. We find that our merger models produce light curves that are observationally too alike to robustly distinguish between the two valid models, offering little hope for constraining kilonova ejecta or the behavior of neutron-rich nuclei.

Keywords: r-process; neutron stars; stellar mergers; gravitational wave sources
The Solar System Notification Alert Processing System (SNAPS): Asteroid Population Outlier Detection

The Solar system Notification Alert Processing System (SNAPS) is a Zwicky Transient Facility (ZTF) and Rubin Observatory alert broker that will send alerts to the community regarding interesting events in the solar system. SNAPS is actively monitoring solar system objects and one of its functions is to compare objects (primarily main belt asteroids) to one another to find those that are outliers relative to the population. In this paper, we use the SNAPShot1 data set, which contains 31,693 objects from ZTF, and derive outlier scores for each of these objects. SNAPS employs an unsupervised approach; consequently, to derive outlier rankings for each object, we propose four different outlier metrics such that we can explore variants of the outlier scores and add confidence to the outlier rankings. We also provide outlier scores for each object in each permutation of 15 feature spaces, between two and 15 features, which yields 32,752 total feature spaces. We show that we can derive population outlier rankings each month at Rubin Observatory scale using four Nvidia A100 GPUs, and present several avenues of scientific investigation that can be explored using population outlier detection.

Keywords: asteroids; small solar system bodies; sky surveys; astroinformatics; gpu computing
BAT AGN Spectroscopic Survey. XX. Molecular Gas in Nearby Hard-X-Ray-selected AGN Galaxies

We present the host-galaxy molecular gas properties of a sample of 213 nearby (0.01 < z < 0.05) hard-X-ray-selected active galactic nucleus (AGN) galaxies, drawn from the 70-month catalog of Swift's Burst Alert Telescope (BAT), with 200 new CO(2-1) line measurements obtained with the James Clerk Maxwell Telescope and the Atacama Pathfinder Experiment telescope. We find that AGN in massive galaxies ( $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 10.5$ ) tend to have more molecular gas and higher gas fractions than inactive galaxies matched in stellar mass. When matched in star formation, we find AGN galaxies show no difference from inactive galaxies, with no evidence that AGN feedback affects the molecular gas. The higher molecular gas content is related to AGN galaxies hosting a population of gas-rich early types with an order of magnitude more molecular gas and a smaller fraction of quenched, passive galaxies (∼5% versus 49%) compared to inactive galaxies. The likelihood of a given galaxy hosting an AGN (Lbol > 1044 erg s-1 ) increases by ∼10-100 between a molecular gas mass of 108.7M⊙ and 1010.2M⊙. AGN galaxies with a higher Eddington ratio (log(L/LEdd) > -1.3) tend to have higher molecular gas masses and gas fractions. The log(NH/ cm-2 ) > 23.4) of AGN galaxies with higher column densities are associated with lower depletion timescales and may prefer hosts with more gas centrally concentrated in the bulge that may be more prone to quenching than galaxy-wide molecular gas. The significant average link of host-galaxy molecular gas supply to supermassive black hole (SMBH) growth may naturally lead to the general correlations found between SMBHs and their host galaxies, such as the correlations between SMBH mass and bulge properties, and the redshift evolution of star formation and SMBH growth.

Keywords: active galactic nuclei; agn host galaxies; molecular gas; surveys; x-ray active galactic nuclei; survival analysis; submillimeter astronomy; high energy astrophysics; seyfert galaxies; catalogs
Evidence of Solar-cycle-related Structural Changes in the Solar Convection Zone

While it has been relatively easy to determine solar-cycle related changes in solar dynamics, determining changes in structure in the deeper layers of the Sun has proved to be difficult. By using helioseismic data obtained over two solar cycles, and sacrificing resolution in favor of lower uncertainties, we show that there are significant changes in the solar convection zone, and perhaps even below it. Using Michelson Doppler Imager (MDI) data, we find a relative squared sound-speed difference of (2.56 ± 0.71) × 10-5 at the convection-zone base between the maximum of solar Cycle 23 and the minimum between Cycles 23 and 24. The squared sound-speed difference for the maximum of Cycle 24 obtained with Helioseismic and Magnetic Imager (HMI) data is (1.95 ± 0.69) × 10-5. Global Oscillation Network Group (GONG) data support these results. We also find that the sound speed in the solar convection zone decreases compared to the sound speed in the layers below it as the Sun becomes more active. We find evidence of changes in the radial derivative of the sound-speed difference between the solar minimum and other epochs at the base of the convection zone, implying possible small changes in the position of the convection-zone base; however, the results are too noisy to make any definitive estimates of the change.

Keywords: solar cycle; helioseismology; solar interior; solar activity
Thermal Evolution of Neo-neutron Stars. I. Envelopes, Eddington Luminosity Phase, and Implications for GW170817

A neo-neutron star is a hot neutron star that has just become transparent to neutrinos. In a core-collapse supernova or accretion-induced collapse of a white dwarf, the neo-neutron star phase directly follows the proto-neutron star phase, about 30-60 s after the initial collapse. It will also be present in a binary neutron star merger in the case where the "born-again" hot massive compact star does not immediately collapse into a black hole. Eddington or even super-Eddington luminosities are present for some time. A neo-neutron star produced in a core-collapse supernova is not directly observable, but the one produced by a binary merger, likely associated with an off-axis short gamma-ray burst, may be observable for some time as well as when produced in the accretion-induced collapse of a white dwarf. We present a first step in the study of this neo-neutron star phase in a spherically symmetric configuration, thus ignoring fast rotation and also ignoring the effect of strong magnetic fields. We put particular emphasis on determining how long the star can sustain a near-Eddington luminosity and also show the importance of positrons and contraction energy during the neo-neutron star phase. We finally discuss the observational prospects for neutron star mergers triggered by LIGO and for accretion-induced collapse transients.

Keywords: neutron stars; type ii supernovae; gamma-ray bursts; x-ray point sources
The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

We present ALMA observations of CO isotopologues and high-density molecular tracers (HCN, HCO+, CN, etc.) in NGC 7465, an unusually gas-rich early-type galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular gas kinematics are misaligned with respect to all other galaxy components; as the gas works its way inward, it is torqued into polar orbits about the stellar kinematically decoupled core (KDC), indicating that the stellar KDC is not related to the current gas accretion event. The galaxy also exhibits unusually high 12CO/13CO line ratios in its nucleus but typical 13CO/C18O ratios. Our calculations show that this result does not necessarily indicate an unusual [12CO/13CO] abundance ratio but rather that 12CO (1-0) is optically thin due to high temperatures and/or large line widths associated with the inner decoupled, misaligned molecular structure. Line ratios of the higher-density tracers suggest that the densest phase of molecular gas in NGC 7465 has a lower density than is typical for nearby galaxies, possibly as a result of the recent gas accretion. All of the observed molecular properties of NGC 7465 are consistent with it having acquired its molecular (and atomic) gas from a spiral galaxy. Further detailed studies of the CO isotopologues in other early-type galaxies would be valuable for investigating the histories of those that may have acquired their gas from dwarfs. Finally, these ALMA data also show an unidentified line source that is probably a background galaxy similar to those found at z = 1-3 in blind CO surveys.

Keywords: early-type galaxies; interstellar molecules; co line emission; molecular gas
Inferring the Gas-to-Dust Ratio in the Main Planet-forming Region of Disks

Measuring the amount of gas and dust in protoplanetary disks is a key challenge in planet formation studies. Here we provide a new set of dust depletion factors and relative mass surface densities of gas and dust for the innermost regions of a sample of protoplanetary disks. We do this by combining stellar theory with observed refractory element abundances in both disk hosts and open cluster stars. Our results are independent of, and complementary to, those obtained from spatially resolved disk observations.

Keywords: circumstellar disks; protoplanetary disks; stellar accretion disks; stellar abundances
Stability Constrained Characterization of the 23 Myr Old V1298 Tau System: Do Young Planets Form in Mean Motion Resonance Chains?

A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages (<1%), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than ≲100 Myr, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits' near-integer period ratios. We incorporate recent transit and radial velocity (RV) observations of the V1298 Tau system, and investigate constraints on the system's orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system's age. We show that the recent RV mass measurement of V1298 Tau b places it within a factor of 2 of the instability limit, and that this allows us to set significantly lower limits on the eccentricity (e b ≤0.17 at 99.7% confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at ≳99% confidence. Thus, if the ~23 Myr old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multiplanet systems will be valuable in informing planet formation models.

Keywords: exoplanet dynamics; exoplanet evolution; exoplanet formation; orbital resonances
Equatorial Waves and Superrotation in the Stratosphere of a Titan General Circulation Model

We investigate the characteristics of equatorial waves associated with the maintenance of superrotation in the stratosphere of a Titan general circulation model. A variety of equatorial waves are present in the model atmosphere, including equatorial Kelvin waves, equatorial Rossby waves, and mixed Rossby-gravity waves. In the upper stratosphere, acceleration of superrotation is strongest around solstice and is due to interaction between equatorial Kelvin waves and Rossby-type waves in winter hemisphere midlatitudes. The existence of this "Rossby-Kelvin"-type wave appears to depend on strong meridional shear of the background zonal wind that occurs in the upper stratosphere at times away from the equinoxes. In the lower stratosphere, acceleration of superrotation occurs throughout the year and is partially induced by equatorial Rossby waves, which we speculate are generated by quasigeostrophic barotropic instability. Acceleration of superrotation is generally due to waves with phase speeds close to the zonal velocity of the mean flow. Consequently, they have short vertical wavelengths that are close to the model's vertical grid scale and therefore likely to be not properly represented. We suggest that this may be a common issue among Titan general circulation models that should be addressed by future model development.

Keywords: titan; planetary atmospheres; planetary science