adsabs/SciX_UAT_keywords huggingface dataset:
Coronal Bright Points as Possible Sources of Density Variations in the Solar Corona

Recent analysis of high-cadence white-light images taken by the Solar-Terrestrial RElations Observatory near solar maximum has revealed that outflowing density structures are released in a ubiquitous manner in the solar wind. The present study investigates whether these density fluctuations could originate from the transient heating of the low corona observed during coronal bright points (CBPs). We assume that part of the intense heating measured during CBPs occurs at the coronal base of open magnetic fields that channel the forming solar wind. We employ the solar wind model MULTI-VP to quantify the plasma compression induced by transient heating and investigate how the induced perturbation propagates to the upper corona. We show that for heating rates with statistics comparable to those observed during CBPs, the compressive wave initially increases the local plasma density by a factor of up to 50% at 5 R⊙. The wave expands rapidly beyond 30 solar radii and the local enhancement in density decreases beyond. Based on the occurrence rates of CBPs measured in previous studies, we impose transient heating events at the base of thousands of open magnetic field lines to study the response of the entire 3D corona. The simulated density cubes are then converted into synthetic white-light imagery. We show that the resulting brightness variations occupy all position angles in the images on timescales of hours. We conclude that a significant part of the ubiquitous brightness variability of the solar corona could originate in the strong transient heating of flux tubes induced by CBPs.

Keywords: solar corona; solar wind; magnetohydrodynamics
Exoplanets in the Antarctic Sky. III. Stellar Flares Found by AST3-II (CHESPA) within the Southern CVZ of TESS

The CHinense Exoplanet Searching Program from Antarctica is a ground-based wide-field photometric survey using the AST3 and CSTAR telescopes located at Dome A, Antarctica. Blessed with the unparalleled observing conditions on the highest point of the Antarctic plateau, three remotely controlled, fully automatic telescopes (AST3-I, AST3-II, and CSTAR-II) carried out continuous high-precision photometric surveys through the polar nights of 2016 and 2017. During the observing seasons of 2016, a total of 26,578 light curves were obtained for stars within the area of the southern continuous viewing zone of TESS, covering an i-band magnitude range from 7.5 to 15. At mi = 10, photometric precision reaches ∼2 mmag, allowing possible discoveries of sub-Jupiter-size exoplanets. Here we report 20 stellar flares with i-band energies larger than 1034 erg detected in the 2016 data set of AST3-II, all from different sources. We model the stellar flares and calculate the durations, amplitudes, energies, and skewnesses. The flare properties and the stellar properties of their sources are presented in this work.

Keywords: stellar flares; photometry; astrostatistics; stellar activity; astronomy data analysis; surveys
Interferometric Monitoring of Gamma-Ray Bright AGNs: OJ 287

We present the results of simultaneous multifrequency imaging observations at 22, 43, 86, and 129 GHz of OJ 287. We used the Korean Very Long Baseline Interferometry Network as part of the Interferometric Monitoring of Gamma-ray Bright active galactic nuclei (iMOGABA). The iMOGABA observations were performed during 31 epochs from 2013 January 16 to 2016 December 28. We also used 15 GHz OVRO and 225 GHz SMA flux density data. We analyzed four flux enhancements in the light curves. The estimated timescales of three flux enhancements were similar with timescales of ∼50 days at two frequencies. A fourth flux enhancement had a variability timescale approximately twice as long. We found that 225 GHz enhancements led the 15 GHz enhancements by a range of 7-30 days in the time delay analysis. We found the fractional variability did not change with frequency between 43 and 86 GHz. We could reliably measure the turnover frequency, ${\nu }_{{\rm{c}}}$ , of the core of the source in three epochs. This was measured to be in a range from 27 to 50 GHz and a flux density at the turnover frequency, ${S}_{{\rm{m}}}$ , ranging from 3 to 6 Jy. The derived SSA magnetic fields, ${B}_{\mathrm{SSA}}$ , are in a range from 0.157 ± 0.104 to 0.255 ± 0.146 mG. We estimated the equipartition magnetic field strengths to be in a range from 0.95 ± 0.15 to 1.93 ± 0.30 mG. The equipartition magnetic field strengths are up to a factor of 10 higher than the values of ${B}_{\mathrm{SSA}}$ . We conclude that the downstream jet may be more particle energy dominated.

Keywords: very long baseline interferometry; bl lacertae objects; active galactic nuclei; radio jets
A Coupled Analysis of Atmospheric Mass Loss and Tidal Evolution in XUV Irradiated Exoplanets: The TRAPPIST-1 Case Study

Exoplanets residing close to their stars can experience evolution of both their physical structures and their orbits due to the influence of their host stars. In this work, we present a coupled analysis of dynamical tidal dissipation and atmospheric mass loss for exoplanets in X-ray and ultraviolet (XUV) irradiated environments. As our primary application, we use this model to study the TRAPPIST-1 system and place constraints on the interior structure and orbital evolution of the planets. We start by reporting on an ultraviolet continuum flux measurement (centered around ∼1900 Å) for the star TRAPPIST-1, based on 300 ks of Neil Gehrels Swift Observatory data, and which enables an estimate of the XUV-driven thermal escape arising from XUV photodissociation for each planet. We find that the X-ray flaring luminosity, measured from our X-ray detections, of TRAPPIST-1 is 5.6 × 10-4 L*, while the full flux including non-flaring periods is 6.1 × 10-5 L*, when L* is TRAPPIST-1's bolometric luminosity. We then construct a model that includes both atmospheric mass loss and tidal evolution and requires the planets to attain their present-day orbital elements during this coupled evolution. We use this model to constrain the ratio $Q^{\prime} =3Q/2{k}_{2}$ for each planet. Finally, we use additional numerical models implemented with the Virtual Planet Simulator VPLanet to study ocean retention for these planets using our derived system parameters.

Keywords: exoplanets; extrasolar rocky planets; exoplanet atmospheres; exoplanet structure
Roaming the Relativistic Realm: Short-term Dynamical Evolution of Atira 2021 PH27

General relativity effects coupled with those derived from the von Zeipel-Lidov-Kozai mechanism may play a significant role on the evolution of members of the Atira dynamical class, particularly in the case of those with the shortest sidereal orbital periods. Here, we provide a preliminary assessment of the short-term orbital evolution of 2021 PH27, a recently discovered Atira that has the shortest period among known asteroids. Our calculations, based on a publicly available orbit determination and including post-Newtonian terms in the numerical integrations, show that 2021 PH27 is a robust member of the Atira class and it may indeed be used to explore the combined effects of general relativity and the von Zeipel-Lidov-Kozai mechanism once its orbit determination is sufficiently improved.

Keywords: solar system; asteroids
Detailed Characterization of Heartbeat Stars and Their Tidally Excited Oscillations

Heartbeat stars are a class of eccentric binary stars with short-period orbits and characteristic "heartbeat" signals in their light curves at periastron, caused primarily by tidal distortion. In many heartbeat stars, tidally excited oscillations can be observed throughout the orbit, with frequencies at exact integer multiples of the orbital frequency. Here, we characterize the tidally excited oscillations in the heartbeat stars KIC 6117415, KIC 11494130, and KIC 5790807. Using Kepler light curves and radial-velocity measurements, we first model the heartbeat stars using the binary modeling software ELLC, including gravity darkening, limb darkening, Doppler boosting, and reflection. We then conduct a frequency analysis to determine the amplitudes and frequencies of the tidally excited oscillations. Finally, we apply tidal theories to stellar structure models of each system to determine whether chance resonances can be responsible for the observed tidally excited oscillations, or whether a resonance-locking process is at work. We find that resonance locking is likely occurring in KIC 11494130, but not in KIC 6117415 or KIC 5790807.

Keywords: stellar oscillations; asteroseismology; close binary stars; stellar evolutionary models; time series analysis
Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY

We present K-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained K-band spectra and 100 μas precision astrometry of both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of 0.17 ± 0.06, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10 MJup, while the mass of PDS 70 c was unconstrained. The GRAVITY K-band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets' 1-5 μm spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-astronomical-unit spatial resolution, placing an upper limit of 0.3 au on the size of a bright disk around PDS 70 b. ∗ Based on observations collected at the European Southern Observatory under ESO programmes 0101.C-0281(B), 1103.B-0626(A), 2103.C-5018(A), and 1104.C-0651(A).

Keywords: exoplanet formation; exoplanet atmospheres; orbit determination; long baseline interferometry
Atmospheric Erosion by Giant Impacts onto Terrestrial Planets: A Scaling Law for any Speed, Angle, Mass, and Density

We present a new scaling law to predict the loss of atmosphere from planetary collisions for any speed, angle, impactor mass, target mass, and body composition, in the regime of giant impacts onto broadly terrestrial planets with relatively thin atmospheres. To this end, we examine the erosion caused by a wide range of impacts, using 3D smoothed particle hydrodynamics simulations with sufficiently high resolution to directly model the fate of low-mass atmospheres around 1% of the target's mass. Different collision scenarios lead to extremely different behaviors and consequences for the planets. In spite of this complexity, the fraction of lost atmosphere is fitted well by a power law. Scaling is independent of the system mass for a constant impactor mass ratio. Slow atmosphere-hosting impactors can also deliver a significant mass of atmosphere, but always accompanied by larger proportions of their mantle and core. Different Moon-forming impact hypotheses suggest that around 10%-60% of a primordial atmosphere could have been removed directly, depending on the scenario. We find no evident departure from the scaling trends at the extremes of the parameters explored. The scaling law can be incorporated readily into models of planet formation.

Keywords: earth atmosphere; planetary atmospheres; impact phenomena; hydrodynamical simulations
Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z 0 Dwarf Galaxies

Current observational facilities have yet to conclusively detect 103-104 M ⊙ intermediate-mass black holes (IMBHs) that fill in the evolutionary gap between seed black holes in the early universe and z ~ 0 supermassive black holes. Dwarf galaxies present an opportunity to reveal active IMBHs amidst persistent star formation. We introduce photoionization simulations tailored to address key physical uncertainties: coincident versus noncoincident mixing of IMBH and starlight excitation, open versus closed geometries of surrounding gas clouds, and different shapes of the spectral energy distribution of active galactic nuclei (AGN). We examine possible AGN emission line diagnostics in the optical and mid-IR, and find that the diagnostics are often degenerate with respect to the investigated physical uncertainties. In spite of these setbacks, and in contrast to recent work, we are able to show that [O III]/Hβ typically remains bright for dwarf AGN powered by IMBHs down to 103 M ⊙. Dwarf AGN are predicted to have inconsistent star-forming and Seyfert/LINER classifications using the most common optical diagnostics. In the mid-IR, [O IV] 25.9 μm and [Ar II] 6.98 μm are less sensitive to physical uncertainties than are optical diagnostics. Based on these emission lines, we provide several diagrams of mid-IR emission line diagnostic diagrams with demarcations for separating starbursts and AGN with varying levels of activity. The diagrams are valid over a wide range of ionization parameters and metallicities out to z ~ 0.1, so will prove useful for future JWST observations of local dwarf AGN in the search for IMBHs. We make our photoionization simulation suite freely available. *Released on XXXX, XXXX, 2021

Keywords: dwarf galaxies; active galactic nuclei; intermediate-mass black holes; starburst galaxies; emission line galaxies
The DECam Ecliptic Exploration Project (DEEP). IV. Constraints on the Shape Distribution of Bright Trans-Neptunian Objects

We present the methods and results from the discovery and photometric measurement of 26 bright VR > 24 trans-Neptunian objects (TNOs) during the first year (2019–20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive probabilistic Hough transform to identify linearly moving transient sources within DEEP photometric catalogs. After subsequent visual vetting, we provide a photometric and astrometric catalog of our TNOs. By modeling the partial lightcurve amplitude distribution of the DEEP TNOs using Monte Carlo techniques, we find our data to be most consistent with an average TNO axis ratio b/a < 0.5, implying a population dominated by non-spherical objects. Based on ellipsoidal gravitational stability arguments, we find our data to be consistent with a TNO population containing a high fraction of contact binaries or other extremely non-spherical objects. We also discuss our data as evidence that the expected binarity fraction of TNOs may be size-dependent.

Keywords: trans-neptunian objects; surveys; kuiper belt; small solar system bodies; solar system; photometry
Tracking the Evolution of Lithium in Giants Using Asteroseismology: Super-Li-rich Stars Are Almost Exclusively Young Red-clump Stars

We report novel observational evidence on the evolutionary status of lithium-rich giant stars by combining asteroseismic and lithium abundance data. Comparing observations and models of the asteroseismic gravity-mode period spacing ΔΠ1, we find that super-Li-rich giants (SLRs, A(Li) > 3.2 dex) are almost exclusively young red-clump (RC) stars. Depending on the exact phase of evolution, which requires more data to refine, SLR stars are either (i) less than ∼2 Myr or (ii) less than ∼40 Myr past the main core helium flash (CHeF). Our observations set a strong upper limit for the time of the inferred Li-enrichment phase of <40 Myr post-CHeF, lending support to the idea that lithium is produced around the time of the CHeF. In contrast, the more evolved RC stars (>40 Myr post-CHeF) generally have low lithium abundances (A(Li) <1.0 dex). Between the young, super-Li-rich phase, and the mostly old, Li-poor RC phase, there is an average reduction of lithium by about 3 orders of magnitude. This Li destruction may occur rapidly. We find the situation to be less clear with stars having Li abundances between the two extremes of super-Li-rich and Li-poor. This group, the "Li-rich" stars (3.2 > A(Li) > 1.0 dex), shows a wide range of evolutionary states.

Keywords: stellar abundances; asteroseismology; stellar interiors; low mass stars
Identification of Galaxy-Galaxy Strong Lens Candidates in the DECam Local Volume Exploration Survey Using Machine Learning

We perform a search for galaxy-galaxy strong lens systems using a convolutional neural network (CNN) applied to imaging data from the first public data release of the DECam Local Volume Exploration Survey, which contains ~520 million astronomical sources covering ~4000 deg2 of the southern sky to a 5σ point-source depth of g = 24.3, r = 23.9, i = 23.3, and z = 22.8 mag. Following the methodology of similar searches using Dark Energy Camera data, we apply color and magnitude cuts to select a catalog of ~11 million extended astronomical sources. After scoring with our CNN, the highest-scoring 50,000 images were visually inspected and assigned a score on a scale from 0 (not a lens) to 3 (very probable lens). We present a list of 581 strong lens candidates, 562 of which are previously unreported. We categorize our candidates using their human-assigned scores, resulting in 55 Grade A candidates, 149 Grade B candidates, and 377 Grade C candidates. We additionally highlight eight potential quadruply lensed quasars from this sample. Due to the location of our search footprint in the northern Galactic cap (b > 10 deg) and southern celestial hemisphere (decl. < 0 deg), our candidate list has little overlap with other existing ground-based searches. Where our search footprint does overlap with other searches, we find a significant number of high-quality candidates that were previously unidentified, indicating a degree of orthogonality in our methodology. We report properties of our candidates including apparent magnitude and Einstein radius estimated from the image separation.

Keywords: strong gravitational lensing
The High-ionization IR Fine Structure Lines as Bolometric Indicators of the AGN Power: Study of the Complete 12 μm AGN Sample

The high-ionization mid-IR lines, excited in the narrow-line regions of active galactic nuclei (AGN), barely affected by stellar excitation and dust extinction, trace the AGN bolometric power. We used the complete 12 μm sample of Seyfert galaxies, for which 100/116 objects have reliable 2-10 keV observations. The [Ne V] and [O IV] mid-IR lines linearly correlate with several AGN bolometric indicators (intrinsic 2-10 keV and observed 14-195 keV X-ray emission, compact nuclear 12 μm emission, [O III] λ5007 Å line emission) in terms of both flux and luminosity. No evidence of systematic differences in these correlations is found among the Seyfert populations, including types 1 and 2 and Compton-thick and Compton-thin AGN. Nevertheless, we find that a sequence of high-to-low Eddington ratios together with strong-to-weak line excitation (traced by the [O IV]/[Ne II] line ratio) encompasses from type 1 through type 2 AGN to low-ionization nuclear emission-line region galaxies, showing intrinsic differences in these three AGN populations. A positive correlation between the black hole accretion rate (BHAR) and the star formation rate (SFR) is found, but no correlation between the specific SFR and the ratio BHAR/M BH, simply reflecting the fact that the more massive a galaxy is, the more it is forming stars and feeding its central black hole. The JWST, just beginning operations, will allow large samples of AGN to be observed in these lines in the nearby universe (z < 0.9).

Keywords: active galaxies; agn host galaxies; infrared galaxies; seyfert galaxies; starburst galaxies; infrared spectroscopy; x-ray active galactic nuclei; x-ray observatories
A Community Data Set for Comparing Automated Coronal Hole Detection Schemes

Automated detection schemes are nowadays the standard approach for locating coronal holes in extreme-UV images from the Solar Dynamics Observatory (SDO). However, factors such as the noisy nature of solar imagery, instrumental effects, and others make it challenging to identify coronal holes using these automated schemes. While discrepancies between detection schemes have been noted in the literature, a comprehensive assessment of these discrepancies is still lacking. The contribution of the Coronal Hole Boundary Working Team in the COSPAR ISWAT initiative to close this gap is threefold. First, we present the first community data set for comparing automated coronal hole detection schemes. This data set consists of 29 SDO images, all of which were selected by experienced observers to challenge automated schemes. Second, we use this community data set as input to 14 widely applied automated schemes to study coronal holes and collect their detection results. Third, we study three SDO images from the data set that exemplify the most important lessons learned from this effort. Our findings show that the choice of the automated detection scheme can have a significant effect on the physical properties of coronal holes, and we discuss the implications of these findings for open questions in solar and heliospheric physics. We envision that this community data set will serve the scientific community as a benchmark data set for future developments in the field.

Keywords: solar coronal holes; solar corona; solar wind
Accelerated Structural Evolution of Galaxies in a Starbursting Cluster at z = 2.51

Structural properties of cluster galaxies during their peak formation epoch, z ~ 2-4 provide key information on whether and how the environment affects galaxy formation and evolution. Based on deep Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) imaging toward the z = 2.51 cluster, J1001, we explore environmental effects on the structure, color gradients, and stellar populations of a statistical sample of cluster star-forming galaxies (SFGs). We find that the cluster SFGs are on average smaller than their field counterparts. This difference is most pronounced at the high-mass end (M ⋆ > 1010.5 M ⊙), with nearly all of them lying below the mass-size relation of field galaxies. The high-mass cluster SFGs are also generally old, with a steep negative color gradient, indicating an early formation time likely associated with strong dissipative collapse. For low-mass cluster SFGs, we unveil a population of compact galaxies with steep positive color gradients that are not seen in the field. This suggests that the low-mass compact cluster SFGs may have already experienced strong environmental effects, e.g., tidal/ram pressure stripping, in this young cluster. These results provide evidence on the environmental effects at work in the earliest formed clusters with different roles in the formation of low- and high-mass galaxies.

Keywords: high-redshift galaxy clusters; galaxy structure; galaxy evolution