adsabs/SciX_UAT_keywords huggingface dataset:
Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging Spectroscopy

Nonthermal sources located above bright flare arcades, referred to as the "above-the-loop-top" sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the Expanded Owens Valley Solar Array and the Reuven Ramaty High Energy Solar Spectroscopic Imager, respectively. By combining the microwave and HXR imaging spectroscopy observations with multifilter extreme ultraviolet and soft X-ray imaging data, we derive the coronal magnetic field and energetic electron distribution of the source over a broad energy range from <10 keV up to ∼MeV during the early impulsive phase of the flare. The source has a strong magnetic field of over 800 G. The best-fit electron distribution consists of a thermal "core" from ∼25 MK plasma. A nonthermal power-law "tail" joins the thermal core at ∼16 keV with a spectral index of ∼3.6, which breaks down at above ∼160 keV to >6.0. Temporally resolved analysis suggests that the electron distribution above the break energy rapidly hardens with the spectral index decreasing from >20 to ∼6.0 within 20 s, or less than ∼10 Alfvén crossing times in the source. These results provide strong support for the above-the-loop-top source as the primary site where an ongoing bulk acceleration of energetic electrons is taking place very early in the flare energy release.

Keywords: solar flares; solar coronal mass ejections; non-thermal radiation sources; solar x-ray emission; solar radio emission; solar magnetic reconnection; solar energetic particles
Optical Monitoring and Variability Analyses of the FSRQ 3C 454.3

Based on the database monitored by the 1.26 m National Astronomical Observatory-Guangzhou University Infrared/Optical Telescope, we studied the optical variabilities of FSRQ 3C454.3. The monitoring period was from 2016 October 17 to 2018 December 14, and there were 6701 observations covering the g, r, and i bands (2196 at the g band, 2214 at the r band, and 2291 at the i band). (1) The maximum variabilities were Δm g = 2.806 ± 0.124 mag at the g band; Δm r = 2.365 ± 0.160 mag at the r band; and Δm i = 3.126 ± 0.070 mag at the i band. (2) Among the gri intraday lightcurves, there are 172 portions of the data sets showing intraday variability (IDV). The distributions of IDV timescales (ΔT) can be profiled by a three-order Gaussian function, with the center values ΔT 1 = 17.18 minutes, ΔT 2 = 34.91 minutes, and ΔT 3 = 68.92 minutes. These results imply that the origin of IDVs is very complicated. (3) Based on the IDV timescales, we obtained the emission size R ≤ 7.17 × 1015 cm, fixed the broad-line region and modeled the spectral energy distributions. (4) We used the Jurkevich method, red-noise fitting, and the weighted wavelet Z-transform to analyze the long-term variabilities and obtained indications of a possible period of P = 2.92 ± 0.85 yr, and used the binary black hole system to explain this period. Based on the long-term period, we can estimate the time until merger of the binary black hole, t merge = 6.69 × 103 yr, and the luminosity of gravitational waves, L G = 1.56 × 1048 erg s-1.

Keywords: galaxies; blazars; ccd photometry
The Solar Probe ANalyzer-Ions on the Parker Solar Probe

The Solar Probe ANalyzer for Ions (SPAN-I) onboard NASA's Parker Solar Probe spacecraft is an electrostatic analyzer with time-of-flight capabilities that measures the ion composition and three-dimensional distribution function of the thermal corona and solar-wind plasma. SPAN-I measures the energy per charge of ions in the solar wind from 2 eV to 30 keV with a field of view of 247.°5 × 120° while simultaneously separating H+ from He++ to develop 3D velocity distribution functions of individual ion species. These observations, combined with reduced distribution functions measured by the Sun-pointed Solar Probe Cup, will help us further our understanding of the solar-wind acceleration and formation, the heating of the corona, and the acceleration of particles in the inner heliosphere. This paper describes the instrument hardware, including several innovative improvements over previous time-of-flight sensors, the data products generated by the experiment, and the ground calibrations of the sensor.

Keywords: heliosphere; the sun; solar physics
Fragmentation of the High-mass "Starless" Core G10.21-0.31: A Coherent Evolutionary Picture for Star Formation

G10.21-0.31 is a 70 μm dark high-mass starless core (M > 300 M ⊙ within r < 0.15 pc) identified in the Spitzer, Herschel, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging within 11-18 M ⊙, characterized by a turbulent fragmentation. Cores 1, 2, and 3 represent a coherent evolution of three different stages, characterized by outflows (CO and SiO), gas temperature (H2CO), and deuteration (N2D+/N2H+). We confirm the potential for formation of high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time.

Keywords: massive stars; infrared dark clouds; star formation; protostars
Mid-infrared Outbursts in Nearby Galaxies: Nuclear Obscuration and Connections to Hidden Tidal Disruption Events and Changing-look Active Galactic Nuclei

We study the properties of galaxies hosting mid-infrared outbursts in the context of a catalog of 500,000 galaxies from the Sloan Digital Sky Survey. We find that nuclear obscuration, as inferred by the surrounding dust mass, does not correlate with host galaxy type, stellar properties (e.g., total mass and mean age), or with the extinction of the host galaxy as estimated by the Balmer decrement. This implies that nuclear obscuration may not be able to explain any overrepresentation of tidal disruption events in particular host galaxies. We identify a region in the galaxy catalog parameter space that contains all unobscured tidal disruption events but only harbors ≲11% of the mid-infrared outburst hosts. We find that mid-infrared outburst hosts appear more centrally concentrated and have higher galaxy Sérsic indices than galaxies hosting active galactic nuclei (AGNs) selected using the Baldwin-Phillips-Terlevich classification. We thus conclude that the majority of mid-infrared outbursts are not hidden tidal disruption events but are instead consistent with being obscured AGN that are highly variable, such as changing-look AGN.

Keywords: galaxy nuclei; agn host galaxies; tidal disruption; infrared sources
The BUFFALO HST Survey

The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope (HST) Treasury program taking data from 2018 to 2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in Wide Field Camera 3/IR F105W, F125W, and F160W and Advanced Camera for Surveys/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multiwavelength data sets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies that would otherwise lie below HST detection limits and model foreground clusters to study the properties of dark matter and galaxy assembly. The expanded area will provide the first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient follow-up. BUFFALO data including mosaics, value-added catalogs, and cluster mass distribution models will be released via MAST on a regular basis as the observations and analysis are completed for the six individual clusters.

Keywords: hubble space telescope; galaxy clusters; galaxy evolution; gravitational lensing; catalogs; supernovae; high-redshift galaxies
Pegasus W: An Ultrafaint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization

We report the discovery of an ultrafaint dwarf (UFD) galaxy, Pegasus W, located on the far side of the Milky Way-M31 system and outside the virial radius of M31. The distance to the galaxy is ${915}_{-91}^{+60}$ kpc, measured using the luminosity of horizontal branch stars identified in Hubble Space Telescope optical imaging. The galaxy has a half-light radius (r h ) ${100}_{-13}^{+11}$ pc, ${M}_{V}=-{7.20}_{-0.16}^{+0.17}$ mag, and a present-day stellar mass ${6.5}_{-1.4}^{+1.1}\times {10}^{4}$ M ⊙. We identify sources in the color-magnitude diagram (CMD) that may be younger than ~500 Myr, suggesting late-time star formation in the UFD galaxy, although further study is needed to confirm these are bona fide young stars in the galaxy. Based on fitting the CMD with stellar evolution libraries, Pegasus W shows an extended star formation history. Using the τ 90 metric (defined as the timescale by which the galaxy formed 90% of its stellar mass), the galaxy was quenched only ${7.4}_{-2.6}^{+2.2}$ Gyr ago, which is similar to the quenching timescale of a number of UFD satellites of M31 but significantly more recent than the UFD satellites of the Milky Way. Such late-time quenching is inconsistent with the more rapid timescale expected by reionization and suggests that, while not currently a satellite of M31, Pegasus W was nonetheless slowly quenched by environmental processes.

Keywords: hertzsprung russell diagram; local group
The 3D Dust and Opacity Distribution of Protoplanets in Multifluid Global Simulations

The abundance and distribution of solids inside the Hill sphere are central to our understanding of the giant planet dichotomy. Here, we present a 3D characterization of the dust density, mass flux, and mean opacities in the envelope of subthermal and superthermal-mass planets. We simulate the dynamics of multiple dust species in a global protoplanetary disk model accounting for dust feedback. We find that the meridional flows do not effectively stir dust grains at scales of the Bondi sphere. Thus the dust settling driven by the stellar gravitational potential sets the latitudinal dust density gradient within the planet envelope. Not only does the planet's potential enhance this gradient, but also the spiral wakes serve as another source of asymmetry. These asymmetries substantially alter the inferred mean Rosseland and Planck opacities. In cases with moderate-to-strong dust settling, the opacity gradient can range from a few percent to more than two orders of magnitude between the midplane and the polar regions of the Bondi sphere. Finally, we show that this strong latitudinal opacity gradient can introduce a transition between optically thick and thin regimes at the scales of the planet envelope. We suggest that this transition is likely to occur when the equilibrium scale height of hundred-micron-sized particles is smaller than the Hill radius of the forming planet. This work calls into question the adoption of a constant opacity derived from well-mixed distributions and demonstrates the need for global radiation hydrodynamics models of giant planet formation that account for dust dynamics.

Keywords: planet formation; planetary atmospheres
ALMA and IRIS Observations of the Solar Chromosphere. II. Structure and Dynamics of Chromospheric Plages

We propose and employ a novel empirical method for determining chromospheric plage regions, which seems to better isolate a plage from its surrounding regions than other methods commonly used. We caution that isolating a plage from its immediate surroundings must be done with care in order to successfully mitigate statistical biases that, for instance, can impact quantitative comparisons between different chromospheric observables. Using this methodology, our analysis suggests that λ = 1.25 mm free-free emission in plage regions observed with the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may not form in the low chromosphere as previously thought, but rather in the upper chromospheric parts of dynamic plage features (such as spicules and other bright structures), i.e., near geometric heights of transition-region temperatures. We investigate the high degree of similarity between chromospheric plage features observed in ALMA/Band6 (at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph (IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are not as well correlated with ALMA/Band6 as was previously thought, and we discuss discrepancies with previous works. Lastly, we report indications of chromospheric heating due to propagating shocks supported by the ALMA/Band6 observations.

Keywords: solar chromosphere; solar chromospheric heating; solar electromagnetic emission; solar extreme ultraviolet emission; solar physics; solar radio emission; solar spicules; solar transition region; solar ultraviolet emission
The Clustering Properties of AGNs/Quasars in CatWISE2020 Catalog

We study the clustering properties of 1,307,530 AGNs/quasars in the CatWISE2020 catalog prepared using the Wide-field Infrared Survey Explorer and Near-Earth Object Wide-field Infrared Survey Explorer survey data. For angular moments ℓ ⪆ 10 (⪅18°) down to nonlinear scales, the results are in agreement with the standard ΛCDM cosmology, with a galaxy bias roughly matching that of the NRAO VLA Sky Survey (NVSS) AGNs. We further explore the redshift dependence of the fraction of infrared-bright AGNs on stellar mass, ${f}_{\mathrm{IB}}\sim {M}_{* }^{{\alpha }_{0}+{\alpha }_{1}z}$ , and find ${\alpha }_{1}={1.27}_{-0.30}^{+0.25}$ , ruling out a nonevolution hypothesis at a ≈4.6σ confidence level. The results are consistent with the measurements obtained with NVSS AGNs, though considerably more precise thanks to the significantly higher number density of objects in CatWISE2020. The excess dipole and high clustering signal above angular scale ≈18° remains anomalous.

Keywords: cosmology; large-scale structure of the universe; observational cosmology; infrared astronomy; quasars; active galactic nuclei
The Outburst of Centaur 29P/Schwassmann-Wachmann on 2020 February 4th

We observed the 2020 February 4th outburst of the Centaur 29P/Schwassmann-Wachmann, using the James Gregory Telescope in St Andrews/UK. The brightness of the comet increased by ∼3 mag in VRI within 1-2 days, followed by a more gradual incline. This was one of the largest documented outbursts of this object over the past few years, but is consistent with previously observed events.

Keywords: comets; centaur group; small solar system bodies; ccd photometry
Early Planet Formation in Embedded Disks (eDisk). III. A First High-resolution View of Submillimeter Continuum and Molecular Line Emission toward the Class 0 Protostar L1527 IRS

Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here we present Atacama Large Millimeter/submillimeter Array observations of dust continuum at ~0.″06 (8 au) resolution and molecular line emission at ~0.″17 (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of 12CO, 13CO, C18O, H2CO, c-C3H2, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in 12CO. The 13CO brightness temperature and the H2CO line ratio confirm that the disk is too warm for CO freezeout, with the snowline located at ~350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk-envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk-envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100″ or 14,000 au) outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

Keywords: interstellar molecules; protostars
The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b: No Evidence for a Cloud-free Primordial Atmosphere and Constraints on Starspot Contamination

Orbiting an M dwarf 12 pc away, the transiting exoplanet GJ 1132b is a prime target for transmission spectroscopy. With a mass of 1.7 M ⊕ and radius of 1.1 R ⊕, GJ 1132b's bulk density indicates that this planet is rocky. Yet with an equilibrium temperature of 580 K, GJ 1132b may still retain some semblance of an atmosphere. Understanding whether this atmosphere exists and its composition will be vital for understanding how the atmospheres of terrestrial planets orbiting M dwarfs evolve. We observe five transits of GJ 1132b with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We find a featureless transmission spectrum from 1.1 to 1.7 μm, ruling out cloud-free atmospheres with metallicities <300× solar with >4.8σ confidence. We combine our WFC3 results with transit depths from TESS and archival broadband and spectroscopic observations to find a featureless spectrum across 0.7 to 4.5 μm. GJ 1132b therefore has a high mean molecular weight atmosphere, possesses a high-altitude aerosol layer, or has effectively no atmosphere. Higher-precision observations are required in order to differentiate between these possibilities. We explore the impact of hot and cold starspots on the observed transmission spectrum GJ 1132b, quantifying the amplitude of spot-induced transit depth features. Using a simple Poisson model, we estimate spot temperature contrasts, spot covering fractions, and spot sizes for GJ 1132. These limits, as well as the modeling framework, may be useful for future observations of GJ 1132b or other planets transiting similarly inactive M dwarfs.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; extrasolar rocky planets; exoplanets; transmission spectroscopy; starspots
Disproving the High-eccentricity Planet HD 220773b

HD 220773 has been announced to host a giant planet in an eccentric orbit. Global Architecture of Planetary Systems collaboration followed this target up with the HARPS-N spectrograph at Telescopio Nazionale Galileo, in order to search for additional small planets in the system. This radial velocity monitoring produced approximately 130 HARPS-N data points, leading to the refutation of the announced planet.

Keywords: exoplanet astronomy; exoplanet detection methods; radial velocity
Properties of PSR J1023+0038 Based on Kepler, TESS, and FAST

The pulsar system PSR J1023+0038 is a very interesting binary with radio millisecond pulsar and low-mass X-ray binary transitions, which depend on the stellar accretion process. We have used Kepler light curves with 1 minute cadence and TESS light curves with 2 minute cadence to study the flare properties of PSR J1023+0038. We detected 516 flare events in the K2 data and 84 flare events in the TESS survey data. We determined the flare rise and delay times, the flare durations and amplitudes, and flare energies. We obtained a value of the power-law index of 0.359 ± 0.023 between the flare energies and decay times, which is similar to the theoretically predicted value of 1/3. This in turn indicates that PSR J1023+0038 might be exhibiting physical mechanisms described by magnetic reconnection theory. Using the maximum likelihood estimation method, we also calculated the power-law index of the cumulative flare frequency distribution, finding 1.87 ± 0.27 for the Kepler data and 1.74 ± 0.29 for the TESS data. Meanwhile, we reduced six FAST observations of PSR J1023+0038 from 2019-2021 using a standard pulsar search procedure. We report that we detected a prompt signal with a period compatible with that found in previous observations of PSR J1023+0038. However, there are several reasons (statistical, excess DM, pulse shape, etc.) as to why the association is not likely.

Keywords: stellar activity; stellar flares; pulsars
Observation Strategy Optimization for Distributed Telescope Arrays with Deep Reinforcement Learning

Time-domain astronomy is an active research area now, which requires frequent observations of the whole sky to capture celestial objects with temporal variations. In the optical band, several telescopes in different locations could form a distributed telescope array to capture images of celestial objects continuously. However, there are millions of celestial objects to observe each night, and only limited telescopes could be used for observation. Besides, the observation capacity of these telescopes would be affected by different effects, such as the sky background or the seeing condition. It would be necessary to develop an algorithm to optimize the observation strategy of telescope arrays according to scientific requirements. In this paper, we propose a novel framework that includes a digital simulation environment and a deep reinforcement learning algorithm to optimize observation strategy of telescope arrays. Our framework could obtain effective observation strategies given predefined observation requirements and observation environment information. To test the performance of our algorithm, we simulate a scenario that uses distributed telescope arrays to observe space debris. Results show that our algorithm could obtain better results in both discovery and tracking of space debris. The framework proposed in this paper could be used as an effective strategy optimization framework for distributed telescope arrays, such as the Sitian project or the TIDO project.

Keywords: optical observation; neural networks; optical telescopes; astronomical simulations
Revisiting the Transit Timing and Atmosphere Characterization of the Neptune-mass Planet HAT-P-26 b

We present a transit-timing variation (TTV) and planetary atmosphere analysis of the Neptune-mass planet HAT-P-26 b. We present a new set of 13 transit light curves from optical ground-based observations and combine them with light curves from the Wide Field Camera 3 on the Hubble Space Telescope, the Transiting Exoplanet Survey Satellite, and previously published ground-based data. We refine the planetary parameters of HAT-P-26 b and undertake a TTV analysis using 33 transits obtained over seven years. The TTV analysis shows an amplitude signal of 1.98 ± 0.05 minutes, which could result from the presence of an additional ~0.02 M Jup planet at a 1:2 mean-motion resonance orbit. Using a combination of transit depths spanning optical to near-infrared wavelengths, we find that the atmosphere of HAT-P-26 b contains ${2.4}_{-1.6}^{+2.9}$ % H2O with a derived temperature of ${590}_{-50}^{+60}$ K.

Keywords: exoplanet astronomy; exoplanet atmospheres; timing variation methods