adsabs/SciX_UAT_keywords huggingface dataset:
Dynamic Evolution of Magnetic Flux Ropes in Active Region 11429. I. EUV Observations

Studying the formation and dynamic evolution of the magnetic flux rope (MFR) is key to understanding the physics of most solar eruptions. In the present study, we investigate the dynamic evolution of four MFRs, which involve in a major eruption. The MFR1, which represents as filament (F1), first appears about 31 hr before the major eruption. The MFR2 appears as a hot-channel with a small filament (F2) in its east part. The hot-channel becomes intermittently visible about 2 hr before the major eruption. The MFR3 is formed by the reconnection between MFR1 and MFR2. The annular components of MFR3 along the MFR2 part appear as a hollow helical structure from the background with the temperature of several MK after the reconnection. Coronal material then flows along the hollow structure from MFR1 part to MFR2 part to form a new filament (F3), which is hosted by MFR3 and acts as the axial component of MFR3 in the following evolution. The MFR4 appears during MFR3's eruption phase as conjugated extreme ultraviolet (EUV) brightenings. Both brightenings extend outward into irregular ribbons with conjugate EUV dimmings inside. Meanwhile, an erupted hot-channel, which roots in the conjugated brightening, is identified. The morphology of the MFRs are also profiled by four associated flare ribbon pairs. The on-disk observations shed light on our understanding of the topology of the MFRs and their formation and eruption. Further work should lay emphasis on the magnetic environment for the MFR formation and evolution.

Keywords: solar filaments
Limits on the Auroral Generation of H3 + in Brown Dwarf and Extrasolar Giant Planet Atmospheres with the Keck Near Infrared Echelle Spectrograph

The molecular ion H3 + is a potentially powerful tracer of the ionospheres and thermal structures of Jovian planets but has never been detected in a planetary mass object outside of the solar system. Models predict that H3 + emission driven by EUV flux and solar wind on hot Jupiters, or by powerful aurorae on brown dwarfs, will be between 102 and 105 × more intense than that of Jupiter. If optimal conditions for the production of emission do exist, the emission may be detectable by current ground-based instruments or in the near future. We present the first search for H3 + line emission in brown dwarfs with Keck Near Infrared Echelle Spectrograph L' high-resolution spectroscopy. Additionally, we survey stars hosting giant planets at semimajor axes near 0.1-0.2 au, which models suggest may be the best planetary targets. No candidate H3 + emission is found. The limits we place on the emission of H3 + from brown dwarfs indicate that auroral generation of H3 + in these environments likely does not linearly scale from the processes found on Jupiter, plausibly due to deeper atmospheric penetration by precipitating auroral electrons. Detection of H3 + emission in brown dwarfs may be possible with the James Webb Space Telescope, or future 33 m class telescopes.

Keywords: exoplanet astronomy; exoplanet atmospheres; brown dwarfs; hot jupiters; star-planet interactions; extrasolar gaseous giant planets
Deriving the Stellar Labels of LAMOST Spectra with the Stellar LAbel Machine (SLAM)

The LAMOST survey has provided 9 million spectra in its Data Release 5 (DR5) at R ∼ 1800. Extracting precise stellar labels is crucial for such a large sample. In this paper, we report the implementation of the Stellar LAbel Machine (SLAM), which is a data-driven method based on support vector regression (SVR), a robust nonlinear regression technique. Thanks to the capability to model highly nonlinear problems with SVR, SLAM can generally derive stellar labels over a wide range of spectral types. This gives it a unique capability compared to other popular data-driven methods. To illustrate this capability, we test the performance of SLAM on stars ranging from T eff ∼ 4000 to ∼8000 K trained on LAMOST spectra and stellar labels. At g-band signal-to-noise ratio (S/N g ) higher than 100, the random uncertainties of T eff, log g, and [Fe/H] are 50 K, 0.09 dex, and 0.07 dex, respectively. We then set up another SLAM model trained by APOGEE and LAMOST common stars to demonstrate its capability of dealing with high dimensional problems. The spectra are from LAMOST DR5 and the stellar labels of the training set are from APOGEE DR15, including T eff, log g, [M/H], [α/M], [C/M], and [N/M]. The cross-validated scatters at {{S}}/{{{N}}}g∼ 100 are 49 K, 0.10 dex, 0.037 dex, 0.026 dex, 0.058 dex, and 0.106 dex for these parameters, respectively. This performance is at the same level as other up-to-date data-driven models. As a byproduct, we also provide the latest catalog of ∼1 million LAMOST DR5 K giant stars with SLAM-predicted stellar labels in this work.

Keywords: astronomical methods; astronomy data analysis; bayesian statistics; stellar abundances; chemical abundances; fundamental parameters of stars; catalogs; surveys
A Multiwavelength Study of Active Galactic Nuclei in Post-merger Remnants

We investigate the role of galaxy mergers in triggering active galactic nuclei (AGN) in the nearby universe. Our analysis is based on a sample of 79 post-merger remnant galaxies with deep X-ray observations from Chandra/XMM-Newton capable of detecting a low-luminosity AGN of ≥1040.5 erg s-1. This sample is derived from a visually classified, volume-limited sample of 807 post-mergers identified in the Sloan Digital Sky Survey Data Release 14 with log M */M ⊙ ≥ 10.5 and 0.02 ≤ z ≤ 0.06. We find that the X-ray AGN fraction in this sample is 55.7% ± 5.6% compared to 23.6% ± 2.8% for a mass- and redshift-matched noninteracting control sample. The multiwavelength AGN fraction (identified as an AGN in one of X-ray, IR, radio or optical diagnostics) for post-mergers is 76.6% ± 4.8% compared to 39.1% ± 3.2% for controls. Thus post-mergers exhibit a high overall AGN fraction with an excess between 2 and 4 depending on the AGN diagnostics used. In addition, we find most optical, IR, and radio AGN are also identified as X-ray AGN while a large fraction of X-ray AGN are not identified in any other diagnostic. This highlights the importance of deep X-ray imaging to identify AGN. We find that the X-ray AGN fraction of post-mergers is independent of the stellar mass above log M */M ⊙ ≥ 10.5 unlike the trend seen in control galaxies. Overall, our results show that post-merger galaxies are a good tracer of the merger-AGN connection and strongly support the theoretical expectations that mergers trigger AGN.

Keywords: galaxy evolution; galaxy interactions; active galactic nuclei; galaxy mergers
The Circumstellar Environment around the Embedded Protostar EC 53

EC 53 is an embedded protostar with quasi-periodic emission in the near-IR and submillimeter. We use Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution observations of continuum and molecular line emission to describe the circumstellar environment of EC 53. The continuum image reveals a disk with a flux that suggests a mass of 0.075 M⊙, much less than the estimated mass in the envelope, and an in-band spectral index that indicates grain growth to centimeter sizes. Molecular lines trace the outflow cavity walls, infalling and rotating envelope, and/or the Keplerian disk. The rotation profile of the C17O 3-2 line emission cannot isolate the Keplerian motion clearly, although the lower limit of the protostellar mass can be calculated as 0.3 ± 0.1 M⊙ if the Keplerian motion is adopted. The weak CH3OH emission, which is anticorrelated with the H13CO+ 4-3 line emission, indicates that the water snow line is more extended than what expected from the current luminosity, attesting to bygone outburst events. The extended snow line may persist for longer at the disk surface because the lower density increases the freeze-out timescale of methanol and water.

Keywords: protostars; protoplanetary disks; spectral index; interstellar molecules
Hot Degenerates in the MCT Survey. III. A Sample of White Dwarf Stars in the Southern Hemisphere

We present optical spectra of 144 white dwarfs detected in the Montreal-Cambridge-Tololo colorimetric survey, including 120 DA, 12 DB, 4 DO, 1 DQ, and 7 DC stars. We also perform a model atmosphere analysis of all objects in our sample using the so-called spectroscopic technique, or the photometric technique in the case of DC white dwarfs. The main objective of this paper is to contribute to the ongoing effort of confirming spectroscopically all white dwarf candidates in the Gaia survey, in particular in the southern hemisphere. All our spectra are made available in the Montreal White Dwarf Database.

Keywords: white dwarf stars; surveys; fundamental parameters of stars
Model of a Gap Formed by a Planet with Fast Inward Migration

A planet is formed within a protoplanetary disk. Recent observations have revealed substructures such as gaps and rings, which may indicate forming planets within the disk. Due to disk-planet interaction, the planet migrates within the disk, which can affect the shape of a planet-induced gap. In this paper, we investigate effects of fast inward migration of the planet on the gap shape, by carrying out hydrodynamic simulations. We found that when the migration timescale is shorter than the timescale of the gap-opening, the orbital radius is shifted inward as compared to the radial location of the gap. We also found a scaling relation between the radial shift of the locations of the planet and the gap as a function of the ratio of the timescale of the migration and gap-opening. Our scaling relation also enables us to constrain the gas surface density and the viscosity when the gap and the planet are observed. Moreover, we also found the scaling relation between the location of the secondary gap and the aspect ratio. By combining the radial shift and the secondary gap, we may constrain the physical condition of the planet formation and how the planet evolves in the protoplanetary disk, from the observational morphology.

Keywords: planet formation; protoplanetary disks
First Discovery of New Pulsars and RRATs with CHIME/FRB

We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment's Fast Radio Burst (CHIME/FRB) backend. These sources were first identified via single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients, pulsar-like sources with occasional single-pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter two. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources.

Keywords: pulsars; radio pulsars
Early Results from GLASS-JWST. XIII. A Faint, Distant, and Cold Brown Dwarf

We present the serendipitous discovery of a late T-type brown dwarf candidate in JWST NIRCam observations of the Early Release Science Abell 2744 parallel field. The discovery was enabled by the sensitivity of JWST at 4 μm wavelengths and the panchromatic 0.9-4.5 μm coverage of the spectral energy distribution. The unresolved point source has magnitudes F115W = 27.95 ± 0.15 and F444W = 25.84 ± 0.01 (AB), and its F115W-F444W and F356W-F444W colors match those expected for other known T dwarfs. We can exclude it as a reddened background star, high redshift quasar, or a very high redshift galaxy. Comparison with stellar atmospheric models indicates a temperature of T eff ≈ 650 K and surface gravity $\mathrm{log}g\approx 5.25$ , implying a mass of 0.03 M ⊙ and age of 5 Gyr. We estimate the distance of this candidate to be 570-720 pc in a direction perpendicular to the Galactic plane, making it a likely thick disk or halo brown dwarf. These observations underscore the power of JWST to probe the very low-mass end of the substellar mass function in the Galactic thick disk and halo. *Based on data collected with JWST.

Keywords: t dwarfs
Detection of Close Kuiper Belt Binaries with HST WFC3

Binaries in the Kuiper Belt are common. Here we present our analysis of the Solar System Origins Legacy Survey (SSOLS) to show that using a point-spread function (PSF)-fitting method can roughly double the number of binaries identified in that data set. Out of 198 Kuiper Belt objects (KBOs) observed by SSOLS, we find 23 to be visually separated binaries, while a further 19 are blended PSF binaries detectable with the method we present here. This is an overall binary fraction of 21% for the SSOLS data set of cold classical KBOs. In addition, we tested our fitting methods on synthetic data, and while we were able to show them to be very effective at detecting certain blended-PSF binary KBOs, fainter or closer binary KBOs may easily be missed, suggesting that the close binary KBO fraction could be even higher. These results strongly support the idea that most (if not all) KBOs were formed through the streaming instability process, and as a consequence, most KBOs were formed as near-equal mass binaries.

Keywords: asteroid satellites; classical kuiper belt objects; trans-neptunian objects
Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S5)

We present new spectroscopic observations of the diffuse Milky Way satellite galaxies Antlia 2 and Crater 2, taken as part of the Southern Stellar Stream Spectroscopic Survey (S5). The new observations approximately double the number of confirmed member stars in each galaxy and more than double the spatial extent of spectroscopic observations in Antlia 2. A full kinematic analysis, including Gaia EDR3 proper motions, detects a clear velocity gradient in Antlia 2 and a tentative velocity gradient in Crater 2. The velocity gradient magnitudes and directions are consistent with particle stream simulations of tidal disruption. Furthermore, the orbit and kinematics of Antlia 2 require a model that includes the reflex motion of the Milky Way induced by the Large Magellanic Cloud. We also find that Antlia 2's metallicity was previously overestimated, so it lies on the empirical luminosity-metallicity relation and is likely only now experiencing substantial stellar mass loss. Current dynamical models of Antlia 2 require it to have lost over 90% of its stars to tides, in tension with the low stellar mass loss implied by the updated metallicity. Overall, the new kinematic measurements support a tidal disruption scenario for the origin of these large and extended dwarf spheroidal galaxies.

Keywords: dwarf galaxies; stellar kinematics; stellar streams; milky way galaxy; large magellanic cloud; dark matter
Discovery of a Dusty Yellow Supergiant Progenitor for the Type IIb SN 2017gkk

Type IIb supernovae are an important subclass of stripped-envelope supernovae (SNe), which show H lines only at early times. Their progenitors are believed to contain a low-mass H envelope before explosion. This work reports the discovery of a progenitor candidate in preexplosion Hubble Space Telescope images for the Type IIb SN 2017gkk. With detailed analysis of its spectral energy distribution and local environment, we suggest that the progenitor is most likely a yellow supergiant with significant circumstellar extinction and has an initial mass of about 16 M ⊙, effective temperature log(T eff/K) = 3.72 ± 0.08, and luminosity log(L/L ⊙) = 5.17 ± 0.04. This progenitor is not massive enough to strip envelope through stellar wind, and it supports an interacting binary progenitor channel and adds to the growing list of direct progenitor detections for Type IIb SNe. Future late-time observations will confirm whether this progenitor candidate has disappeared and reveal the putative binary companion that has survived the explosion.

Keywords: core-collapse supernovae; type ii supernovae; circumstellar dust
Determining the Physical Conditions of an Extremely Young Class 0 Circumbinary Disk around VLA 1623A

We present a detailed analysis of high-resolution C18O (2-1), SO (88-77), CO (3-2), and DCO+ (3-2) data obtained by the Atacama Large Millimeter/submillimeter Array toward a class 0 Keplerian circumbinary disk around VLA 1623A, which represents one of the most complete analyses toward a class 0 source. From the dendrogram analysis, we identified several accretion flows feeding the circumbinary disk in a highly anisotropic manner. Stream-like SO emission around the circumbinary disk reveals the complicated shocks caused by the interactions between the disk, accretion flows, and outflows. A wall-like structure is discovered south of VLA 1623B. The discovery of two outflow cavity walls at the same position traveling at different velocities suggests that the two outflows from both VLA 1623A and VLA 1623B are on top of each other in the plane of the sky. Our detailed flat and flared disk modeling shows that Cycle 2 C18O J = 2-1 data are inconsistent with the combined binary mass of 0.2 M⊙, as suggested by early Cycle 0 studies. The combined binary mass for VLA 1623A should be modified to 0.3-0.5 M⊙.

Keywords: shocks; accretion; stellar accretion; stellar accretion disks; observational astronomy; protostars; young stellar objects; radio interferometry; radio astronomy; circumstellar disks; star formation
Dissecting the γ-Ray Emissions of the Nearby Galaxies NGC 1068 and NGC 253

Intrigued by recent high-energy study results for nearby galaxies with γ-ray emission and in particular NGC 1068 that has been detected as a neutrino-emitting source by the IceCube Neutrino Observatory, we conduct a detailed analysis of the γ-ray data of the galaxies NGC 1068 and NGC 253, obtained with the Large Area Telescope on board the Fermi γ-ray Space Telescope. By checking their possible spectral features and then constructing light curves in the corresponding energy ranges, we identify spectral-change activity from NGC 1068 in the ≥2 GeV energy range and long-term, statistically significant changes for NGC 253 in the ≥5 GeV energy range. In the former, the emission appears harder in two half-year periods than in the otherwise "quiescent" state. In the latter, an ~two-fold decrease in the detection significance after MJD = 57023 is clearly revealed by the test-statistic maps we obtain. Considering the previous studies carried out and the various models proposed for the γ-ray emissions of the two sources, we discuss the implications of our findings. We suspect that a jet (or outflow) in NGC 1068 might contribute to the γ-ray emission. The nature of the long-term statistically significant changes for NGC 253 is not clear, but since the part of the GeV emission may be connected to the very-high-energy (VHE) emission from the center of the galaxy, it could be further probed with VHE observations.

Keywords: gamma-rays; seyfert galaxies; post-starburst galaxies
Mutual Orbital Inclinations between Cold Jupiters and Inner Super-Earths

Previous analyses of Doppler and Kepler data have found that Sun-like stars hosting “cold Jupiters” (giant planets with a ≳ 1 au) almost always host “inner super-Earths” (1-4 R ⊕, a ≲ 1 au). Here we attempt to determine the degree of alignment between the orbital planes of the cold Jupiters and the inner super-Earths. The key observational input is the fraction of Kepler stars with transiting super-Earths that also have transiting cold Jupiters. This fraction depends on both the probability for cold Jupiters to occur in such systems and the mutual orbital inclinations. Since the probability of occurrence has already been measured in Doppler surveys, we can use the data to constrain the mutual inclination distribution. We find σ = 11.°8-5.°5 +12.°7 (68% confidence) and σ > 3.°5 (95% confidence), where σ is the scale parameter of the Rayleigh distribution. This suggests that planetary orbits in systems with cold Jupiters tend to be coplanar—although not quite as coplanar as those in the solar system, which have a mean inclination from the invariable plane of 1.°8. We also find evidence that cold Jupiters have lower mutual inclinations relative to inner systems with higher transit multiplicity. This suggests a link between the dynamical excitation in the inner and outer systems. For example, perturbations from misaligned cold Jupiters may dynamically heat or destabilize systems of inner super-Earths.

Keywords: exoplanet astronomy; exoplanet systems; exoplanet formation; exoplanet evolution; exoplanets; extrasolar gaseous giant planets; super earths; astronomy data analysis; astrostatistics
Mining the Information Content of Member Galaxies in Halo Mass Modeling

Motivated by previous findings that the magnitude gap between certain satellite galaxies and the central galaxy can be used to improve the estimation of halo mass, we carry out a systematic study of the information content of different member galaxies in the modeling of the host halo mass using a machine-learning approach. We employ data from the hydrodynamical simulation IllustrisTNG and train a random forest algorithm to predict a halo mass from the stellar masses of its member galaxies. Exhaustive feature selection is adopted to disentangle the importance of different galaxy members. We confirm that an additional satellite does improve the halo mass estimation compared to that estimated by the central alone. However, the magnitude of this improvement does not differ significantly using different satellite galaxies. When three galaxies are used in the halo mass prediction, the best combination is always that of the central galaxy with the most massive satellite and the smallest satellite. Furthermore, among the top seven galaxies, the combination of a central galaxy and two or three satellite galaxies gives a near-optimal estimation of halo mass, and further addition of galaxies does not raise the precision of the prediction. We demonstrate that these dependences can be understood from the shape variation of the conditional satellite distribution, with different member galaxies accounting for distinct halo-dependent features in different parts of the cumulative stellar mass function.

Keywords: galaxy dark matter halos; stellar mass functions; random forests
Orbital and Precession Periods in Repeating FRB 20121102A

Li et al. reported a 4.605 days period in the repeating FRB 20121102A in addition to its previously reported 157 days modulation of activity. This note suggests that the shorter period is the orbital period of a mass-transferring star orbiting a black hole, possibly of intermediate mass, and that the 157 days period is the precession period of an accretion disk around the black hole. The mass-losing star must be evolved.

Keywords: radio transient sources