adsabs/SciX_UAT_keywords huggingface dataset:
Dippers from TESS Full-frame Images. II. Spectroscopic Characterization of Four Young Dippers

Photometric monitoring by the Transiting Exoplanet Survey Satellite (TESS) has discovered not only periodic signals by transiting exoplanets but also episodic or quasiperiodic dimming around young stellar objects. The dimming mechanisms of these objects, the so-called "dippers," are thought to be related to either the accretion property or the structure of protoplanetary disks especially in regions close to the host star. Recently, we have created a catalog of dippers from one year of TESS full-frame image data. In this paper, we report on the spectral features of four newly found dippers in that catalog and show that they potentially shed light on the dimming mechanisms. We found that all of the targets exhibit the Hα emission line, which is an indicator of ongoing accretion. Based on their line profiles and/or their variability, we characterized the properties of the disks of each source, which can support dimming mechanisms via a dusty disk wind or an accretion-driven inner-disk warp. Also, we found an interesting dipper (TIC 317873721), a "close-in binary dipper," showing a complex variability of the line profile and a large radial velocity variation. Because the dimming intervals are similar to the orbital period of the binary, we suggest that the dips are caused by dust in the accretion warp from a circumbinary disk onto stars. Such a close-in (<0.1 au) binary dipper has been rarely reported thus far; further investigation will reveal new aspects of disk evolution and planetary formation.

Keywords: variable stars; protoplanetary disks
Characterizing Quasar C IV Emission-line Measurements from Time-resolved Spectroscopy

We use multiepoch quasar spectroscopy to determine how accurately single-epoch spectroscopy can locate quasars in emission-line parameter space in order to inform investigations where time-resolved spectroscopy is not available. We explore the improvements in emission-line characterization that result from using nonparametric information from many lines as opposed to a small number of parameters for a single line, utilizing reconstructions based on an independent component analysis applied to the data from the Sloan Digital Sky Survey Reverberation Mapping project. We find that most of the quasars are well described by just two components, while more components signal a quasar likely to yield a successful reverberation mapping analysis. In single-epoch spectroscopy the apparent variability of equivalent width is exaggerated because it is dependent on the continuum. Multiepoch spectroscopy reveals that single-epoch results do not significantly change where quasars are located in C IV parameter space and do not have a significant impact on investigations of the global Baldwin effect. Quasars with emission-line properties indicative of higher L/LEdd are less variable, consistent with models with enhanced accretion disk density. Narrow absorption features at the systemic redshift may be indicative of orientation (including radio-quiet quasars) and may appear in as much as 20% of the quasar sample. Future work applying these techniques to lower-luminosity quasars will be important for understanding the nature of accretion disk winds.

Keywords: quasars; black hole physics
On the Magnetic Nature of an Exploding Granule as Revealed by Sunrise/IMaX

We study the photospheric evolution of an exploding granule observed in the quiet Sun at high spatial (∼0"3) and temporal (31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009 June. These observations show that the exploding granule is cospatial to a magnetic flux emergence event occurring at mesogranular scale (up to ∼12 Mm2 area). Using a modified version of the SIR code for inverting the IMaX spectropolarimetric measurements, we obtain information about the magnetic configuration of this photospheric feature. In particular, we find evidence of highly inclined emerging fields in the structure, carrying a magnetic flux content up to ∼4 × 1018 Mx. The balance between gas and magnetic pressure in the region of flux emergence, compared with a very quiet region of the Sun, indicates that the additional pressure carried by the emerging flux increases the total pressure by about 5% and appears to allow the granulation to be modified, as predicted by numerical simulations. The overall characteristics suggest that a multipolar structure emerges into the photosphere, resembling an almost horizontal flux sheet. This seems to be associated with exploding granules. Finally, we discuss the origin of such flux emergence events.

Keywords: solar granulation; solar granules; mesogranulation; solar photosphere; solar magnetic fields; solar magnetic flux emergence; spectropolarimetry
Improved Methods for Estimating Peculiar Velocity Correlation Functions Using Volume Weighting

We present an improved method for calculating the parallel and perpendicular velocity correlation functions directly from peculiar velocity surveys using weighted maximum-likelihood estimators. A central feature of the new method is the use of a position-dependent weighting scheme that reduces the influence of nearby galaxies, which are typically overrepresented relative to more distant galaxies in most surveys. We demonstrate that correlation functions calculated in this way are less susceptible to biases due to our particular location in the universe, and thus are more easily comparable to linear theory and between surveys. Our results suggest that the parallel velocity correlation function is a promising cosmological probe, given that it provides a better approximation of a Gaussian distribution than other velocity correlation functions and that its bias is more easily minimized by weighting. Though the position-weighted parallel velocity correlation function increases the statistical uncertainty, it decreases the cosmic variance and is expected to provide more stable and tighter cosmological parameter constraints than other correlation methods in conjunction with more precise velocity surveys in the future.

Keywords: cosmology
3D Spectroscopy with GTC-MEGARA of the Triple AGN Candidate in SDSS J102700.40+174900.8

Triple-active galactic nucleus (AGN) systems are expected to be the result of the hierarchical model of galaxy formation. Since there are very few of them confirmed as such, we present the results of a new study of the triple AGN candidate SDSS J102700.40+174900.8 (center nucleus) through observations with the GTC-MEGARA Integral Field Unit. 1D and 2D analysis of the line ratios of the three nuclei allow us to locate them in the EW(Hα) versus [N II]/Hα diagram. The central nucleus is found to be a retired galaxy (or fake AGN). The neighbors are found to be a strong AGN (southeastern nucleus, J102700.55+174900.2), compatible with a Seyfert 2 (Sy2) galaxy, and a weak AGN (northern nucleus, J102700.38+174902.6), compatible with a LINER2. We find evidence that the neighbors constitute a dual AGN system (Sy2-LINER2) with a projected separation of 3.98 kpc in the optical bands. The Hα velocity map shows that the northern nucleus has an Hα emission with a velocity offset of ~-500 km s-1, whereas the southeastern nucleus has a rotating disk and Hα extended emission at kiloparsec scales. Chandra archival data confirm that the neighbors have X-ray (0.5-2) keV and (2-7) keV emission, whereas the center nucleus shows no X-ray emission. A collisional ring with knots is observed in Hubble Space Telescope images of the southeastern nucleus. These knots coincide with star formation regions that, along with the ring, are predicted in a head-on collision. In this case, the morphology changes are probably due to a minor merger that was produced by the passing of the northern through the southeastern nucleus.

Keywords: active galactic nuclei; astronomical techniques; galaxy interactions; seyfert galaxies; galaxy spectroscopy; x-ray active galactic nuclei
Insights into the Evolution of Five Isolated Galaxies

Galaxy evolution is believed to be conditioned by the environment. Isolated galaxies or galaxies in poor groups are an excellent laboratory to study evolutionary mechanisms where effects of the environment are minimal. We present new Swift-UVOT data in six filters, three in the ultraviolet (UV), of five isolated galaxies aiming at shedding light into their evolution. For all of our targets, we present new UV integrated fluxes, and for some of them also new UBV magnitudes. Our observations allow us to improve their multiwavelength spectral energy distributions, extending them over about three orders of magnitude in wavelength. We exploit our smooth particle hydrodynamical simulations with chemo-photometric implementation anchored, a posteriori, to the global multiwavelength properties of our targets, to give insight into their evolution. Then we compare their evolutionary properties with those previously derived for several galaxies in groups. The evolution of our targets is driven by a merger that occurred several gigayears ago, in the redshift range 0.5 ≤ z ≤ 4.5, not unlike what we have already found for galaxies in groups. The merger shapes the potential well where the gas is accreting, driving the star formation rate and the galaxy evolution. Isolated galaxies should not have suffered from interactions for at least 3 Gyr. However, the initial merger is still leaving its signature on the properties of our targets. Several rejuvenation episodes, triggered by in situ accretion, are highlighted. Moreover, jellyfish morphologies appear as these galaxies achieve their maximum star formation rate, before their quenching phase.

Keywords: early-type galaxies; observational astronomy; galaxy evolution; hydrodynamical simulations; galaxy mergers; near ultraviolet astronomy
Advancing Solar Magnetic Field Extrapolations through Multiheight Magnetic Field Measurements

Nonlinear force-free extrapolations are a common approach to estimate the 3D topology of coronal magnetic fields based on photospheric vector magnetograms. The force-free assumption is a valid approximation at coronal heights, but for the dense plasma conditions in the lower atmosphere, this assumption is not satisfied. In this study, we utilize multiheight magnetic field measurements in combination with physics-informed neural networks to advance solar magnetic field extrapolations. We include a flexible height-mapping, which allows us to account for the different formation heights of the observed magnetic field measurements. The comparison to analytical and simulated magnetic fields demonstrates that including chromospheric magnetic field measurements leads to a significant improvement of our magnetic field extrapolations. We also apply our method to chromospheric line-of-sight magnetograms from the Vector Spectromagnetograph (VSM) on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) observatory, in combination with photospheric vector magnetograms from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The comparison to observations in extreme-ultraviolet wavelengths shows that the additional chromospheric information leads to a better agreement with the observed coronal structures. In addition, our method intrinsically provides an estimate of the corrugation of the observed magnetograms. With this new approach, we make efficient use of multiheight magnetic field measurements and advance the realism of coronal magnetic field simulations.

Keywords: solar magnetic fields; neural networks; solar corona
Electromagnetic Precursors to Black Hole-Neutron Star Gravitational Wave Events: Flares and Reconnection-powered Fast Radio Transients from the Late Inspiral

The presence of magnetic fields in the late inspiral of black hole-neutron star binaries could lead to potentially detectable electromagnetic precursor transients. Using general-relativistic force-free electrodynamics simulations, we investigate premerger interactions of the common magnetosphere of black hole-neutron star systems. We demonstrate that these systems can feature copious electromagnetic flaring activity, which we find depends on the magnetic field orientation but not on black hole spin. Due to interactions with the surrounding magnetosphere, these flares could lead to fast-radio-burst-like transients and X-ray emission, with ${{ \mathcal L }}_{\mathrm{EM}}\lesssim {10}^{41}{\left({B}_{* }/{10}^{12}\,{\rm{G}}\right)}^{2}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ as an upper bound on the luminosity, where B * is the magnetic field strength on the surface of the neutron star.

Keywords: astrophysical black holes; neutron stars; radio transient sources; magnetospheric radio emissions; plasma astrophysics; general relativity; gravitational wave sources
Parameterizing the Outflow from a Central Black Hole in Dwarf Spheroidal Galaxies: A 3D Hydrodynamic Simulation

Large galaxies harbor massive central black holes and their feedback exerts a substantial impact on their evolution. Recently, observations have suggested that dwarf galaxies might host black holes in their centers, but with lower masses (intermediate-mass black holes-IMBHs). The impact of IMBHs on the evolution of dwarf spheroidal galaxies (dSphs), however, has so far not been properly analyzed. In this work, we investigate the effects of an outflow from an IMBH on gas dynamics in dSphs by means of noncosmological, three-dimensional hydrodynamic simulations, letting the galactic gas distribution evolve over 3 Gyr under the influence of the IMBH's outflow and supernova feedback. All simulations have a numerical resolution of 20.0 pc cell-1. Two scenarios are considered to infer differences in the propagation of the outflow, one with a homogeneous interstellar medium (ISM) and another one with inhomogeneities caused by supernova feedback. A minimal initial speed and a minimal initial density are required for the outflow to propagate, with the values depending on the conditions of the medium. In an unperturbed medium, the outflow propagates freely in both directions with the same velocity (lower than the initial one), removing a small fraction of gas from the galaxy (the exact fraction depends on the initial physical conditions of the outflow). However, in an inhomogeneous ISM, the impact of the outflow is substantially reduced, and its contribution to the removal of gas from the galaxy is almost negligible.

Keywords: hydrodynamical simulations; dwarf galaxies; local group
MOPSS. II. Extreme Optical Scattering Slope for the Inflated Super-Neptune HATS-8b

We present results for the inflated super-Neptune HATS-8b from the Michigan Optical Planetary Spectra Survey (MOPSS). This program is aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. HATS-8b orbits a G dwarf and is a low-density super-Neptune with a radius of 0.873 R Jup, a mass of 0.138 M Jup, and a density of 0.259 g cm-3. Two transits of HATS-8b were observed in 2017 July and August with the Inamori-Magellan Areal Camera and Spectrograph (IMACS) instrument on the Magellan Baade 6.5 m telescope. We find an enhanced scattering slope on each night that agree within 2.3σ. This slope is stronger than one due only to Rayleigh scattering and cannot be fully explained by unocculted starspots. We explore the impact of condensates on the scattering slope and determine that MnS particulates smaller than 10-2 μm can explain up to 80% of our measured slope if the planet is warmer than equilibrium, or 50% of the slope at the equilibrium temperature of the planet for a low mean molecular weight atmosphere. The scattering slope that we observe is thus beyond even the most extreme haze case we consider. We suggest further follow up on this target and host star to determine if the temporal variation of the slope is primarily due to stellar or planetary effects, and to better understand what these effects may be.

Keywords: extrasolar gaseous giant planets; exoplanet atmospheres; exoplanets; hot jupiters; hot neptunes
Quiet-time Spectra of Suprathermal Heavy Ions near 1 au in Solar Cycles 23 and 24

We report on the annual variation of quiet-time suprathermal heavy ion spectral indices for C through Fe in the energy range 0.3–1.28 MeV nuc‑1 during Solar Cycle 23's rising phase through Solar Cycle 24's declining phase. These Advanced Composition Explorer/Ultra-Low Energy Isotope Spectrometer measurements cover 1998–2019. We show that the average quiet-time suprathermal spectral index across species is γ = 2.5 ± 0.3. Such observations may imply that quiet-time suprathermals are the result of a superposition of various underlying acceleration and transport processes that accelerate suprathermal ions. As such, they may be remnants of particles from discrete events like large and impulsive solar energetic particle events along with corotating interaction regions that have decayed in intensity.

Keywords: solar energetic particles; solar wind; adaptive interferometry; interplanetary particle acceleration; heliosphere
Potential Atmospheric Compositions of TRAPPIST-1 c Constrained by JWST/MIRI Observations at 15 μm

The first James Webb Space Telescope observations of TRAPPIST-1 c showed a secondary eclipse depth of 421 ± 94 ppm at 15 μm, which is consistent with a bare rock surface or a thin, O2-dominated, low-CO2 atmosphere. Here we further explore potential atmospheres for TRAPPIST-1 c by comparing the observed secondary eclipse depth to synthetic spectra of a broader range of plausible environments. To self-consistently incorporate the impact of photochemistry and atmospheric composition on atmospheric thermal structure and predicted eclipse depth, we use a two-column climate model coupled to a photochemical model and simulate O2-dominated, Venus-like, and steam atmospheres. We find that a broader suite of plausible atmospheric compositions are also consistent with the data. For lower-pressure atmospheres (0.1 bar), our O2-CO2 atmospheres produce eclipse depths within 1σ of the data, consistent with the modeling results of Zieba et al. However, for higher-pressure atmospheres, our models produce different temperature-pressure profiles and are less pessimistic, with 1-10 bar O2, 100 ppm CO2 models within 2.0σ-2.2σ of the measured secondary eclipse depth and up to 0.5% CO2 within 2.9σ. Venus-like atmospheres are still unlikely. For thin O2 atmospheres of 0.1 bar with a low abundance of CO2 (~100 ppm), up to 10% water vapor can be present and still provide an eclipse depth within 1σ of the data. We compared the TRAPPIST-1 c data to modeled steam atmospheres of ≤3 bars, which are 1.7σ-1.8σ from the data and not conclusively ruled out. More data will be required to discriminate between possible atmospheres or more definitively support the bare rock hypothesis.

Keywords: exoplanet atmospheres; extrasolar rocky planets
Dust Growth in Molecular Cloud Envelopes: A Numerical Approach

Variations in the grain size distribution are to be expected in the interstellar medium (ISM) owing to grain growth and destruction. In this work, we present a dust collision model to be implemented inside a magnetohydrodynamic (MHD) code that takes into account grain growth and shattering of charged dust grains of a given composition (silicate or graphite). We integrate this model in the MHD code Athena and build on a previous implementation of the dynamics of charged dust grains in the same code. To demonstrate the performance of this coagulation model, we study the variations in the grain size distribution of a single-sized population of dust with radius 0.05 μm inside several dust filaments formed during a 2D MHD simulation. We also consider a realistic dust distribution with sizes ranging from 50 Å to 0.25 μm and analyze the variations in both the size distribution for graphite and silicates and the far-ultraviolet extinction curve. From the obtained results, we conclude that the methodology here presented, based on the MHD evolution of the equation of motion for a charged particle, is optimal for studying the coagulation of charged dust grains in a diffuse regime such as a molecular cloud envelope. Observationally, these variations in the dust size distribution are translated into variations in the far-ultraviolet extinction curve, and they are mainly caused by small graphite dust grains.

Keywords: interstellar medium; interstellar dust; ultraviolet extinction
Large Adaptive Optics Survey for Substellar Objects around Young, Nearby, Low-mass Stars with Robo-AO

We present results from the Large Adaptive optics Survey for Substellar Objects, where the goal is to directly image new substellar companions (<70 MJup) at wide orbital separations (≳50 au) around young (≲300 Myr), nearby (<100 pc), low-mass (≈0.1-0.8 ${M}_{\odot }$ ) stars. We report on 427 young stars imaged in the visible (i') and near-infrared (J or H ) simultaneously with Robo-AO on the Kitt Peak 2.1 m telescope and later the Maunakea University of Hawaii 2.2 m telescope. To undertake the observations, we commissioned a new infrared camera for Robo-AO that uses a low-noise high-speed SAPHIRA avalanche photodiode detector. We detected 121 companion candidates around 111 stars, of which 62 companions are physically associated based on Gaia DR2 parallaxes and proper motions, another 45 require follow-up observations to confirm physical association, and 14 are background objects. The companion separations range from 2 to 1101 au and reach contrast ratios of 7.7 mag in the near-infrared compared to the primary. The majority of confirmed and pending candidates are stellar companions, with ~5 being potentially substellar and requiring follow-up observations for confirmation. We also detected a 43 ± 9 MJup and an 81 ± 5 MJup companion that were previously reported. We found 34 of our targets have acceleration measurements detected using Hipparcos-Gaia proper motions. Of those, ${58}_{-14}^{+12}$ % of the 12 stars with imaged companion candidates have significant accelerations ( ${\chi }^{2}\gt 11.8$ ), while only ${23}_{-6}^{+11}$ % of the remaining 22 stars with no detected companion have significant accelerations. The significance of the acceleration decreases with increasing companion separation. These young accelerating low-mass stars with companions will eventually yield dynamical masses with future orbit monitoring.

Keywords: low mass stars; binary stars; brown dwarfs; surveys; optical observation; infrared astronomy; astronomical instrumentation