adsabs/SciX_UAT_keywords huggingface dataset:
A Closer Look at Exoplanet Occurrence Rates: Considering the Multiplicity of Stars without Detected Planets

One core goal of the Kepler mission was to determine the frequency of Earth-like planets that orbit Sun-like stars. Accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stars searched for planets. Previous ground-based follow-up observations have, through a variety of methods, sought to improve our knowledge of stars that are known to host planets. Kepler targets without detected planets, however, have not been subjected to the same intensity of follow-up observations. In this paper, we constrain better the stellar multiplicity for stars around which Kepler could have theoretically detected a transiting Earth-sized planet in the habitable zone. We subsequently aim to improve estimates of the exoplanet search completeness—the fraction of exoplanets that were detected by Kepler—with our analysis. By obtaining adaptive optics observations of 71 Kepler target stars from the Shane 3 m telescope at Lick Observatory, we detected 14 candidate stellar companions within 4″ of 13 target stars. Of these 14 candidate stellar companions, we determine through multiple independent methods that 3 are likely to be bound to their corresponding target star. We then assess the impact of our observations on exoplanet occurrence rate calculations, finding an increase in occurrence of 6% (0.9σ) for various estimates of the frequency of Earth-like planets and an increase of 26% (4.5σ) for super-Earths and sub-Neptunes. These occurrence increases are not entirely commensurate with theoretical predictions, though this discrepancy may be due to differences in the treatment of stellar binarity.

Keywords: binary stars; near infrared astronomy; observational astronomy; exoplanet catalogs
Toward Understanding the B[e] Phenomenon. IX. Nature and Binarity of MWC645

We present the results of optical and near-IR spectroscopy and multicolor photometry of the emission-line star MWC 645, which exhibits the B[e] phenomenon. The presence of positionally variable absorption lines of a cool star detected for the first time indicates that the object is a binary system. Using a combination of the photometric and spectroscopic data as well as the Gaia EDR3 distance (D = 6.5 ± 0.9 kpc), we disentangled the components' contributions and estimated their surface temperatures and luminosities (18, 000 ± 2000 K and 4250 ± 250 K, log L/L ⊙ = 4.0 ± 0.5 and 3.1 ± 0.3 for the hot and cool components, respectively). Quasi-cyclic short-period (months) and long-period (~4 yr) photometric variations were detected in both optical and near-IR regions, and are most likely due to variable circumstellar extinction. Our analysis suggests that MWC 645 is a member of the FS CMa group. The object's properties can be described by an evolutionary model of a close binary system that currently undergoes a nonconservative mass transfer between intermediate-mass stars (e.g., 7 M ⊙ + 2.8 M ⊙).

Keywords: a stars; binary stars; spectroscopic binary stars; be stars; emission line stars
On the Feasibility of Informative Biosignature Measurements Using an Enceladus Plume Organic Analyzer

The icy moons of Saturn and Jupiter are high priority locations in which to search for biomarkers of life elsewhere in our solar system. In particular, the ice plumes that jet out through the ice surface at Enceladus provide an enticing opportunity to sample the organic components of its subsurface ocean for possible biosignatures while ameliorating challenges of planetary protection. Extensive high- and hypervelocity light gas gun experiments, the first to model the Enceladus ice plume encounter accurately, have demonstrated that organic-rich ice particles can be efficiently captured using plume transits at and below 3 km s-1 without significant organic destruction. Realistic scenarios for the amount of ice captured and for the ability of organic chemical analysis instruments, especially microfluidic capillary electrophoresis with laser-induced fluorescence, to produce meaningful detection levels for biosignatures are then presented and compared with results from terrestrial models. This analysis indicates that an Enceladus plume fly-by mission carrying microfluidic instrumentation is capable of biosignature measurements with a sensitivity and analytical capability that is highly informative about the extent of extraterrestrial biological processes.

Keywords: saturnian satellites; biosignatures; impact phenomena
Identifying the Gamma-Ray Emission of the Nearby Galaxy M83

We report on the detection of a γ-ray source at the position of the nearby star-forming galaxy (SFG) M83, which is found from our analysis of 14 yr of the data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi). The source is weakly detected, with a significance of ~5σ, and its emission can be described with an exponentially cutoff power law. At a distance of 4.61 Mpc, the source's γ-ray luminosity is ~1.4 × 1039 erg s-1, roughly along the correlation line between the γ-ray and IR luminosities determined for nearby SFGs. Because of the weak detection, the source spectrum can not be used for checking its similarity with those of other SFGs. Given the positional matches and the empirical expectation for γ-ray emission from M83 due to the galaxy's star-forming activity, we conclude that the γ-ray source is the likely counterpart to M83. The detection thus adds another member to the group of approximately a dozen SFGs, whose γ-ray emissions mostly have a cosmic-ray origin.

Keywords: gamma-ray sources; starburst galaxies
Local Simulations of Spiral Galaxies with the TIGRESS Framework. I. Star Formation and Arm Spurs/Feathers

Spiral arms greatly affect gas flows and star formation in disk galaxies. We use local three-dimensional simulations of the vertically stratified, self-gravitating, differentially rotating interstellar medium (ISM) subject to a stellar spiral potential to study the effects of spiral arms on star formation and formation of arm spurs/feathers. We adopt the TIGRESS framework of Kim & Ostriker to handle radiative heating and cooling, star formation, and ensuing supernova (SN) feedback. We find that more than 90% of star formation takes place in spiral arms, but the global star formation rate (SFR) in models with spiral arms is enhanced by less than a factor of 2 compared to the no-arm counterpart. This results from a quasi-linear relationship between the SFR surface density ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ and the gas surface density Σ, and supports the picture that spiral arms do not trigger star formation but rather concentrate star-forming regions. Correlated SN feedback produces gaseous spurs/feathers downstream from arms in both magnetized and unmagnetized models. These spurs/feathers are short lived and have magnetic fields parallel to their length, in contrast to the longer-lived features with perpendicular magnetic fields induced by gravitational instability. SN feedback drives the turbulent component of magnetic fields, with the total magnetic field strength sublinearly proportional to Σ. The total midplane pressure varies by a factor of ∼10 between arm and interarm regions but agrees locally with the total vertical ISM weight, while ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ is locally consistent with the prediction of pressure-regulated, feedback-modulated theory.

Keywords: interstellar medium; magnetohydrodynamical simulations; disk galaxies; agn host galaxies; star formation; spiral galaxies; galaxy magnetic fields; superbubbles
Pwyll and Manannán Craters as a Laboratory for Constraining Irradiation Timescales on Europa

We examine high-spatial-resolution Galileo/Near-Infrared Mapping Spectrometer observations of the young (∼1 My–∼20 My) impact features, Pwyll and Manannán craters, on Europa's trailing hemisphere in an effort to constrain irradiation timescales. We characterize their composition using a linear spectral modeling analysis, and find that both craters and their ejecta are depleted in hydrated sulfuric acid relative to nearby older terrain. This suggests that the radiolytic sulfur cycle has not yet had enough time to build up an equilibrium concentration of H2SO4, and places a strong lower limit of the age of the craters on the equilibrium timescale of the radiolytic sulfur cycle on Europa's trailing hemisphere. Additionally, we find that the dark and red material seen in the craters and proximal ejecta of Pwyll and Manannán show the spectroscopic signature of hydrated, presumably endogenic salts. This suggests that the irradiation-induced darkening and reddening of endogenic salts thought to occur on Europa's trailing hemisphere has already happened at Pwyll and Manannán, thereby placing an upper limit on the timescale by which salts are irradiation reddened.

Keywords: galilean satellites; europa; planetary surfaces; surface composition; surface ices
Solar Flare-CME Coupling throughout Two Acceleration Phases of a Fast CME

Solar flares and coronal mass ejections (CMEs) are closely coupled through magnetic reconnection. CMEs are usually accelerated impulsively within the low solar corona, synchronized with the impulsive flare energy release. We investigate the dynamic evolution of a fast CME and its associated X2.8 flare occurring on 2013 May 13. The CME experiences two distinct phases of enhanced acceleration, an impulsive one with a peak value of ∼5 km s-2, followed by an extended phase with accelerations up to 0.7 km s-2. The two-phase CME dynamics is associated with a two-episode flare energy release. While the first episode is consistent with the "standard" eruption of a magnetic flux rope, the second episode of flare energy release is initiated by the reconnection of a large-scale loop in the aftermath of the eruption and produces stronger nonthermal emission up to γ-rays. In addition, this long-duration flare reveals clear signs of ongoing magnetic reconnection during the decay phase, evidenced by extended hard X-ray bursts with energies up to 100-300 keV and intermittent downflows of reconnected loops for >4 hr. The observations reveal that the two-step flare reconnection substantially contributes to the two-phase CME acceleration, and the impulsive CME acceleration precedes the most intense flare energy release. The implications of this non-standard flare/CME observation are discussed.

Keywords: solar coronal mass ejections; solar magnetic reconnection; solar flares
Laboratory Observation of Radiative Shock Deceleration and Application to SN 1987A

The first laboratory evidence of a radiative shock (RS) decelerating during its free expansion phase in an optically thick medium is presented. A shock is generated in a multilayer solid target under the irradiation of a high-power laser at the GEKKO XII laser facility. The rear surface of the target is connected to a gas cell filled with Xe. Upon breakout, an RS, characterized by low Boltzmann number Bo ≪ 1 and Mihalas number R ≈ 10, is generated. Experimental results reveal that radiative losses through the radiative precursor cause the shock to lose energy and decelerate. A model is developed that describes the shock propagation as a function of time. The model is in agreement with both numerical simulations and experimental results. These results have tremendous consequences for astrophysical systems, such as SN 1987A, where radiative deceleration may play a role in the formation of the observed hotspots in the circumstellar ring.

Keywords: laboratory astrophysics; experimental techniques; shocks
Optical Observations Reveal Strong Evidence for High-energy Neutrino Progenitor

We present the earliest astronomical observation of a high-energy neutrino error box of which the variability was discovered after high-energy-neutrino detection. The one robotic telescope of the MASTER global international networks automatically imaged the error box of the very high-energy-neutrino event IceCube-170922A. Observations were carried out in minutes after the IceCube-170922A neutrino event was detected by the IceCube observatory at the South Pole. MASTER found the blazar TXS 0506+056 to be in the off-state after one minute and then switched to the on-state no later than two hours after the event. The effect is observed at a 50σ significance level. We also present own a unique 16 yr light curve of blazar TXS 0506+056 (518 data set).

Keywords: neutrino astronomy; blazars; active galactic nuclei; automated telescopes; automatic patrol telescopes; high energy astrophysics; black holes; particle astrophysics; ultra-high-energy cosmic radiation
Characteristics of the Accelerated Electrons Moving along the Loop Derived from Cyclical Microwave Brightenings at the Footpoints

Many particles are accelerated during solar flares. To understand the acceleration and propagation processes of electrons, we require the pitch-angle distributions of the particles. The pitch angle of accelerated electrons has been estimated from the propagation velocity of a nonthermal microwave source archived in Nobeyama Radioheliograph data. We analyzed a flare event (an M-class flare on 2014 October 22) showing cyclical microwave brightenings at the two footpoint regions. Assuming that the brightenings were caused by the accelerated electrons, we approximated the velocity parallel to the magnetic field of the accelerated electrons as ~7.7 × 104 and 9.0 × 104 km s -1. The estimated pitch angle of the accelerated electrons is 69°-80° and the size of the loss cone at the footpoint (estimated from the magnetic field strength in the nonlinear force-free field model) is approximately 43°. Most of the accelerated electrons could be reflected at the footpoint region. This feature can be interpreted as brightenings produced by bouncing motion of the accelerated electrons.

Keywords: solar flares; solar radio emission
A More Efficient Search for H2O Megamaser Galaxies: The Power of X-Ray and Mid-infrared Photometry

We present an investigation of the dependence of H2O maser detection rates and properties on the mid-IR active galactic nucleus (AGN) luminosity, LAGN, and the obscuring column density, NH, based on mid-IR and hard X-ray photometry. Based on spectral energy distribution fitting that allows for decomposition of the black hole accretion and star formation components in the mid-infrared, we show that the megamaser (disk maser) detection rate increases sharply for galaxies with 12 μm AGN luminosity L12 μmAGN greater than 1042 erg s-1, from ≲3% (≲2%) to ∼12% (∼5%). By using the ratio of the observed X-ray to mid-IR AGN luminosity as an indicator of NH, we also find that megamaser (disk maser) detection rates are boosted to 15% (7%) and 20% (9%) for galaxies with NH ≥ 1023 cm-2 and NH ≥ 1024 cm-2, respectively. Combining these column density cuts with a constraint for high L12 μmAGN (≥1042 erg s-1) predicts further increases in the megamaser (disk maser) detection rates to 19% (8%) and 27% (14%), revealing unprecedented potential increases of the megamaser and disk maser detection rates by a factor of 7-15 relative to the current rates, depending on the chosen sample selection criteria. A noteworthy aspect of these new predictions is that the completeness rates are only compromised mildly, with the rates remaining at the level of ∼95%(∼50%) for sources with NH ≥ 1023 cm-2 (NH ≥ 1024 cm-2). Applying these selection methods to current X-ray AGN surveys predicts the detection of ≳15 new megamaser disks.

Keywords: megamasers; astrophysical masers; active galactic nuclei; active galaxies; x-ray active galactic nuclei; x-ray surveys; surveys; broad band photometry; infrared photometry
Diffuser-assisted Infrared Transit Photometry for Four Dynamically Interacting Kepler Systems

We present ground-based infrared transit observations for four dynamically interacting Kepler planets, including Kepler-29b, Kepler-36c, KOI-1783.01, and Kepler-177c, obtained using the Wide-field Infrared Camera on the Hale 200 inch telescope at Palomar Observatory. By utilizing an engineered diffuser and custom guiding software, we mitigate time-correlated telluric and instrumental noise sources in these observations. We achieve an infrared photometric precision comparable to or better than that of space-based observatories such as the Spitzer Space Telescope, and detect transits with greater than 3σ significance for all planets. For Kepler-177c (J = 13.9), our measurement uncertainties are only 1.2 times the photon noise limit and 1.9 times better than the predicted photometric precision for Spitzer IRAC photometry of this same target. We find that a single transit observation obtained 4-5 yr after the end of the original Kepler mission can reduce dynamical mass uncertainties by as much as a factor of 3 for these systems. Additionally, we combine our new observations of KOI-1783.01 with information from the literature to confirm the planetary nature of this system. We discuss the implications of our new mass and radius constraints in the context of known exoplanets with low incident fluxes, and we note that Kepler-177c may be a more massive analog to the currently known super-puffs given its core mass (3.8 $\,\pm \,0.9{M}_{\oplus }$ ) and large gas-to-core ratio (2.8 ± 0.7). Our demonstrated infrared photometric performance opens up new avenues for ground-based observations of transiting exoplanets previously thought to be restricted to space-based investigation.

Keywords: exoplanet astronomy; exoplanet dynamics; ground-based astronomy; exoplanet systems
An Astronomical Image Content-based Recommendation System Using Combined Deep Learning Models in a Fully Unsupervised Mode

We have developed a method that maps large astronomical images onto a two-dimensional map and clusters them. A combination of various state-of-the-art machine-learning algorithms is used to develop a fully unsupervised image-quality assessment and clustering system. Our pipeline consists of a data pre-processing step where individual image objects are identified in a large astronomical image and converted to smaller pixel images. This data is then fed to a deep convolutional auto-encoder jointly trained with a self-organizing map (SOM). This part can be used as a recommendation system. The resulting output is eventually mapped onto a two-dimensional grid using a second, deep, SOM. We use data taken from ground-based telescopes and, as a case study, compare the system's ability and performance with the results obtained by supervised methods presented by Teimoorinia et al. The availability of target labels in this data allowed for a comprehensive performance comparison between our unsupervised and supervised methods. In addition to image-quality assessments performed in this project, our method can have various other applications. For example, it can help experts label images in a considerably shorter time with minimum human intervention. It can also be used as a content-based recommendation system capable of filtering images based on the desired content.

Keywords: astronomy data analysis; astronomy data modeling
X-Ray Flares in the Long-term Light Curve of Low-luminosity Active Galactic Nucleus M81*

Most active galactic nuclei at the center of the nearby galaxies have supermassive black holes accreting at sub-Eddington rates through hot accretion flows or radiatively inefficient accretion flows, which efficiently produce jets. The association of radio and X-ray flares with the knot ejection from M81* inspires us to model its multiwavelength spectral energy distribution (SED) during these flares to constrain the physical parameters of the jet. Moreover, we construct a long-term light curve in X-rays to identify the flares in the available data and constrain the jet parameters during those periods. The jet activity may vary on short as well as long timescales, which may produce flares in different frequency bands. The SEDs from radio to X-ray during the quiescent as well as flaring states are found to be satisfactorily explained by synchrotron emission of relativistic electrons from a single zone. The variation in the values of the jet parameters during the different states is shown and compared with high-synchrotron peaked blazars.

Keywords: spectral energy distribution; low-luminosity active galactic nuclei; x-ray active galactic nuclei
Introducing the FLAMINGOS-2 Split-K Medium-band Filters: The Impact on Photometric Selection of High-z Galaxies in the FENIKS-pilot survey

Deep near-infrared photometric surveys are efficient in identifying high-redshift galaxies, however, they can be prone to systematic errors in photometric redshift. This is particularly salient when there is limited sampling of key spectral features of a galaxy's spectral energy distribution (SED), such as for quiescent galaxies where the expected age-sensitive Balmer/4000 Å break enters the K-band at z > 4. With single-filter sampling of this spectral feature, degeneracies between SED models and redshift emerge. A potential solution to this comes from splitting the K band into multiple filters. We use simulations to show an optimal solution is to add two medium-band filters, K blue (λ cen = 2.06 μm, Δλ = 0.25 μm) and K red (λ cen = 2.31 μm, Δλ = 0.27 μm), that are complementary to the existing K s filter. We test the impact of the K-band filters with simulated catalogs comprised of galaxies with varying ages and signal-to-noise. The results suggest that the K-band filters do improve photometric redshift constraints on z > 4 quiescent galaxies, increasing precision and reducing outliers by up to 90%. We find that the impact from the K-band filters depends on the signal-to-noise, the redshift, and the SED of the galaxy. The filters we designed were built and used to conduct a pilot of the FLAMINGOS-2 Extragalactic Near-Infrared K-band Split survey. While no new z > 4 quiescent galaxies are identified in the limited area pilot, the K blue and K red filters indicate strong Balmer/4000 Å breaks in existing candidates. Additionally, we identify galaxies with strong nebular emission lines, for which the K-band filters increase photometric redshift precision and in some cases indicate extreme star formation.

Keywords: high-redshift galaxies; photometry; galaxy evolution
The Science Performance of the Gemini High Resolution Optical Spectrograph

The Gemini High Resolution Optical Spectrograph (GHOST) is a fiber-fed spectrograph system on the Gemini South telescope that provides simultaneous wavelength coverage from 348 to 1061 nm, and is designed for optimal performance between 363 and 950 nm. It can observe up to two objects simultaneously in a 7.'5 diameter field of regard at R ≃ 56,000 or a single object at R ≃ 75,000. The spectral resolution modes are obtained by using integral field units to image slice a 1.″2 aperture by a factor of five in width using 19 fibers in the high resolution mode and by a factor of three in width using 7 fibers in the standard resolution mode. GHOST is equipped with hardware to allow for precision radial velocity measurements, expected to approach meters per second precision. Here, we describe the basic design and operational capabilities of GHOST, and proceed to derive and quantify the key aspects of its on-sky performance that are of most relevance to its science users.

Keywords: astronomical instrumentation; high resolution spectroscopy