Table of contents

Using data from the MEarth-North and MEarth-South transit surveys, we present the detection of eclipses in four mid M-dwarf systems: LP 107-25, LP 261-75, LP 796-24, and LP 991-15. Combining the MEarth photometry with spectroscopic follow-up observations, we show that LP 107-25 and LP 796-24 are short-period (1.388 and 0.523 day, respectively) eclipsing binaries in triple-lined systems with substantial third-light contamination from distant companions. LP 261-75 is a short-period (1.882 day) single-lined system consisting of a mid M-dwarf eclipsed by a probable brown dwarf secondary, with another distant visual brown dwarf companion. LP 991-15 is a long-period (29.3 day) double-lined eclipsing binary on an eccentric orbit with a geometry that produces only primary eclipses. A spectroscopic orbit is given for LP 991-15, and initial orbits for LP 107-25 and LP 261-75.

Axisymmetric disks of eccentric Kepler orbits are vulnerable to an instability that causes orbits to exponentially grow in inclination, decrease in eccentricity, and cluster in their angle of pericenter. Geometrically, the disk expands to a cone shape that is asymmetric about the mid-plane. In this paper, we describe how secular gravitational torques between individual orbits drive this "inclination instability". We derive growth timescales for a simple two-orbit model using a Gauss N-ring code, and generalize our result to larger N systems with N-body simulations. We find that two-body relaxation slows the growth of the instability at low N and that angular phase coverage of orbits in the disk is important at higher N. As $N\to \infty$, the e-folding timescale converges to that expected from secular theory.

The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic data set for hundreds of open clusters, and to constrain key Galactic dynamical and chemical parameters from this sample. This second contribution from the OCCAM survey presents analysis of 259 member stars with [Fe/H] determinations in 19 open clusters, using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data from the Apache Point Observatory Galactic Evolution Experiment and ESA Gaia. This analysis, which includes clusters with R_GC ranging from 7 to 13 kpc, measures an [Fe/H] gradient of −0.061 ± 0.004 dex kpc⁻¹. We also confirm evidence of a significant positive gradient in the α-elements ([O/Fe], [Mg/Fe], and [Si/Fe]) and present evidence for a significant negative gradient in iron-peak elements ([Mn/Fe] and [Ni/Fe]).

The recently discovered TRAPPIST-1 system is exciting due to the possibility of several rocky, Earth-sized planets harboring liquid water on their surface. To assess the detectability of oceans on these planets, we model the disk-integrated phase curves and polarization signals for planets in this system for reflected starlight. We examine four cases: (1) dry planet, (2) cloud-covered planet, (3) planet with regional-scale oceans, and (4) planet with global oceans. Polarization signals are strongest for optically thin (≲0.1) atmospheres over widespread oceans, with the degree of polarization being up to 90% for a single planet or on the order of 100 parts per billion for the star–planet system. In cases where reflected light from different planets in a tightly packed system cannot be separated, observing in polarized light allows for up to a tenfold increase in star–planet contrast compared to photometric observations alone. However, polarization from other sources, such as atmospheric scattering and cloud variability, will pose major challenges to the detection of glint (specularly reflected starlight) polarization signals. Planned telescopes like LUVOIR may be capable of observing glint from Earth-like planets around Sun-like stars, and if equipped with a polarimeter can significantly improve our ability to detect and study oceans on rocky exoplanets.

After an 11-year observing campaign, we present the combined visual–spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD 181655, HIP 94981, GJ 754.2). Using the Separated Fringe Packet method with the CHARA Array, we were able to determine a difficult-to-complete orbital period of 331.609 ± 0.004 days. The 11-month period causes the system to be hidden from interferometric view behind the Sun for three years at a time. Due to the high-eccentricity orbit of about 90% of a year, after 2018 January the periastron phase will not be observable again until late 2021. Hindered by its extremely high eccentricity of 0.9322 ± 0.0001, the double-lined spectroscopic phase of HR 7345 is observable for 15 days. Such a high eccentricity for HR 7345 places it among the most eccentric systems in catalogs of both visual and spectroscopic orbits. For this system, we determine nearly identical component masses of 0.941 ± 0.076 M_⊙ and 0.926 ± 0.075 M_⊙ as well as an orbital parallax of 41.08 ± 0.77 mas.

Converting a noisy parallax measurement into a posterior belief over distance requires inference with a prior. Usually, this prior represents beliefs about the stellar density distribution of the Milky Way. However, multiband photometry exists for a large fraction of the Gaia-TGAS Catalog and is incredibly informative about stellar distances. Here, we use 2MASS colors for 1.4 million TGAS stars to build a noise-deconvolved empirical prior distribution for stars in color–magnitude space. This model contains no knowledge of stellar astrophysics or the Milky Way but is precise because it accurately generates a large number of noisy parallax measurements under an assumption of stationarity; that is, it is capable of combining the information from many stars. We use the Extreme Deconvolution (XD) algorithm—which is an empirical-Bayes approximation to a full-hierarchical model of the true parallax and photometry of every star—to construct this prior. The prior is combined with a TGAS likelihood to infer a precise photometric-parallax estimate and uncertainty (and full posterior) for every star. Our parallax estimates are more precise than the TGAS catalog entries by a median factor of 1.2 (14% are more precise by a factor >2) and they are more precise than the previous Bayesian distance estimates that use spatial priors. We validate our parallax inferences using members of the Milky Way star cluster M67, which is not visible as a cluster in the TGAS parallax estimates but appears as a cluster in our posterior parallax estimates. Our results, including a parallax posterior probability distribution function for each of 1.4 million TGAS stars, are available in companion electronic tables.

Future space telescopes will directly image extrasolar planets at visible wavelengths. Time-resolved reflected light from an exoplanet encodes information about atmospheric and surface inhomogeneities. Previous research has shown that the light curve of an exoplanet can be inverted to obtain a low-resolution map of the planet, as well as constraints on its spin orientation. Estimating the uncertainty on 2D albedo maps has so far remained elusive. Here, we present exocartographer, a flexible open-source Bayesian framework for solving the exocartography inverse problem. The map is parameterized with equal-area Hierarchical, Equal Area, and isoLatitude Pixelation (HEALPix) pixels. For a fiducial map resolution of 192 pixels, a four-parameter Gaussian process describing the spatial scale of albedo variations, and two unknown planetary spin parameters, exocartographer explores a 198-dimensional parameter space. To test the code, we produce a light curve for a cloudless Earth in a face-on orbit with a 90° obliquity. We produce synthetic white-light observations of the planet: five epochs of observations throughout the planet's orbit, each consisting of 24 hourly observations with a photometric uncertainty of 1% (120 data points). We retrieve an albedo map and—for the first time—its uncertainties, along with spin constraints. The albedo map is recognizably of Earth, with a typical 90% uncertainty of 0.14. The retrieved characteristic length scale is ∼9800 km. The obliquity is recovered to be >879 at the 90% credible level. Despite the uncertainty in the retrieved albedo map, we robustly identify a high-albedo region (the Sahara desert) and a large low-albedo region (the Pacific Ocean).

Kepler-1656b is a 5 ${R}_{\oplus }$ planet with an orbital period of 32 days initially detected by the prime Kepler mission. We obtained precision radial velocities of Kepler-1656 with Keck/HIRES in order to confirm the planet and to characterize its mass and orbital eccentricity. With a mass of 48 ± 4 ${M}_{\oplus }$, Kepler-1656b is more massive than most planets of comparable size. Its high mass implies that a significant fraction, roughly 80%, of the planet's total mass is in high-density material such as rock/iron, with the remaining mass in a low-density H/He envelope. The planet also has a high eccentricity of 0.84 ± 0.01, the largest measured eccentricity for any planet less than 100 ${M}_{\oplus }$. The planet's high density and high eccentricity may be the result of one or more scattering and merger events during or after the dispersal of the protoplanetary disk.

The study of extended, cold dust envelopes surrounding R Coronae Borealis (RCB) stars began with their discovery by the Infrared Astronomical Satellite. RCB stars are carbon-rich supergiants characterized by their extreme hydrogen deficiency and their irregular and spectacular declines in brightness (up to 9 mag). We have analyzed new and archival Spitzer Space Telescope and Herschel Space Observatory data of the envelopes of seven RCB stars to examine the morphology and investigate the origin of these dusty shells. Herschel, in particular, has revealed the first-ever bow shock associated with an RCB star with its observations of SU Tauri. These data have allowed the assembly of the most comprehensive spectral energy distributions (SEDs) of these stars with multiwavelength data from the ultraviolet to the submillimeter. Radiative transfer modeling of the SEDs implies that the RCB stars in this sample are surrounded by an inner warm (up to 1200 K) and an outer cold (up to 200 K) envelope. The outer shells are suggested to contain up to 10⁻³M_⊙ of dust and have existed for up to 10⁵ years depending on the expansion rate of the dust. This age limit indicates that these structures have most likely been formed during the RCB phase.

We present thermodynamic material and transport properties for the extreme conditions prevalent in the interiors of massive giant planets and brown dwarfs. They are obtained from extensive ab initio simulations of hydrogen–helium mixtures along the isentropes of three representative objects. In particular, we determine the heat capacities, the thermal expansion coefficient, the isothermal compressibility, and the sound velocity. Important transport properties such as the electrical and thermal conductivity, opacity, and shear viscosity are also calculated. Further results for associated quantities, including magnetic and thermal diffusivity, kinematic shear viscosity, as well as the static Love number k₂ and the equidistance, are presented. In comparison to Jupiter-mass planets, the behavior inside massive giant planets and brown dwarfs is stronger dominated by degenerate matter. We discuss the implications on possible dynamics and magnetic fields of those massive objects. The consistent data set compiled here may serve as a starting point to obtain material and transport properties for other substellar H–He objects with masses above one Jovian mass and finally may be used as input for dynamo simulations.

The unique binary AR Scorpii consists of an asynchronously rotating, magnetized white dwarf (WD) that interacts with its red-dwarf companion to produce a large-amplitude, highly coherent pulsation every 1.97 minutes. Over the course of two years, we obtained 39 hours of time-resolved, optical photometry of AR Sco at a typical cadence of 5 s to study this pulsation. We find that it undergoes significant changes across the binary orbital period and that its amplitude, phase, and waveform all vary as a function of orbital phase. We show that these variations can be explained by constructive and destructive interference between two periodic, double-peaked signals: the spin–orbit beat pulse, and a weaker WD spin pulse. Modeling of the light curve indicates that in the optical, the amplitude of the primary spin pulse is 50% of the primary beat amplitude, while the secondary maxima of the beat and spin pulses have similar amplitudes. Finally, we use our timings of the beat pulses to confirm the presence of the disputed spin-down of the WD. We measure a beat-frequency derivative of $\dot{\nu }=(-5.14\pm 0.32)\times {10}^{-17}$ Hz s⁻¹ and show that this is attributable to the spin-down of the WD. This value is approximately twice as large as the estimate from Marsh et al. but is nevertheless consistent with the constraints established in Potter & Buckley. Our precise measurement of the spin-down rate confirms that the decaying rotational energy of the magnetized WD is sufficient to power the excess electromagnetic radiation emitted by the binary.

The availability of bioessential elements for "life as we know it", such as phosphorus (P) or possibly molybdenum (Mo), is expected to restrict the biological productivity of extraterrestrial biospheres. Here, we consider worlds with subsurface oceans and model the dissolved concentrations of bioessential elements. In particular, we focus on the sources and sinks of P (available as phosphates) and find that the average steady-state oceanic concentration of P is likely to be lower than the corresponding value on Earth by a few orders of magnitude, provided that the oceans are alkaline and possess hydrothermal activity. While our result does not eliminate the prospects of life on subsurface worlds like Enceladus, it suggests that the putative biospheres might be oligotrophic and perhaps harder to detect. Along these lines, potential biospheres in the clouds of Venus may end up being limited by the availability of Mo. We also point out the possibility that stellar spectroscopy can be used to deduce potential constraints on the availability of bioessential elements on planets and moons.

We use several mathematical methods, such as the continuous wavelet transform, the wavelet coherence (WTC), and the partial wavelet coherence, to investigate the distribution and oscillation periods of the daily interplanetary magnetic field (IMF) intensity as well as the connection between IMF fluctuations and solar activity indices (the magnetic plage strength index and the Mount Wilson sunspot index). The daily IMF intensity generally approximately follows a log-normal distribution that is directly related to the distribution of the active region flux. The short-term periods of the IMF are about 13.7, 27.6, 37.1, and 75.3 days. They are driven by the quasi-periodicity of the magnetic surges on the solar surface. The medium-term periods of 1.07 and 1.82 years need to be derived from the stochastic interaction of local fields and meridional flows, since coronal holes reflect the transport of the magnetic flux on the solar surface and variations in the meridional flow are seen in the heliosphere. The 10.9-year period is the Schwabe solar cycle and is to be mentioned first. The solar cycle variation of the IMF is not thought to be related to weak solar magnetic activity, but is dominated by the strong solar magnetic field activity seen on the disk, because the footpoints of the time-varying component of the interplanetary magnetic flux are rooted in regions that are located near the sources of coronal mass ejections that are related to active regions, while the constant component in the IMF is thought to initially and mainly come from the weak solar magnetic field activity. Finally, the slow variation of the IMF indicates that it may have a period of longer than 50 years.

We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS J0632+2536 (J0632+2536), RZ Leo, TW Vir and the pre-CV WD 1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ Leo and TW Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD 1144+011 can explain its single-hump modulation and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of ∼0.11. The disk model of RZ Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW Vir and WD 1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semi-empirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy.

We have obtained >10 hr of medium-resolution (R ∼ 15,000) spectroscopic exposures on the transiting exoplanet host star WASP-12, including ∼2 hr while its planet, WASP-12b, is in transit, with the Hobby-Eberly Telescope. The out-of-transit and in-transit spectra are coadded into master out-of-transit and in-transit spectra, from which we create a master transmission spectrum. Strong, statistically significant absorption features are seen in the transmission spectrum at Hα and Na i (the Na D doublet). There is the suggestion of pre- and post-transit absorption in both Hα and Na i when the transmission spectrum is examined as a function of phase. The timing of the pretransit absorption is roughly consistent with previous results for metal absorption in WASP-12b, and the level of the Na i absorption is consistent with a previous tentative detection. No absorption is seen in the control line of Ca i at λ6122. We discuss in particular whether or not the WASP-12b Hα absorption signal is of circumplanetary origin—an interpretation that is bolstered by the pre- and post-transit evidence—which would make it one of only a small number of detections of circumplanetary Hα absorption in an exoplanet to date, the most well-studied being HD 189733b. We further discuss the notable differences between the HD 189733 and WASP-12 systems and the implications for a physical understanding of the origin of the absorption.

The occultation of the radio galaxy 0141+268 by the asteroid (372) Palma on 2017 May 15 was observed using six antennas of the Very Long Baseline Array (VLBA). The shadow of Palma crossed the VLBA station at Brewster, Washington. Owing to the wavelength used, and the size and the distance of the asteroid, a diffraction pattern in the Fraunhofer regime was observed. The measurement retrieves both the amplitude and the phase of the diffracted electromagnetic wave. This is the first astronomical measurement of the phase shift caused by diffraction. The maximum phase shift is sensitive to the effective diameter of the asteroid. The bright spot at the shadow's center, the so called Arago–Poisson spot, is clearly detected in the amplitude time-series, and its strength is a good indicator of the closest angular distance between the center of the asteroid and the radio source. A sample of random shapes constructed using a Markov chain Monte Carlo algorithm suggests that the silhouette of Palma deviates from a perfect circle by 26 ± 13%. The best-fitting random shapes resemble each other, and we suggest their average approximates the shape of the silhouette at the time of the occultation. The effective diameter obtained for Palma, 192.1 ± 4.8 km, is in excellent agreement with recent estimates from thermal modeling of mid-infrared photometry. Finally, our computations show that because of the high positional accuracy, a single radio interferometric occultation measurement can reduce the long-term ephemeris uncertainty by an order of magnitude.

The NIRC2 vortex coronagraph is an instrument on Keck II designed to directly image exoplanets and circumstellar disks at mid-infrared bands L' (3.4–4.1 μm) and M_s (4.55–4.8 μm). We analyze imaging data and corresponding adaptive optics telemetry, observing conditions, and other metadata over a three-year time period to characterize the performance of the instrument and predict the detection limits of future observations. We systematically process images from 359 observations of 304 unique stars to subtract residual starlight (i.e., the coronagraphic point-spread function) of the target star using two methods: angular differential imaging (ADI) and reference star differential imaging (RDI). We find that for the typical parallactic angle (PA) rotation of our data set (∼10°), RDI provides gains over ADI for angular separations smaller than 025. Furthermore, we find a power-law relation between the angular separation from the host star and the minimum PA rotation required for ADI to outperform RDI, with a power-law index of −1.18 ± 0.08. Finally, we use random forest models to estimate ADI and RDI post-processed detection limits a priori. These models, which we provide publicly on a website, explain 70%–80% of the variance in ADI detection limits and 30%–50% of the variance in RDI detection limits. Averaged over a range of angular separations, our models predict both ADI and RDI contrast to within a factor of 2. These results illuminate important factors in high-contrast imaging observations with the NIRC2 vortex coronagraph, help improve observing strategies, and inform future upgrades to the hardware.

The hypothesis of an additional planet in the outer solar system has gained new support as a result of the confinement noted in the angular orbital elements of distant trans-Neptunian objects. Orbital parameters proposed for the external perturber suggest semimajor axes between 500 and 1000 au, perihelion distances between 200 and 400 au for masses between 10 and 20 M_⊕. In this paper, we study the possibility that lower perihelion distances for the additional planet can lead to angular confinements as observed in the population of objects with semimajor axes greater than 250 au and perihelion distances higher than 40 au. We performed numerical integrations of a set of particles subjected to the influence of the Sun, the known giant planets, and the putative perturber during the age of the solar system and compared our outputs with the observed population through a statistical analysis. Our investigations showed that lower perihelion distances from the outer planet usually lead to more substantial confinements than higher ones, while retaining the Classical Kuiper Belt as well as the ratio of the number of detached with perihelion distances higher than 42 au to scattering objects in the range of semimajor axes from 100 to 200 au.

Atmospheric characterization of directly imaged planets has thus far been limited to ground-based observations of young, self-luminous, Jovian planets. Near-term space- and ground- based facilities like WFIRST and ELTs will be able to directly image mature Jovian planets in reflected light, a critical step in support of future facilities that aim to directly image terrestrial planets in reflected light (e.g., HabEx, LUVOIR). These future facilities are considering the use of photometry to classify planets. Here, we investigate the intricacies of using colors to classify gas-giant planets by analyzing a grid of 9120 theoretical reflected light spectra spread across different metallicities, pressure–temperature profiles, cloud properties, and phase angles. We determine how correlated these planet parameters are with the colors in the WFIRST photometric bins and other photometric bins proposed in the literature. Then we outline under what conditions giant planet populations can be classified using several supervised multivariate classification algorithms. We find that giant planets imaged in reflected light can be classified by metallicity with an accuracy of >90% if they are a prior known to not have significant cloud coverage in the visible part of the atmosphere, and at least three filter observations are available. If the presence of clouds is not known a priori, directly imaged planets can be more accurately classified by their cloud properties, as oppposed to metallicity or temperature. Furthermore, we are able to distinguish between cloudy and cloud-free populations with >90% accuracy with three filter observations. Our statistical pipeline is available on GitHub and can be extended to optimize science yield of future mission concepts.

We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double-corkscrew morphology with two near-polar jets oriented approximately east–west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of R.A./decl. = 81°/+29° with an obliquity of 97° and a sidereal rotation period of 41.45 ± 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long −80°/125° and an ∼10° radius and a western source area at lat/long +77°/245° and an ∼20° radius, ∼4× larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology based on OH was quite different from that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO₂. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H₂O⁺ and OH⁺, respectively. We measured water production both before and after perihelion and extrapolated peak water production at perihelion to be about 1.0 × 10²⁹ molecules s⁻¹. We estimated an active fraction of only 4%–5% and a nucleus radius of up to ∼8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.

We present nbodykit, an open-source, massively parallel Python toolkit for analyzing large-scale structure (LSS) data. Using Python bindings of the Message Passing Interface, we provide parallel implementations of many commonly used algorithms in LSS. nbodykit is both an interactive and scalable piece of scientific software, performing well in a supercomputing environment while still taking advantage of the interactive tools provided by the Python ecosystem. Existing functionality includes estimators of the power spectrum, two- and three-point correlation functions, a friends-of-friends grouping algorithm, mock catalog creation via the halo occupation distribution technique, and approximate N-body simulations via the FastPM scheme. The package also provides a set of distributed data containers, insulated from the algorithms themselves, that enables nbodykit to provide a unified treatment of both simulation and observational data sets. nbodykit can be easily deployed in a high-performance computing environment, overcoming some of the traditional difficulties of using Python on supercomputers. We provide performance benchmarks illustrating the scalability of the software. The modular, component-based approach of nbodykit allows researchers to easily build complex applications using its tools. The package is extensively documented at http://nbodykit.readthedocs.io, which also includes an interactive set of example recipes for new users to explore. As open-source software, we hope nbodykit provides a common framework for the community to use and develop in confronting the analysis challenges of future LSS surveys.

We present four daytime thermal images of Europa taken with the Atacama Large Millimeter Array. Together, these images comprise the first spatially resolved thermal data set with complete coverage of Europa's surface. The resulting brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a typical linear resolution of roughly 200 km. At this resolution, the images capture spatially localized thermal variations on the scale of geologic and compositional units. We use a global thermal model of Europa to simulate the ALMA observations in order to investigate the thermal structure visible in the data. Comparisons between the data and model images suggest that the large-scale daytime thermal structure on Europa largely results from bolometric albedo variations across the surface. Using bolometric albedos extrapolated from Voyager measurements, a homogenous model reproduces these patterns well, but localized discrepancies exist. These discrepancies can be largely explained by spatial inhomogeneity of the surface thermal properties. Thus, we use the four ALMA images to create maps of the surface thermal inertia and emissivity at our ALMA wavelength. From these maps, we identify a region of either particularly high thermal inertia or low emissivity near 90° west and 23° north, which appears anomalously cold in two of our images.

We have used high-resolution images obtained with JunoCam onboard the Juno spacecraft during its close flyby of Jupiter on 2017 July 11, to study the dynamics of the Great Red Spot (GRS) at the upper cloud level. We have measured the horizontal velocity and vorticity fields using the clouds as tracers of the flow. We have analyzed a variety of cloud morphologies that serve to characterize different underlying dynamic processes. Long undulating dark gray filaments (2000–10000 km) circulate around the outer part of the vortex moving at high speed (∼120–140 m s⁻¹) where mesoscale waves (wavelength 75 km) indicate stable conditions in this region. At mid distance from the center, a large eddy (radius ∼500 km) is observed in a region of intense horizontal wind shear whereas on the opposite side, compact cloud clusters with cell sizes of ∼50 km, indicative of shallow convection, are observed. The core of the GRS (∼5000 × 3000 km²) is turbulent where the circulation has weakly cyclonic and anticyclonic regions. This variety of phenomena occurs in the upper ammonia cloud layer and haze (thickness ∼20–50 km) that represents the top of a dynamical system with a much deeper circulation.

New Chandra High Resolution Camera pointings on the "non-coronal" red giant Arcturus (HD 124897; α Boo: K1.5 III) corroborate a tentative soft X-ray detection in a shorter exploratory exposure 16 years earlier. The apparent source followed the (large) proper motion of the nearby bright star over the intervening years, and there were null detections at the previous location in the current epoch, as well as at the future location in the earlier epoch, reducing the possibility of chance coincidences with unrelated high-energy objects. The apparent X-ray brightness at Earth, averaged over the 98 ks of total exposure and accounting for absorption in the red giant's wind, is ∼2 × 10⁻¹⁵ erg cm⁻² s⁻¹ (0.2–2 keV). Systematic errors in the energy conversion factor, devolving from the unknown spectrum, amount to only about 10%, smaller than the ∼30% statistical uncertainties in the count rates. The X-ray luminosity is only 3 × 10²⁵ erg s⁻¹, confirming Arcturus as one of Chandra's darkest bright stars.

While satellites of mid- to small-Kuiper Belt objects tend to be similar in size and brightness to their primaries, the largest Kuiper Belt objects preferentially have satellites with small fractional brightness. In the two cases where the sizes and albedos of the small faint satellites have been measured, these satellites are seen to be small icy fragments consistent with collisional formation. Here, we examine Dysnomia and Vanth, the satellites of Eris and Orcus, respectively. Using the Atacama Large Millimeter Array, we obtain the first spatially resolved observations of these systems at thermal wavelengths. Vanth is easily seen in individual images, and we find a 3.5σ detection of Dysnomia by stacking all of the data on the known position of the satellite. We calculate a diameter for Dysnomia of 700 ± 115 km and for Vanth of 475 ± 75 km, with albedos of ${0.04}_{-0.01}^{+0.02}$ and 0.08 ± 0.02, respectively. Both Dysnomia and Vanth are indistinguishable from typical Kuiper Belt objects of their size. Potential implications for the formation of these types of satellites are discussed.

Main-sequence turnoff ages in young open clusters are complicated by turnoffs that are sparse, have high binarity fractions, can be affected by differential reddening, and typically include a number of peculiar stars. Furthermore, stellar rotation can have a significant effect on a star's photometry and evolutionary timescale. In this paper we analyze in 12 nearby open clusters, ranging in age from 50 to 350 Myr, how broadband UBV color–color relations can be used to identify turnoff stars that are Be stars, blue stragglers, certain types of binaries, or those affected by differential reddening. This UBV color–color analysis also directly measures a cluster's E(B − V) and estimates its [Fe/H]. The turnoff stars unaffected by these peculiarities create a narrower and more clearly defined cluster turnoff. Using four common isochronal models, two of which consider rotation, we fit cluster parameters using these selected turnoff stars and the main sequence. Comparisons of the photometrically fit cluster distances to those based on parallaxes from Gaia data release 2 find that they are consistent for all clusters. For older (>100 Myr) clusters, such as the Pleiades and the Hyades, comparisons to ages based on the lithium depletion boundary method find that these cleaned turnoff ages agree to within ∼10% for all four isochronal models. For younger clusters, however, only the Geneva models that consider rotation fit turnoff ages consistent with lithium-based ages, while the ages based on non-rotating isochrones quickly diverge to become 30%–80% younger. This illustrates the importance of rotation in deriving ages in the youngest (<100 Myr) clusters.

We study a gas-rich merging dwarf system KUG 0200-096. Deep optical imaging reveals an optically faint tail with a length of 20 kpc, giving a visual impression of tidal antenna similar to NGC 4038/39. The interacting dwarf galaxies have B-band absolute magnitudes of −18.06 and −16.63 mag. We identify a young stellar clump with a stellar mass of 2 × 10⁷M_⊙ at the tip of the antenna, possibly a tidal dwarf galaxy (TDG). The putative TDG candidate is quite blue with a g − r color index of −0.07 mag, whereas the interacting dwarf galaxies have g − r color indices 0.29 and 0.19 mag. The TDG is currently forming stars at the rate of 0.02 M_⊙ yr⁻¹. We obtained H i 21 cm line data of KUG 0200-096 using the Giant Metrewave Radio Telescope to get a more detailed view of neutral hydrogen (H i) emission in interacting dwarf galaxies and its TDG. Evidence of a merger between the dwarf galaxy pair is also present in H i kinematics and morphology where we find the H i contents of the interacting pair is disturbed, forming an extended tail toward the TDG. The H i velocity field shows a strong gradient along the H i tidal tail extension. We present a comparative study between the Antennae galaxy, NGC 4038/39, and KUG 0200-096 in both optical and H i gas properties and discuss the possible origin of the KUG 0200-096 TDG.

Auroral emissions provide opportunities to study the tenuous atmospheres of solar system satellites, revealing the presence and abundance of molecular and atomic species as well as their spatial and temporal variability. Far-UV aurorae have been used for decades to study the atmospheres of the Galilean satellites. Here we present the first detection of Europa's visible-wavelength atomic oxygen aurora at 6300/6364 Å arising from the metastable ${\rm{O}}{(}^{1}{\rm{D}}$) state, observed with the Keck I and Hubble Space Telescope while Europa was in eclipse by Jupiter on six occasions in 2018 February–April. The disk-integrated O(¹D) brightness varies from <500 R up to more than 2 kR between dates, a factor of 15 higher than the O i 1356 Å brightness on average. The ratio of emission at 6300/5577 Å is diagnostic of the parent molecule; the 5577 Å emission was not detected in our data set, which favors O₂ as the dominant atmospheric constituent and rules out an O/O₂ mixing ratio above 0.35. For an O₂ atmosphere and typical plasma conditions at Europa's orbit, the measured surface brightness range corresponds to column densities of (1–9) × 10¹⁴ cm⁻².

We observed eclipses of the transiting brown dwarf CWW 89Ab at 3.6 and 4.5 μm using Spitzer/IRAC. The CWW 89 binary system is a member of the 3.0 ± 0.25 Gyr old open cluster Ruprecht 147 and is composed of a Sun-like primary and an early M-dwarf secondary separated by a projected distance of 25 au. CWW 89Ab has a radius of 0.937 ± 0.042 ${R}_{{\rm{J}}}$ and a mass of 36.5 ± 0.1 ${M}_{{\rm{J}}}$, and is on a 5.3 day orbit about CWW 89A with a non-zero eccentricity of e = 0.19. We strongly detect the eclipses of CWW 89Ab in both Spitzer channels as δ_3.6 = 1147 ± 213 ppm and δ_4.5 = 1097 ± 225 ppm after correcting for the dilution from CWW 89B. After accounting for the irradiation that CWW 89Ab receives from its host star, these measurements imply that the brown dwarf has an internal luminosity of $\mathrm{log}({L}_{\mathrm{bol}}/{L}_{\odot })=-4.19\pm 0.14$. This is 16 times, or 9.3σ, higher than model predictions given the known mass, radius, and age of CWW 89Ab. As we discuss, this overluminosity is explainable neither by an inaccurate age determination, nor additional stellar heating, nor tidal heating. Instead, we suggest that the anomalous luminosity of CWW 89Ab is caused by a dayside temperature inversion—though a significant error in the evolutionary models is also a possibility. Importantly, a temperature inversion would require a superstellar C/O ratio in CWW 89Ab's atmosphere. If this is indeed the case, it implies that CWW 89Ab is a 36.5 ${M}_{{\rm{J}}}$ object that formed via core accretion processes. Finally, we use our measurement of CWW 89Ab's orbital eccentricity, improved via these observations, to constrain the tidal quality factors of the brown dwarf and the host star CWW 89A to be ${Q}_{\mathrm{BD}}\gt {10}^{4.15}$ and ${Q}_{* }\gt {10}^{9}$, respectively.

Jupiter's atmosphere has been sounded in transmission from the UV to the IR, as if it were a transiting exoplanet, by observing Ganymede while passing through Jupiter's shadow. The spectra show strong extinction due to the presence of aerosols and haze in Jupiter's atmosphere and strong absorption features of methane. Here, we report a new detailed analysis of these observations, with special emphasis on the retrievals of the vertical distribution of the aerosols and their sizes, and the properties and distribution of the stratospheric water ice. Our analysis suggests the presence of aerosols near the equator in the altitude range of 100 hPa up to at least 0.01 hPa, with a layer of small particles (mean radius of 0.1 μm) in the upper part (above 0.1 hPa), an intermediate layer of aerosols with a radius of 0.3 μm, extending between ∼10 and 0.01 hPa, and a layer with larger sizes of ∼0.6 μm at approximately 100–1 hPa. The corresponding loads for each layer are ∼2 × 10⁻⁷ g cm⁻², ∼3.4 × 10⁻⁷ g cm⁻², and ∼1.5 × 10⁻⁶ g cm⁻², respectively, with a total load of ∼2.0 × 10⁻⁶ g cm⁻². The lower and middle layers agree well with previous measurements; but the finer particles of 0.1 μm above 0.01 hPa have not been reported before. The spectra also show two broad features near 1.5 and 2.0 μm, which we attribute to a layer of very small (∼10 nm) H₂O crystalline ice in Jupiter's lower stratosphere (∼0.5 hPa). While these spectral signatures seem to be unequivocally attributable to crystalline water ice, they require a large amount of water ice to explain the strong absorption features.

Here, we report a comparative study of radial velocity (RV) data of two major surveys: Gaia Data Release 2 and RAVE Data Release 5. We restricted the sample to stars with relatively accurate RVs (${\sigma }_{{\mathrm{RV}}_{{Gaia}}}\leqslant 2$ km s⁻¹ or ≤2%, and ${\sigma }_{{\mathrm{RV}}_{\mathrm{RAVE}}}\leqslant 2$ km s⁻¹ or ≤2%). The difference between RV_Gaia and RV_RAVE for a majority of the sample follows a normal distribution with mean = 0.28 km s⁻¹ and σ = 1.49 km s⁻¹. However, we found a very small group of stars (≈0.08% of the total) for which the difference in RVs between the two surveys is significantly larger with an offset of −104.50 km s⁻¹ with σ = 4.92 km s⁻¹. Kinematics based on RV_Gaia suggest that most of the group members belong to the Galactic thin disk, which agrees with the group's metallicity range of −1.2 to +0.5 dex suggesting the offset in RV is probably due to RAVE velocity data for this particular group.

Parameters and abundances have been derived for 435 Cepheids based on an analysis of 1127 spectra. Results from five or more phases are available for 52 of the program stars. The latter set of stars span periods between 1.5 and 68 days. The parameters and abundances show excellent consistency across phase. For iron, the average range in the determined abundance is 0.11 from these 52 stars. For 163 stars with more than one phase available the average range is 0.07. The variation in effective temperature tracks well with phase, as does the total broadening velocity. The gravity and microturbulent velocity follow phase, but with less variation and regularity. Abundance gradients have been derived using Gaia DR2 parallax data, as well as Bayesian distance estimates based upon Gaia DR2 from Bailer-Jones et al. The abundance gradient derived for iron is d[Fe/H]/dR = −0.05 dex kpc⁻¹, similar to gradients derived in previous studies.

We propose a new parameterization of the impact parameter u₀ and impact angle α for microlensing systems composed by an Earth-like exoplanet around a solar-mass star at 1 au. We present the caustic topology of such system, as well as the related light curves generated by using such a new parameterization. Based on the same density of points and accuracy of regular methods, we obtain results five times faster for discovering Earth-like exoplanets. In this big data revolution of photometric astronomy, our method will impact future missions like WFIRST (NASA) and Euclid (ESA) and their data pipelines, providing a rapid and deep detection of exoplanets for this specific class of microlensing event that might otherwise be lost.

Disintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star. Their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of K2-22b), making these good candidates for transmission spectroscopy. To assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5 to 14 μm for the planet tail assuming an optically thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. We find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. For the average transit depth of 0.55% in the Kepler band for K2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the James Webb Space Telescope (JWST) MIRI low-resolution spectrograph in a single transit. The detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. We find most features are still detectable for transit depths of ∼0.3% in the visible range. If more disintegrating planets are found with future missions such as the space telescope TESS, follow-up observations with JWST can explore the range of planetary compositions.

With the aim of contributing to the understanding of the disk formation process in Be stars, we pursued a one-year spectroscopic observing campaign of the Be star μ Centauri in the L-band, using VLT/ISAAC. We present the nine near-IR spectra we obtained in an epoch of relative photometric quiescence prior to an outburst of ΔV = 0.4 magnitude. Visual estimates during the epoch of our L-band spectroscopy are also presented for the first time, together with the unpublished complete visual light curve between the years 1998 and 2014. We observe significant and monotonic changes in emission line strength of Bracket-α and Pfund-γ lines relative to Humphreys lines, and also in the continuum slope. We interpret these observed changes in terms of important changes to the column density of the line emitting regions, moving from an optically thin to an optically thick stage just prior to a major outburst. For each observing date, we provide estimates for the column density and relative extension of the line emitting region. If the changes observed toward the end of our observing campaign were related to mass-loss changes from the central star, they would correspond to an increase in a factor of two in the mass of the disk in the innermost region. If related to the visual outburst observed one month later, the variability observed in our spectra would be the first detection of the early disk formation process in the L-band.

We present here the first application of Stellar and Exoplanetary Atmospheres Bayesian Analysis Simultaneous Spectroscopy (SEA BASS) on real data sets. SEA BASS is a scheme that enables the simultaneous derivation of four-coefficient stellar limb-darkening profiles, transit depths, and orbital parameters from exoplanetary transits at multiple wavelengths. It relies on the wavelength independence of the system geometry and on the reduced limb-darkening effect in the infrared. This approach has been introduced by Morello et al. (without the SEA BASS acronym), who discuss several tests on synthetic data sets. Here, we (1) improve on the original algorithm using multiple Spitzer/InfraRed Array Camera passbands and a more effective set of geometric parameters, (2) demonstrate its ability with Hubble Space Telescope/Space Telescope Imaging Spectrograph data sets by (3) measuring the HD 209458 stellar limb-darkening profile over multiple passbands in the 290–570 nm range with sufficient precision to rule out some theoretical models that have been adopted previously in the literature, and (4) simultaneously extracting the transmission spectrum of the exoplanet atmosphere. The higher photometric precision of the next-generation instruments, such as those on board the James Webb Space Telescope, will enable modeling the star–planet systems with unprecedented detail, and increase the importance of SEA BASS for avoiding the potential biases introduced by inaccurate stellar limb-darkening models.

Refractory metal nuggets (RMNs) are among the first solids formed in the nascent solar system. They contain high abundances of refractory metals like Re, Os, W, Ir, Ru, and Pt. The isotopic compositions of these elements bear testimony to the stellar sources that contributed to the nucleosynthetic makeup of our solar system. We report the first high-precision Ru isotope data for a bulk RMN sample prepared from the Allende meteorite. The RMNs display well-resolved mass-independent anomalies with positive anomalies for ⁹⁶Ru, ⁹⁸Ru, ¹⁰⁰Ru, ¹⁰²Ru, and ¹⁰⁴Ru. These are best explained by a deficit in r-process combined with a slight deficit in p-process nuclides. This finding stands in stark contrast to the s-process deficit isotopic patterns observed for Allende Ca–Al-rich inclusions (CAIs), bulk Allende, and other bulk meteorites. The contrasting r-, p-deficit versus s-deficit Ru isotopic signatures observed between RMNs and CAIs is surprising, given that CAIs are assumed to be a major host phase of RMNs. One way to explain the s-deficit patterns observed for CAIs and bulk meteorites is that r- and p-process Ru nuclides were added to the solar nebula after RMN formation and prior to the formation of CAIs and the accretion of meteorite parent bodies. A possible source may have been a nearby core-collapse supernova that injected freshly synthesized r- and p-process nuclides into the nascent solar system. The injection of such r- and p-enriched matter represents an alternative mechanism to account for the s-process variability presented by CAIs and bulk carbonaceous meteorites.

Aperture synthesis arrays are commonly used in radio astronomy to take images of radio point sources, with the planned Square Kilometre Array (SKA) being the most common example. One approach to enhancing the quality of the images is to optimize an antenna array configuration in a possible SKA implementation. An ideal arrangement must ensure optimal configurations to capture a clear image by either decreasing the sidelobe level (SLL) in the l–m domain or increasing the sampled data in the spatial-frequency domain. In this paper a novel configuration is considered to optimize the array by considering all possible observation situations through the positions of the antenna array elements via a mathematical model that we call geometrical method (GM). To demonstrate its efficiency, the technique is applied to developing an optimal configuration for the elements of the Giant Metrewave Radio Telescope (GMRT). The effect of these changes, particularly in the forms of circular and spiral arrangements, is discussed. It is found that a spiral configuration results in fewer overlapping samples than the number of antennas placed along three arms of the GMRT with fewer than 11% and 27% overlapping samples in the snapshot and 6 hr tracking observations, respectively. Finally, the spiral configuration reduces the first SLL from −13.01 dB, using the arms of the current GMRT configuration, to −15.64 dB.

The seven approximately Earth-sized transiting planets in the TRAPPIST-1 system provide a unique opportunity to explore habitable- and nonhabitable-zone small planets within the same system. Its habitable-zone exoplanets—due to their favorable transit depths—are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two HST Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six planets (b through g). Utilizing our physically motivated detector charge-trap correction and a custom cosmic-ray correction routine, we confirm the general shape of the transmission spectra presented by de Wit et al. Our data reduction approach leads to a 25% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet's transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4 μm similar to an inverted water absorption feature. Including transit depths from K2, the SPECULOOS-South Observatory, and Spitzer, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by HST and JWST and also highlight the challenges in combining multi-epoch observations for planets around rapidly rotating spotted stars.

We present the kinematics of 35 highly r-process-enhanced ([Eu/Fe] ≥ +0.7) metal-poor (−3.8 < [Fe/H] < −1.4) field stars. We calculate six-dimensional positions and velocities, evaluate energies and integrals of motion, and compute orbits for each of these stars using parallaxes and proper motions from the second Gaia data release and published radial velocities. All of these stars have halo kinematics. Most stars (66%) remain in the inner regions of the halo (<13 kpc), and many (51%) have orbits that pass within 2.6 kpc of the Galactic center. Several stars (20%) have orbits that extend beyond 20 kpc, including one with an orbital apocenter larger than the Milky Way virial radius. We apply three clustering methods to search for structure in phase space, and we identify eight groups. No abundances are considered in the clustering process, but the [Fe/H] dispersions of the groups are smaller than would be expected by random chance. The orbital properties, clustering in phase space and metallicity, and the lack of highly r-process-enhanced stars on disk-like orbits, indicate that such stars likely were accreted from disrupted satellites. Comparison with the galaxy luminosity–metallicity relation suggests M_V ≳ −9 for most of the progenitor satellites, characteristic of ultra-faint or low-luminosity classical dwarf spheroidal galaxies. Environments with low rates of star formation and Fe production, rather than the nature of the r-process site, may be key to obtaining the [Eu/Fe] ratios found in highly r-process-enhanced stars.

Starspots, plages, and activity cycles cause radial velocity variations that can either mimic planets or hide their existence. To verify the authenticity of newly discovered planets, observers may search for periodicity in spectroscopic activity indices such as Ca H & K and Hα, then mask out any Doppler signals that match the activity period or its harmonics. However, not every spectrograph includes Ca H & K, and redder activity indicators are needed for planet searches around low-mass stars. Here, we show how new activity indicators can be identified by correlating spectral line depths with a well-known activity index. We apply our correlation methods to archival HARPS spectra of  Eri and α Cen B and use the results from both stars to generate a master list of activity-sensitive lines whose core fluxes are periodic at the star's rotation period. Our newly discovered activity indicators can in turn be used as benchmarks to extend the list of known activity-sensitive lines toward the infrared or UV. With recent improvements in spectrograph illumination stabilization, wavelength calibration, and telluric correction, stellar activity is now the biggest noise source in planet searches. Our suite of >40 activity-sensitive lines is a first step toward allowing planet hunters to access all the information about spots, plages, and activity cycles contained in each spectrum.

We report the photometry of six transits of the hot Jupiter HAT-P-29b obtained from 2013 October to 2015 January. We analyze the new light curves, in combination with the published photometric, Doppler velocimetric, and spectroscopic measurements, finding an updated orbital ephemeris for the HAT-P-29 system, ${T}_{{\rm{C}}}[0]=2456170.5494(15)[{\mathrm{BJD}}_{\mathrm{TDB}}]$ and P = 5.723390(13) days. This result is 17.63 s (4.0σ) longer than the previously published value, amounting to errors exceeding 2.5 hr at the time of writing (on UTC 2018 June 1). The measured transit mid-times for HAT-P-29b show no compelling evidence of timing anomalies from a linear model, which rules out the presence of perturbers with masses greater than 0.6, 0.7, 0.5, and 0.4 M_⊕ near the 1:2, 2:3, 3:2, and 2:1 resonances with HAT-P-29b, respectively.

The quest to discover exoplanets is one of the most important missions in astrophysics, and is widely performed using the transit method, which allows for the detection of exoplanets down to the size of Mercury. However, to confirm these detections, additional vetting is mandatory. We selected six K2 targets from campaigns #1 to #8 that show transit light curves corresponding to Earth-sized to Neptune-sized exoplanets. We aim to discard some scenarios that could mimic an exoplanetary transit, leading to a misinterpretation of the data. We performed direct imaging observations using the SPHERE/VLT instrument to probe the close environment of these stars. For five of the K2 targets, we report no detection and we give the detection limits. For EPIC 206011496, we detect a 0.38 ± 0.06 M_⊙ companion at a separation of 977.12 ± 0.73 mas (140.19 ± 0.11 au). The spectral analysis corresponds to an M4-7 star, and the analysis of the proper motion shows that it is bounded to the primary star. EPIC 206011496 also hosts an Earth-like planetary candidate. If it transits the primary star, its radius is consistent with that of a super-Earth. However, if it transits the companion star, it falls into the mini-Neptune regime.