Table of contents

Multi-planet systems around evolved stars are of interest to trace the evolution of planetary systems into the post-main-sequence phase. HD 47366, an evolved intermediate-mass star, hosts two giant planets on moderately eccentric orbits. Previous analysis of the planetary system has revealed that it is dynamically unstable on timescales much shorter than the stellar age unless the planets are trapped in mutual 2:1 mean-motion resonance, inconsistent with the orbital solution presented in Sato et al., or are moving on mutually retrograde orbits. Here we examine the orbital stability of the system presented in S16 using the n-body code Mercury over a broad range of a–e parameter space consistent with the observed radial velocities, assuming they are on co-planar orbits. Our analysis confirms that the system as proposed in S16 is not dynamically stable. We therefore undertake a thorough reanalysis of the available observational data for the HD 47366 system, through the Levenberg–Marquardt technique and confirmed by MCMC Bayesian methodology. Our reanalysis reveals an alternative, lower-eccentricity fit that is vastly preferred over the highly eccentric orbital solution obtained from the nominal best-fit presented in S16. The new, improved dynamical simulation solution reveals the reduced eccentricity of the planetary orbits, shifting the HD 47366 system into the edge of a broad stability region, increasing our confidence that the planets are all that they seem to be. Our rigorous examination of the dynamical stability of HD 47366 stands as a cautionary tale in finding the global best-fit model.

Thermophysical Models (TPMs), which have proven to be a powerful tool in the interpretation of the infrared emission of asteroid surfaces, typically make use of shape models and spin axes obtained a priori for use as input boundary conditions. We test and then employ a TPM approach—under an assumption of an ellipsoidal shape—that exploits the combination of thermal multi-wavelength observations obtained at pre- and post-opposition. Thermal infrared data, when available at these observing circumstances, are inherently advantageous in constraining thermal inertia and sense of spin, among other physical traits. We show that, despite the lack of a priori knowledge mentioned above, the size, albedo, and thermal inertia of an object are well-constrained with precision comparable to that of previous techniques. Useful estimates of the surface roughness, shape, and spin direction can also be made, to varying degrees of success. Applying the method to Wide-Field infrared Survey Explorer observations, we present best-fit size, albedo, thermal inertia, surface roughness, shape elongation and sense of spin direction for 21 asteroids. We explore the thermal inertia's correlation with asteroid diameter, after accounting for its dependence on the heliocentric distance.

We observed the post-common-envelope eclipsing binary with a white dwarf component, QS Vir, using the 1.88 m telescope of Kotammia Observatory in Egypt. The new observations were analyzed together with all multicolor light curves available online (sampling a period of 25 yr), using a full-feature binary system modeling software based on Roche geometry. This is the first time complete photometric modeling was done with most of these data. QS Vir is a detached system, with the red dwarf component underfilling its Roche lobe by a small margin. All light curves feature out-of-eclipse variability that is associated with ellipsoidal variation, mutual irradiation and irregularities in surface brightness of the tidally distorted and magnetically active red dwarf. We tested models with one, two, and three dark spots and found that one spot is sufficient to account for the light curve asymmetry in all data sets, although this does not rule out the presence of multiple spots. We also found that a single spotted model cannot fit light curves observed simultaneously in different filters. Instead, each filter requires a different spot configuration. To thoroughly explore the parameter space of spot locations, we devised a grid-search procedure and used it to find consistent solutions. Based on this, we conclude that the dark spot responsible for light curve distortions has been stable for the past 15 yr, after a major migration that happened between 1993 and 2002, possibly due to a flip-flop event.

The redshifted 21 cm signal from neutral hydrogen (H i) is potentially a very powerful probe for cosmology, but a difficulty in its observation is that it is much weaker than foreground radiation from the Milky Way as well as extragalactic radio sources. The foreground radiation at different frequencies, however, is coherent along one line of sight, and various methods of foreground subtraction based on this property have been proposed. In this paper, we present a new method based on robust principal component analysis (RPCA) to subtract the foreground and extract the 21 cm signal, which explicitly uses both the low-rank property of the frequency covariance matrix (i.e., frequency coherence) of the foreground and the sparsity of the frequency covariance matrix of the 21 cm signal. The low-rank property of the foreground's frequency covariance has been exploited in many previous works on foreground subtraction, but to our knowledge the sparsity of the frequency covariance of the 21 cm signal is first explored here. By exploiting both properties in the RPCA method, the frequency covariance matrix of the foreground and the 21 cm signal can be separated accurately. We then use the generalized internal linear combination method to recover the 21 cm signal from the data. Our method is applicable both to a small patch of sky with the flat-sky approximation and to a large area of sky where the sphericity has to be considered. It is also easy to extend to deal with more complex conditions such as a sky map with defects.

Due to fortuitous circumstances, the two giant planets around Kepler-419 have well characterized three-dimensional orbits. They are nearly coplanar to each other; the inner one has a large eccentricity (≃0.82); and the apses of the two orbits librate around anti-alignment. Such a state defies available proposals for large eccentricities. We argue that it is instead uniquely produced by a decaying protoplanetary disk. When the disk was massive, its precessional effect on the planets forced the two apses to center around an anti-aligned state. And as the disk is gradually eroded, the pair of planets are adiabatically transported to a new state where most of the eccentricity (or rather, the angular momentum deficit) is transferred to the inner planet, and the two apses are largely anti-aligned. During this transport, any initial mutual inclination may be reduced or enhanced; either may be compatible with the current constraints. So a primordial disk can drive up planet eccentricities both in resonant planet pairs (as has been shown for GJ 876) and in secularly-interacting, non-resonant pairs. The mechanism discussed here may be relevant for forming hot Jupiters and for explaining the observed eccentricities of warm and cold giant planets.

One of the biggest successes of the Cassini mission is the detection of small moons (moonlets) embedded in Saturns rings that cause S-shaped density structures in their close vicinity, called propellers. Here, we present isothermal hydrodynamic simulations of moonlet-induced propellers in Saturn's A ring that denote a further development of the original model. We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirm the predicted scaling laws and the analytical solution for the density in the propeller gaps. Finally, this mean field approach allows us to simulate the pattern of the giant propeller Blériot, which is too large to be modeled by direct N-body simulations. Our results are compared to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS), which intersect the propeller Blériot. Best fits to the UVIS optical depth profiles are achieved for a Hill radius of 590 m, which implies a moonlet diameter of about 860 m. Furthermore, the model favors a kinematic shear viscosity of the surrounding ring material of ν₀ = 340 cm² s⁻¹, a dispersion velocity in the range of 0.3 cm s⁻¹ < c₀ < 1.5 cm s⁻¹, and a fairly high bulk viscosity 7 < ξ₀/ν₀ < 17. These large transport values might be overestimated by our isothermal ring model and should be reviewed by an extended model including thermal fluctuations.

The Lambda Boo-type stars are chemically peculiar stars with deficiencies of iron-peak elements but near-solar C, N, O, and S abundances. Since the prototype Lambda Boötis was first reported as peculiar, this group has been expanded from a small group of early A-type stars to a larger group of late B to early F-type dwarfs. Although a detailed abundance analysis that supports the Lambda Boo-like abundance pattern is the definitive confirmation of this Lambda Boo characteristic, the rapid rotation of many Lambda Boo stars generally limits how much detail can be derived from an abundance analysis. Traditionally, Lambda Boo candidates have been classified by visually examining the difference between their spectra and spectra of standard stars. Therefore, some ambiguity remains especially for mild or borderline Lambda Boo stars. This is the third paper in a series that establishes a straightforward yet reliable way to identify Lambda Boo-type stars. In previous papers, we identified line equivalent width (EW) ratios in the ultraviolet and visible regions that can distinguish Lambda Boo stars from other metal-weak stars. In this paper, we apply the visible line EW ratio diagnostic to 25 Lambda Boo candidates and carry out a detailed abundance analysis of HD 81290, an F2 star with a C i/Mg ii EW ratio in the range expected for Lambda Boo-type stars. Our elemental abundance analysis results confirm HD 81290's Lambda Boo membership and demonstrate the utility of our EW ratio as a diagnostic for cooler F-type Lambda Boo stars.

Digital image sensors are ubiquitous in astronomical instrumentation and it is well known that they suffer from issues that must be corrected for data to be scientifically useful. I present discussion on errors resulting from digitization and characterization of nonlinearity and ADC errors of the PhotonFocus MV-D1024E cameras selected for the K-coronagraph of the Coronal Solar Magnetism Observatory. I derive an analytic expression for quantization errors. The MV-D1024E camera has adequate bit depth for which quantization error is not an issue. I show that this is not the case for all cameras, particularly those with deep wells and low read noise. The impact of nonlinearity and ADC errors on science observations of the K-coronagraph is analyzed using a simplified telescope model. Errors caused by the camera ADCs result in systematic errors in the measurement of the polarimetric signal of several times 10⁻⁹ B_⊙, which is about an order of magnitude above the desired sensitivity. I demonstrate a method for post-facto data correction using a lookup table and derive parameters from camera characterization measurements that were made with a lab setup. Nonlinearity is traditionally addressed with a global correction. I show through analysis of calibration data that for the MV-D1024E this correction leaves residual systematic errors after dark and gain correction of up to 1% of the signal. I demonstrate that a pixel-wise correction of nonlinearity reduces the errors to below 0.1%. These corrections are necessary for the K-coronagraph data products to meet the science requirements. They have been implemented in the instrument data acquisition system and data reduction pipeline. While no other instruments besides the K-coronagraph or cameras besides the MV-D1024E are discussed here, the results are illustrative for all instruments and cameras.

In modern astrophysics, machine learning has increasingly gained popularity with its incredibly powerful ability to make predictions or calculated suggestions for large amounts of data. We describe an application of the supervised machine-learning algorithm, random forests (RF), to the star/galaxy/QSO classification and the stellar effective temperature regression based on the combination of Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Sloan Digital Sky Survey spectroscopic data. This combination enables us to obtain reliable predictions with one of the largest training samples ever used. The training samples are built with a nine-color data set of about three million objects for the classification and a seven-color data set of over one million stars for the regression. The performance of the classification and regression is examined with validation and blind tests on the objects in the RAdial Velocity Extension, 6dFGS, UV-bright Quasar Survey and Apache Point Observatory Galactic Evolution Experiment surveys. We demonstrate that RF is an effective algorithm, with classification accuracies higher than 99% for stars and galaxies, and higher than 94% for QSOs. These accuracies are higher than machine-learning results in former studies. The total standard deviations of the regression are smaller than 200 K, which is similar to those of some spectrum-based methods. The machine-learning algorithm with the broad-band photometry provides us with a more efficient approach for dealing with massive amounts of astrophysical data than do traditional color cuts and spectral energy distribution fits.

We present an expanded investigation of the library of globular cluster (GC) synthetic integrated light (IL) spectra of Young & Short, focusing on the impact of non-local thermodynamic equilibrium (NLTE) modeling effects on cluster parameters derived from photometric colors and sensitivity of near-IR spectral features to cluster age and metallicity. Johnson–Cousins–Bessel UBVIJK photometric colors are produced for 910 synthetic IL spectra with two degrees of α enhancement, in both NLTE and local thermodynamic equilibrium (LTE). These color values are used to investigate the GC age–metallicity degeneracy and compare NLTE and LTE derived [M/H] values for NGC 104, NGC 5139, and NGC 6205. For a given age, derived [M/H] values are shown to increase by up to 0.05 dex when modeled in NLTE. A total of 86 spectral lines in the range λ = 12000–22000 Å, representing 14 different atomic species, were identified as sensitive to either cluster age or metallicity, 12 of which were identified as sensitive to both. Equivalent widths of the lines are measured in NLTE and LTE spectra, with NLTE effects changing the widths by up to ${}_{-0.15}^{+0.25}$ Å depending on the atomic species.

The atmospheres of late M stars represent a significant challenge in the characterization of any transiting exoplanets because of the presence of strong molecular features in the stellar atmosphere. TRAPPIST-1 is an ultracool dwarf, host to seven transiting planets, and contains its own molecular signatures that can potentially be imprinted on planetary transit lightcurves as a result of inhomogeneities in the occulted stellar photosphere. We present a case study on TRAPPIST-1g, the largest planet in the system, using a new observation together with previous data, to disentangle the atmospheric transmission of the planet from that of the star. We use the out-of-transit stellar spectra to reconstruct the stellar flux on the basis of one, two, and three temperature components. We find that TRAPPIST-1 is a 0.08 M_*, 0.117 R_*, M8V star with a photospheric effective temperature of 2400 K, with ∼35% 3000 K spot coverage and a very small fraction, <3%, of ∼5800 K hot spot. We calculate a planetary radius for TRAPPIST-1g to be R_p = 1.124 R_⊕with a planetary density of ρ_p = 0.8214 ρ_⊕. On the basis of the stellar reconstruction, there are 11 plausible scenarios for the combined stellar photosphere and planet transit geometry; in our analysis, we are able to rule out eight of the 11 scenarios. Using planetary models, we evaluate the remaining scenarios with respect to the transmission spectrum of TRAPPIST-1g. We conclude that the planetary transmission spectrum is likely not contaminated by any stellar spectral features and are able to rule out a clear solar H₂/He-dominated atmosphere at greater than 3σ.

We present a catalog of Galactic star clusters, associations and candidates with 10978 entries. This multi-band catalog was constructed over 20 years, starting with visual inspections on the Digital Sky Survey and incremented with the 2MASS, WISE, VVV, Spitzer, and Herschel surveys. Large and small catalogs, as well as papers on individual objects have been systematically cross-identified. The catalog provides Galactic and equatorial coordinates, angular diameters, and chronologically ordered designations, making it simple to assign discoveries and verify how often the objects were cataloged by different authors, search methods, and/or surveys. Detection in a single band is the minimum constraint to validate an entry. About 3200 objects have measured parameters in the literature. A fundamental contribution of the present study is to present an additional ≈7700 objects for the first analyses of nature, photometry, spectroscopy and structure. The present focus is not to compile or determine fundamental parameters, but to provide a catalog uniformly characterizing the entries. A major result is that now 4234 embedded clusters are cataloged, a factor of ≈1.5 larger than open clusters. In addition to cross-identifications in different references and wavelength domains, we also communicate the discovery of 638 star clusters and similar objects. The present general catalog provides previously studied objects and thousands of additional entries in a homogeneous way, a timely contribution to Gaia-related works.

Uranus has a tilted rotation axis, which is supposed to have been caused by a giant impact. In general, an impact event also changes the internal compositional distribution and drives mass ejection from the planet, which may provide the origin of satellites. Previous studies of the impact simulation of Uranus investigated the resultant angular momentum and the ejected mass distribution. However, the effect of changing the initial condition of the thermal and compositional structure is not studied. In this paper, we perform hydrodynamics simulations for the impact events of Uranus-size ice giants composed of a water core surrounded by a hydrogen envelope using two variant methods of the smoothed particle hydrodynamics. We find that the higher-entropy target loses its envelope more efficiently than the low-entropy target. However, the higher-entropy target gains more angular momentum than the lower-entropy target since the higher-entropy target has a more expanded envelope. We discuss the efficiency of angular momentum transport and the amount of the ejected mass and find a simple analytical model to roughly reproduce the outcomes of numerical simulations. We suggest the range of possible initial conditions for the giant impact on proto-Uranus that reproduces the present rotation tilt of Uranus and sufficiently provides the total angular momentum of the satellite system that can be created from the fragments from the giant impact.

We present timely spectroscopic follow-ups of WG0214-2105, a background quasar strongly lensed by a foreground galaxy into four images. WG0204-2105 was recently identified by Agnello from a combination of the mid-infrared quasar color selection using WISE photometry and the exquisite astrometric resolution of Gaia, and can be clearly seen in the Dark Energy Survey, VST-ALTAS, and Pan-STARRS optical imaging. The quasar images are relatively faint, thus prompting us to conduct spectroscopic observations using the Gemini Multi-Object Spectrographs (GMOS) spectrograph on board the 8 m Gemini telescope. The GMOS spectra firmly detected the emission lines, e.g., Lyα, C iv, and C iii], from the background quasar, allowing us to confirm the lensing nature and pin down the quasar redshifts to be z = 3.24. There are also absorption lines, putatively associated with a foreground absorber at z = 0.45. We also derive the broadband photometry of the quasar images using the Pan-STARRS grizy images, as well as the time-delay using the aforementioned redshifts. Future long-term photometric follow-up will help narrow down the time-delays, providing a firm basis to determine Hubble constant.

The issue of CH₄ escape on Titan is still under debate, and a range of escape rates from 10²⁴ to 10²⁷ s⁻¹ has been reported in previous studies. One effective way of solving the CH₄ escape dilemma is to investigate the morphology of the CH₄ torus around Saturn, which varies with both the total CH₄ escape rate on Titan and the CH₄ energy distribution near its exobase. Such a torus is modeled via a test particle Monte Carlo approach in this study for a variety of CH₄ escaping scenarios characterized by different energy distributions near the exobase. The model calculations indicate that the extension of the CH₄ torus depends critically on the population of the high-energy tail of the CH₄ energy distribution. The model also predicts several distinctive cavities in CH₄ density related to mean motion resonances between Titan and the torus particles.

Machine learning (ML) algorithms have become increasingly important in the analysis of astronomical data. However, because most ML algorithms are not designed to take data uncertainties into account, ML-based studies are mostly restricted to data with high signal-to-noise ratios. Astronomical data sets of such high quality are uncommon. In this work, we modify the long-established Random Forest (RF) algorithm to take into account uncertainties in measurements (i.e., features) as well as in assigned classes (i.e., labels). To do so, the Probabilistic Random Forest (PRF) algorithm treats the features and labels as probability distribution functions, rather than deterministic quantities. We perform a variety of experiments where we inject different types of noise into a data set and compare the accuracy of the PRF to that of RF. The PRF outperforms RF in all cases, with a moderate increase in running time. We find an improvement in classification accuracy of up to 10% in the case of noisy features, and up to 30% in the case of noisy labels. The PRF accuracy decreased by less then 5% for a data set with as many as 45% misclassified objects, compared to a clean data set. Apart from improving the prediction accuracy in noisy data sets, the PRF naturally copes with missing values in the data, and outperforms RF when applied to a data set with different noise characteristics in the training and test sets, suggesting that it can be used for transfer learning.

We present the physical properties of EPIC 245932119 (K_p = +9.82) exhibiting both eclipses and pulsations from the K2 photometry. The binary modeling indicates that the eclipsing system is in detached or semi-detached configurations with a mass ratio of 0.283 or 0.245, respectively, and that its light-curve parameters are almost unaffected by pulsations. Multiple frequency analyses were performed for the light residuals in the outside-primary eclipsing phase after subtracting the binarity effects from the observed data. We detected 35 frequencies with signal-to-noise amplitude ratios larger than 4.0 in two regions of 0.62–6.28 day⁻¹ and 19.36–24.07 day⁻¹. Among these, it is possible that some high signals close to the Nyquist limit f_Ny may be reflections of real pulsation frequencies (2${f}_{\mathrm{Ny}}-{f}_{i}$). All frequencies (f₈, f₉, f₁₄, f₁₈, f₂₄, f₃₂) in the lower frequency region are orbital harmonics, and three high frequencies (f₁₉, f₂₀, f₂₂) appear to be sidelobes split from the main frequency of f₁ = 22.77503 day⁻¹. Most of them are thought to be alias effects caused by the orbital frequency. For the 26 other frequencies, the pulsation periods and pulsation constants are in the ranges of 0.041–0.052 days and 0.013–0.016 days, respectively. These values and the position in the Hertzsprung–Russell diagram reveal that the primary component is a δ Sct pulsator. The observational properties of EPIC 245932119 are in good agreement with those for eclipsing binaries with δ Sct-type pulsating components.

Recent studies of stellar occultations observed by the Visual and Infrared Mapping Spectrometer on board the Cassini spacecraft have demonstrated that multiple spiral wave structures in Saturn's rings are probably generated by normal-mode oscillations inside the planet. Wavelet-based analyses have been able to unambiguously determine both the number of spiral arms and the rotation rate of many of these patterns. However, there are many more planetary normal modes that should have resonances in the rings, implying that many normal modes do not have sufficiently large amplitudes to generate obvious ring waves. Fortunately, recent advances in wavelet analysis allow weaker wave signals to be uncovered by combining data from multiple occultations. These new analytical tools reveal that a pattern previously identified as a single spiral wave actually consists of two superimposed waves, one with five spiral arms rotating at 15936/day and one with 11 spiral arms rotating at 14505/day. Furthermore, a broad search for new waves revealed four previously unknown wave patterns with six, seven, eight, and nine spiral arms rotating around the planet at 15382/day, 14925/day, 14542/day, and 14218/day, respectively. These six patterns provide precise frequencies for another six fundamental normal modes inside Saturn, yielding what is now a complete sequence of fundamental sectoral normal modes with azimuthal wavenumbers from 2 to 10. These frequencies should place strong constraints on Saturn's interior structure and rotation rate, while the relative amplitudes of these waves should help clarify how the corresponding normal modes are excited inside the planet.

In 2015, K2 observations of the bright (V = 8.9, K = 7.7) star HIP 41378 revealed a rich system of at least five transiting exoplanets, ranging in size from super-Earths to gas giants. The 2015 K2 observations only spanned 74.8 days, and the outer three long-period planets in the system were only detected with a single transit, so their orbital periods and transit ephemerides could not be determined at that time. Here, we report on 50.8 days of new K2 observations of HIP 41378 from summer 2018. These data reveal additional transits of the long-period planets HIP 41378 d and HIP 41378 f, yielding a set of discrete possible orbital periods for these two planets. We identify the most probable orbital periods for these two planets using our knowledge of the planets' transit durations, the host star's properties, the system's dynamics, and data from the ground-based HATNet, KELT, and WASP transit surveys. Targeted photometric follow-up during the most probable future transit times will be able to determine the planets' orbital periods and will enable future observations with facilities like the James Webb Space Telescope. The methods developed herein to determine the most probable orbital periods will be important for long-period planets detected by the Transiting Exoplanet Survey Satellite, where similar period ambiguities will frequently arise due to the mission's survey strategy.

We present a (sub)millimeter line survey of the methanol maser outflow located in the massive star-forming region DR21(OH) carried out with the Submillimeter Array (SMA) at 217/227 GHz and 337/347 GHz. We find transitions from several molecules toward the maser outflow such as CH₃OH, H₂CS, C¹⁷O, H¹³CO⁺, and C³⁴S. However, with the present observations, we cannot discard the possibility that some of the observed species such as C¹⁷O, C³⁴S, and H₂CS, might be instead associated with the compact and dusty continuum sources located in the MM2 region. Given that most of transitions correspond to methanol lines, we have computed a rotational diagram with CASSIS and an LTE synthetic spectra with XCLASS for the detected methanol lines in order to estimate the rotational temperature and column density in the small solid angle of the outflow where enough lines are present. We obtain a rotational temperature of 28 ± 2.5 K and a column density of 6.0 ± 0.9 × 10¹⁵ cm⁻². These values are comparable to those column densities/rotational temperatures reported in outflows emanating from low-mass stars. Extreme and moderate physical conditions to excite the maser and thermal emission coexist within the CH₃OH flow. Finally, we do not detect any complex molecules associated with the flow, e.g., CH₃OCHO, (CH₃)₂CO, and CH₃CH₂CN.

Exoplanets orbiting close to their host star are expected to support a large ionosphere, which extends to larger pressures than witnessed in our solar system. These ionospheres can be investigated with ground-based transit observations of the optical signatures of alkali metals, which are the source of the ions. However, most ground-based transit spectra do not systematically resolve the wings of the features and continuum, as needed to constrain the alkali abundances. Here we present new observations and analyses of optical transit spectra that cover the Na doublet in the atmosphere of the exoplanet XO-2b. To assess the consistency of our results, observations were obtained from two separate platforms: Gemini/GMOS and Mayall/KOSMOS. To mitigate the systematic errors, we chose XO-2, because it has a binary companion of the same brightness and stellar type, which provides an ideal reference star to model Earth's atmospheric effects. We find that interpretation of the data is highly sensitive to time-varying translations along the detector, which change according to wavelength and differ between the target and reference star. It was necessary to employ a time-dependent cross-correlation to align our wavelength bins and correct for atmospheric differential refraction. This approach allows us to resolve the wings of the Na line across five wavelength bins at a resolution of ∼1.6 nm and limit the abundance of Na. We obtain consistent results from each telescope with an Na amplitude of 521 ± 161 and 403 ± 186 ppm for GMOS and KOSMOS, respectively. The results are analyzed with a radiative transfer model that includes the effects of ionization. The data are consistent with a clear atmosphere between ∼1 and 100 mbar that establishes a lower limit on Na at ${0.4}_{-0.3}^{+2}$ ppm ([Na/H] = $-{0.64}_{-0.6}^{+0.78}$), consistent with solar. However, we cannot rule out the presence of clouds at ∼10 mbar that allow for higher Na abundances, which would be consistent with the stellar metallicity measured for the host star ([Na/H] = 0.485 ± 0.043).

We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific classes of stars, the Luminous Blue Variables (LBVs), B[e] supergiants (sgB[e]), and the high-luminosity yellow hypergiants. We identify two new LBV candidates, and three sgB[e] stars in M81. We also find that some stars that were previously considered LBV candidates are actually field stars. The confirmed and candidate LBVs and sgB[e] stars together with the other confirmed members are shown on the HR Diagrams for their respective galaxies. We also present the HR Diagrams for the two "SN impostors", V37 (SN2002kg) and V12(SN1954J) in NGC 2403 and the stars in their immediate environments.

We show that microlensing event KMT-2016-BLG-1107 displays a new type of degeneracy between wide-binary and close-binary Hollywood events in which a giant-star source envelops the planetary caustic. The planetary anomaly takes the form of a smooth, two-day "bump" far out on the falling wing of the light curve, which can be interpreted either as the source completely enveloping a minor-image caustic due to a close companion with mass ratio q = 0.036, or partially enveloping a major-image caustic due to a wide companion with q = 0.004. The best estimates of the companion masses are both in the planetary regime (${3.3}_{-1.8}^{+3.5}\,{M}_{\mathrm{jup}}$ and ${0.090}_{-0.037}^{+0.096}\,{M}_{\mathrm{jup}}$) but differ by an even larger factor than the mass ratios due to different inferred host masses. We show that the two solutions can be distinguished by high-resolution imaging at first light on next-generation ("30 m") telescopes. We provide analytic guidance to understand the conditions under which this new type of degeneracy can appear.

We report radar observations of near-Earth asteroid 2013 BS45 obtained during the 2013 apparition. This object is in a resonant, Earth-like orbit, and it is a backup target for NASA's NEA Scout mission. 2013 BS45 belongs to the Arjuna orbital domain, which currently has ∼20 discovered representatives. These objects tend to be small and difficult to characterize, and 2013 BS45 is only the third Arjuna object observed with radar to date. We observed 2013 BS45 on three days at Goldstone (8560 MHz, 3.5 cm) between 2013 February 10 and 13. The closest approach occurred on February 12 at a distance of 0.0126 au. We obtained relatively weak echo power spectra and ranging data at resolutions up to 0.125 μs (18.75 m px⁻¹). The Doppler broadening of the echo power spectra strongly suggests an upper bound on the rotation period of 1.9 minutes. The radar data, in combination with an assumption that the asteroid's radar albedo is no higher than that of metallic NEA 1986 DA, constrain the equivalent diameter to 15 m ≤ D ≤ 38 m. The circular polarization ratio is 0.21 ± 0.06, which implies a near-surface that is relatively smooth on decimeter spatial scales. We bounded the OC radar albedo to η_OC ≥ 0.09 and the optical albedo remains relatively unconstrained at 0.05 ≤ p_V ≤ 0.35. The Yarkovsky acceleration has not been detected but, due to the object's rapid rotation, would be dominated by a seasonal component whose direction and magnitude depends on the currently unknown pole orientation and thermal inertia.

One of the unique features associated with the Earth is that the fraction of its surface covered by land is comparable to that spanned by its oceans and other water bodies. Here, we investigate how extraterrestrial biospheres depend on the ratio of the surficial land and water fractions. We find that worlds that are overwhelmingly dominated by landmasses or oceans are likely to have sparse biospheres. Our analysis suggests that major evolutionary events such as the build-up of O₂ in the atmosphere and the emergence of technological intelligence might be relatively feasible only on a small subset of worlds with surface water fractions ranging approximately between 30% and 90%. We also discuss how our predictions can be evaluated by future observations and the implications for the prevalence of microbial and technological species in the universe.

We measure the mean Galactocentric radial component of the velocity of stars (v_R) in the disk at 8 kpc < R < 28 kpc in the direction of the anticenter. For this, we use the Apache Point Galactic Evolution Experiment. Furthermore, we compare the result with H i maps along the same line of sight. We find an increase in positive (expansion) v_R at R ≈ 9–13 kpc, reaching a maximum of ≈6 km s⁻¹, and a decrease at large values of R, reaching a negative (contraction) value of ≈−10 km s⁻¹ for R > 17 kpc. Negative velocities are also observed in 21 cm H i maps, possibly dominated by local gas emission. Among the possible dynamical causes for these non-zero v_R, factors such as the effect of the Galactic bar, streams, or mergers do not seem appropriate to explain our observations. An explanation might be the gravitational attraction of overdensities in a spiral arm. As a matter of fact, we see a change of regime from positive to negative velocities around R ≈ 15 kpc, in the position where we cross the Outer spiral arm in the anticenter. The mass in spiral arms necessary to produce these velocities would be about 3% of the mass of the disk, consistent with our knowledge of the spiral arms. Another scenario that we explore is a simple class of out-of-equilibrium systems in which radial motions are generally created by the monolithic collapse of isolated self-gravitating overdensities.

Solar system bodies such as comets and asteroids are known to eject material from their surface in the form of jets and plumes. Observations of these transient outbursts can offer insight into the inner workings and makeup of their originating body. However, the detection of and response to these events has thus far been manually controlled by ground operations, limiting the response time, due to the light time delay of ground communications. For distant bodies, the delay can exceed the duration of temporary events, making it impossible to respond with follow-up observations. To address this need, we developed a computer vision methodology for detecting plumes of the comet 67P/Churyumov–Gerasimenko from imagery acquired by the OSIRIS scientific camera system. While methods exist for the automatic detection of plumes on spherical and near-convex solar system bodies, this is the first work that addresses the case of highly irregularly shaped bodies such as 67P/Churyumov–Gerasimenko. Our work is divided into two distinct components: an image processing pipeline that refines a model-based estimate of the nucleus body, and an iterative plume detection algorithm that finds regions of local intensity maxima and joins plume segments across successively higher altitudes. Finally, we validate this method by comparing automatically labeled images to those labeled by hand, and find no significant differences in variability. This technique has utility in both ground-based analysis of plume sequences as well as onboard applications, such as isolating short sequences of high activity for priority downloading or triggering follow-up observations with additional instruments.

We present the results from a detailed analysis of our high-resolution spectra and historical photometric observations of the semidetached eclipsing binary V392 Ori with a δ Scuti (δ Sct) pulsating component. A total of 31 spectroscopic observations were carried out at both the Bohyunsan Optical Astronomy Observatory in Korea and the Thai National Observatory in Thailand during the 2016 and 2017 observing seasons. The radial velocities (RVs) of the primary and the faint secondary components were determined, and the effective temperature and projected rotational velocity of the former star were measured as T_eff,1 = 8500 ± 160 K and v₁ sin i = 148 ± 13 km s⁻¹, respectively, through a comparison of the observed spectra and stellar atmosphere models. The physical properties of V392 Ori were determined by analysis of our RVs together with the existing multiband light curves. The results are the following: masses of M₁ = 2.28 ± 0.30 M_⊙ and M₂ = 0.49 ± 0.10 M_⊙, and radii of R₁ = 2.08 ± 0.09 R_⊙ and R₂ = 1.15 ± 0.05 R_⊙. The primary star located inside the main-sequence band exhibits a δ Sct-type pulsation. On the contrary, the less massive secondary component is significantly oversized and overluminous for its mass and temperature.

The cluster NGC 3603 hosts some of the most massive stars in the Galaxy. With a modest 50 ks exposure with the Chandra High Energy Grating Spectrometer, we have resolved emission lines in spectra of several of the brightest cluster members, which are of WNh and O spectral types. This observation provides our first definitive high-resolution spectra of such stars in this nearby starburst region. The stars studied have broadened X-ray emission lines, some with blueshifted centroids, and are characteristic of massive stellar winds with terminal velocities around 2000–$3000\,\mathrm{km}\,{{\rm{s}}}^{-1}$. X-ray luminosities and plasma temperatures are very high for both the WNh and O-stars studied. We conclude that their X-rays are likely the result of colliding winds.

In coupled ring-satellite systems, satellites exchange angular momentum with both the primary through tides and the ring through Lindblad torques, and may exchange material with the ring through accretion and tidal disruption. Here we show that these coupled ring-satellite systems fall into three distinct dynamical regimes, which we refer to as "Boomerang," "Slingshot," and "Torque-dependent." These regimes are determined by the relative locations of the fluid Roche limit, the synchronous orbit, and the maximum orbit in which Lindblad torques can perturb a satellite. Satellites that accrete from rings in the Boomerang regime remain interior to the synchronous orbit, and may be driven back toward the primary by tides. Satellites that accrete from rings in the Slingshot regime form exterior to the synchronous orbit, and are always driven away from the primary. Satellites that accrete from rings in the Torque-dependent regime may exhibit either Boomerang or Slingshot behavior, depending on ring and satellite masses. We consider both known and hypothesized ring-satellite systems in the solar system, and identify which of these three regimes they fall into. We determine that Uranus exists within the Torque-dependent regime. Using the RING-MOONS code, which models the dynamical evolution of coupled ring-satellite systems, we show that the Uranian satellite Miranda may have accreted from a massive ancient Roche-interior ring and followed a Slingshot-like dynamical path to its present orbit beyond the synchronous orbit, while satellites that accreted after Miranda followed Boomerang-like evolutionary paths and remained interior to the synchronous orbit.

We report the discovery of HATS-70b, a transiting brown dwarf at the deuterium burning limit. HATS-70b has a mass of ${M}_{p}={12.9}_{-1.6}^{+1.8}\,{M}_{\mathrm{Jup}}$ and a radius of ${R}_{p}={1.384}_{-0.074}^{+0.079}\,{R}_{\mathrm{Jup}}$, residing in a close-in orbit with a period of $1.89$ days. The host star is a ${M}_{\star }=1.78\pm 0.12\,{M}_{\odot }$ A star rotating at $v\sin {I}_{\star }={40.61}_{-0.35}^{+0.32}\,\mathrm{km}\,{{\rm{s}}}^{-1}$, enabling us to characterize the spectroscopic transit of the brown dwarf via Doppler tomography. We find that HATS-70b, like other massive planets and brown dwarfs previously sampled, orbits in a low projected-obliquity orbit with $\lambda ={8.9}_{-4.5}^{+5.6\circ }$. The low obliquities of these systems is surprising given all brown dwarf and massive planets with obliquities measured orbit stars hotter than the Kraft break. This trend is tentatively inconsistent with dynamically chaotic migration for systems with massive companions, though the stronger tidal influence of these companions makes it difficult to draw conclusions on the primordial obliquity distribution of this population. We also introduce a modeling scheme for planets around rapidly rotating stars, accounting for the influence of gravity darkening on the derived stellar and planetary parameters.

LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from the High Accuracy Radial velocity Planet Searcher, we report the discovery of an additional transiting rocky companion (LHS 1140 c) with a mass of 1.81 ± 0.39 M_⊕ and a radius of 1.282 ± 0.024 R_⊕ on a tighter, 3.77795-day orbit. We also obtain more precise estimates for the mass and radius of LHS 1140 b, which are 6.98 ± 0.89 M_⊕ and 1.727 ± 0.032 R_⊕. The mean densities of planets b and c are 7.5 ± 1.0 g cm⁻³ and 4.7 ± 1.1 g cm⁻³, respectively, both consistent with the Earth's ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are coplanar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.

We present the most sensitive direct imaging and radial velocity (RV) exploration of Eridani to date. Eridani is an adolescent planetary system, reminiscent of the early solar system. It is surrounded by a prominent and complex debris disk that is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 yr ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 yr, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7 μm) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. Eridani b has a mass of ${0.78}_{-0.12}^{+0.38}$M_Jup and is orbiting Eridani at about 3.48 ± 0.02 au with a period of 7.37 ± 0.07 yr. The eccentricity of Eridani b's orbit is ${0.07}_{-0.05}^{+0.06}$, an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet–disk interactions and prospects for future detection and characterization with the James Webb Space Telescope.

We propose an eigenvector-based formalism for the calibration of radio interferometer arrays. In the presence of a strong dominant point source, the complex gains of the array can be obtained by taking the first eigenvector of the visibility matrix. We use the stable principle component analysis method to help separate outliers and noise from the calibrator signal to improve the performance of the method. This method can be applied with poorly known beam model of the antenna, is insensitive to outliers or imperfections in the data, and has low computational complexity. It thus is particularly suitable for the initial calibration of the array, which can serve as the initial point for more accurate calibrations. We demonstrate this method by applying it to the cylinder pathfinder of the Tianlai experiment, which aims to measure the dark energy equation of state using the baryon acoustic oscillation features in the large-scale structure by making intensity mapping observation of the redshifted 21 cm emission of the neutral hydrogen (H i). The complex gain of the array elements and the beam profile in the east–west direction (short axis of the cylinder) are successfully obtained by applying this method to the transit data of bright radio sources.

A large extension of the Sextans dwarf spheroidal galaxy, 7 deg², has been surveyed for variable stars using the Dark Energy Camera at the Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile. We report seven anomalous Cepheids, 199 RR Lyrae stars, and 16 dwarf Cepheids in the field. This is only the fifth extragalactic system in which dwarf Cepheids have been systematically searched. Henceforth, the new stars increase the census of stars coming from different environments that can be used to asses the advantages and limitations of using dwarf Cepheids as standard candles in populations for which the metallicity is not necessarily known. The dwarf Cepheids found in Sextans have a mean period of 0.066 day and a mean g amplitude of 0.87 mag. They are located below the horizontal branch, spanning a range of 0.8 mag: 21.9 < g < 22.7. The number of dwarf Cepheids in Sextans is low compared with other galaxies such as Carina, which has a strong intermediate-age population. On the other hand, the number and ratio of RR Lyrae stars to dwarf Cepheids are quite similar to those of Sculptor, a galaxy which, as Sextans, is dominated by an old stellar population. The dwarf Cepheid stars found in Sextans follow a well-constrained period–luminosity relationship with an rms = 0.05 mag in the g band, which was set up by anchoring to the distance modulus given by the RR Lyrae stars. Although the majority of the variable stars in Sextans are located toward the center of the galaxy, we have found two RR Lyrae stars and one anomalous Cepheid in the outskirts of the galaxy that may be extratidal stars and suggest that this galaxy may be undergoing tidal destruction. These possible extratidal variable stars share the same proper motions as Sextans, as seen by recent Gaia measurements. Two additional stars that we initially classified as foreground RR Lyrae stars may actually be other examples of Sextans extratidal anomalous Cepheids, although radial velocities are needed to prove that scenario.

Precision wavefront control on future segmented-aperture space telescopes presents significant challenges, particularly in the context of high-contrast exoplanet direct imaging. We present a new wavefront control architecture that translates the ground-based artificial guide star concept to space with a laser source on board a second spacecraft, formation flying within the telescope's field of view. We describe the motivating problem of mirror segment motion and develop wavefront sensing requirements as a function of guide star magnitude and segment motion power spectrum. Several sample cases with different values for transmitter power, pointing jitter, and wavelength are presented to illustrate the advantages and challenges of having a non-stellar-magnitude noise limited wavefront sensor for space telescopes. These notional designs allow increased control authority, potentially relaxing spacecraft stability requirements by two orders of magnitude and increasing terrestrial exoplanet discovery space by allowing high-contrast observations of stars of arbitrary brightness.

During the Transiting Exoplanet Survey Satellite (TESS) prime mission, 74% of the sky area will have an observational baseline of only 27 days. For planets with orbital periods longer than 13.5 days, TESS can capture only one or two transits, and the planet ephemerides will be difficult to determine from TESS data alone. Follow-up observations of transits of these candidates will require precise ephemerides. We explore the use of existing ground-based wide-field photometric surveys to constrain the ephemerides of the TESS single-transit candidates, with a focus on the Kilodegree Extremely Little Telescope (KELT) survey. We insert simulated TESS-detected single transits into KELT light curves and evaluate how well their orbital periods can be recovered. We find that KELT photometry can be used to confirm ephemerides with high accuracy for planets of Saturn size or larger, with orbital periods as long as a year, and therefore span a wide range of planet equilibrium temperatures. In a large fraction of the sky, we recover 30%–50% of warm Jupiter systems (planet radius of 0.9–1.1 R_J and 13.5 < P < 50 days), 5%–20% of temperate Jupiters (50 < P < 300 days), and 10%–30% of warm Saturns (planet radius of 0.5–0.9 R_J and 13.5 < P < 50 days). The resulting ephemerides can be used for follow-up observations to confirm candidates as planets, eclipsing binaries, or other false positives, as well as to conduct detailed transit observations with facilities like James Webb Space Telescope or Hubble Space Telescope.

Containing only a few percentages of the mass of the moon, the current asteroid belt is around three to four orders of magnitude smaller than its primordial mass inferred from disk models. Yet dynamical studies have shown that the asteroid belt could not have been depleted by more than about an order of magnitude over the past ∼4 Gyr. The remainder of the mass loss must have taken place during an earlier phase of the solar system's evolution. An orbital instability in the outer solar system occurring during the process of terrestrial planet formation can reproduce the broad characteristics of the inner solar system. Here, we test the viability of this model within the constraints of the main belt's low present-day mass and orbital structure. Although previous studies modeled asteroids as massless test particles because of limited computing power, our work uses graphics processing unit acceleration to model a fully self-gravitating asteroid belt. We find that depletion in the main belt is related to the giant planets' exact evolution within the orbital instability. Simulations that produce the closest matches to the giant planets' current orbits deplete the main belt by two to three orders of magnitude. These simulated asteroid belts are also good matches to the actual asteroid belt in terms of their radial mixing and broad orbital structure.

Young and dynamically active planetary systems can form disks of debris that are easier to image than the planets themselves. The morphology and evolution of these disks can help to infer the properties of the putative planets responsible for generating and shaping the debris structures. We present integral field spectroscopy and dual-band imaging from VLT/SPHERE (1.0–1.7 μm) of the debris disk around the young F2V/F3V star HD 115600. We aim to (1) characterize the geometry and composition of the debris ring, (2) search for thermal emission of young giant planets, and (3) in the absence of detected planets, to refine the inferred properties of plausible planets around HD 115600 to prepare future attempts to detect them. Using a different dust scattering model (ZODIPIC) than in the discovery paper to model the disk geometry, we find a₀ = 46 ± 2 au for the disk's central radius and offsets Δα, Δδ =  −1.0 ± 0.5, 0.5 ± 0.5 au. This offset is smaller than previously found, suggesting that unseen planets of lower masses could be sculpting the disk. Spectroscopy of the disk in Y-J bands with SPHERE shows reddish color, which becomes neutral or slightly blue in H-band seen with GPI, broadly consistent with a mixed bulk disk composition of processed organics and water ice. While our observed field contains numerous background objects at wide separations, no exoplanet has been directly observed to a mass sensitivity limit of 2 − 3(5 − 7) M_J between a projected separation of 40 and 200 au for hot (cold)-start models.