Keywords

The narrow main rings of Uranus are composed of almost exclusively centimeter- to meter-sized particles, with a very small or nonexistent dust component; however, the filling factor, composition, thickness, mass, and detailed particle size distribution of these rings remain poorly constrained. Using millimeter (1.3–3.1 mm) imaging from the Atacama Large (sub-)Millimeter Array and mid-infrared (18.7 μm) imaging from the Very Large Telescope VISIR instrument, we observed the thermal component of the Uranian ring system for the first time. The ring is detected strongly and can be seen by eye in the images; the other main rings are visible in a radial (azimuthally averaged) profile at millimeter wavelengths. A simple thermal model similar to the Near-Earth Asteroid Thermal Model (NEATM) of near-Earth asteroids is applied to the ring to determine a ring particle temperature of 77.3 ± 1.8 K. The observed temperature is higher than expected for fast-rotating ring particles viewed at our observing geometry, meaning that the data favor a model in which the thermal inertia of the ring particles is low and/or their rotation rate is slow. The ring displays a factor of 2–3 brightness difference between periapsis and apoapsis, with 49.1% ± 2.2% of sightlines through the ring striking a particle. These observations are consistent with optical and near-infrared reflected light observations, confirming the hypothesis that micron-sized dust is not present in the ring system.

We report the discovery of a transiting planet first identified as a candidate in Sector 1 of the Transiting Exoplanet Survey Satellite (TESS), and then confirmed with precision radial velocities. HD 1397b has a mass of ${M}_{{\rm{P}}}\,={0.367}_{-0.023}^{+0.022}\,{M}_{{\rm{J}}}$, a radius of ${R}_{{\rm{P}}}={1.023}_{-0.013}^{+0.013}\,{R}_{{\rm{J}}}$, and orbits its bright host star (V = 7.8 mag) with an orbital period of $11.5366\pm 0.0003$ d on a moderately eccentric orbit ($e={0.216}_{-0.026}^{+0.027}$). With a mass of ${M}_{\star }={1.257}_{-0.029}^{+0.029}\,{M}_{\odot }$, a radius of ${R}_{\star }={2.341}_{-0.019}^{+0.022}\,{R}_{\odot }$, and an age of $4.46\pm 0.25$ Gyr, the solar-metallicity host star has already departed from the main sequence. We find evidence in the radial velocity measurements of a secondary signal with a longer period. We attribute it to the rotational modulation of stellar activity, but a long-term radial velocity monitoring would be necessary to discard if this signal is produced by a second planet in the system. The HD 1397 system is among the brightest ones currently known to host a transiting planet, which will make it possible to perform detailed follow-up observations in order to characterize the properties of giant planets orbiting evolved stars.

We report the results of the high-precision photometric follow-up observations of five transiting hot Jupiters, WASP-33b, WASP-50b, WASP-12b, HATS-18b, and HAT-P-36b. The observations are made from the 2 m Himalayan Chandra Telescope at Indian Astronomical Observatory, Hanle, and the 1.3 m J. C. Bhattacharyya Telescope at Vainu Bappu Observatory, Kavalur. This exercise is a part of the capability testing of the two telescopes and their back-end instruments. Leveraging the large aperture of both the telescopes used, the images taken during several nights were used to produce the transit light curves with high photometric signal-to-noise ratio (>200) by performing differential photometry. In order to reduce the fluctuations in the transit light curves due to various sources such as stellar activity, varying sky transparency, etc., we preprocessed them using wavelet denoising and applied a Gaussian process correlated noise modeling technique while modeling the transit light curves. To demonstrate the efficiency of the wavelet denoising process we have also included the results without the denoising process. A state-of-the-art algorithm used for modeling the transit light curves provided the physical parameters of the planets with more precise values than reported earlier.

We report the discovery of a Spitzer microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio q ∼ 2 × 10⁻⁴. The planetary signal, which is characterized by a short (∼1 day) "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from Gaia, the Spitzer satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of M_p = 13.9 ± 1.6 M_⊕ orbiting a mid M-dwarf with a mass of M_h = 0.23 ± 0.03 M_⊙. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields M_p = 1.2 ± 0.2 M_⊕ and M_h = 0.15 ± 0.02 M_⊙. By combining the microlensing and Gaia data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance D_L ∼ 6 ± 1 kpc. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.

We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planet's existence with a direct detection of CO in the planet's atmosphere. We also calculate a mass of 11.6 M_J based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the K-band. This magnitude implies the planet formed via a "hot start" formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent dynamical mass.

The detection of gas in debris disks raises the question of whether this gas is a remnant from the primordial protoplanetary phase, or released by the collision of secondary bodies. In this paper we analyze ALMA observations at 1''–15 resolution of three debris disks where the ¹²CO(2–1) rotational line was detected: HD 131835, HD 138813, and HD 156623. We apply the iterative Lucy–Richardson deconvolution technique to the problem of circumstellar disks to derive disk geometries and surface brightness distributions of the gas. The derived disk parameters are used as input for thermochemical models to test both primordial and cometary scenarios for the origin of the gas. We favor a secondary origin for the gas in these disks and find that the CO gas masses ($\sim 3\times {10}^{-3}$ M${}_{\oplus }$) require production rates (∼5 × 10⁻⁷ M_⊕ yr⁻¹) similar to those estimated for the bona fide gas-rich debris disk β Pic.

The dense clusters within the Serpens Molecular Cloud are among the most active regions of nearby star formation. In this paper, we use Gaia DR2 parallaxes and proper motions to statistically measure ∼1167 kinematic members of Serpens, few of which have been previously identified, to evaluate the star formation history of the complex. The optical members of Serpens are concentrated in three distinct groups located at 380–480 pc; the densest clusters are still highly obscured by optically thick dust and have few optical members. The total population of young stars and protostars in Serpens is at least 2000 stars, including past surveys that were most sensitive to protostars and disks, and may be much higher. Distances to dark clouds measured from deficits in star counts are consistent with the distances to the optical star clusters. The Serpens Molecular Cloud is seen in the foreground of the Aquila Rift, dark clouds located at 600–700 pc, and behind patchy extinction, here called the Serpens Cirrus, located at ∼250 pc. Based on the lack of a distributed population of older stars, the star formation rate throughout the Serpens Molecular Cloud increased by at least a factor of 20 within the past ∼5 Myr. The optically bright stars in Serpens Northeast are visible because their natal molecular cloud has been eroded, not because they were flung outwards from a central factory of star formation. The separation between subclusters of 20–100 pc and the absence of an older population together lead to speculation that an external forcing was needed to trigger the active star formation.

Here we present the first open-source radiative transfer model for computing the reflected light of exoplanets at any phase geometry, called PICASO: the planetary intensity code for atmospheric scattering observations. This code, written in Python, has heritage from a decades-old, well-known Fortran model used for several studies of planetary objects within the solar system and beyond. We have adopted it to include several methodologies for computing both direct and diffuse-scattering phase functions, and have added several updates including the ability to compute Raman scattering spectral features. Here we benchmark PICASO against two independent codes and discuss the degree to which the model is sensitive to a user's specification for various phase functions. Then, we conduct a full information-content study of the model across a wide parameter space in temperature, cloud profile, signal-to-noise ratio, and resolving power.

We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semimajor axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M_* > 1.5 M_⊙ more likely to host planets with masses between 2 and 13M_Jup and semimajor axes of 3–100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semimajor axis (a) for planet populations around high-mass stars (M_* > 1.5 M_⊙) of the form ${d}^{2}N/({dm}\,{da})\propto {m}^{\alpha }\,{a}^{\beta }$, finding α = −2.4 ± 0.8 and β = −2.0 ± 0.5, and an integrated occurrence rate of ${9}_{-4}^{+5}$% between 5–13M_Jup and 10–100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with ${0.8}_{-0.5}^{+0.8}$% of stars hosting a brown dwarf companion between 13–80M_Jup and 10–100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between ∼1 and 10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.