Mass and radius are two of the most fundamental properties of an astronomical object. Increasingly, new planet discoveries are being announced with a measurement of one of these terms, but not both. This has led to a growing need to forecast the missing quantity using the other, especially when predicting the detectability of certain follow-up observations. We present am unbiased forecasting model built upon a probabilistic mass-radius relation conditioned on a sample of 316 well-constrained objects. Our publicly available code, Forecaster, accounts for observational errors, hyper-parameter uncertainties and the intrinsic dispersions observed in the calibration sample. By conditioning our model upon a sample spanning dwarf planets to late-type stars, Forecaster can predict the mass (or radius) from the radius (or mass) for objects covering nine orders-of-magnitude in mass. Classification is naturally performed by our model, which uses four classes we label as Terran worlds, Neptunian worlds, Jovian worlds and stars. Our classification identifies dwarf planets as merely low-mass Terrans (like the Earth), and brown dwarfs as merely high-mass Jovians (like Jupiter). We detect a transition in the mass-radius relation at $2.0_{-0.6}^{+0.7} M_\oplus$, which we associate with the divide between solid, Terran worlds and Neptunian worlds. This independent analysis adds further weight to the emerging consensus that rocky Super-Earths represent a narrower region of parameter space than originally thought. Effectively, then, the Earth is the Super-Earth we have been looking for.

https://iopscience.iop.org/article/10.3847/1538-4357/834/1/17/pdf

Probabilistic forecasting of the masses and radii of other worlds

Research Corporation for Science Advancement (Rescorp); Center for Exoplanets and Habitable Worlds; Pennsylvania State University; Pennsylvania Space Grant Consortium; Leifur Eiriksson Foundation; NASA [NNX16AO28H, NAS5-26555]; Jet Propulsion Laboratory (JPL) - NASA; NSF [AST-1006676, AST-1126413, AST-1310885, AST-1517592]; NASA Astrobiology Institute (NAI) [NNA09-DA76A]; PSARC; NASA Office of Space Science [NNX09AF08G]; NASA Science Mission directorate; National Aeronautics and Space Administration; Eberly College of Science

/pdf/toward-space-like-photometric-precision-from-the-ground-with-3whffhpt20.pdf

Toward Space-like Photometric Precision from the Ground with Beam-shaping Diffusers

The rotation of a star and the revolutions of its planets are not necessarily aligned. This article reviews the measurement techniques, key findings, and theoretical interpretations related to the obliquities (spin–orbit angles) of planet-hosting stars. The best measurements are for stars with short-period giant planets, which have been found on prograde, polar, and retrograde orbits. It seems likely that dynamical processes such as planet–planet scattering and secular perturbations are responsible for tilting the orbits of close-in giant planets, just as those processes are implicated in exciting orbital eccentricities. The observed dependence of the obliquity on orbital separation, planet mass, and stellar structure suggests that in some cases, tidal dissipation damps a star’s obliquity within its main-sequence lifetime. The situation is not as clear for stars with smaller or wider-orbiting planets. Although the earliest measurements of such systems tended to find low obliquities, some glaring exceptions are now known in which the star’s rotation is misaligned with respect to the coplanar orbits of multiple planets. In addition, statistical analyses based on projected rotation velocities and photometric variability have found a broad range of obliquities for F-type stars hosting compact multiple-planet systems. The results suggest it is unsafe to assume that stars and their protoplanetary disks are aligned. Primordial misalignments might be produced by neighboring stars or more complex events that occur during the epoch of planet formation.

Stellar Obliquities in Exoplanetary Systems

The Rossiter-McLaughlin effect occurs during a planet's transit. It provides the main means of measuring the sky-projected spin-orbit angle between a planet's orbital plane, and its host star's equatorial plane. Observing the Rossiter-McLaughlin effect is now a near routine procedure. It is an important element in the orbital characterisation of transiting exoplanets. Measurements of the spin-orbit angle have revealed a surprising diversity, far from the placid, Kantian and Laplacian ideals, whereby planets form, and remain, on orbital planes coincident with their star's equator. This chapter will review a short history of the Rossiter-McLaughlin effect, how it is modelled, and will summarise the current state of the field before describing other uses for a spectroscopic transit, and alternative methods of measuring the spin-orbit angle.

The Rossiter-McLaughlin effect in Exoplanet Research

Probabilistic Forecasting of the Masses and Radii of Other Worlds

By analyzing K2 short-cadence observations, we detect starspots on WASP-85A, the host star of the hot Jupiter WASP-85Ab. The detection of recurring starspot occultation events indicates that the planet's orbit is aligned with the star's rotational axis () and suggests a stellar rotational period of 15.1 ± 0.6 days. The K2 light curve reveals a rotational modulation with a period of 13.6 ± 1.6 days, which is consistent with the period determined from starspots. There are no significant transit-timing variations, and thus no evidence of any additional planet in the system. Given the pronounced rotational modulation, we are only able to place an upper limit of 100 parts per million for any phase-curve modulations and the secondary eclipse.

Starspots on wasp-85

By analysing K2 short-cadence observations we detect starspots on WASP-85A, the host star of the hot Jupiter WASP-85Ab. The detection of recurring starspot occultation events indicates that the planet's orbit is aligned with the star's rotational axis ($\lambda<14^{\circ}$) and suggests a stellar rotational period of $15.1 \pm 0.6$ d. The K2 lightcurve reveals a rotational modulation with a period of $13.6 \pm 1.6$ d, consistent with the period determined from starspots. There are no significant transit-timing variations and thus no evidence of any additional planet in the system. Given the pronounced rotational modulation we are only able to place an upper limit of 100 parts per million for any phase-curve modulations and the secondary eclipse.

Starspots on WASP-85

We gratefully acknowledge the financial support from the Science and Technology Facilities Council (STFC), under grants ST/J001384/1, ST/M001040/1 and ST/M50354X/1.

WASP-157b, a Transiting Hot Jupiter Observed with K2

We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet has a Saturn-like density with a mass of $0.57 \pm 0.10$ M$_{\rm Jup}$ and a radius of $1.06 \pm 0.05$ R$_{\rm Jup}$. We do not detect any rotational or phase-curve modulations, nor the secondary eclipse, with conservative semi-amplitude upper limits of 250 and 20 ppm, respectively.

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Starspots on wasp-85

Starspots on WASP-85

WASP-157b, a Transiting Hot Jupiter Observed with K2

WASP-157b, a Transiting Hot Jupiter Observed with K2