KIC 12557548b: Transit Variations in the Disintegrating Mercury Class ExoPlanet

The Relation between the Transit Depths of KIC 12557548b & the Stellar Rotation Period

Authors:

Croll et al

Abstract:

Kawahara and collaborators analyzed the transits of the candidate disintegrating Mercury-mass planet KIC 12557548b and suggested that the transit depths were correlated with the phase of the stellar rotation. We analyze the transit depths of KIC 12557548b and confirm that there is indeed a robust, statistically significant signal in the transit depths at the rotation period of the spotted host star. This signal is more prominent in the first-half of the Kepler data, and is not due to leakage of the rotating spot signal into our measurement of the transit depths, or due to unocculted starspots. We investigate the suggestion that this signal could be due to an active region on the star, emitting enhanced ultraviolet or X-ray radiation leading to an increased mass loss rate of the planet; we confirm that such a scenario could cause both modulation of the transit depths of KIC 12557548b, and small enough transit-timing variations that they might not be detected in the Kepler data. Our preferred explanation for the fact that the transit depths of KIC 12557548b are modulated with the stellar rotation phase is that the candidate transiting planet is occulting starspots on this highly spotted star; such a scenario could cause transit depth variations as large as have been observed, and cause transit-timing variations small enough that they are arguably consistent with the Kepler data.

Fast Rotating Stars eat Their Short Period Exoplanets

Why is there a Dearth of Close-In Planets around Fast-Rotating stars?

Authors:

Teitler et al

Abstract:

We propose that the reported dearth of Kepler Objects of Interest (KOIs) with orbital periods Porb≲2−3days around stars with rotation periods Prot≲5−10days can be attributed to tidal ingestion of close-in planets by their host stars. We show that the planet distribution in this region of the logPorb−logProt plane is qualitatively reproduced with a model that incorporates tidal interaction and magnetic braking as well as the dependence on the stellar core--envelope coupling timescale. We demonstrate the consistency of this scenario with the inferred break in the Porb distribution of close-in KOIs and point out a potentially testable prediction of this interpretation.

KOI-2700b: An Exoplanet With a Comet-like Tail

KOI-2700b—A PLANET CANDIDATE WITH DUSTY EFFLUENTS ON A 22 hr ORBIT

Authors:

Rappaport et al

Abstract:

Kepler planet candidate KOI-2700b (KIC 8639908b), with an orbital period of 21.84 hr, exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents, and reminiscent of KIC 1255b. The host star has T eff = 4435 K, M sime 0.63 M ☉, and R sime 0.57 R ☉, comparable to the parameters ascribed to KIC 12557548. The transit egress can be followed for ~25% of the orbital period and, if interpreted as extinction from a dusty comet-like tail, indicates a long lifetime for the dust grains of more than a day. We present a semiphysical model for the dust tail attenuation and fit for the physical parameters contained in that expression. The transit is not sufficiently deep to allow for a study of the transit-to-transit variations, as is the case for KIC 1255b; however, it is clear that the transit depth is slowly monotonically decreasing by a factor of ~2 over the duration of the Kepler mission. We infer a mass-loss rate in dust from the planet of ~2 lunar masses per Gyr. The existence of a second star hosting a planet with a dusty comet-like tail would help to show that such objects may be more common and less exotic than originally thought. According to current models, only quite small planets with Mp lsim 0.03 M ⊕ are likely to release a detectable quantity of dust. Thus, any "normal-looking" transit that is inferred to arise from a rocky planet of radius greater than ~1/2 R ⊕ should not exhibit any hint of a dusty tail. Conversely, if one detects an asymmetric transit due to a dusty tail, then it will be very difficult to detect the hard body of the planet within the transit because, by necessity, the planet must be quite small (i.e., lsim 0.3 R ⊕).