EPIC 212110888b: a hot Jupiter Spotted by Kepler's K2 Mission in a Prograde Orbit

The K2-ESPRINT Project IV: A Hot Jupiter in a Prograde Orbit with a Possible Stellar Companion

Authors:

Hirano et al

Abstract:

We report on the detection and early characterization of a hot Jupiter in a 3-day orbit around EPIC 212110888, a metal-rich F-type star located in the K2 Cycle 5 field. Our follow-up campaign involves precise radial velocity (RV) measurements and high-contrast imaging using multiple facilities. The absence of a bright nearby source in our high-contrast data suggests that the transit-like signals are not due to light variations from such a contaminant star. Our intensive RV measurements show that EPIC 212110888b has a mass of 1.726±0.085MJ, confirming its status as a planet. We also detect the Rossiter-McLaughlin effect for EPIC 212110888b and show that the system has a good spin-orbit alignment (λ=4+11−10 degrees). High-contrast images obtained by the HiCIAO camera on the Subaru 8.2-m telescope reveal a faint companion candidate (ΔmH=6.19±0.11) at a separation of $\sim 0\farcs36$. Follow-up observations are needed to confirm that the companion candidate is physically associated with EPIC 212110888. EPIC 212110888b appears to be an example of a typical ``hot Jupiter,' albeit one which can be precisely characterized using a combination of K2 photometry and ground-based follow-up.

Stellar Rotating Spots Induced Kepler Transits Time Variation and Kepler Objects of Interest

Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion. II. Application to KOIs

Authors:

Holczer et al

Abstract:

Mazeh, Holczer, and Shporer (2015) have presented an approach that can, in principle, use the derived transit timing variation (TTV) of some transiting planets observed by the Kepler mission to distinguish between prograde and retrograde motion of their orbits with respect to the rotation of their parent stars. The approach utilizes TTVs induced by spot-crossing events that occur when the transiting planet moves across a spot on the stellar surface, by looking for a correlation between the derived TTVs and the stellar brightness derivatives at the corresponding transits, even in data that can not resolve the spot-crossing events themselves. We present here the application of this approach to the Kepler KOIs, identifying nine systems where the photometric spot modulation is large enough and the transit timing accurate enough to allow detection of a TTV-brightness-slope correlation. Excluding KOI-1546, which has been found recently to be a stellar binary, we are left with eight hot-Jupiter systems with high sensitivity to the correlation detection. Five of those eight systems show highly significant prograde motion, including two confirmed planets (KOI-203.01 = Kepler-17b and KOI-217.01 = Kepler-71b) and three planetary candidates (KOI-883.01, KOI-895.01, and KOI-1074.01), while no system displays retrograde motion, consistent with the suggestion that planets orbiting cool stars have prograde motion. All five systems have derived impact parameter ≲0.5, and all systems with an impact parameter in that range show significant correlation, except KOI-3.01 (= Kepler-3b = HAT-P-11b) where the lack of a correlation is explained by its large stellar obliquity. Although our sample is small, these findings hint that stellar spots, or at least the larger ones, have a tendency to be located at a low latitude on the stellar disc, similar to the Sun.

Next Gen Telescopes Required to Determine if ExoMoons Have Prograde or Retrograde Orbits

Next Generation of Telescopes or Dynamics Required to Determine if Exo-Moons have Prograde or Retrograde Orbits

Authors:

Lewis et al

Abstract:

We survey the methods proposed in the literature for detecting moons of extrasolar planets in terms of their ability to distinguish between prograde and retrograde moon orbits, an important tracer of moon formation channel. We find that most moon detection methods, in particular, sensitive methods for detecting moons of transiting planets, cannot observationally distinguishing prograde and retrograde moon orbits. The prograde and retrograde cases can only be distinguished where dynamical evolution of the orbit due to e.g. three body effects is detectable, where one of the two cases is dynamically unstable or where new observational facilities which can implement a technique capable of differentiating the two cases, come on line. In particular, directly imaged planets are promising targets as repeated spectral and photometric measurements, required to determine moon orbit direction, could also be conducted with the primary interest of characterising the planet itself.

Using Host Star Activity to Distinguish Pro & Retrograde Exoplanet Orbits

Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion I. Theory

Authors:

Mazeh et al

Abstract:

Some transiting planets discovered by the Kepler mission display transit timing variations (TTVs) induced by stellar spots that rotate on the visible hemisphere of their parent stars. A TTV can be derived when a planet crosses a spot, modifying the shape of the transit light curve. We present an approach that can, in principle, use the derived TTVs of a planet to distinguish between a prograde and a retrograde planetary motion with respect to the stellar rotation. Assuming a single spot darker than the stellar disc, spot crossing by the planet can induce measured positive (negative) TTV, if the crossing occurs in the first (second) half of the transit. On the other hand, the motion of the spot towards (away from) the center of the stellar visible disc causes the stellar brightness to decrease (increase). Therefore, for a planet with prograde motion, the TTV is positive when the local slope of the stellar flux at the time of transit is negative, and vice versa. Using a simplistic model we show that TTVs induced by spot crossing depend linearly on the local photometric slopes at the transit timings for most cases. The coefficient of this dependence is negative (positive) for prograde (retrograde) motion. One can identify the linear dependence even in transiting systems with Kepler long cadence data, where the obtained light curve cannot resolve individual spot-crossing events, provided the systems display transits with high enough signal-to-noise ratio and relatively large spot-induced modulation. This paper presents the concept in details and discusses its applicability to the Kepler light curves. In coming papers we present analyses of all KOIs and Kepler eclipsing binaries, following the formalism developed here.