Unexplained High Order Harmonics in Light Curves of Kepler Planets

High Order Harmonics in Light Curves of Kepler Planets

Authors:

Armstrong et al

Abstract:

The Kepler mission was launched in 2009 and has discovered thousands of planet candidates. In a recent paper, Esteves et al. (2013) found a periodic signal in the light curves of KOI-13 and HAT-P-7, with a frequency triple the orbital frequency of a transiting planet. We found similar harmonics in many systems with a high occurrence rate. At this time, the origins of the signal are not entirely certain.

We look carefully at the possibility of errors being introduced through our data processing routines but conclude that the signal is real. The harmonics on multiples of the orbital frequency are a result of non-sinusoidal periodic signals. We speculate on their origin and generally caution that these harmonics could lead to wrong estimates of planet albedos, beaming mass estimates, and ellipsoidal variations.

Searching for Stellar Companions for Transiting Exoplanet Host Stars

A Lucky Imaging search for stellar companions to transiting planet host stars

Authors:

Wöllert et al

Abstract:

The presence of stellar companions around planet hosting stars influences the architecture of their planetary systems. To find and characterise these companions and determine their orbits is thus an important consideration to understand planet formation and evolution. For transiting systems even unbound field stars are of interest if they are within the photometric aperture of the light curve measurement. Then they contribute a constant flux offset to the transit light curve and bias the derivation of the stellar and planetary parameters if their existence is unknown. Close stellar sources are, however, easily overlooked by common planet surveys due to their limited spatial resolution. We therefore performed high angular resolution imaging of 49 transiting exoplanet hosts to identify unresolved binaries, characterize their spectral type, and determine their separation. The observations were carried out with the Calar Alto 2.2m telescope using the Lucky Imaging camera AstraLux Norte. All targets were imaged in i' and z' passbands. We found new companion candidates to WASP-14 and WASP-58, and we re-observed the stellar companion candidates to CoRoT-2, CoRoT-3, CoRoT-11, HAT-P-7, HAT-P-8, HAT-P-41, KIC 10905746, TrES-2, TrES-4, and WASP-2. We deduce from the stellar density around all sources that two companion candidates out of the targets with the first position measurement (CoRoT-11, HAT-P-41, KIC 10905746, WASP-14 and WASP-58) are probably unbound. In addition, we re-analyse the influence of the sources close to WASP-14 and WASP-58 on the planetary parameters given in the literature and find no significant changes.

HAT-P-7b is in a Near Polar Orbit (and fluffy)

Asteroseismic inference on the spin-orbit misalignment and stellar parameters of HAT-P-7

Authors:

Lund et al

Abstract:

The measurement of obliquities in star-planet systems is of great importance for the understanding of planet system formation and evolution. The bright and well studied HAT-P-7 system is intriguing as several Rossiter-McLaughlin (RM) measurements found a large projected obliquity in this system, but it was so far not possible to determine if the orbit is polar and/or retrograde. The goal of this study is to measure the stellar inclination and hereby the full 3D obliquity of the HAT-P-7 system instead of only the 2D projection as measured by the RM effect. In addition we provide an updated set of stellar parameters for the star. We use the full set of available observations from Kepler spanning Q0-Q17 to produce the power spectrum of HAT-P-7. We extract oscillation mode frequencies via an MCMC peak-bagging routine, and use the results from this to estimate the stellar inclination angle. Combining this with the projected obliquity from RM and the inclination of the orbital plane allows us to determine the stellar obliquity. We use asteroseismology to model the star from the extracted frequencies using two different approaches to the modelling where either the MESA or the GARSTEC stellar evolution codes are adopted. Using our updated asteroseismic modelling we find, i.a., the following stellar parameters for HAT-P-7: M=1.51{+0.04}{-0.05}Msun, $R=2.00{+0.01}{-0.02}Rsun, and age = 2.07{+0.28}{-0.23} Gyr. Our asteroseismic modelling offers a high precision on the stellar parameters, for instance is the uncertainty on age of the order ~11%. For the stellar inclination we estimate i_starless than 36.5 deg., which translates to an obliquity between 83 and 111 deg. We find that the planet HAT-P-7b is likely retrograde in its orbit, and that the orbit is close to being polar. The new parameters for the star gives an updated planetary density of 0.65+-0.03 g cm^{-3}, which is lower than previous estimates.

Superrotation Detected in Four Hot Jupiters

BEER analysis of Kepler and CoRoT light curves: II. Evidence for emission phase shift due to superrotation in four Kepler hot Jupiters

Authors:

Faigler et al

Abstract:

We analyzed the Kepler light curves of four transiting hot-Jupiter systems- KOI-13, HAT-P-7, TrES-2 and Kepler-76, which show BEaming, Ellipsoidal and Reflection (BEER) phase modulations. The mass of the four planets can be estimated from either the beaming or the ellipsoidal amplitude, given the mass and radii of their parent stars. For all four systems, we find that the beaming-based planetary-mass estimate is larger than the mass estimated from the ellipsoidal amplitude, consistent with previous studies for three of these systems- KOI-13, TrES-2 and Kepler-76. We suggest the apparent discrepancy is due to superrotation, first observed for HD 189733b in the infrared. Superrotation of a tidally-locked hot-Jupiter involves an eastward displacement of the planet hot spot from the substellar point, probably due to winds in the planetary atmosphere, an effect that induces an angle shift of the planet reflection/emission phase modulation. In our analysis this angle shift "leaks" into the beaming modulation, artificially increasing its amplitude. Therefore, the mass derived from the beaming amplitude is larger than the real one. We propose a modified BEER model that includes superrotation and provides a photometry-consistent estimate of the planetary mass. Our analysis shows that the new superrotation BEER model fits the data better than a zero phase-shift null model for KOI-13, HAT-P-7, TrES-2 and Kepler-76. The new model mass estimates are in excellent agreement with the planetary masses derived from radial-velocity measurements, available for HAT-P-7, TrES-2 and Kepler-76. This makes the superrotation BEER model a viable tool for estimating the masses of hot-Jupiters from the photometric BEER modulations alone. We conclude that hot-Jupiter superrotation may be a common phenomena that can be detected in the Kepler light curves of planets that show significant BEER phase modulations.