Improving transit characterisation with Gaussian process modelling of stellar variability

Abstract

New photometric space missions to detect and characterise transiting exoplanets are focusing on bright stars to obtain high cadence, high signal-to-noise light curves. Since these missions will be sensitive to stellar oscillations and granulation even for dwarf stars, they will be limited by stellar variability. We tested the performance of Gaussian process (GP) regression on the characterisation of transiting planets, and in particular to determine how many components of variability are necessary to describe high cadence, high signal-to-noise light curves expected from CHEOPS and PLATO. We found that the best GP stellar variability model contains four to five variability components: one stellar oscillation component, two to four granulation components, and/or one rotational modulation component. This high number of components is in contrast with the one-component GP model (1GP) commonly used in the literature for transit characterisation. Therefore, we compared the performance of the best multi-component GP model with the 1GP model in the derivation of transit parameters of simulated transits. We found that for Jupiter- and Neptune-size planets the best multi-component GP model is slightly better than the 1GP model, and much better than the non-GP model that gives biased results. For Earth-size planets, the 1GP model fails to retrieve the transit because it is a poor description of stellar activity. The non-GP model gives some biased results and the best multi-component GP is capable of retrieving the correct transit model parameters. We conclude that when characterising transiting exoplanets with high signal-to-noise ratios and high cadence light curves, we need models that couple the description of stellar variability with the transits analysis, like GPs. Moreover, for Earth-like exoplanets a better description of stellar variability improves the planetary characterisation.

13 pages, 5 figures, 11 tables accepted for publication in A&A

References in corpus (11)

• The Transiting Exoplanet Survey Satellite
• The connection between stellar granulation and oscillation as seen by the Kepler mission
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• Precise time-series photometry for the Kepler-2.0 mission
• Large eccentricity, low mutual inclination: the three-dimensional architecture of a hierarchical system of giant planets
• Accurate p-mode measurements of the G0V metal-rich CoRoT target HD 52265
• Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler
• WASP-10b: a 3M_J, gas-giant planet transiting a late-type K star
• Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star
• Revisiting the transits of CoRoT-7b at a lower activity level
• The Sun-like activity of the solar twin 18 Scorpii