Practical planet prospecting

Abstract

(Abridged) Space missions to search for exo-planets via the transit method, such as COROT, Eddington and Kepler, will need to address problems associated with the automated and efficient detection of planetary transits in light curves affected by a variety of noise sources, including stellar variabilility. Starting from a general purpose maximum likelihood approach we discuss the links between a variety of period and transit finding methods. The natural endpoint of this hierarchy of methods is shown to be a fast, robust and statistically efficient least-squares algorithm based on box-shaped transits. This approach is predicated on the assumption of periodic transits hidden in random noise, usually assumed to be superposed on a flat continuum with regular continuous sampling. We next show how to generalise the transit finding method to the more realistic scenario where complex stellar (micro) variability, irregular sampling and long gaps in the data are all present. Tests of this methodology on simulated Eddington light curves including realistic stellar micro-variability, irregular sampling and data gaps, are used to quantify the performance. In the case where transit durations are short compared to the dominant timescales for stellar variability and data record segments, it is possible to decouple the transit signal from the remainder. We conclude that even with realistic contamination from stellar variability, irregular sampling, and gaps in the data record, it is still possible to detect transiting planets with an efficiency close to the idealised theoretical bound. In particular, space missions have the potential to approach the regime of detecting earth-like planets around G2V-type stars.