The XO Transiting Exoplanet Survey

The XO project aimed at detecting transiting exoplanets around bright stars from the ground using small telescopes. The original configuration of XO (McCullough et al. 2005) has been changed and extended between 2011 and 2012. This chapter describes this second version of the XO project. The instrumental setup consists of three identical units located at different sites, each composed of two lenses equipped with CCD cameras mounted on the same mount. Two strips of the sky covering an area of 520∘2 were observed for twice 9 months. Lightcurves were built for ∼20,000 stars up to magnitude R ≈ 12.5 using a custom-made photometric data reduction pipeline. The photometric precision is around 1–2% for most stars, and the large quantity of data yields a millimagnitude precision when folding the lightcurves on timescales that are relevant to exoplanetary transits. After a search for periodic signals, several hundreds of variable stars and a few tens of transiting planet candidates were identified. Follow-up observations have been carried out to confirm or reject these candidates. Two close-in gas giant planets were found so far, in line with the expected yield.