The XO Project: Searching for Transiting Extrasolar Planet Candidates

The XO project’s first objective is to find hot Jupiters transiting bright stars (i.e., V<12) by precision differential photometry. Two XO cameras have been operating since 2003 September on the 10,000 foot Haleakala summit on Maui. Each XO camera consists of a 200 mm f/1.8 lens coupled to a 1024 × 1024 pixel, thinned CCD operated by drift‐scanning. In its first year of routine operation, XO has observed 6.6% of the sky within six 7° wide strips scanned from 0° to +63° of declination and centered at R.A. = 0, 4, 8, 12, 16, and 20 hr. Autonomously operating, XO records 1 billion pixels per clear night, calibrates them photometrically and astrometrically, performs aperture photometry, archives the pixel data, and transmits the photometric data to the Space Telescope Science Institute for further analysis. From the first year of operation, the resulting database consists of photometry of ∼100,000 stars at more than 1000 epochs per star, with differential photometric precision better than 1% per epoch. Analysis of the light curves of those stars produces transiting‐planet candidates requiring detailed follow‐up, described elsewhere, culminating in spectroscopy to measure radial velocity variation in order to differentiate genuine planets from the more numerous impostors, primarily eclipsing binary and multiple stars.