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D. A. Caldwell (NRC/NASA Ames Research Center), J. M. Jenkins (SETI Institute), W. J. Borucki, D. G. Koch (NASA Ames Research Center), Kepler Mission Team
The Discovery-class {\em Kepler Mission} will monitor 100,000 stars for four years to detect and characterize terrestrial and larger planets in or near the habitable zone using transit photometry. We present a summary of the data acquisition and processing routines planned for {\em Kepler} and demonstrate their ability to achieve differential photometric precision of 10-5 on timescales of several hours. The data pipeline begins with large--format CCD images read out every three seconds. A cosmic ray rejection filter is applied and the images are binned in spacecraft memory to a nominal 15 minutes. Star aperture and calibration pixels are downlinked from the spacecraft. The image sections are corrected for non-linearity, bias, and smear resulting from shutterless operation. Aperture photometry is then performed on the stars using optimally weighted pixels to minimize the effects of image motion and point spread function changes. Three month time series for each star are normalized by an ensemble of stable stars taken from the same CCD quadrant. Slowly varying systematic errors are removed by decorrelating stellar light curves. The observation noise for each star is characterized and a matched filter detection algorithm is used to detect transits. Additional photometry will be carried out on the light curves to detect reflected light from giant planets, stellar variability modes, etc. An end-to-end laboratory simulation demonstrated the ability of these algorithms to achieve the photometric precision needed to detect Earth-sized transits under realistic observing conditions. Total shot + instrument noise levels on a 6.5 hour timescale were below 1.7 \times 10-5 for a mv = 12 star in a long duration test, demonstrating that SNRs of 4.6 without stellar variability (4.0 with stellar variability) are achievable for Earth--size transits of 9\rm th to 12\rm th magnitude stars.
This work was supported in part by NASA's Discovery Program.
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