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A. Quirrenbach, J. Cooke, D. Mitchell, J. Willis (UCSD), EXPORT Team
We report on the status of an ongoing photometric search for giant extrasolar planets in the open clusters NGC2682, NGC6819, and NGC7789. The goal of this program is the detection of transits of giant planets in close orbits around the main-sequence stars in these clusters. The transits of Jupiter-size planets cause dips in the light curves which are about 1% deep and last about one to a few hours. The recent results from radial-velocity surveys suggest that a few per cent of all Solar-type stars have giant planets with orbital periods of a few days; the probability that such a system has a suitable inclination that leads to eclipses is several per cent. Therefore looking at a few thousand stars should give a few planet detections. We are monitoring about 1000 stars in each of the three clusters with the 1m Nickel Telescope at Lick Observatory, and with the 1m Jacobus Kapteyn Telescope at La Palma; the JKT observations are part of the 1998 / 1999 La Palma International Time Project carried out by the EXPORT team. The most comprehensive data set so far has been obtained on a field in NGC6819, where we have accumulated 857 R-band images over 37 nights. The photometric accuracy achieved with 10-minute exposures is 0.3% or better for about 900 stars. A transiting Jupiter-like planet would thus be easily detectable because it produces a 3\sigma-event in at least three or four successive frames. The detection of two such events in the same star is a robust detection criterion, since it allows the prediction of future eclipses. We present some sample light curves and an analysis of our detection limits from a Monte-Carlo simulation.
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