A search for planets in the old open cluster NGC 6791 ^*

¹ Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, 8000 Aarhus C, Denmark
² Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, British Columbia V9E 2E7, Canada

Corresponding author: H. Bruntt, bruntt@phys.au.dk

Received: 2 May 2003
Accepted: 31 July 2003

Abstract

We describe the results of a search for transit-like events caused by giant planets occulting stars in the old, metal-rich open cluster NGC 6791 based on BVI-colour photometry from eight nights of observations with the 2.54 m Nordic Optical Telescope. To extract the light curves we have used both PSF photometry (daophot) and the difference imaging technique (isis). We have re-analyzed observations from earlier campaigns to search for multiple transits, determine periods of long-period variables, and detect eclipsing binaries. We confirm 20 known variables and have discovered 22 new low-amplitude variables with amplitudes in the range 7–40 mmag and periods 1–16 days. We have found the primary and secondary eclipses of two eclipsing binaries based on the new and older photometric campaigns. The search for transit-like events has turned up a few single-transit candidates. The transit depths are 10 mmag in both the V and I filters over periods of 1.0–2.5 hours, but future observations are required to see whether identical transit-like events recur in these same stars.