Extrasolar planets and brown dwarfs around A-F type stars - IV. A candidate brown dwarf around the A9V pulsating star HD180777

We present here the detection of a brown dwarf orbiting the A9V star HD 180777. The radial velocity measurements, obtained with the ELODIE echelle spectrograph at the Haute-Provence Observatory, show a main variation with a period of 28.4 days. Assuming a primary mass of 1.7 M-circle dot, the best Keplerian fit to the data leads to a minimum mass of 25 M-Jup for the companion ( the true mass could be significantly higher). We also show that, after subtraction of the Keplerian solution from the radial velocity measurements, the residual radial velocities are related to phenomena intrinsic to the star, namely pulsations with typical periods of gamma Dor stars. These results show that in some cases, it is possible to disentangle radial velocity variations due to a low mass companion from variations intrinsic to the observed star.