Session 70 - Searching for Other Planetary Systems.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

## [70.08] The Search for Jupiter-Mass Companions to Nearby Stars

A. R. Walker, G. A. H. Walker (U. British Columbia), S. L. S. Yang, A. M. Larson, A. W. Irwin (U. Victoria)

In 1992 we completed a 12 year program on the Canada-France-Hawaii telescope to monitor the radial velocities of 18 dwarf and 13 evolved stars, with captive hydrogen flouride as a wavelength fiducial. None of the dwarfs has shown any reflex motion due to a substellar companion to an upper limit of between 1 and 3 Jupiter masses (\times \sin i) for orbital periods of less than 15 years.

On the other hand, we see low-amplitude periodicities in the radial velocities of 3 evolved stars (\beta Gem [K0 IIIb], \gamma Cep [K1 III-IV], and \delta Sgr [K2.5 IIIa]), with semi-amplitudes, K, of 46, 27, and 85 ms^-1 and periods of 580, 920, and 63 days respectively. Such variation could be explained in terms of orbiting planets of order of a Jupiter mass.

However, rotational modulation, supported by chromospheric activity of a similar period to that of the radial velocity variation in the case of \gamma Cep, is thought to be a more viable explanation. For the case of \beta Gem we find a more marginal chromospheric activity signal at around the period of the radial velocity variations. However, such a rotation period is inconsistent with v \sin i measurements of the star.

In the case of \delta Sgr the reader is referred to the work by Irwin et al. at this meeting.

Our results on the evolved stars are of obvious interest in light of the recent claim by Mayor and Queloz, of a planetary companion to 51 Peg [G2-3 V (IAU Circular No. 6253)], with P \sim 4 days and K \sim 60ms^-1. Although the period is much shorter than for the stars above, it would be useful to exclude the possibility of rotational modulation or intrinsic variability as the source of such a signal.