BERYLLIUM ABUNDANCES IN PARENT STARS OF EXTRASOLAR PLANETS - 16-CYGNI-A-AND-B AND RHO(1)-CANCRI

The Be-9 II lambda 3131 Angstrom doublet has been observed in the sola r-type stars 16 Cyg A & B and in the late G-type star rho(1) Cnc, to d erive their beryllium abundances. 16 Cyg A & B show similar (solar) be ryllium abundances while 16 Cyg B, which has been proposed to have a p lanetary companion of similar to 2 M-Jup, is known to be depleted in l ithium by a factor larger than 6 with respect to 16 Cyg A. Differences in their rotational histories which could induce different rates of i nternal mixing of material, and the ingestion of a similar planet by 1 6 Cyg A are discussed as potential explanations. The existence of two other solar-type stars which are candidates to harbour planetary-mass companions and which show lithium and beryllium abundances close to th ose of 16 Cyg A, requires a more detailed inspection of the peculiarit ies of the 16 Cyg system. For rho(1) Cnc, which is the coolest known o bject candidate to harbour a planetary-mass companion (M>0.85 M-Jup), we establish a precise upper limit for its beryllium abundance, showin g a strong Be depletion which constrains the available mixing mechanis ms. Observations of similar stars without companions are required to a ssess the potential effects of the planetary companion on the observed depletion. It has been recently claimed that rho(1) Cnc appears to be a subgiant. If this were the case, the observed strong Li and Be depl etions could be explained by a dilution process taking place during it s post-main sequence evolution.