Astron. Astrophys. 334, 599-605 (1998)

Beryllium abundances in parent stars of extrasolar planets: 16 Cygni A & B and ¹ Cancri^*

R.J. García López ¹ and M.R. Pérez de Taoro <sup>2

1</sup> Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
² Museo de la Ciencia y el Cosmos de Tenerife, E-38200 La Laguna, Tenerife, Spain

Received 20 January 1998 / Accepted 9 March 1998

Abstract

The ⁹ Be II 3131 Å doublet has been observed in the solar-type stars 16 Cyg A & B and in the late G-type star Cnc, to derive their beryllium abundances. 16 Cyg A & B show similar (solar) beryllium abundances while 16 Cyg B, which has been proposed to have a planetary companion of , is known to be depleted in lithium by a factor larger than 6 with respect to 16 Cyg A. Differences in their rotational histories which could induce different rates of internal mixing of material, and the ingestion of a similar planet by 16 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 those of 16 Cyg A, requires a more detailed inspection of the peculiarities of the 16 Cyg system.

For Cnc, which is the coolest known object candidate to harbour a planetary-mass companion ( ), we establish a precise upper limit for its beryllium abundance, showing a strong Be depletion which constrains the available mixing mechanisms. Observations of similar stars without companions are required to assess the potential effects of the planetary companion on the observed depletion. It has been recently claimed that Cnc appears to be a subgiant. If this were the case, the observed strong Li and Be depletions could be explained by a dilution process taking place during its post-main sequence evolution.

Key words: stars: individual: 16 Cyg A,B stars: individual: ae1 Cnc stars: abundances stars: evolution planetary systems

* Based on observations made with the Nordic Optical and William Herschel Telescopes, which are operated on the island of La Palma by the NOT Scientific Association and the Isaac Newton Group, respectively, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Send offprint requests to: R.J. García López, (rgl@ll.iac.es)

© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998

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