1999A&A...348..133L

The results of molecular line observations with the 15m Sest^* of southern Vega-excess stars are presented. The stars α PsA, ε Eri and HR 4796A were observed in the CO(1-0) and (2-1) lines and β Pic was observed in the vibrational ground state of SiO, in the (2-1) and (5-4) transitions. In spite of considerably more sensitive observations than in previous attempts, none of these systems was detected with the Sest. We use theoretical models of stellar atmospheres, of the structure and chemistry of interface regions (Pdrs) and of molecular excitation in Keplerian disks of gas and dust to analyze these observational results. Among the observed objects, the K2V star εEri appears particularly suitable and the analysis focusses on this system. A disk model with simple geometry is capable of explaining recent dust continuum observations. Applying this model to the associable molecular gas leads to the conclusion that it is most likely that the disk/ring around εEri is largely devoid of any gas (m_gas/m_dust less than 10^–3 of the interstellar value), presumably due to consumption during planetary system formation. We propose that εEri should be a prime candidate for searches for extrasolar planets. In the βPic disk, the gas content may be as low, or even lower, as for εEri which could be taken as indirect support of the suggested existence of a planetary system associated with this star.