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Astron. Astrophys. 348, 133-138 (1999)

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Molecular line observations of southern main-sequence stars with dust disks: [FORMULA] Ps A, [FORMULA] Pic, [FORMULA] Eri and HR 4796 A *

Does the low gas content of the [FORMULA] Pic and [FORMULA] Eri disks hint at the presence of planets?

R. Liseau

Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden (rene@astro.su.se)

Received 21 January 1999 / Accepted 10 May 1999


The results of molecular line observations with the 15 m SEST [FORMULA] of southern Vega-excess stars are presented. The stars [FORMULA], [FORMULA] and [FORMULA] were observed in the CO (1-0) and (2-1) lines and [FORMULA] 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 (PDR s) and of molecular excitation in Keplerian disks of gas and dust to analyze these observational results. Among the observed objects, the K2 V star [FORMULA] 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 [FORMULA] is largely devoid of any gas ([FORMULA] less than 10[FORMULA] of the interstellar value), presumably due to consumption during planetary system formation. We propose that [FORMULA] should be a prime candidate for searches for extrasolar planets.

In the [FORMULA] disk, the gas content may be as low, or even lower, as for [FORMULA] which could be taken as indirect support of the suggested existence of a planetary system associated with this star.

Key words: stars: individual: " Eri – stars: formation – stars: evolution – stars: circumstellar matter – stars: planetary systems – radio lines: stars

* Based on observations collected with the Swedish Eso Submillimetre Telescope, Sest, in La Silla, Chile.

Send offprint requests to: R. Liseau

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© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999