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Astron. Astrophys. 334, 935-942 (1998)


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High sensitivity search for molecular gas in the [FORMULA] Pic disk *

On the low gas-to-dust mass ratio of the circumstellar disk around [FORMULA] Pic toris

René Liseau and Pawel Artymowicz

Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
(e-mail: rene@astro.su.se; web: http://www.astro.su.se/~rene/;
e-mail: pawel@astro.su.se; web: http://www.astro.su.se/~pawel/)

Received 6 October 1997 / Accepted 4 March 1998

Abstract

We report on high sensitivity observations of the [FORMULA] system in four molecular transitions with the 15 m SEST, tracing carbon, silicon and sulphur bearing species (CO, SiO and CS) and, as such, the gaseous component of the circumstellar disk. The lack of signal in the CO (2-1) line is consistent with an interstellar value of CO/H and a very low column density of hydrogen gas [ [FORMULA] cm-2 ]. The data do not require that CO is severely depleted with respect to hydrogen. Rather, we find that the gas-to-dust mass ratio in the disk is abnormally low, viz. [FORMULA] ([FORMULA] at the [FORMULA] level), implying an upper limit to the mass of hydrogen gas [FORMULA] [FORMULA] [FORMULA] (5 [FORMULA]). Evidently, any nebular disk gas from the formation stage of [FORMULA] has been consumed in planet formation and/or blown out during the early mass loss history of the system. The sensitive search for SiO gas, believed to be presently produced in evaporative grain-grain collisions, gave likewise negative results. From the modeling of the line emission from the [FORMULA] disk we deduce that this non-detection could be explained by insufficient filling of the SEST beam and that the testing of the theory has to await the advent of the new generation of millimeter interferometers in the southern hemisphere.

Key words: stars: individual: fi Pic toris – stars: formation – stars: evolution – stars: circumstellar matter – stars: planetary systems – radio lines: stars

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

Send offprint requests to: R. Liseau

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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