A search for molecular gas components in prototypal Vega-excess systems

Details A search for molecular gas components in prototypal Vega-excess systems A search for molecular gas components in prototypal Vega-excess systems

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.277l..25d&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 277, Issue 1, pp. L25-L29.

Astronomy and Astrophysics

Astronomy

35

Circumstellar Matter, Ism: Molecules, Infrared: Stars

Scientific paper

We report the results of a deep search for submillimetre lines of ^12CO around the nearby main-sequence stars Vega (alphaLyr), epsilonEridanus, Fomalhaut (alphaPsA), beta Leo and betaPictoris. Upper limits on CO masses about 10 to 100 times lower than those previously reported have been obtained. If `normal' interstellar medium CO abundances are assumed, the data suggest that the gas:dust mass ratio is reduced by a factor of >~10^3 below that found in molecular clouds. These apparently low values can be explained by photodissociation of CO in the stellar or, in the case of epsilonEri, the interstellar UV radiation field. The predicted CO column densities are similar to our limits if the CO is not replenished. Although the betaPic disc has the highest dust mass, the large grain size results in a relatively low UV extinction to the central star, and so CO photodissociation can readily occur. It has been suggested by others that the CO could be replenished by the occasional infall of comets, and we place an upper limit on the rate of cometary accretion for epsilonEri.

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