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

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5. Conclusions

Our main conclusions from this work can be summarized as follows:

  • Sensitive CO (2-1) observations of [FORMULA] with the SEST provided merely an upper limit on the line. We combine these observations with the dust continuum result by Chini et al. (1991), obtained at the same wavelength and with the same telescope, in a model of the [FORMULA] disk. Comparing predicted CO line intensities with the observed upper limits leads to an upper limit on the gas-to-dust mass ratio in the disk of [FORMULA] [FORMULA] 0.1. This implies that at most a few [FORMULA] [FORMULA] of hydrogen gas reside at present in the circumstellar disk of [FORMULA].
  • The derived limiting CO column density ([FORMULA] [FORMULA] cm-2) refers to regions in the disk, where temperatures are significantly higher than those inferred by Vidal-Madjar et al. (1994) and by Jolly et al. (1996) from UV absorption features in the stellar spectrum and which correspond to a CO column [FORMULA] [FORMULA] cm-2. It seems likely, therefore, that this gas is not widespread throughout the disk but confined to a localized region. An additional conclusion is that the available observational evidence does not require any severe CO under-abundance with respect to hydrogen.
  • Very sensitive SEST observations of [FORMULA] in the SiO (v =0, J =2-1) line did not detect the postulated source. We find it most likely that insufficient filling of the 60 [FORMULA] telescope beam is responsible for this failure. The testing of the theory of SiO gas production from grain-grain collisions in the disk and, eventually, the mapping of the rotation curve of the [FORMULA] disk will have to await the next generation of millimeter wave interferometers in the southern hemisphere.
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© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998