Astron. Astrophys. 345, 605-610 (1999)

5. Summary

From the fluxes of atomic fine structure lines observed in the SWS spectra of Ori and Sco, we can deduce the temperature of the emitting regions to be 1230 and 1785 K, respectively. Both stars have similar outflow velocities hence the radii of the emitting gas are about the same, 20 R_*, assuming that both have similar temperature structures in the inner part. This region of the envelope is just inside the dust forming region as seen from interferometry from the radio and infrared (Bester et al. 1991; Skinner et al. 1997). From the mass loss rates, the emitting regions of both stars have density above the critical density to thermalize both [Fe II] and [Si II] lines. In both stars, the source of the UV photons which ionize these observed lines is their chromospheres. In Sco, where the highest ratio of Si [II]/Fe [II] lines is observed, the abundance of Si may be higher than in Ori. We also find that there is contribution from [O I] line fluxes exterior to the emitting region of [Fe II] and [Si II], although most of the fluxes come from this same region.

The masses of gas which cooled via the atomic fine structure lines in both supergiants are very comparable and are of the order of 10^-4 M. The derived mass loss rate of this region, assuming a thermal velocity of 2 km s^-1 is M yr^-1. The gas-to-dust mass ratio of both stars are much higher than observed in AGB stars.

© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999
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