4. The LRS classification
From Tables 3 and 4 it is seen that only 9, out of 20 Tc-deficient samples and 18, out of 24 Tc-rich ones have a LRS classification. It is shown that (1) more than half Tc-rich stars exhibit a silicate feature, whereas Tc-deficient ones have definitely no silicate feature as already pointed out by Chen & Kwok (1993); (2) most Tc-deficient S stars with a LRS classification show photospheric features which characterize the group S, and some are featureless and belong to group F. Therefore, for more than 700 IRAS associations of S stars listed by Chen et al. (1995), we can tentatively conclude that those in group E are likely to be Tc-rich stars, while candidates of Tc-deficient S stars can be selected from samples in groups S and F.
© European Southern Observatory (ESO) 1998
Online publication: April 20, 1998