SMR STARS, STRONG-CN STARS, AND R-STARS

The strong-CN stars (including the SMR stars) and the R-type carbon st ars are similar in that they occupy nearly the same part of the H-R di agram, in that their distribution in the medium-thick disk is similar, and in having about the same proportion of binary systems as are foun d in ordinary G and K giants. The spectra of both groups are alike in lacking enhancement of the s-process elements. The major difference be tween them is that at least most of the strong-CN stars are metal rich , while the R stars have nearly solar abundances of the common metals. This suggests the possibility that a few of the strong-CN stars are n ot SMR stars, but may be marginal R stars.