Abstract
CH giants, with Mv around -1 to 0.5 (refs 1,2), are stars which have the following well-known properties: (1) weak lines of iron-group elements2, (2) rich in carbon, exceptionally strong features of CH, moderately strong (depending on the surface temperature) C2 and CN (refs 1,2), (3) relatively strong lines of the s-process elements (especially Sr and Ba), and (4) halo-population kinematics3,4. CH giants are also found in globular clusters: ω Cen, M22 and M55 (refs, 5,6). Later, Bond7 discovered a group of field stars, called CH subgiants, with Mv from 2 to 4 (ref. 8). The four properties listed above are shared by the CH subgiants. We discuss here a possible CH subdwarf. First, we establish its subdwarf nature through photometry and proper motion, then we discuss spectroscopic data. Finally, we review how CH giants, CH subgiants and the CH subdwarf constitute a sequence of increasingly challenging cases for the stellar evolution theory. © 1982 Nature Publishing Group.