The Horizontal-Branch Stars of the Globular Cluster NGC 6397

Spectroscopic observations at 86 A/mm have been made of a number of blue horizontal-branch stars in the nearby globular cluster NGC 6397. These stars are shown to be metal-deficient by a factor of about 100, and evidence is presented that they are also helium-deficient although by a much smaller factor. Spectroscopic gravities deduced from the hydrogen-line strengths lead to masses of 1.3 Al0 for these stars. The spectra of the horizontal-branch stars in NGC 6397 differ from the spectra of blue halo stars that have been called "horizontal-branch stars." A subdwarf 0 star occurring in the cluster is briefly discussed.