Abundance sensitive parameters for red giants in globular clusters

Photoelectric VIsub(KC) photometry yields structural parameters for the giant branch in nine clusters. Three features are studied spectroscopically in the 500-6200 A region. The TiO bands are closely correlated with V-1 colour and do not provide an independent abundance criterion. The Mg b lines depend on abundance but lose sensitivity at high metal content, apparently because of the strengthening of the overlapping MgH bands. The Na D lines are adversely affected by interstellar absorption and atmospheric emission. They show a wide scatter at a given colour in 47 Tuc, similar to that found among hotter stars, as well as a strong positive correlation with metal abundance. Several stars lying above the giant branch also show TiO bands, including the RV Tauri variable V17 and the W Virginis star V21 in NGC 6626. (author)