Standard globular cluster giant branches in the (MSUBI,/V-I/sub/SUB O) plane

CCD photometry in the V, I (Cousins) bandpasses is presented for a large number of giants in eight galactic globular clusters. The (V-I)sub O color of the giant branch accurately ranks clusters in metal abundance, and can accordingly be used to ascertain both metal abundances and abundance dispersions in old stellar populations. A relation is derived that yields the bolometric correction to the I magnitude for red giants as a function of (V-I)sub O color. With this relation, and the assumption of the LDZ distance scale, the bolometric magnitudes of the brightest red giants in the clusters were determined; good agreement is obtained with the predictions of stellar evolution theory for the luminosity of the He core flash.