Raudonųjų milžinių Vašingtono fotometrija penkiuose galaktikos kamuoliniuose spiečiuose

Surface metal abundances and effective temperatures of 165 stars in the Galactic globular clusters NGC 288, NGC 6397, NGC 6656., NGC 7078 and NGC 7089 are determined from photoelectric photometry in the Washington system. Mean cluster metal abundances are determined by the tw-o-color diagram (TCD) technique described by Geisler et al. (1991). The resulting metallicities are compared with those derived by the standard giant branches (SGBs) method developed by Geisler and Sarajedini (1999). Although both methods provide metallicities in reasonably good agreement, we find that the SGBs technique yields metallicities in a better agreement with the existing metallicity scales. This is due to the higher metallicity sensitivity of the SGBs method as well as to its lower sensitivity to reddening and photometric errors