Metal abundance and helium content of the open cluster NGC 7789: Evidence for mass loss

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Interstellar reddening, the ratio [Fe/H], effective temperatures, surface gravities, and masses for twelve ‘clump’ stars at the blue end of the giant branch and for seven non-clump red giant members in NGC 7789 have been determined from existingUBV andDDO photoelectric data. For the metal abundance and helium content of the clump stars we foundZ∼0.01 andY∼0.38, respectively. The masses of the red giants are found to be higher than those of the clump stars. On average, the masses of the clump stars are about half of the turnoff point mass. We conclude that the clump stars could have undergone mass loss before reaching their helium core burning phase of evolution. This conclusion arises from an analysis of the several sources entering our mass determination.