Observations of the 4000 Å break strength in the spectra of elliptical and S0 galaxies

Spectrophotometric observations of the 4000 Å break strength in a large sample of nearby E and S0 galaxies are described. A tight relationship between luminosity and break strength is found, though it is too shallow at the bright end to serve as a useful distance indicator. Correlations are found between the break strength and various metal lines, Balmer lines, and the Greenwich gradient, which demonstrate the sensitivity of the break to both metallicity and composite temperature effects.