Dependence of Chromospheric Activity upon Age in Main-Sequence Stars: Additional Evidence.

Spectrograms of 10 A/mm dispersion have been obtained of 142 field stars from the catalogue of Str6mgren and Perry for those objects with b - y > 0.325. Mter elimination of known spectroscopic binaries and stars of higher luminosity, a sample of 114 main-sequence stars remains. In this sample seventeen stars showing H and K bright reversals are found, and all but two of these lie close to the lower boundary (zero-age edge) of the distribution in a Ci - (b - y) diagram. This result is taken as evidence in support of the view that chromospheric activity of main-sequence stars decreases with age. In particular, it removes the possibility that stars formed in large clusters differ significantly in respect to their chromospheric properties from those formed in small groups or singly.