Effects of stellar rotation on age determination from Strömgren photometry

The effects of stellar rotation on the photometric derivation of atmospheric parameters, ages and masses of main sequence B7-A4 stars are evaluated.Monte-Carlo simulations, used to generate a sample in themass range 1-5 M with all necessary individual rotational parameters and fundamental quantities, and the corrections on the photometric indices proposed by Collins & Sonneborn (1977), provide an approximate quantification of the differences between true parameters and those obtained with classical procedures in which the effects of stellar rotation on photometric indices are ignored. Mean statistical corrections to the photometric indices related to temperature as a function of (v · sin i) are proposed. The results obtained indicate that stellar main-sequence ages are clearly enhanced by an average 30-50% when rotation is not considered whereas mass changes are, in practice, below the mean error level. We conclude that rotation effects on the photometric indices should be taken into account in general studies of galactic evolution in which young stars are involved.