We have presented a procedure that allows us to determine the age and mass, and their corresponding errors, in a HR region where only one evolutionary phase is possible (e.g., Main Sequence), considering that their metallicity, effective temperature and surface gravity are known. As a first step, the algorithm interpolates, by means of the stellar metallicity, a set of stellar evolutionary models among other sets of published models at different metallicities, which allows us to work at the appropriate chemical composition. A second interpolation procedure is followed to determine age and mass from the new set of models. A complementary analysis is performed to extend the method to stars in the Overlap Region, where more than one evolutionary phase is compatible with a given temperature and gravity. A MonteCarlo simulation has been applied to evaluate the errors propagated from atmospheric parameters (errors in metallicity are not considered, though they should not significantly affect the results obtained for A type stars). Typical errors in ages are between 10 and 30% -increasing considerably when approaching the ZAMS- and between 7 and 15% in mass.
Some of the most recent sets of stellar evolutionary models are compared with the aid of very accurate data from detached, double lined eclipsing binary systems. Models that consider the overshooting effect on the limits of the convective layers are more compatible with the precise data than the others. In particular, our tests indicate that BFBC and SSMM models are the most realistic. Further work is currently been done to introduce metallicity as a new variable in our test to evolutionary models (Ribas et al., 1997).
The procedure presented here can probably provide sufficiently good ages and masses for Main Sequence B and F type stars, although high rotational velocities -for B stars- and uncertainties in the metallicity determination -for F stars- may considerably affect the results.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998