CALIBRATION OF THE ALPHA-CENTAURI SYSTEM - METALLICITY AND AGE

The binary system alpha Cen A and B, with its well known parallaxe, its high quality orbit and the reasonable hypothesis of a common origin and age for both components is a useful test of stellar evolution models. We computed evolutionary sequences for 1.085 M(.) and 0.9 M(.) with different values of Z, Y and alpha-( = l/Hp). Adopting luminosities and effective temperatures as derived from the observations, we find Z = 0.04, Y = 0.32, alpha = 1.6 and t = 5 Gyr. We also show that the Z-value derived from evolutionary sequences is very sensitive to the difference in effective temperature between the two components.