1 research outputs found
Theoretical stellar models for old galactic clusters
We present new evolutionary stellar models suitable for old Population I
clusters, discussing both the consequences of the most recent improvements in
the input physics and the effect of element diffusion within the stellar
structures. Theoretical cluster isochrones are presented, covering the range of
ages from 1 to 9 Gyr for the four selected choices on the metallicity Z= 0.007,
0.010, 0.015 and 0.020. Theoretical uncertainties on the efficiency of
superadiabatic convection are discussed in some details. Isochrone fitting to
the CM diagrams of the two well observed galactic clusters NGC2420 and M67
indicates that a mixing length parameter alpha = 1.9 appears adequate for
reproducing the observed color of cool giant stars. The problems in matching
theoretical preditions to the observed slope of MS stars are discussed.Comment: 7 pages, 14 postscript figures, accepted for publication on MNRA