Grids of stellar models VIII. From 0.4 to 1.0 M circle dot at Z = 0.020 and Z = 0.001, with the MHD equation of state

We present stellar evolutionary models covering the mass range from 0.4 to 1 M. calculated for metallicities Z = 0.020 and 0.001 with the MHD equation of state (Hummer & Mihalas 1988; Mihalas et al. 1988; Dappen et al. 1988). A parallel calculation using the OPAL (Rogers et al. 1996) equation of sta te has been made to demonstrate the adequacy of the MHD equation of state i n the range of 1.0 to 0.8 M. (the lower end of the OPAL tables). Below, dow n to 0.4 M., we have justified the use of the MI-ID equation of state by th eoretical arguments and the findings of Chabrier & Baraffe (1997). We use the radiative opacities by Iglesias & Rogers (1996), completed with the atomic and molecular opacities by Alexander & Fergusson (1994). We foll ow the evolution from the Hayashi fully convective configuration up to the red giant tip for the most massive stars, and up to an age of 20 Gyr for th e less massive ones. We compare our solar-metallicity models with recent mo dels computed by other groups and with observations. The present stellar models complete the set of grids computed with the same up-to-date input physics by the Geneva group (Z = 0.020 and 0.001, Schalle r et al. 1992; Bernasconi 1996, and Charbonnel et al. 1996; Z = 0.008, Scha erer et al. 1992; Z = 0.004, Charbonnel et al. 1993; Z = 0.040, Schaerer et al. 1993; Z = 0.10, Mowlavi et al. 1998; enhanced mass loss rate evolution ary tracks, Meynet et al. 1994).