AGB STARS - DENSITIES AND FORMATION RATES OBTAINED FROM OH IR STARS/

We determine densities and star formation rates of AGB stars from an a nalysis of OH/LR stars in the solar neighbourhood. The stars are divid ed into three distinct mass ranges corresponding to the precursors of type I, II and III planetary nebulae, according to the Peimbert classi fication scheme. The adopted distance scale is based on the period-lum inosity relationship by Feast et al. (1989). The formation (or death) rates are calculated using stellar evolution models for AGB stars, and are compared with the corresponding rates for planetary nebulae and w hite dwarfs. The results indicate that both surface and volume densiti es of AGB stars are in good agreement with previous determinations in the literature. The formation rates are found to be very sensitive to the evolution time at the AGB, and depend also on the adopted model.