Rotational properties of composite polytrope models

Factional radii of gyration for both the convective envelope and the radiative core have been determined using the composite-polytrope model of Rappaport et al. (1983) which describes low-mass stars by appropriately matched polytropes n(outer) = 3/2 and n(inner) = 3. Radii of gyration computed for ZAMS stars with masses of 0.4-1.2 solar masses are used to obtain ZAMS angular momenta for low-mass rapidly rotating stars in the Pleiades and Alpha Persei clusters. Results indicate that there is little chance of observing single young early G and late F type stars in rapid rotation because of the very short timescales for braking of their thin convective envelopes. (R.R.)