THE STRUCTURE AND EVOLUTION OF THORNE-ZYTKOW OBJECTS

We construct models of spherically symmetric stars in which a central neutron star core is accreting material from an envelope (Thorne-Zytkow objects or TZOs). Core masses are allowed to grow by accretion from approximately 0.5 to 2.0 M., and envelope masses range from approximately 0 to 30 M.. We find models populating the entire range of both parameters, and a limited range of parameter space in which two distinct types of model can coexist, one where gravitational energy and one where nuclear energy is the dominant source of energy.