The Kinematic Nature and Evolution of OH/IR Maser Sources

Abstract

The statistical properties of the expansion velocity (V_e) of OH/IR maser envelopes are studied with the objective of determining the evolution of V_e and the spatial (Z) distribution of the central star in time. From the observational database of 195 OH/IR stars a relation between V_e and Z is found. The dependence of V_e on the pulsation period (P) is also investigated. Assuming that radiation pressure is the mechanism of mass loss and the Interacting Winds model of planetary nebulae formation, we derive the dynamic age of the circumstellar envelope. This is then related to the progenitor mass for OH/IR stars of different periods. We find that unidentified OH/IR stars with periods >1500 days originate from stars of main-sequence masses of 5–10 M_⊙ whereas optical Miras descend from stars of 0.7–1 M_⊙.