Molecular Line Studies of Circumstellar Envelopes

150 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.This dissertation addresses several problems in the study of the dusty, gaseous envelopes commonly found around highly evolved stars. Most of the objects observed are M or N giants and are typically long-period variables. We also observed some objects with hotter central stars which may be young or forming planetary nebulae.Through a long-term monitoring project, we studied the properties of circumstellar ground rotational state OH masers. We found that for most sources, the variations of the OH masers at 1612, 1665, and 1667 MHz smoothly tracked the stellar variations, indicating that the masers are saturated and radiatively pumped. We obtained extensive monitoring data on the unusual object U Orionis, which has shown non-periodic maser variations and may in transition from one evolutionary stage to another. By carefully measuring the relative phase of variation of maser emission arising from the front and back of the circumstellar object IRC +10011, we were able to determine the linear diameter of its envelope. This was the first statistically significant measurement using this technique.To further investigate the excitations and pumping of circumstellar OH, we undertook a thorough search for OH masers in the two rotational states just above the ground state. We obtained sensitive upper limits on many sources and detected a new 6035 MHz OH maser in the object Vy 2-2. This source is thought to be a young, compact planetary nebula. The masers may reside in the remnant of a red giant envelope.Finally, we studied the chemical composition of circumstellar envelopes and their possible contributions to the make-up of the interstellar medium through a search for the molecules HC(,3)N, HC(,5)N, and CS. We made four new detections of HC(,3)N, one of CS, and a possible new detection of HC(,5)N. We obtained enough data to perform an excitation and abundance analysis of HC(,3)N in the sources IRC +10216 and CIT 6.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD