Physics
Scientific paper
Aug 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983phdt.........6r&link_type=abstract
Ph.D. Thesis Massachusetts Univ., Amherst.
Physics
Interstellar Masers, Molecular Excitation, Silicon Oxides, Stellar Envelopes, Acceleration (Physics), Escape, Ground State, Mira Variables, Variable Stars
Scientific paper
The envelopes of Mira variables and VY CMa are modeled as time independent, spherically symmetric, outflowing gas. The excitation of SiO in this environment is studied as it pertains to inversion mechanisms, using the Sobolev formalism. A new mechanism, anisotropic escape, is presented for generating ground state SiO masers, and is shown to produce luminosities comparable to those observed for v 0 masers. A search for ground state maser emission produced only upper limits of T(A) 1K for 41 late type giant stars. This may indicate that there is a lower limit on mass loss rates for maser stars. In the models, excited vibrational state masers are found to have low luminosities. It is shown that suppression of the anisotropic escape mechanism by judicious choice of velocity law can increase the efficiency of the Kwan and Scoville radiative trapping process, and yield maser fluxes comparable to those observed. This may indicate large regions of moderate acceleration in maser star envelopes. Smoothly distributed dust shells are found to make no qualitative changes in earlier models. They do, however, suppress the anisotropic escape process within the shell cavity, resulting in increased photon fluxes from v 0 masers, and decreased fluxes from v = 0 masers.
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