Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...285..971b&link_type=abstract
Astronomy and Astrophysics 285, 971-978 (1994)
Astronomy and Astrophysics
Astrophysics
25
Masers, Stars: Asymptotic, Post-Asymptotic Giant Branch (Agb, Post-Agb), Stars: Circumstellar Matter, Stars: Late Type, Radio Lines: Stars
Scientific paper
This is the second paper of a series devoted to the detailed study of the theoretical properties of SiO masers in evolved stars. In the first paper we present the maser model, discussing the numerical noise and general reliability of the calculations. The physical and chemical conditions probably present in the maser region are also discussed in that article. This second paper deals with the theoretical apparent extent of the masers. The numerical treatment of the maser excitation takes into account the non-local radiative interactions between distant points in the maser cloud, and is therefore particularly well adapted to the study of the brightness spatial distribution of the maser emission. The calculations predict the existence of both very compact spots and wider distributions, emitting comparable total fluxes and possibly coexisting in the same objects. The extended features are probably ring-like and have a radius of a few 10^14^ cm. The compact spots can be smaller than or of the order of 10^12^ cm in diameter, and are expected to be distributed in the above wide structure. The variability during the stellar cycle of both components is expected to be different, the compact emission is predicted to present relatively small variations, though the extended emission should vary somewhat more strongly than the stellar IR continuum. These numerical results are in general agreement with the observations, but existing data are scarce and some observational work would still be necessary to confirm the theoretical predictions.
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