Astron. Astrophys. Suppl. Ser. 146, 179-215
Long-term OH variability of Miras
S. Etoka1,2 - A.M. Le Squeren3
Send offprint request: S. Etoka,
1 -Torun Center for Astronomy, Nicolaus Copernicus University, PL-87100 Torun, Poland
2 - Observatoire de Meudon, F-92195 Meudon Principal Cedex,
3 - GRAAL Université de Montpellier II, F-34095 Montpellier Cedex,
Received January 7, 1999; accepted July 4, 2000
We present here the results and interpretation of a long-term OH variability
program conducted with the French Nançay Radiotelescope from 1980 to 1995. It
concerns seven Mira stars: R Aql, RS Vir, S CrB, R LMi, RR Aql, U Her and
UX Cyg. This study deals with the three OH maser lines observed in the
Miras at 1612, 1665 and 1667 MHz. These OH variable stars have
periods ranging from 290 to 580 days. The study presents the first insight of
the long-term temporal behaviour of OH integrated flux variations as well as
spectral component variations. The main aims are to determine the
temporal behaviour of the OH maser emission and the longevity and variability
of the spectral components.
We find that the shapes of the OH curve are closer to the IR than the
optical shapes and that the emissions at 1665 and 1667 MHz have a
very similar behaviour while the emission at 1612 MHz behaves differently.
The 1612 MHz emission shows smoother temporal variations and
greater component longevity than the main line emission, leading to the
conclusion that the 1612 MHz emission is coming from an outer part of the
circumstellar shell and is more saturated than the main line emission.
The study also shows the existence of inhomogeneities, especially differences
between the front and back parts of the shell can be seen, and that OH
variability curves undergo long term variations over several cycles.
Key words: masers -- stars: circumstellar matter -- stars: AGB and post-AGB;
variables -- ISM: molecules
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