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Variability of masers in circumstellar shells on timescales of decades

Published online by Cambridge University Press:  01 March 2007

D. Engels
Affiliation:
Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany email: dengels@hs.uni-hamburg.de
A. Winnberg
Affiliation:
Onsala Rymdobservatorium, Observatorievägen, S-43992 Onsala,at 1612 MHz Sweden email: anders.winnberg@chalmers.se
J. Brand
Affiliation:
INAF - Istituto di Radioastronomia, Via Gobetti 101, I-40129 Bologna, Italy email: j.brand@ira.inaf.it
F. Jiménez-Esteban
Affiliation:
Observatorio Astronomico Nacional, Apartado 112, E-28803 Alcala de Henares, Spain email: f.jimenez-esteban@oan.es
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Abstract

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Based on a 15–20 year long monitoring program of H2O masers and new observations of OH masers discovered 35 years ago, we studied the variability of maser emission in AGB stars over timescales of decades. The H2O maser features in the semi-regular variable stars RX Boo and SV Peg, and of the Mira stars U Her and R Cas, showed strong fluctuations superposed in case of the Mira stars on regular variations due to the pulsation of the stars. The spatial distribution of the emission regions in RX Boo and U Her showed deviations from spherical symmetry, which remained unchanged over >10 years. We conclude that the spatial asymmetry is determined by the underlying asymmetry of the mass loss process. There is no evidence that mass loss rates or the wind geometry in these stars have varied over the last 20 years. In 2005 we re-detected at 1612 MHz the 114 OH/IR stars discovered before 1978, implying an OH maser lifetime of >2800 years (1σ).

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

References

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