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标题：OH26.5+0.6: insight into the circumstellar structure of an extreme OH/IR star
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作者：S. Etoka ; P. Diamond
期刊名称：PoS - Proceedings of Science
印刷版ISSN：1824-8039
出版年度：2006
出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The OH/IR stage is important in the life of an evolved star. This short transitional phase towards the proto-planetary stage is a crucial point in the life of an intermediate- or high-mass star. Indeed, the mass-loss rate when a star reaches this stage is at its highest. The resulting circumstellar shell – interface between the central object and the interstellar medium – is a rich environment of dust and molecules. It is at this stage that asymmetries are detected, even in the outermost part of the circumstellar shell where OH radicals are formed. OH26.5+0.6 is an extreme OH/IR star with a mass-loss rate of the order of 5×10−4 M⊙/yr. It is one of the brightest OH maser emitters in our Galaxy and it is suspected of experiencing a superwind which emerged less than 150 years ago. MERLIN OH observations at 18 cm in the 1667, 1665 and 1612-MHz maser line allowed the first combined insight into the geometric and polarimetric structure of the circumstellar material surrounding this object. This work intends to bring a new insight into the structural changes undergone by the circumstellar material of an evolved star when it enters the OH/IR stage.