EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 393/2 Article
Free access article

Issue A&A
Volume 393, Number 2, October II 2002
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20021169



A&A 393, L33-L36 (2002)
DOI: 10.1051/0004-6361:20021169

Letter

Astrometry of the stellar image of U Her amplified by the circumstellar 22 GHz water masers

W. H. T. Vlemmings1, H. J. van Langevelde2 and P. J. Diamond3

1  Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
2  Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
3  Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire, SK11 9DL, England, UK

(Received 10 July 2002 / Accepted 9 August 2002 )

Abstract
The 22 GHz H 2O masers in the circumstellar envelope of the Mira variable star U Her have been observed with MERLIN using a phase referencing technique to determine accurate astrometric positions. The positions were compared with the optical positions obtained with the Hipparcos satellite to an accuracy of 18 mas. The absolute radio position of the brightest H 2O maser spot is found to match the optical position, indicating that this spot is the stellar image amplified by the maser screen in front of it. The occurrence of an amplified image in the 22 GHz maser can be used to accurately determine the positions of the H 2O with respect to the star as well as with respect to the SiO and OH masers. Our observations seem to indicate that the star is not in the centre of the distribution of maser spots, which has been interpreted as a ring.


Key words: masers -- stars: circumstellar matter -- stars: individual: U Her -- stars: AGB and post-AGB -- techniques: interferometric -- astrometry

Offprint request: W. H. T. Vlemmings, vlemming@strw.leidenuniv.nl

SIMBAD Objects



© ESO 2002


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.