Issue |
A&A
Volume 407, Number 1, August III 2003
|
|
---|---|---|
Page(s) | 213 - 224 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20030766 | |
Published online | 17 November 2003 |
VLBI astrometry of circumstellar OH masers: Proper motions and parallaxes of four AGB stars
1
Department of Astronomy, Cornell University, Ithaca, NY 14853-6801, USA
2
Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
3
Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4
Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire, SK11 9DL, UK
Corresponding author: W. H. T. Vlemmings, wouter@astro.cornell.edu
Received:
20
March
2003
Accepted:
16
May
2003
The main-line OH masers around 4 AGB stars have
been observed with the NRAO Very Long Baseline Array (VLBA) at 8 epochs over a period of 2.5 yrs. Using a phase referencing
technique, the position of the most compact maser spot of each star
was monitored with respect to two extragalactic reference
sources. For U Her and W Hya, we observe the most blue-shifted maser
spot, while for R Cas and S CrB we only detect a compact red-shifted
maser spot. We managed to determine an accurate proper motion and
parallax for U Her, R Cas and S CrB, while additional motion of the
compact blue-shifted maser of W Hya is shown to possibly be related
to the stellar pulsation. The motion and radio position are compared
with the stellar trajectory and absolute optical position determined
by the Hipparcos satellite. For U Her and W Hya, the most
blue-shifted maser is consistent with the amplified stellar
image. The new distances are compared with several published
relations, and in this respect the VLBI distances seem an
improvement upon the Hipparcos distances.
Key words: masers / stars: circumstellar matter / stars: AGB and post-AGB / techniques: interferometric / astrometry
© ESO, 2003
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