Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-05-21
Astron.Astrophys. 407 (2003) 213-224
Astronomy and Astrophysics
Astrophysics
13 pages, 12 figures; accepted by A&A
Scientific paper
10.1051/0004-6361:20030766
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 years. 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 P--L relations, and in this respect the VLBI distances seem an improvement upon the Hipparcos distances.
Diamond Phil J.
Habing Harm J.
Schilizzi Richard T.
van Langevelde Hubrecht Jan
Vlemmings Wouter H. T.
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