VLBI Observations of OH stars: S Persei |
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| Institution: | 1. Department of Physics, University of Bristol, Tyndall Ave, Bristol, BS8 1TL, UK;2. JIVE, Postbus 2, 7990 AA Dwingeloo, The Netherlands;3. NRAL, Jodrell Bank, Macclesfield, Cheshire, SK11 9DL, UK;4. Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA;5. Department of Physics and Astronomy, University of Wales, Cardiff, CF2 3YB, UK;1. Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, 84/32 Profsoyuznaya st., Moscow, GSP-7, 117997, Russia;2. Astronomical Observatory, Institute for Natural Sciences and Mathematics, Ural Federal University, 19 Mira Street, Ekaterinburg 620002, Russia;3. Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;4. Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58090, Mexico;1. Service d’imagerie médicale, hôpital Fattouma-Bourguiba, Monastir, Tunisie;2. Service de chirurgie orthopédique, hôpital Fattouma-Bourguiba, Monastir, Tunisie |
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| Abstract: | The masers in three stars, S Per, OH53.6-0.2 and VXSgr, were observed in the main lines of OH at λ18 cm in March 1997 with a VLBI array consisting of 6 EVN antennas and 3 in the USA. Both S Per and VX Sgr were detected on transatlantic baselines, showing that at least some of the maser spots are very compact with sizes less than around 2 mas. The observations confirm that in S Per there is main line OH emission close to star at a similar distance (≈ 100 AU) as the H2O shell. The most blue-shifted emission comes from the centre of the object suggesting radial amplification of the maser radiation, whilst most of the remainder comes from a thick shell, some 100 AU from the star. This contrasts with the 1612 MHz OH emission that comes from an outer shell some 1000 AU from the star. Estimates of the magnetic fields in the shell from Zeeman pairs in S Per show fields of a few hundred nT. |
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