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The H2O maser proper motions of RT Vir and VX Sgr

Published online by Cambridge University Press:  03 August 2017

Jeremy Yates ,
Anita Richards  and
Malcolm Gray
Jeremy Yates
Affiliation:
Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
Anita Richards
Affiliation:
JBO, University of Manchester, Jodrell Bank, Macclesfield, Cheshire, SK11 9DL, UK
Malcolm Gray
Affiliation:
Department of Physics, UMIST, P.O. Box 88, Manchester, M60 1QD, UK

Abstract

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We have measured significant proper motions using the water maser clouds in the outflows from RT Vir (6 epochs) and VX Sgr (2 epochs). In both cases proper motions are measured in the bright emission found perpendicular to the OH emission. This strongly suggests latitude dependent mass-loss with the water masers tracing a dense equatorial outflow and the OH emission tracing a less dense polar outflow. In both cases the rotational velocities are < 1 km s−1 thus ruling out a strongly rotating circumstellar envelope. This suggests the outflow is not shaped by an orbiting companion. In the case of VX Sgr the proper motions are contained in a wedge perpendicular to the measured magnetic field axis, thus strongly suggesting that the magnetic field is helping to shape the mass outflow.

The proper motion results have thrown up a puzzle. For VX Sgr the material is being radially accelerated and material enters the water maser zone at 4 km s−1. This is consistent with the mass loss model of Bowen (1988). However the RT Vir proper motion results show no such radial acceleration. The masers have already received their acceleration before they reach the water maser zone at 3-AU (our numerical models seem to support the small radius). This was probably done in the pulsation zone. The acceleration mechanism is unclear for this source.

Type
Part 2. Stellar Masers
Information
Symposium - International Astronomical Union , Volume 206: Cosmic Masers: From Protostars to Blackholes , 2002 , pp. 298 - 305
Copyright
Copyright © Astronomical Society of the Pacific 2002 

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