Volume 385, Number 1, April I 2002
|Page(s)||L1 - L4|
|Published online||15 April 2002|
Letter to the Editor
Submilliarcsecond-resolution mapping of the 43 GHz SiO maser emission in the bipolar post-AGB nebula OH231.8+4.2*
Observatorio Astronómico Nacional (OAN), Apdo. 1143, 28800 Alcalá de Henares, Spain e-mail: sanchez,bujarrabal,desmurs,j.alcolea,firstname.lastname@example.org
2 Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, 4800 Oak Grove Dr., Pasadena, CA 91109 e-mail: email@example.com
Corresponding author: C. Sánchez Contreras, firstname.lastname@example.org
Accepted: 11 February 2002
We present ~0.3 milliarcsec-resolution maps of the SiO (, ) maser emission in the bipolar post-AGB nebula obtained with the Very Long Baseline Array. These observations have provided for the first time the structure and kinematics of the close stellar environment in a proto-Planetary Nebula. Our observations reveal the SiO maser emission arising in several bright spots of less than ~1013 cm in size forming a structure elongated in the direction perpendicular to the symmetry axis of the nebula. Such a distribution is consistent with an equatorial torus with a radius of ~6 AU around the central star. A complex velocity gradient is found along the torus, which suggests rotation and infall of material towards the star. The rotation and infalling velocities deduced are of the same order and range between ~7 and ~10 km s-1. From our data, we estimate the mass of the SiO torus and the central star, as well as a stringent upper limit to the present stellar mass-loss rate.
Key words: masers / stars: AGB and post-AGB / stars: mass-loss / circumstellar matter / stars: individual: OH231.8+4.2 / stars: variables: general
© ESO, 2002
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