Letter to the Editor

First VLBI mapping of circumstellar SiO maser emission

¹ Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain e-mail: r.soria@oan.es
² Observatorio Astronómico Nacional, Apartado 112, 28803 Alcalá de Henares, Spain
³ American Astronomical Society, 2000 Florida Avenue, NW Suite 400, Washington, DC 20009-1231, USA

Received: 15 December 2004
Accepted: 27 January 2005

Abstract

We report the first VLBI map of the 1–0 maser line of ²⁹SiO in the long-period variable star IRC +10011. We have found that this maser emission is composed of multiple spots distributed in an incomplete ring, suggesting that this maser is also amplified tangentially, as already proposed in other SiO circumstellar masers. We present also VLBI maps for the 7 mm ²⁸SiO and 2 1–0 and the 3 mm 2–1 lines. The ²⁹SiO masing region appears to be located in a layer in between the ²⁸SiO 1–0 and ²⁸SiO 2–1 lines. In addition, we confirm that the 86 GHz maser 2–1 forms in an outer region of the circumstellar envelope compared to the other ²⁸SiO masers studied. Finally, we discuss the possible implications of the observational results on the SiO maser pumping theory.