Milliarcsecond structure of water maser emission in two young high-mass stellar objects associated with methanol masers^⋆

¹ Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toruń, Poland
e-mail: annan@astro.uni.torun.pl; msz@astro.uni.torun.pl
² Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: langevelde@jive.nl
³ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

Received: 9 February 2012
Accepted: 12 March 2012

Abstract

Context. The 22.2 GHz water masers are often associated with the 6.7 GHz methanol masers but owing to the different excitation conditions they likely probe independent spatial and kinematic regions around the powering young massive star.

Aims. We compared the emission of these two maser species on milliarcsecond scales to determine in which structures the masers arise and to test a disc-outflow scenario where the methanol emission arises in a circumstellar disc while the water emission comes from an outflow.

Methods. We obtained high-angular and spectral resolution 22.2 GHz water maser observations of the two sources G31.581+00.077 and G33.641−00.228 using the EVN.

Results. In both objects the water maser spots form complex and filamentary structures of sizes 18–160 AU. The emission towards the source G31.581 + 00.077 comes from two distinct regions of which one is related to the methanol maser source of ring-like shape. In both targets the main axis of methanol distribution is orthogonal to the water maser distribution. Most of water masers appear to trace shocks on a working surface between an outflow/jet and a dense envelope. Some spots are possibly related to the disc-wind interface which is as close as 100–150 AU to the regions of methanol emission.