Associations of H₂O and CH₃OH masers at milli-arcsec angular resolution in two high-mass YSOs

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: cgoddi@arcetri.astro.it
² INAF, Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Str. 54, 09012 Capoterra (CA), Italy
³ Service d'Astrophysique, DAPNIA/DSM/CEA Saclay, 91191 Gif-sur-Yvette, France

Received: 28 July 2006
Accepted: 10 October 2006

Abstract

Context.While high-angular resolution observations have clarified that water masers originate from shocks associated with protostellar jets, different environments have been proposed in several sources to explain the origin of CH₃OH masers.

Aims.We wish to investigate the nature of the CH₃OH maser birthplace in SFRs and the association between the H₂O and CH₃OH maser emission in the same YSO.

Methods.We have conducted phase-reference VLBI observations of H₂O and CH₃OH masers toward two high-mass SFRs, Sh 2-255 IR and AFGL 5142.

Results.In Sh 2-255 IR water masers are aligned along a direction close to the orientation of the molecular outflow observed on angular scales of 1–10 arcsec, tracing possibly the disk-wind emerging from the disk atmosphere. In AFGL 5142 water masers trace expansion at the base of a protostellar jet, whilst methanol masers are more probably tracing infalling than outflowing gas.

Conclusions.The results for AFGL 5142 suggest that water and methanol masers trace different kinematic structures in the circumstellar gas.