Letter to the Editor

Discovery of two new methanol masers in NGC 7538

Locating of massive protostars

¹ School of Physics, Astronomy and Mathematics, University of Hertfordshire, AL10 9BS Hatfield, UK e-mail: michele@star.herts.ac.uk
² Service d'Astrophysique, DAPNIA/DSM/CEA Saclay, 91191 Gif-sur-Yvette, France
³ AIM, UMR 7158, CEA-CNRS-Université Paris VII, CEA/Saclay, 91191 Gif sur Yvette, France
⁴ Onsala Space Observatory, 439 92 Onsala, Sweden

Received: 12 October 2005
Accepted: 19 January 2006

Abstract

Context.NGC 7538 is known to host a 6.7 and 12.2 GHz methanol maser cospatial with a Ultra Compact (UC)  region, IRS 1.Aims.We report on the serendipitous discovery of two additional 6.7 GHz methanol masers in the same region, not associated with IRS 1.Methods.Interferometry maser positions are compared with recent single-dish and interferometry continuum observations.Results.The positions of the masers agree to high accuracy with the 1.2 mm continuum peak emission in NGC 7538 IRS 9 and NGC 7538 S. This clear association is also confirmed by the positional agreement of the masers with existing high resolution continuum observations at cm and/or mm wavelengths.Conclusions.Making use of the established strong relation between methanol masers and high-mas star formation, we claim that we have accurately positioned the high-mass protostars within the regions where they are detected. The variety of objects hosting a 6.7 GHz methanol maser in NGC 7538 shows that this emission probably traces different evolutionary stages within the protostellar phase.