Trigonometric parallaxes of 6.7 GHz methanol masers^*

¹ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [kazi;brunthal;kmenten]@mpifr-bonn.mpg.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: reid@cfa.harvard.edu
³ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands e-mail: langevelde@jive.nl
⁴ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
⁵ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 21008, PR China e-mail: xuye@pmo.ac.cn

Received: 18 August 2009
Accepted: 30 September 2009

Abstract

Aims. Emission from the 6.7 GHz methanol maser transition is very strong, is relatively stable, has small internal motions, and is observed toward numerous massive star-forming regions in the Galaxy. Our goal is to perform high-precision astrometry using this maser transition to obtain accurate distances to their host regions.

Methods. Eight strong masers were observed during five epochs of VLBI observations with the European VLBI Network between 2006 June, and 2008 March.

Results. We report trigonometric parallaxes for five star-forming regions, with accuracies as good as ~22 µas. Distances to these sources are  kpc for ON 1,  kpc for L 1206,  kpc for L 1287,  kpc for NGC 281-W, and  kpc for S 255. The distances and proper motions yield the full space motions of the star-forming regions hosting the masers, and we find that these regions lag circular rotation on average by ~17 km s^-1, a value comparable to those found recently by similar studies.