Letter to the Editor Observations of methanol masers in NGC7538: probable detection of a circumstellar disc

We present VLBI observations of 6.7 and 12.2 GHz methanol masers in the star forming region NGC7538. Our results show the existence of two groups of masers. The first group exhibits a linear velocity gradient and forms a line in our VLBI map which is consistent with a rotating disc of masers seen edge-on around a massive star. The second group of masers are blueshifted with respect to the first group and lie in a conical region south of the inferred disc. We argue that these masers probably arise in an outflow emerging approximately perpendicularly to the disc. We find that the maser positions at 6.7 and 12.2 GHz are coincident and those of the second group correspond approximately to the absolute positions of NH3, H2CO and OH masers associated with the radio-continuum and infrared source NGC7538-IRS1.