Mapping Observations of 6.7GHz Methanol Masers with the Japanese VLBI Network

Abstract We have observed 13 methanol maser sources associated with massive star-forming regions: W 3(OH), Mon R2, S 255, W 33A, IRAS 18151 $-$ 1208, G 24.78 $+$ 0.08, G 29.95 $-$ 0.02, IRAS 18556 $+$ 0136, W 48, OH 43.8 $-$ 0.1, ON 1, Cep A, and NGC 7538 at 6.7GHz using the Japanese VLBI Network (JVN). Twelve of the thirteen sources were detected at our longest baseline of $\sim$ 50M $\lambda$ , and their images are presented. Seven of them are the first VLBI images at 6.7GHz. The high detection rate and the small fringe spacing of $\sim$ 4 mas suggest that most of the methanol maser sources have compact structures. Given this compactness as well as the known properties of long life and small internal motion, the methanol maser line is suitable for astrometry with VLBI.