Mapping Observations of 6.7 GHz Methanol Masers with Japanese VLBI Network

TL;DR

This study used the Japanese VLBI Network to observe 13 methanol maser sources in star-forming regions at 6.7 GHz, producing high-resolution images that demonstrate the compact nature of these sources and their suitability for precise astrometry.

Contribution

First VLBI images at 6.7 GHz for seven methanol maser sources, highlighting their compact structure and potential for astrometric applications.

Findings

High detection rate of methanol masers at 6.7 GHz

Most sources have compact structures suitable for VLBI astrometry

Seven sources are imaged at 6.7 GHz for the first time

Abstract

We have observed 13 methanol maser sources associated with massive star-forming regions; W3(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 6.7 GHz using the Japanese VLBI Network (JVN). Twelve of the thirteen sources were detected at our longest baseline of $\sim$50 M$\lambda$, and their images are presented. Seven of them are the first VLBI images at 6.7 GHz. This high detection rate and the small fringe spacing of $\sim$4 milli-arcsecond suggest that most of the methanol maser sources have compact structure. Given this compactness as well as the known properties of long-life and small internal-motion, this methanol maser line is suitable for astrometry with VLBI.