Internal Motion of 6.7-GHz Methanol Masers in H II Region S269

TL;DR

This study measures the internal motion of 6.7-GHz methanol masers in the HII region S269, revealing expansion and velocity gradients that suggest the masers trace a bipolar outflow.

Contribution

First measurement of internal maser motions in S269, providing insights into the dynamics and structure of the region.

Findings

Maser groups show an expansion velocity of ~10 km/s.

Detected velocity gradient in maser distribution.

Support for bipolar outflow hypothesis.

Abstract

We present the first internal motion measurement of the 6.7-GHz methanol maser within S269, a small HII region in the outer Galaxy, which was carried out in 2006 and 2011 using the Japanese VLBI Network (JVN). Several maser groups and weak isolated spots were detected in an area spanning by ~200 mas (1000 AU). Three remarkable maser groups are aligned at a position angle of 80 degree. Two of three maser groups were also detected by a previous observation in 1998, which allowed us to study a long-term position variation of maser spots from 1998 to 2011. The angular separation between the two groups increased ~10 mas, which corresponds to an expansion velocity of ~10 km s^{-1}. Some velocity gradient (~10^{-2} km s^{-1} mas^{-1}) in the overall distribution was found. The internal motion between the maser groups support the hypothesis that the methanol masers in S269 could trace a bipolar outflow.