Milliarcsecond structure and variability of methanol maser emission in three high-mass protostars

TL;DR

This study investigates the milliarcsecond-scale structure and variability of 6.7 GHz methanol masers in three high-mass protostars, revealing stable morphologies over 7-15 years and insights into their physical conditions.

Contribution

It provides detailed VLBI imaging and variability analysis of methanol masers in three high-mass star-forming regions, highlighting structural stability and potential pumping mechanism changes.

Findings

Masers form stable groups of cloudlets with linear or arched structures.

Cloudlet sizes are approximately 3.5 milliarcseconds.

Source morphologies remain stable over 7-15 years.

Abstract

{The variability study of 6.7\,GHz methanol masers has become a useful way to improve our understanding of the physical conditions in high-mass star-forming regions.} {Based on the single-dish monitoring using the Irbene telescopes, we selected three sources with close sky positions.} {We imaged them using the European Very Long Baseline Interferometer Network and searched available data on VLBI archives to follow detailed changes in their structures and single maser spot variability.} {All three targets show a few groups of maser cloudlets of a typical size of 3.5\,mas and the majority of them show linear or arched structures with velocity gradients of order 0.22\kms\,mas$^{-1}$. The cloudlets and overall source morphologies are remarkably stable on time scales of 7-15\,yr supporting a scenario of variability due to changes in the maser pumping rate.}