Presentation #348.08 in the session “Star Formation”.
Class I methanol masers in star forming regions are generally found in outflows. There, shocks provide the collisional pumping that causes the population inversion necessary for maser action. Being compact and intense sources, class I methanol masers present excellent opportunities to observe high mass star forming regions at high angular resolution. We present an investigation of the intensities of Class I methanol masers toward the high mass star forming region DR21(OH). Our study uses data from three epochs (2001, 2012, 2017); the 2001 results are taken from the literature. All the data were observed with the Very Large Array (VLA). A total of 57 maser spots were found in the 2017 data, with center velocities ranging between -8.5 to +2.5 km s-1. Of interest is that the strongest maser in 2001 becomes the second strongest maser in 2012, whereas the second strongest maser in 2001 becomes the strongest maser in 2012. This shift is substantiated by the 2017 observations. Finally, an additional maser discovered in the 2012 undergoes a 55% drop in brightness between 2012 and 2017; this maser is found 0.5" north of the strongest maser (from 2012) in the field. Our observations suggest that class I methanol masers are variable on long timescales (of the order of 5-10 years).