College of Science and Health Theses and Dissertations

Date of Award

Summer 8-22-2021

Degree Type


Degree Name

Master of Science (MS)



First Advisor

Anuj Sarma, PhD

Second Advisor

Jesus Pando, PhD

Third Advisor

Bernhard Beck-Winchatz, PhD


Class I methanol masers in high mass star forming regions are generally found in outflows. There, shocks provide the collisional pumping that causes the population inversion necessary for maser action. Less is known about Class I methanol masers compared to Class II. A better understanding of Class I masers will allow them to be used as more effective probes of high mass star formation, about which much remains to be learned. In particular, the variability of these masers could potentially be used to investigate activity in high mass star forming regions. I present an investigation of the long-term variability of Class I methanol masers at 44 GHz toward the high mass star forming region DR21(OH). This study uses data from three epochs. Analysis of data observed in 2017 was compared to data observed in 2012, and data taken from the literature in 2001. All the data were observed with the Karl G. Jansky Very Large Array (VLA). A total of 57 maser spots were found in the 2017 data, with center velocities ranging between –8.65 km/s to +2.56 km/s. The masers are arranged in a western and an eastern lobe, with two arcs in each lobe that look like bowshocks, consistent with previous observations. Based on those masers for which data are available for all three epochs, most masers appear to have increased in intensity from 2001 to 2012, then decreased in intensity from 2012 to 2017. Activity in the inner arc of the western lobe appears to be more intense than in the outer arc. I speculate that this may be a consequence of episodic accretion, in which a later accretion event has resulted in ejection of material whose shock reached the inner arc at some point in time after 2001. This thesis establishes that class I methanol masers are variable on long timescales (of the order of 5-10 years).

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