Insights into High Mass Star Formation from Methanol Maser Observations

Author

Hontas Freeman Farmer, DePaul UniversityFollow

Date of Award

Spring 6-14-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics

First Advisor

Anuj Sarma, Ph.D.

Second Advisor

Susan Fischer, Ph.D.

Third Advisor

W. Robert Matson, Ph.D.

Abstract

We present high angular resolution data on Class I and Class II methanol masers, together with other tracers of star formation like H₂O masers, ultracompact (UC) ionized hydrogen (H II) regions, and 4.5 µm infrared sources, taken from the literature. The aim is to study what these data tell us about the process of high mass star formation; in particular, whether disk-outflow systems are compatible with the morphology exhibited by Class I and Class II methanol masers. Stars form in the dense cores inside molecular clouds, and while the process of the formation of stars like our Sun is reasonably well understood, details of the formation of stars with masses eight times that of our Sun or greater, the so-called high mass stars, remain a mystery. Being compact and bright sources, masers provide an excellent way to observe high mass star forming regions. In particular, Class II methanol masers are found exclusively in high mass star forming regions. Based on the positions of the Class I and II methanol and H₂O masers, UC H II regions and 4.5 µm infrared sources, and the center velocities (v_LSR) of the Class I methanol and H₂O masers, compared to the v_LSR of the Class II methanol masers, we propose three disk-outflow models that may be traced by methanol masers. In all three models, we have located the Class II methanol maser near the protostar, and the Class I methanol maser in the outflow, as is known from observations during the last twenty years. In our first model, the H₂O masers trace the linear extent of the outflow. In our second model, the H₂O masers are located in a circumstellar disk. In our third model, the H₂O masers are located in one or more outflows near the terminating shock where the outflow impacts the ambient interstellar medium. Together, these models reiterate the utility of coordinated high angular resolution observations of high mass star forming regions in maser lines and associated star formation tracers.

Recommended Citation

Farmer, Hontas Freeman, "Insights into High Mass Star Formation from Methanol Maser Observations" (2013). College of Science and Health Theses and Dissertations. 45.
https://via.library.depaul.edu/csh_etd/45