AAS 201st Meeting, January, 2003
Session 20. Star Formation I
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[20.16U] High Resolution Observations of Class I Methanol Masers Toward NGC7538

A. Schwartz, Preethi Pratap (MIT Haystack Observatory)

Methanol masers have been detected in galactic molecular clouds and regions of known star formation. They are classified in two categories dependent on their pumping mechanisms and relative positions. Class I methanol masers result from collisional excitation, followed by spontaneous radiative decay. They arise at the interface between outflows and the interstellar medium, separated from centers of star formation. These masers have often been overlooked in traditional, pointed searches since they are offset from compact HII regions and strong infrared sources. In order to detect such maser sites, observations were conducted systematically over the entire molecular cloud. The source, NGC 7538, is a known region of star formation located in the Perseus arm. Observations were made with the 37-meter radio telescope at Haystack Observatory with frequencies of 24, 36, and 44 GHz, as well as with the Very Large Array at 44 GHz. Analysis of the VLA data provided positions, velocities, intensities and widths of the masers. A new maser was identified near infrared source IRS 9. Also, two masers were detected near IRS 11 with velocities of roughly 57 km/s and 53 km/s. These velocities are shifted from the systemic velocity of 56 km/s detected by ammonia emission. These masers may indicate lobes of bipolar outflow created by a very young embedded star. This could imply that class I methanol masers are associated with very early star formation. Data received from the Haystack Antenna will also be presented. A comparison will be made between the line spectra widths and intensities of corresponding offsets at the 36 and 44 GHz frequencies.


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