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[71.07] Methyl Cyanide (CH₃CN) Observations of W51

A. J. Remijan, S.-Y. Liu, L. E. Snyder (Department of Astronomy, UIUC), C.C. Pei (PMO, China)

W51 is a large star forming region located in the Sagittarius arm about 7 kpc away from the Sun. Since the 1960s it has been a prime target for radio astronomy observations because of the large emission measure and the abundance of molecular absorption lines. We continue this effort by observing W51 at millimeter wavelengths with the BIMA array looking for methyl cyanide (CH₃CN) emission.

Many large molecules have been observed in the region around W51 These large molecular species are found to exist mainly in two compact hot core regions, W51 e1/e2 and W51 IRS 2. Only very recently have attempts been made to observe methyl cyanide in this region. The motivation to observe methyl cyanide is due to the fact that it is an abundant symmetric top molecule which is a good temperature tracer.

From observations of the emission lines, we can get an indication of the excitation temperature of the gas in the region. Derived temperature and column density will put constraints on the physical and chemical models for the hot cores. What we have found is that our observations agree very well with the observations of Zhang, Q. et al. (1998, ApJ, 494, 636) that the cores of each region have a temperature of greater than 100K and a number density greater than 100 cm^-3.

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