THE INFRARED (3.2-3.6 MU-M) SPECTRUM OF COMET P/SWIFT-TUTTLE - DETECTION OF METHANOL AND OTHER ORGANICS

We present an infrared spectrum of comet P/Swift-Tuttle which exhibits broad emission features at 3.4 and 3.52 mu m with fluxes of (5.7 +/- 0.25) x10(-15) and (0.8 +/- 0.14) x10(-15) Wm(12) respectively, but has no pronounced feature near 3.28 mu m. We show that the 3.52-mu m feature and much of the 3.4-mu m emission can be attributed to fluorescence from methanol, but that some other source is required to explain residual emission centred on 3.43 mu m. The derived methanol production rate is (1.6 +/- 0.3) X10(28) molecule s(-1) which implies a ratio of methanol to water of approximately 0.05, a value more typical of dynamically new comets than of periodic comets.