Gas-to-dust ratio and chemical composition in comet 55P / Tempel-Tuttle

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We carried out spectroscopic observations of comet 55P/Tempel-Tuttle, the parentbody of the Leonid meteor stream, on 1998 January 23 and 24, using a mid-dispersion spectrographin the wavelength ranges 4700-5500Å and 5700-6500Å. We detected species such as C2, NH2 , and[OI] . To characterize the comet, we estimated the gas-production rates of C2 and NH2 relative tothat of H20 and the gas-to-dust ratio based on the Haser model. The dust color was also estimatedby the method of Jewitt & Meech (1986).The gas-production rates were Q(NH2/H20)=0.23%, Q(C2/H20) = O.10%. These values aretypical for the Borrelly class which is characterized by the depletion of C2 molecule relative tothat of the Halley class. Since about 30% of detected comets belong to the Borrelly class, comet55P/Tempel-Tuttele can not be a peculiar comet, at least from spectroscopic point of view.The gas-to-dust ratio was log(Q(H20)/Afp)= 26.7, which means this comet was gas-rich relativeto comet Halley. The dust color was roughly estimated by using continuum windows, andthe dust reddening was 9.69% per 1000Å, which was consistent with other nine comets observedby Jewitt & Meech (1986).It is plausible that comet 55P/Tempel-Tuttle is not an exotic comet at any rate, except thefact that it is the parent body of the Leonid meteor stream.
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