Observations of CH in Comets P/Brorsen-Metcalf and P/Halley

A common feature in the visual spectra of comets is the A2Δ - X2π transition of CH at 4314 Å (Δv = 0). This feature is very weak and is easily "lost" in the continuum or noise. However, the oscillator strength is very small, so even a weak feature indicates a large amount of CH. Understanding the parent of the CH in the comae of comets is very important for understanding the chemistry of comets and, thus, the early solar nebula. Potential parents for the CH are CH4 or more complex hydrocarbons, including polyoxymethanes (POMs). The ratio of CH4 to H2O is indicative of possible sites of formation of the comets. Past observations of comets have shown that the CH is present in the coma. However, because of the intrinsic weakness of the feature and the ease of photodissociating CH, the distribution of the CH in the coma has only been traced in the inner coma, where the fall-off is still p-1, where p is the impact parameter. The first data sets tracing the distribution of CH to large distances from the nucleus in two comets is presented. Some preliminary models are presented pertaining to the parent of the CH.