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G.L. Villanueva (NASA-Goddard Space Flight Center), M. Kueppers, P. Hartogh (Max-Planck-Institut fur Sonnensystemforschung, Germany)
We have performed a high-resolution spectroscopic chemical survey of molecular species and isotopic ratios in comet C/2004 Q2 (Machholz), 2001 Q4 (NEAT) and 2002 T7 (LINEAR). The measurements were focused on the study of the cyanide chemistry with the detection of HCN, HNC and H13CN, as well as other important molecular species in the cometary coma, i.e. H2CO, CS, CH3OH and CO. Rotational temperatures in the coma were retrieved from the intensity ratio between different methanol lines, and production rates have been estimated from the integrated line intensities. Molecular abundances for comet Q2 and T7 near perihelion are similar to those observed in other comets, while the H2CO abundance relative to water is high. Since CO is partly originated from the photodissociation of H2CO, we also expected an enhancement in the CO production rates. However, our observations show a depletion of CO if compared to other comets, implying that CO is mainly originated from a different depleted source. The study of the isotopic ratios in Q2 revealed that the comet probably formed coevally with the solar system, since the measured [HCN]/[H13CN] is similar to the terrestrial value. Furthermore, the detected isomeric column density ratio of [HNC]/[HCN] in Q2 at 1.2 AU heliocentric distance is particularly high, and could be related to unprocessed interstellar material.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.