The composition of comet C/1999H1 (Lee) from radio observations

Details The composition of comet C/1999H1 (Lee) from radio observations The composition of comet C/1999H1 (Lee) from radio observations

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.1703b&link_type=abstract

American Astronomical Society, DPS meeting #31, #17.03

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Scientific paper

We report on coordinated radio spectroscopic observations of comet C/1999H1 (Lee) undertaken from May to September 1999. Some early results were given in Biver et al. (1999, IAU Cir. 7203). The 18-cm lines of the OH radical were monitored at the Nançay radio telescope, providing measurements of the water production rate Q(H_2O) from mid-may to mid-august. For the May-June period, the following average Q(H_2O) were derived: 5.5 10(28) s(-1) (May 19--23); 8. 10(28) s(-1) (May 24--June 3); 1.2 10(29) s(-1) (June 4-13); 1.5 10(29) s(-1) (June 14-25). Observations of parent molecules were made with the Swedish-ESO telescope (SEST), the Caltech Submillimeter Observatory (CSO), the James Clerk Maxwell telescope (JCMT), and the 30-m telescope of the Institut de Radioastromie millimetrique (IRAM). The HCN, HNC, CH_3OH, H_2CO, and CS species were detected through one or several of their rotational transitions. Abundances relative to water are estimated to 0.1% (HCN), 0.012% (HNC), 4% (CH_3OH), 1.3% (H_2CO), and 0.08% (CS). Observations of H_2S and CO yield upper limits of 0.9 % and 5%, respectively. Molecular abundances are within the range of values measured in other comets. When compared to comets C/1995O1 (Hale-Bopp) and C/1996B2 (Hyakutake), comet Lee is enriched in CH_3OH by a factor of ~ 2 and depleted in CO by a factor of ~ 4. The most surprising result is the HNC/HCN mixing ratio of 12%. This value is close to that measured in comet Hale-Bopp near perihelion and twice higher than that inferred in comet Hyakutake. Observations of HNC in comet Hale-Bopp and chemical modelling have suggested that HNC could be the product of coma chemistry. This new measurement in a moderatly active comet should provide further constraints on the origin of HNC in comets.

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