New molecular species in comet C/1995 O1 (Hale-Bopp) observed with the Caltech Submillimeter Observatory

D.C. Lis, D. Mehringer, D. Benford, M. Gardner, T.G. Phillips (Caltech), D. Bockelée-Morvan, N. Biver, P. Colom, J. Crovisier, E. Gérard, D. Gautier (Obs. Paris), D. Despois (Obs. Bordeaux), H. Rauer (DLR, Berlin)

We present millimeter-wave observations of HNCO, H tex2html_wrap_inline14 CN, HC tex2html_wrap_inline16 N, SO, NH tex2html_wrap_inline18 CHO, and H tex2html_wrap_inline16 O tex2html_wrap_inline22 in comet C/1995 O1 (Hale-Bopp) obtained in February-April 1997 with the Caltech Submillimeter Observatory. HNCO, first detected at the CSO in comet C/1996 B2 (Hyakutake), is securely confirmed in Hale-Bopp via observations of four rotational transitions at 219.798, 241.774, 263.749 and 351.633 GHz. The derived HNCO abundance with respect to HCN is approximately 50%. The 265.886 GHz transition of H tex2html_wrap_inline14 CN is detected and the implied HCN/H tex2html_wrap_inline14 CN abundance ratio is 90 +/- 15, consistent with the solar value. HC tex2html_wrap_inline16 N, SO, and NH tex2html_wrap_inline18 CHO are detected for the first time in a comet. The fractional abundance of HC tex2html_wrap_inline16 N based on observations of three rotational lines at 218.324, 254.700, and 263.792 GHz is 7% with respect to HCN, similar to that measured for CH tex2html_wrap_inline16 CN. Two transitions of SO at 251.826 and 304.078 GHz are detected and the derived fractional abundance relative to water is higher than that implied by previous upper limits in the UV. Observations of the 254.877 GHz transition of NH tex2html_wrap_inline18 CHO imply a fractional abundance of 4% with respect to HCN. H tex2html_wrap_inline16 O tex2html_wrap_inline22 is detected for the first time from the ground through its 364.797 GHz line. In addition, a number of other molecular species are detected, including HNC, OCS, HCO tex2html_wrap_inline22 , CO tex2html_wrap_inline22 , and CN (the last two are first detections in a comet at radio wavelengths). The HCN/HNC abundance ratio is found to be highly variable between December 1996 and April 1997.