N2+ and CO+ in comets 122P/1995 S1 (deVico) and C/1995 O1 (Hale-Bopp)

We observed Comets 122P/1995S1 (deVico) and C/1995O1 (Hale-Bopp) with high spectral resolving power in order to determine the ratio of N-2(+)/CO+ in their comae. While we clearly detected the CO+ in both of these comets, no N-2 was detected in either comet. From these spectra, we derive sensitive upper limits for N-2(+)/CO+. These upper limits are substantially below other reported detections of N-2(+)/CO+ in other comets. We discuss the prior N-2(+) detections and compare them with our observations. The abundance of N-2 in comets is important to our understanding of the condensation of ices in the solar nebula. In addition, N-2 is a tracer of Ar so the study of N-2 allows an understanding of the role of comets for delivering volatiles to the terrestrial planets. It appears that many, if not most, comets are depleted in N-2 and it will be necessary to search for a mechanism for depleting this molecule in order to be consistent with current models of the solar nebula. (C) 2000 Academic Press.