Methane in Oort cloud comets
Abstract
We detected CH 4 in eight Oort cloud comets using high-dispersion ( λ/Δ λ∼2×10 4) infrared spectra acquired with CSHELL at NASA's IRTF and NIRSPEC at the W.M. Keck Observatory. The observed comets were C/1995 O1 (Hale-Bopp), C/1996 B2 (Hyakutake), C/1999 H1 (Lee), C/1999 T1 (McNaught-Hartley), C/1999 S4 (LINEAR), C/2000 WM 1 (LINEAR), C/2001 A2 (LINEAR), and 153/P Ikeya-Zhang (C/2002 C1). We detected the R0 and R1 lines of the ν3 vibrational band of CH 4 near 3.3 μm in each comet, with the exception of McNaught-Hartley where only the R0 line was measured. In order to obtain production rates, a fluorescence model has been developed for this band of CH 4. We report g-factors for the R0 and R1 transitions at several rotational temperatures typically found in comet comae and relevant to our observations. Using g-factors appropriate to Trot as determined from HCN, CO and/or H 2O and C 2H 6, CH 4 production rates and mixing ratios are presented. Abundances of CH 4/H 2O are compared among our existing sample of comets, in the context of establishing their place of origin. In addition, CH 4 is compared to native CO, another hypervolatile species, and no correlation is found among the comets observed.
- Publication:
-
Icarus
- Pub Date:
- October 2003
- DOI:
- 10.1016/S0019-1035(03)00201-X
- Bibcode:
- 2003Icar..165..391G