Far Ultraviolet Spectroscopic Explorer observations of CO and H2 emission in comet C/2001 A2 (LINEAR)

Observations of comet C/2001 A2 (LINEAR) were made with the Far Ultraviolet Spectroscopic Explorer beginning 2001 July 12.58 and coinciding with a photometric increase of similar to1.5 mag. Spectra were obtained in the 905-1180 Angstrom range at 0.25 Angstrom spectral resolution using the 30" x 30" aperture. Several new cometary emissions were identified, particularly the (0, 0) bands of the CO Hopfield-Birge systems C-X and B-X at 1088 and 1151 Angstrom, respectively, O I (D-1-D-1) at 1152 Angstrom, and three lines of the H-2 Lyman system at 1071.6, 1118.6, and 1166.8 Angstrom, pumped by solar Lybeta fluorescence. Also detected were O I multiplets at 989, 1027, and 1040 Angstrom and several lines of the H I Lyman series. The rotational envelopes of the CO bands are resolved and appear to consist of both "cold" and "hot" components, the cold component accounting for 70% of the flux and with a rotational temperature of 55 + 5 K. The hot component may be indicative of a CO2 source. The CO bands, H-2 lines, and O I lambda1152 all decreased by a factor of 2 over the 7.5 hr observation. The derived time-averaged production rates are Q(CO) = 1.3 x 10(27) molecules s(-1) and Q(H2O) = 2.1 x 10(29) molecules s(-1). These values may be uncertain by as much as a factor of 2 because of uncertainties in the solar flux and the electron impact contribution to the excitation.