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P.D. Feldman (JHU), H. A. Weaver (JHU/APL), D. Christian (Queen's U), M. R. Combi (U Michigan), V. Krasnopolsky (Catholic U), C. M. Lisse (U Maryland), M. J. Mumma (NASA/GSFC), D. E. Shemansky (USC), S. A. Stern (SWRI)
We report observations of comet C/2001 Q4 (NEAT) with the Far Ultraviolet Spectroscopic Explorer (FUSE) beginning 00:40 UT on 2004 April 24. This was the first moving target observation made by FUSE since the failure of two reaction wheels in December 2001. Spectra were obtained in the 905--1180~Å\ range at 0.3 Å\ spectral resolution using the 30'' \times 30'' aperture and closely resemble the spectra of three comets observed in 2001 and reported previously. The principal features are the (0,0) bands of the CO Birge-Hopfield systems, atomic lines of \ion{O}{1} and \ion{H}{1}, and three lines of the H2 Lyman pumped by solar Lyman-\beta fluorescence. The CO C - X (0,0) band showed a nearly sinusoidal variation over the 27 hr observation interval with a period of 17.0 hr and a peak to minimum ratio of 1.56. The derived average CO production rate is Q({\rm CO}) = 8 \times 1027 molecules s-1 which is about 4% that of H2O based on concurrent HST/STIS observations of OH emission. As in the previous observations, only upper limits are found for emission from \ion{Ar}{1} and N2. A relatively strong feature near 1031.8~Å\ is most likely the H2 Werner (1,1)~Q3 line pumped by solar \ion{O}{6} and \ion{N}{3}, as the corresponding lines in the (1,3) and (1,4) bands are also present. There may be evidence for weak \ion{O}{6} emission at 1031.9~Å, in the wing of the H2 line, and at 1037.6~Å. The roughly two dozen other emissions that were not identified in the earlier spectra are also present in C/2001 Q4 at comparable strength to those in comet C/2001 A2 (LINEAR). As C/2001 A2 had a comparable water production rate to that of C/2001 Q4 at the time of observation, the source(s) of these emissions may be ubiquitous in comets.
This work is based on data obtained by the NASA-CNES-CSA FUSE mission operated by The Johns Hopkins University. Financial support was partly provided by NASA contract NAS5-32985.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.