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J. C. Cook, S. J. Desch, S. Wyckoff (ASU)
Since its discovery, Comet 29P/Schwassmann-Wachmann 1 (hereafter SW1) has been considered unique because it orbits the sun in a nearly circular orbit at 5.7 A.U. and, prior to the discovery of Comet Hale-Bopp, SW1 was the only comet to show unpredictable but persistent cometary activity at that distance. Outbursts occur about 1 to 2 times per year, during which an icy grain halo likely forms around the nucleus and slowly sublimates releasing additional gas and dust (Gunnarsson, 2003). SW1 can brighten 5 to 8 magnitudes over a few nights (Roemer, 1958) and remain bright for several months.
Previous spectra of SW1 have shown the presence of CO+ (ex. Larson, 1980; Cochran \emph{et al.}, 1991) from 3500 to 5500 Å, another trademark unique to SW1. High resolution spectra of SW1 obtained in 1989 (Cochran & Cochran, 1991) show detection of CN and an unidentified line at 3908 Å. Both of these lines have not been observed since then.
Here we report new spectra of SW1 from 3000-7000 Å (\lambda/\Delta \lambda ~750) taken at Kitt Peak from the Bok 90'' telescope using the B & C Spectrograph. The spectra were obtained on several nights in September and October of 2003 and 2004. The comet was active in 2003 while the following year it was nearly quiescent. Yet our spectra show CO+ is present during both observing runs. In addition, we have detected CN during both runs and possibly N2+.
Icy grain halos have been seen with Hale-Bopp and C/2002 T7 (Davies, 1997; Kawakita \emph{et al.}, 2004) at 7~A.U. and 3.5~A.U. from the sun, respectively. Hanner (1981) showed that these halos have a short lifetime once a comet is closer than 2.5~A.U. from the sun. At SW1's distance, such a halo should survive a long time, longer than the time between outbursts. We present results of SW1 spectra taken from 1.4-2.5 \mum (\lambda/\Delta \lambda ~1200) using Gemini North and NIRI spectrograph. During our observations in June 2004, the comet showed signs of recent activity, and a bright antisymmetric coma.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.