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M. A. DiSanti, D. C. Reuter, M. J. Mumma (NASA-GSFC), N. Dello Russo (CUA @ NASA-GSFC), K. Magee-Sauer (Rowan University), E. L. Gibb (Notre Dame University), B. Bonev (U. Toledo @ NASA-GSFC), W. M. Anderson (CUA @ NASA-GSFC)
In spring 2004 we were fortunate to obtain high signal-to-noise spectra of C/2002 T7 (LINEAR, hereafter C/T7), a long period (Oort cloud) comet with an extremely rich volatile chemistry. We used the facility long-slit echelle spectrometer (CSHELL) at the NASA-IRTF. This instrument operates from ~ 1 – 5.5 \mu m with sufficiently high spectral resolving power ( \nu / \Delta \nu ~ ~~ 2.5 ~ \times ~ 104 ) to isolate individual comet lines. Coupling this with small pixels provides the high (seeing limited) angular resolution required for detailed study of the spatial distribution of cometary emissions. This permits distinguishing native sources from potential extended sources in the coma.
The carbon-oxygen chemistry is an integral part of our overall study of cometary volatiles in the infrared. Here, we apply a fluorescence model for formaldehyde (H2CO) to our C/T7 spectra. The model (Reuter et al. 1989 Ap. J. 341:1045) was originally developed for predicting line-by-line intensities in high resolution spectra, but until now could only be tested by comparison with low-resolution Vega-IKS spectra of 1P/Halley. Now, however, it can be tested against line-by-line intensities acquired at high spectral resolution. Our C/T7 data obtained between UT 2004 May 3 – 9 provide the best opportunity to date to test the model.
Predicted line g-factors are temperature-dependent over the range expected in C/T7 at the time of observation (e.g., ~ 100 -- 150 K), thus we expect to obtain well-constrained measures of rotational temperature and hence accurate production rates of formaldehyde stored as ice in the nucleus. When combined with production rates for native CO and CH3OH, these should test the efficiency of conversion of CO ice through H-atom addition on grain surfaces prior to incorporation into the nucleus. The conversion efficiency appears to be quite high in C/T7, and this may indicate that the pre-cometary ice was exposed to harsher conditions (e.g., higher H-atom densities) compared to other comets in our database.
This work was supported by NASA grants RTOP 344-33-55 and 344-32-98 to M. A. DiSanti.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.