Charge coupled device (CCD) spectroscopy of comets: Tuttle, Stephan-Oterma, Brooks 2, and Bowell

Spectra of the four comets, Tuttle, Stephan-Oterma, Brooks 2, and Bowell, were taken with a prototype space telescope charge coupled device (CCD) camera using a 500 × 500 Texas Instruments chip. The spectra extended from 5600 to 10,400 Å at a resolution of ∼25 A ̊. The spatial coverage along the slit was 180^{{upwards double arrow}}; its resolution was defined by the seeing (2-3^{{upwards double arrow}}). Both absolute flux scales and spectral albedos were determined with the data reduction procedure which included flat fielding and sky subtraction. Comet Tuttle displayed extensive emissions by NH₂, the red system of CN, and the C₂ Swan bands as well as emissions by the forbidden oxygen lines [OI] ¹D at 6300 and 6364 Å, and the ionic species H₂O⁺. A feature at 6851 Å has been tentatively identified as the 3-0 band of CS⁺. Notable is the absence of the C₂ Phillips bands whose transitions are optimally placed in our spectrum. The much dustier comet, Stephan-Oterma showed emissions by CN, NH₂, and [OI] while only [OI] could be discerned in the noisier Brooks 2 spectrum. The fresh comet Bowell exhibited an unusually extended coma with an albedo times cross section two orders of magnitude larger than the other comets, a very flat albedo spectrum, and no emission features. For Tuttle and Stephan-Oterma, CN and NH₂ column densities using a number of bands were calculated. The CN band intensity ratios show good agreement with theoretical fluorescence models. The spatial profiles for CN and NH₂ were compared to two step Haser model decay calculations. The scale lengths most consistent with the data were compared with values previously reported and with values expected for various photodissociation reactions. Production rates were calculated for CN and NH₂. These should be less model dependent because of the simultaneous collection of spectral and spatial information. The production rate ratios of the parents of CN and NH₂ to the parent of OH are several orders of magnitude smaller than the solar abundance ratios of C/O and N/O.