COMET
17P HOLMES
The comet was large and diffuse by this date (approximately 2 weeks after the outburst) so the spectrum could not be produced using a slitless setup. It was instead was recorded using a spectrograph design incorporating the Star Analyser 100 grating in a slit based design. This allowed a small slice of the comet to be isolated.
This design was realised in practise using an adjustable slit and a 25mm eyepiece. It is similar to the arrangement used previously. The assembly was mounted on the VC200L with focal reducer (200mm f6.4 nominal) An ATK16IC camera was used.
The slit was centred on the brightest region of the coma and the spectrum recorded (20x 3min exposure). The resolution of the spectrum is limited by the width of the slit (R~40) The dispersion was 17A/pixel
The majority of the light from this object is from scattered sunlight. The raw spectrum was calibrated for wavelength and instrument response using Vega. The result was divided by the library spectrum of a sun like star of spectral class G2v. The result was normalised relative to the smoothed continuum to produce the spectrum shown below.
Some evidence of weak C2 ion emission is evident a few percent above the continuum