SECOND ORDER UV CONTAMINATION IN ASTRONOMICAL SPECTRA

Observations of the planetary nebula Me 2-1 are used to discuss some effects of contamination produced by the second order ultraviolet spectrum in the first order red, longer than approximately 6200 A. It is found that this contamination is present with some instrument set-ups, and that the contaminating lines are displaced in wavelength with respect to the predictions from diffraction theory by an amount which varies slightly for different set-ups. From the theoretical and empirical analysis of these displacements, it is concluded that the shift in wavelength is due to the presence of chromatic difference in magnification in spectrograph cameras including any transmission element, as is the case in teh semi-solid Schmidt-Cassegrain cameras used in our observations.