Method
Spectra of Zeta Cas and Z And were collected, the latter was exposed for 240s to avoid saturating the H alpha emission line and then a further set of exposures for 600s were taken in order to show more detail in the continuum and other emission lines. Towards the end of the series taken for 600s the telescope reached the meridian and the lamp image for that set was not taken until after the meridian flip. On the other occasions the lamp image was taken immediately after the end of a capture sequence.
Results
The spectra were processed in ISIS in three different ways.
Balmer lines only
This couldn’t calibrate Zeta Cas so was not suitable for Z And either
Mixed Balmer and lamp lines calibration
Each time the lamp lines for the particular target were used.
Zeta Cas H alpha blue shift 1 A, accurate from H beta onwards towards the UV end.
Z And (600s) H alpha red shift 2 A, gradually increasing so at H delta the red shift was 3.4 A.
Z And (240s) H alpha blue shift 6 A, reducing so at H delta the blue shift was 4.0 A.
In all targets using the mixed method the wavelength errors become more shifted towards the red at shorter wavelengths.
Lamp lines only calibration
Zeta Cas H alpha blue shift 1 A, increasing so at H delta the blue shift was 4.5 A.
Z And (600s) H alpha red shift 0.7, accurate calibration from H beta to H delta. H epsilon was blue shifted by 1.5 A.
Z And (240s) H alpha blue shift 6.0 A, increasing so that at H delta the blue shift was 7.7 A.
So in all the targets calibrated by the lamp lines alone, the wavelength error shifts towards the blue at shorter wavelengths.
I will be very interested to see the result of your Filly Dot experiment. I may have to throw away my calibration module. (I’ll keep it for the flat fields actually).
Cheers, John