Hi David,
Thank you for your reply.
No, I have left the data of NGC2903 as is,I will return to it and do a subtraction. You are right though the much stronger lines are from my sky background and I used the sodium D (5896A) to match up with the sodium in the A class star,or am I wrong in doing this? I feel a lot happier now though that I have got the calibration nearly right if there is indeed a redshift 🙂
Regards
Alun