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Thanks for your helpful advice. The chart relating error to altitude was very useful Robin. For other readers this is the final link to it.
http://www.astronomie-amateur.fr/Documents%20Spectro/Ref_013.pdf
I must try and find my targets before they get too low in the sky!
I would be interested in tackling some test targets. More help with ISIS would be useful and also the advanced processing too. I can get ISIS to work but I nearly always hit a problem that takes a lot of effort to overcome.
Dear Robin, your method worked. Thanks a lot. The calibration is shifted to the blue by about 1.5 A, so I guess the lesson to learn here is for me to get my spectrum straight and try again. Here are my first spectra with this set up.
i was surprised that ISIS doesn’t recalculate the X position if the spectrum is rotated. I knew the spectrum was not horizontal, it was my first one with the new camera, but assumed that when ISIS measured the tilt it would make the necessary corrections. Thanks again, I am babysitting today but will try your sugestions tomorrow.
Dear Robin, I hope you were up observing and not just working on my problem. I am most grateful for your help and will follow your advice.
Many thanks, John
Dear Robin, I tried checking that the smile correction is working but unfortunately I couldn’t get a result. I am obviously not doing it properly. I will look at your lamp image.
i calibrated the same star in RSpec using a third order polynomial and with an RMS of 0.6539, just by using the Balmer lines. I’d really rather be able to use ISIS as it is so much more powerful and does all the stacking etc.
Thanks for your suggestion. The best calibration I can get with the method you suggested gives an RMS of 19.976 Angstroms. I hope I am using the correct neon line (marked below with an arrow). I have even updated the version of ISIS to the latest one. I have also tried adjusting the pixel scale by increments of 0.02, but no luck.
I didn’t notice this request for spectroscopic monitiring of this object in the spectroscopy section.
Thank you both for your very helpful comments and for the trouble you have taken to produce your data. I will experiment to see how much I can cool the camera. I didn’t realise that ‘warm pixels‘ can still collect useful information and that is reassuring.
Thanks, that makes sense. The DSLR will probably need changing for a CCD when I tackle fainter targets and funds become available. John.
Why are there emission lines for Fe but not C, N, and O which must be present in the star before iron can be formed? If the iron is dredged up from the star’s core wouldn’t C, N and O be dredged up too? The ionisation potential for Fe is similar to the other metals. Surely it can’t be just centrifugal force that brings the Fe to the surface and into the circum-stellar disc in preference to the lighter elements?
Thanks everyone for all your help. Here is the final calibrated spectrum of Merak captured with a full spectrum modified Canon 450D and an Alpy. I was using a 500 mm focal length refractor and used a QHYCCD Polemaster as an electronic finder. It has a huge field of view (11 x 8 deg) but showed stars down to magnitude 8 surprisingly.
Thanks Robin, that’s really useful advice. I do have the Alpy barlow. I changed the pixel size as you suggested and it worked. RMS now 0.12. John
Thanks for the above advice. I’ve also installed Starlight Live to use with a Lodestar to make a sensitive electronic finder.
i took Alun’s advice and bought the secondhand Lodestar. The QHY5 is now attached to the finder and the Lodestar to the guide module on the Alpy.
I lined them up on a radio mast a mile away.
Here’s a write up. All I need is a clear night!
John
