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I want to calibrate my reduced spectral image, I am reading Phil Massey's guide, but I got totally stuck!
On page 23 it describes what to do after using the task identify, [ Each time, you will be asked for the corresponding wavelength. You can enter an approximatevalue for this...... etc]
I have no clue what ESTIMATED value to use, I am not familiar with spectroscopy ranges, can anyone help me with this.
By the was here, I am using HeNeAr, not HeAr as used in the guide.
Thanks a lot,

By reduced image, you mean a spectrum, right? The identify task is used to wavelength calibrate the spectrum, for which a lamp is used. The identify task will ask you to identify the lines after which it will calculate the best available fit for the spectrum. To do that use the "m" key to mark the line. I am sure you know that already. Now to decide on what the wavelength of that emission line should be, do the following: 1. Find out the wavelengths of the emission lines for the lamp from the observatory you observed. They should have a database of lines.
2. If they don't have such line database, go to NIST database (google it) and find the strengths and the wavelengths of these lines. Use these wavelength values to identify the lines and do the wavelength calibration. The rest of the procedure should be in the manual. Hope this helps!

[quote:1693a0e9ef="rohit"]By reduced image, you mean a spectrum, right? The identify task is used to wavelength calibrate the spectrum, for which a lamp is used. The identify task will ask you to identify the lines after which it will calculate the best available fit for the spectrum. To do that use the "m" key to mark the line. I am sure you know that already. Now to decide on what the wavelength of that emission line should be, do the following: 1. Find out the wavelengths of the emission lines for the lamp from the observatory you observed. They should have a database of lines.
2. If they don't have such line database, go to NIST database (google it) and find the strengths and the wavelengths of these lines. Use these wavelength values to identify the lines and do the wavelength calibration. The rest of the procedure should be in the manual. Hope this helps![/quote:1693a0e9ef]Thanks a lot for your answer, I got the spectral lines for the 1.5-m R-C Spectrograph here: http://www.ctio.noao.edu/spectrographs/60spec/comps.html
but, it's hard to find similarities between this and the one I have. Is that normal, or I am missing something?

Most often the lamps regrade with time. So it is possible your lines may not match exactly while some lines may show up which are not there. I would still have a look at the NIST or the VALD line database for wavelengths just to compare, they are quite precise.

It is quite normal to spend a lot of time trying to match what you see in an arc spectrum, particularly with data you've not had experience with, and a line chart. I have spent many hours struggling with this. Partly this is because the charts either have a different resolution or the strengths of the lines are different because of a different type of lamp or even when a lamp ages.The task autoidentify was written to try and help but this can fail, primarily when the spectra are quite non-linear (the relation between pixel and wavelength is not linear).The other thing that might be helpful is the URLhttp://www.noao.edu/kpno/specatlas/which lets you make a finding chart the more closely matches the expected range of your spectrum.Another hint, use the identify feature to flip the spectrum because seeing the patterns is harder when the spectrum and the finding chart increase wavelength in opposite directions.Frank Valdes