2D spectrum to check wavelength of various features

2D spectrum to check wavelength of various features

Postby Hamish Barker » Sat Aug 13, 2022 11:32 pm

I'd like to backcheck the final stacked image file in ISIS for skyglow and telluric lines (useful to check absolute calibration), cosmic hits and cosmetic issues, so it would be useful to have a 2D spectrum image so that when I mouse over it I will see the wavelength and intensity assigned to each pixel.

I can't see such a file in the intermediate files which ISIS makes. Does anyone know if this is already produced?
Hamish Barker
 
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Re: 2D spectrum to check wavelength of various features

Postby Robin Leadbeater » Sun Aug 14, 2022 2:25 pm

Hi Hamish,

That would indeed be useful but the intermediate images are only in pixels.

An alternative could be to run the reduction unchecking the "spectral calibration" box which should produce a 1d spectrum calibrated in pixels (possibly up sampled x2), though I have not tried it.

Alternatively if you display the calibrated spectrum profiles eg @pro etc in VSpec you can read off the bin number corresponding to the wavelength which can be roughly converted to pixels by dividing by 2 (ISIS up samples the bin size relative to pixels x2). This is only approximate though as the bin size is constant across the spectrum, mapped from the non linear pixel/wavelength dispersion relationship.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
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Re: 2D spectrum to check wavelength of various features

Postby Robin Leadbeater » Sun Aug 14, 2022 2:39 pm

Robin Leadbeater wrote:
An alternative could be to run the reduction unchecking the "spectral calibration" box which should produce a 1d spectrum calibrated in pixels (possibly up sampled x2), though I have not tried it.



Just tried it and it appears to work, producing 1D spectrum profiles with the X axis direct in pixels (no up sampling)

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1874
Joined: Mon Sep 26, 2011 4:41 pm

Re: 2D spectrum to check wavelength of various features

Postby Hamish Barker » Sun Aug 14, 2022 8:36 pm

yes, i have previously used switching off the calibration.

what i wanted was to be able to look up a wavelength (which shows an emission), be able to tell which pixel number it should be, and make sure that it's not just a single hot pixel causing it.

ok, seems like the feature doesnt exist. That's ok, just wanted to make sure I wasn't missing something.

i guess I could program the wavelength function into my calculator and use that and a very zoomed in view on a different image program.
Hamish Barker
 
Posts: 211
Joined: Thu Jun 20, 2019 12:11 am


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