spectro-aras.com

Hello all,

When the target is rather large (eg galaxy, nebula) exceeding the slit length, one can't directly remove the sky background with Isis.
So i used to record the spectrum of the sky backgound near the target.
Now i have some doubt about processing.
I think there could be two methods :

Method 1 :

- processing the target without removing the background -> spectrum 1
- processing the background images -> spectrum 2
- Arithmetic subtraction spectrum1 - spectrum 2 with Isis
Method 2 :

- getting a master background from the background images
- processing the target images with the master background dark
My question (at last...) : which is the best way to go ?

Thank you in advance for your responses.

Best regards,

Hello Jacques,
The first method makes sense, pretreating the target and closeby sky background, then substrating the target spectrum by the sky background spectrum. Not sure about the second one, as you want to substract the sky spectrum and not its image. With the second one, you also need to verify how Isis is going to scale the dark to the target.
My two cents..
Jean-Philippe

Thank you Jean-Philippe.
For the two cents, you accept Visa card ?