Atmospheric telluric lines on ISIS
Posted: Wed Sep 21, 2022 5:14 pm
Hello.
I am still fighting to fully understand how to use ISIS. I found another problem.
After processing the spectrum, i get the telluric lines at the red part of the spectrum as emision lines, obviously wrong.
In the next image, the blue filter, processed with ISIS shows some of those lines. On the other hand, the same one processed with Demetra -green spectrum- does not. It seems Demetra is doing a better job. I found out that the aparition of those lines depends on how the instrumental response is built.
In Demetra, in the "Instrumental response builder", there is the option to tick or not the button "Atmospheric lines". I always leave it ticked ON, as then, when the reponse line is fitted, the area of the instrumental response where the atmospheric lines is will stay flat. While if i untick it OFF, that line shows waves and the resulting spectrum will result with atmospheric lines on emission. See the next attached image. The inset shows how the instrumental response, at the red end of the spectrum, will look if "Atmospheric lines" is not ticked. I did not find how to do this same and simple procedure with ISIS, while Demetra makes it very simple.
Building the instrumental response with ISIS, if the curve is properly fitted, the atmospheric lines area is not correct. With the following curve the final spectrum will show those atmospheric emissions. While to fit the curve in the atmospheric area correctly, the rest of the curve will be poorly fitted. I already tried many fittings to arrive at a good final result but i did not manage to achieve it.
I found a workaround, though. I just build the response with Demetra and afterwards i use this response in ISIS, instead of building it with ISIS directly.
Anyway i would like to do all with ISIS directly, but i did not find out how. I am probably missing a step here.
Any advice would be most welcome.
ISIS learning curve is very very steep indeed!
I am still fighting to fully understand how to use ISIS. I found another problem.
After processing the spectrum, i get the telluric lines at the red part of the spectrum as emision lines, obviously wrong.
In the next image, the blue filter, processed with ISIS shows some of those lines. On the other hand, the same one processed with Demetra -green spectrum- does not. It seems Demetra is doing a better job. I found out that the aparition of those lines depends on how the instrumental response is built.
In Demetra, in the "Instrumental response builder", there is the option to tick or not the button "Atmospheric lines". I always leave it ticked ON, as then, when the reponse line is fitted, the area of the instrumental response where the atmospheric lines is will stay flat. While if i untick it OFF, that line shows waves and the resulting spectrum will result with atmospheric lines on emission. See the next attached image. The inset shows how the instrumental response, at the red end of the spectrum, will look if "Atmospheric lines" is not ticked. I did not find how to do this same and simple procedure with ISIS, while Demetra makes it very simple.
Building the instrumental response with ISIS, if the curve is properly fitted, the atmospheric lines area is not correct. With the following curve the final spectrum will show those atmospheric emissions. While to fit the curve in the atmospheric area correctly, the rest of the curve will be poorly fitted. I already tried many fittings to arrive at a good final result but i did not manage to achieve it.
I found a workaround, though. I just build the response with Demetra and afterwards i use this response in ISIS, instead of building it with ISIS directly.
Anyway i would like to do all with ISIS directly, but i did not find out how. I am probably missing a step here.
Any advice would be most welcome.
ISIS learning curve is very very steep indeed!