ISIS Continuum: what math is used?

[Peter Somogyi]

Dear Christian,

I'm being included in a paper under preparation (along with other AAVSO+ARAS observers), where the author is asking specifically about the instrumental response calibration technique I've used in ISIS.

I need shortly refer by math language, what did I do when:

(1) used ISIS->Continuum->"Automatic 1"
Looks to me to be a 3rd order polynom. Am I true?
This is my preference for "narrow band" (med - high res.), to avoid suspects of human interventions, and being more independent from poor SNR and tellurics.

(2) ISIS->Continuum->arbitrary mode (x0.1 slide bar - alternative for Filter)
It seems to be spline, however can't find any reference that it really is.
Exact value is less important here, just need to refer to the math anyhow.

Could you please be so kind, to shortly name the mathematical methods you are using here?

Thank you in advance,
Peter

[Christian Buil]

Dear Peter,

For the first question. Yes, the ISIS->Continuum->"Automatic 1 function adjust a 3rd order polynom to the given profile.
The Automatic 2 function fit a 5rd order polynomial.

For the second question. The ISIS->Continuum->arbitrary mode if based on a modified powerfull version of spline (with ponderation). The reference of the used algorithm is: Christian H. Reinsch, Numerische Mathematik 10, 177-183 (1967)

You can download the original paper here: https://pdfs.semanticscholar.org/3d59/0 ... 3d5890.pdf

All the best,

Christian

[Peter Somogyi]

Thank you Christian for this key information (especially the 3rd order polynom), forwarding it to the author!
Peter