RIQ MET-2109 MvdA : Telluric absorption correction for IFU data

[astronomyk]

https://jira.eso.org/browse/MET-2109

For IFU data the telluric correction will have to be done for each spatial element, but can only be derived with molecfit or the classic standard star approach for the position of the (standard or target) star. Is the basic assumption that is being made that the LSF for the telluric correction does not vary across the field-of-view, and if so how valid is this assumption?

@wkausch and @ivh , as you are our resident spectroscopists, are you able to answer Mario's question about spatial-variations in the LSF?

Action Item: https://jira.eso.org/browse/MET-2242

As a major action item, the METIS consortium will look into the expected magnitude of the effect based on the optical model, and if necessary define mitigating measures to be implemented in the pipeline design.

[wkausch]

Actually, no one can answer that at this point. MET-2164 is on a similar topic. We will only see how the LSF will look like when we have real data.... ;-). Before that we cannot know if/how much the LSF is varying over the field-of-view.

[ivh]

No, I cannot answer either. This is a question for Roy & Wolfgang again, I would say.

[wkausch]

I agree.

We could only argue that for the time being a constant LSF is an assumption only. Realistically, the spaxel-to-spaxel variations of the LSF should be small, but that can sum up. As fallback option, molecfit can be applied really individually to every spaxel. But this doesn't help in case a telluric standard star is incorporated. Then we only have one single point in the FoV.

[hugobuddel]

Email from Wolfgang to Wolfgang and Roy:

Dear Roy & Wolfgang,

There's a RIQ from MvA (MET-2109) concerning the variation of the LSF
over the IFU field-of-view. Sure, no one can reliably predict such
variations yet, but are there estimates on that or experiences from
other instruments on that? My first guess would be that the changes will
be smooth and not dramatic, but that's just a gut feeling.

Cheers,
Wolfgang

I don't have anything to add; so far I'm fully trusting others in how to do the telluric absorption correction.

[Rumpelstil]

I would not expect any strong variations across the small (~1 arcsec) field of view of the IFU.

[wkausch]

I propose the following answer:

---

We do not expect strong LSF variations across the field-of-view as it is very small (~1arcsec) and will test that during AIV.

---

[hugobuddel]

I took the liberty to answer with @wkausch answer. Keeping this open because I don't know whether there already is a test for this in the AIV plan

[wkausch]

Hi Hugo, we discussed that topic yesterday. Wolfgang B wanted to ask Alistair on that topic to make sure this assumption is true (or better: in how far that is true)....

[hugobuddel]

Oh sorry, I thought you provided this answer after that discussion. I'll add a comment.

[astronomyk]

Hi @wkausch @Rumpelstil @ivh @hugobuddel
Was there any response from Alastair Glasse?
Currently what I will put in the FDR slide on this topic is our state of knowledge - i.e. we do not expect large variations, and are on the lookout for experiences in this regard on other instruments.

[wkausch]

Not that I know....

[Rumpelstil]

On 13. Nov 2023, at 10:58, Kieran Leschinski ***@***.***> wrote: Hi @wkausch @Rumpelstil @ivh @hugobuddel Was there any response from Alastair Glasse?

No reply, yet, from Alastair. He also didn’t attend the last Thurday morning METIS telecons, thus I couldn’t remind him “in person” Greetings, Wolfgang

…

Currently what I will put in the FDR slide on this topic is our state of knowledge - i.e. we do not expect large variations, and are on the lookout for experiences in this regard on other instruments. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

[hugobuddel]

I don't know how to proceed with this questions about the spatial variation of the LSF. Our Action Item is

As a major action item, the METIS consortium will look into the expected magnitude of the effect based on the optical model, and if necessary define mitigating measures to be implemented in the pipeline design.

We did get some new traces from Alistair, but I don't know how these relate to this issue.

@wkausch do you know how to proceed?

[wkausch]

We recently got new traces for the LSS mode. I don't know whether there are also new ones for the LMS.

I'm just here in vienna to focus on the LSS LSF part. The goal is slightly different, we should show that molecfit can model the LSF (which is a bit of... as it has been shown to work for several instruments already...). My idea is to make simulations of a constant source switch on the atmosphere, apply the rectifying script, collapse the rectified spectrum toa 1d and try to get a good correction with mf, which demonstrates the ability to model the LSF.

I assume you can make a similar approach: make simulations with the LMS, extract 1d spectra at several positions in the FoV and determine the LSF. Then you should see how much the LSF varies.