Air2vac correction for XShooter standards

[freddavies]

Finally addressing (at least one part of) #941, as the issue has become even more obvious for the UVB arm of XShooter.

Might be worth checking whether any of the other standard files also need this fix...

[codecov-commenter]

Codecov Report

Merging #1633 (1c0944f) into develop (6b2b85c) will increase coverage by 0.00%.
The diff coverage is 50.00%.

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@@           Coverage Diff            @@
##           develop    #1633   +/-   ##
========================================
  Coverage    39.89%   39.89%           
========================================
  Files          190      190           
  Lines        42875    42877    +2     
========================================
+ Hits         17105    17106    +1     
- Misses       25770    25771    +1     

Impacted Files	Coverage Δ
pypeit/core/flux_calib.py	31.92% <50.00%> (+0.06%)	⬆️

[jhennawi]

Hi @freddavies can you please modify the README file at:

~/PypeIt/pypeit/data/standards/xshooter

To explicitly note that the data stored in the files is in air. Also, does the reference say anything about it?

[profxj]

nice catch

[freddavies]

README updated.

Also, does the reference say anything about it?

Unfortunately it does not say anything explicitly, but one can guess it from the fact that they are using the ESO pipeline to reduce the data, which spits out air wavelengths by default. Otherwise the only other evidence is the much better agreement between the model and the (PypeIt-reduced) data in the absorption line cores...