Feature Request: Absolute flux calibration of IGRINS spectra

[gully]

@kfkaplan has developed code for absolute flux calibration of IGRINS. He raised the question of whether muler would be the right destination for it.

[kfkaplan]

Currently I am porting portions of my IGRINS absolute flux calibration code from plotspec to muler and you can see what I am doing in the following PR: #136

For IGRINS absolute flux calibration: it requires throughput estimates, standard star observations, matching synthetic spectra for the standard star (gollum is providing this), and knowing the exposure time ON target for the science and std star exposures The plan is to make it as general as possible for people to use what pieces they need. Sometimes only relative flux calibration is needed and the absolute can be ignored. Some instruments don't have throughput estimates (e.g. HPF which is fiber fed).

Currently i have added in the ability for muler spectra to resample gollum spectra with the method LinResample(). This is to get a synthetic spectrum generated by a stellar atmosphere model matched to a standard star spectrum in muler.

I am working on is slit throughput estimates (fraction of light that makes it through the slit for a star). It is copied from my code in plotspec.

The next step will be to add methods in to the classes EchelleSpectrum and EchelleSpectrumList for relative and absolute flux calibration. For the relative flux calibration, the standards star and matching synthetic spectrum of the standard star will be the inputs. For the absolute flux calibration, the user will also need to provide the slit throughput estimates and exposure times ON the science target and standard star.

The IGRINS classes will include a method to read in the 1D slit profile for the H and K band outputted for standard stars and outputting an estimate the wavelength dependent slit throughput. Since this is be instrument dependent, similar slit spectrometers will need their own methods.

[gully]

Thanks Kyle! (link to the plotspec code Kyle mentioned)

The key idea here is that the collapsed spatial profile contains information about the wavelength dependence of the extent and amplitude of the PSF. The shape of the PSF is used to infer how much of the total flux spilled outside of the slit edges, enabling a coarse estimate of a scalar correction factor that can be applied to the observed spectrum to get to an absolute flux.

This proposal would expand which inputs muler would have to support, which catalyzed a second consideration: which operations should live in muler, versus plp, versus third party.

I walk through my thinking in that issue with absolute flux calibration as a case study. My instinct is that some of the need for spatial profiles could be offloaded to plp, and the portion that needs fine-adjustment of telluric templates could be done with a combination of muler and gollum.

This feature is a useful case study, and so I think walking through the design considerations and long-term maintenance implications is really helpful. Thanks again @kfkaplan !!