Do compact features (PAHs/absorption/etc) need resolution "coarsening"?

[jdtsmith]

PAH features like 3.3um are fairly compact, e.g. the main 3.3um PAH has an effective resolution of R=77. What this means is:

1. The fitted FWHM of these features was in fact resolution-dependent (e.g. from IRS low-res, Akari), and will likely need to be tuned for higher resolution of e.g. NIRSPEC/MIRI. Features will get sharper.
2. Our current assumption that all dust/attenuation features in a science pack are resolution-independent may be incorrect (more so for the most compact feature: 3.3, 11.3, 16.4, etc.).

We should test this on e.g. Akari vs. NIRSPEC when available (@ThomasSYLai ?).

Possible Solutions:

• Ensure all science packs reference features are expressed/calibrated at their high resolution limit (R>1000 is probably sufficient).
• Add a "coarsening" step of dilating the FWHM of all dust features in a science pack by gaussian-summing the local line FWHM in (and test this!).

This is a bit awkward for features which span segments of different resolution, e.g. Akari + MIRI. If this is implemented, we may need to make these power-tied "ghost" features, similar to how we treat lines.

A more robust solution would be to build the model at "infinite" resolution and directly convolve with the (wavelength+segment-varying) line spread function but this is 1) inefficient, and 2) ill-defined for stitched spectra. So hopefully a simpler coarsening step would be sufficient.

Features that may need this "coarsening" treatment:

1. PAH features and sub-features
2. Absorption Drude features
3. Attenuation model (?)

[jdtsmith]

Also: this means you'd better not stitch spectra with widely differing resolutions, since we can't really allow PAH features widths to vary like lines can, since they cover much more territory.