Add support for ATMO2020

[gully]

I had a great conversation with Mark Phillips at CoolStars21 in Toulouse, France. We discussed the prospect of adding support for the ATMO2020 model grid [^1] into gollum. ATMO2020 would be the third model grid we support, with existing support for PHOENIX and Sonora-Bobcat. This support could include both Equilibrium and Disequilibrium chemistry options.

It would be straightforward to add in ATMO2020, since it would follow the same overall structure as PHOENIX and Sonora-Bobcat. In particular, it would inherit from the PrecomputedSpectrum class, which provides a majority of the standardized operations. We'd make a new module and class:

from gollum.atmo import Atmo2020Spectrum, Atmo2020Grid

native_spectrum = Atmo2020Spectrum(teff=700, logg=5.0)

native_spectrum.normalize().plot()

[^1]: Philips et al. 2020