>The dcr.get_refraction function is kind of an implementation detail. This function is the one that users will primarily interact with. So I think the parameter descriptions should be made explicit here.

>Also, I would leave off the LSST references in the @param descriptions, since we don't want to be too partisan in GalSim.

Here's the new docstring:
```
    """Return a ChromaticObject implementing two atmospheric chromatic effects: differential
    chromatic refraction (DCR) and wavelength-dependent seeing.

    Due to DCR, blue photons land closer to the zenith than red photons.  Kolmogorov turbulence
    also predicts that blue photons get spread out more by the atmosphere than red photons,
    specifically FWHM is proportional to wavelength^(-0.2).  Both of these effects can be
    implemented by wavelength-dependent shifts and dilations.

    The default values for temperature, pressure and water vapor pressure are expected to be
    appropriate for LSST at Cerro Pachon, Chile, but they are broadly reasonable for most
    observatories.

    @param base_obj           Fiducial PSF, equal to the monochromatic PSF at base_wavelength
    @param base_wavelength    Wavelength represented by the fiducial PSF.
    @param zenith_angle       Angle from object to zenith, expressed as a galsim.Angle
    @param alpha              Power law index for wavelength-dependent seeing.  Default of -0.2
                              is the prediction for Kolmogorov turbulence.
    @param position_angle     Angle pointing toward zenith, measured from "up" through "right".
    @param pressure           Air pressure in kiloPascals.  (default 69.328 kPa)
    @param temperature        Temperature in Kelvins.  (default: 293.15 K)
    @param H2O_pressure       Water vapor pressure in kiloPascals.  (default: 1.067 kPa)
    @returns  ChromaticObject representing a chromatic atmospheric PSF.
    """
```
and similarly for `dcr.air_refractive_index_minus_one()`...