Add RSUN_REF FITS keyword

[mgalloy]

I need a value for RSUN_REF for the UCoMP wave regions. See discussion in KCor issue 360 about this value for KCor. This is needed for SunPy to display a UCoMP image without warnings.

Also see SunPy docs about RSUN: The role of “rsun” in sunpy.

Questions

• Are the values listed below OK? These are values of the closest wavelength in the top half of Table 2 from the paper Joan gives.

[jburkepile]

Here is a paper that appears to have determination of the radius of the solar photosphere vs. wavelength.

[mgalloy]

Tentative keyword and comment, for example for 1074 nm:

RSUN_REF=          696136000.0 / [m] solar radius at 1025.0 nm

Using these values from the paper, for 530 nm:

solar_radius                     : type=float, default=696096000.0
solar_radius_wavelength          : type=float, default=535.7

For 637 nm:

solar_radius                     : type=float, default=696157000.0
solar_radius_wavelength          : type=float, default=607.1

For 656 nm:

solar_radius                     : type=float, default=696157000.0
solar_radius_wavelength          : type=float, default=607.1

For 670 nm:

solar_radius                     : type=float, default=696157000.0
solar_radius_wavelength          : type=float, default=607.1

For 691 nm:

solar_radius                     : type=float, default=696157000.0
solar_radius_wavelength          : type=float, default=607.1

For 706 nm:

solar_radius                     : type=float, default=696168000.0
solar_radius_wavelength          : type=float, default=782.1

For 761 nm:

solar_radius                     : type=float, default=696168000.0
solar_radius_wavelength          : type=float, default=782.1

For 789 nm:

solar_radius                     : type=float, default=696168000.0
solar_radius_wavelength          : type=float, default=782.1

For 802 nm:

solar_radius                     : type=float, default=696168000.0
solar_radius_wavelength          : type=float, default=782.1

For 991 nm:

solar_radius                     : type=float, default=696136000.0
solar_radius_wavelength          : type=float, default=1025.0

For 1074 nm:

solar_radius                     : type=float, default=696136000.0
solar_radius_wavelength          : type=float, default=1025.0

For 1079 nm:

solar_radius                     : type=float, default=696136000.0
solar_radius_wavelength          : type=float, default=1025.0

For 1083 nm:

solar_radius                     : type=float, default=696136000.0
solar_radius_wavelength          : type=float, default=1025.0