3.6. Flux Calibration
Three independent components of the surface brightness calibration will affect its final accuracy: point source calibration (which includes the sensitivity and extinction corrections); aperture correction (which compensates for the loss of light from point source observations which does not occur in observation of a uniform aperture-filling source); and the fiducial standard star system. The flux calibrated spectrum for a uniform source can be expressed as
in which C(), is the wavelength calibrated spectrum in DN sec-1 Å-1 per pixel, S() is the sensitivity function in ergs DN-1, T(A) is the aperture correction for the slit size in question, is the airmass of the observation, () is the extinction correction expressed in mag airmass-1, and is the solid angle of each pixel in steradians per pixel. We discuss each component of the calibration separately below.