New Measurement of the Facular Contrast near the Solar Limb

摘要

A new measurement of the contrast of solar faculae at 525 nm and 800 nm is presented using photometer data taken during the summer of 1982. We find that the contrast is decreasing with heliocentric angle Theta from mu approx. 0.2 to mu approx. 0.08, where mu = cos Theta. Parameterizing the contrast function with (Delta I)/I = 0.2 + alpha(mu - 0.2) over the range 0.08 < or = mu < or = 0.2, we obtain the best fit values of alpha: alpha(green) = 0.33 + or - 0.14, and alpha(red) = 0.25 + or - 0.08. These results differ from the facular contrast measurement of Chapman and Klabunde, who find the contrast increasing toward the limb. Selection effects in their data are suggested which could explain the discrepancy. Our results are in good agreement with the facular model of Spruit, assuming a fixed magnetic field strength of 2000 gauss. Keywords: Sun: Faculae; Sun: Limb darkening, Reprints.