Facular influences on the apparent solar shape

Abstract

Schatten and Sofia1 have recently reconsidered the question of whether the 1966 solar ellipticity measurements2 were seriously contaminated by excess brightness of faculae near the solar limb3–7. They considered several different functions for the variations of the facular contrast with position relative to the solar limb. With their own facular contrast function, Schatten and Sofia obtain only a small contribution of faculae to the 1966 apparent solar ellipticity, but with the Chapman function they obtain a substantial contribution. New observations of faculae during the summer of 1982 and a novel analytical technique determine a facular contrast which is constant or decreasing towards the limb, consistent with the Schatten and Sophia function but inconsistent with Chapman's function. We show here that the statistical analysis of the 1966 data8 supports this result. We disagree with the earlier conclusion1, that with an acceptable facular contrast function one can obtain “an acceptable fit to the oblateness measurements” as a purely facular effect. For 20–30% of the observational days in 1966 only a few small, weak facular patches were present at the limb, but the ellipticity signal was present and it was not reduced in magnitude for those days.