A Statistical Analysis of the Characteristics of Sunspots and Faculae

Abstract

We present results from a study of sunspots and faculae on continuum and Ca ii K images taken at the San Fernando Observatory (SFO) during 1989–1992; a total of approximately 800 images in each bandpass were used. About 18 000 red sunspots, 147 000 red faculae, and 800 000 Ca ii K faculae were identified based on their contrasts. In addition, we computed the contrasts of pixels on the red images cospatial with Ca ii K faculae. Sunspot contrasts show a strong dependence on size but no dependence on heliocentric angle. There are continuous but systematic differences among facular regions. We find that the contrast of Ca ii K faculae is relatively insensitive to heliocentric angle, but is a strong function of facular size, in the sense that larger Ca ii K faculae are always brighter. The contrast of red faculae is a function of both heliocentric angle and size: the contrast functions show that larger regions contain larger flux tubes, contain deeper flux tubes, and have larger filling factors than small facular regions. Comparisons of cospatial pixels on red and Ca ii K images show a tight correlation between the average contrast of a region in the continuum and its size and heliocentric angle in the Ca ii K images. The average contrast of all facular regions is positive everywhere on the disk, even though the largest regions contain flux tubes which appear dark at disk center.