An Improved Determination of the Area Ratio of Faculae to Sunspots

Abstract

We report new results on the ratio of facular area to sunspot area from a program of continuing photometric observations using the Cartesian Full Disk Telescope No. 1 (CFDT1) at the San Fernando Observatory (SFO). The facular areas are determined from images obtained with a 1 nm bandpass Ca II K line Ðlter, and sunspot areas are determined from red images at 672 nm with a 10 nm bandpass Ðlter. On the K line images faculae were identiÐed by pixels that had a contrast equal to or greater than 4.8% divided by k. Previously, we found that the average facular-to-spot area ratio was 16.7 ^ 0.5 during the latter part of solar cycle 22 and that there was a small but statistically signiÐcant rise in the ratio with time. If we take an average from the beginning of the K line data (mid-1988) until the middle of 1996, excluding days of zero sunspot area, the average ratio is 16.4 ^ 0.4. The average ratio from mid-1996 to the end of 1999 November is 12.6 ^ 0.5. Including days of zero sunspot area for these same intervals we Ðnd average ratios of 16.8 ^ 0.5 and 13.2 ^ 0.6, respectively. We have recently reprocessed our K line images, which have been photometrically "" cleaned.ÏÏ We can now reliably identify facular pixels with a contrast criterion of 2.4%, resulting in an increase in the average facular-to-spot ratio of approximately 3. The average facular and sunspot areas for cycle 23 are signiÐcantly lower than for cycle 22.