An Improved Determination of the Area Ratio of Faculae to Sunspots

Details An Improved Determination of the Area Ratio of Faculae to Sunspots An Improved Determination of the Area Ratio of Faculae to Sunspots

Jul 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...555..462c&link_type=abstract

The Astrophysical Journal, Volume 555, Issue 1, pp. 462-465.

Astronomy and Astrophysics

Astronomy

12

Sun: Activity, Sun: Faculae, Plages, Sun: Sunspots

Scientific paper

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 filter, and sunspot areas are determined from red images at 672 nm with a 10 nm bandpass filter. On the K line images faculae were identified by pixels that had a contrast equal to or greater than 4.8% divided by μ. 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 significant 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 find 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.'' 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 significantly lower than for cycle 22.

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