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Photometry of active regions and their relation to the solar irradiance variation
The Extreme Limb Photometer was used to carry out photometry of active regions in 1980 and 1982 at various positions on the solar disk. The wavelength used was 525 nm, and the measurements were taken at the San Fernando Observatory. The brightness fluctuation has been calculated for both spot and plage areas for a total of 45 regions. This fluctuation was then correlated to the Photometric Sunspot Index (PSI) and the Photometric Facular Index (PFI). These indices have the form of PSI= CsAs( 3µ2 + 2µ ) and PFI = CPAP( 2 + µ - 3µ2 ) where As and Ap are the published region areas for spot and plage respectively and can be found in the Solar Geophysical Data Bulletin. The value of is the cosine of the viewing angle and Cs = 0.1635 ± 0.0083 and Cp = 0.0089 ± 0.0014 which are the coefficients found by least squares for the 45 regions. A high degree of correlation is seen when comparing the PSI and PFI values with their respective brightness fluctuations. Regressions of observed brigthness fluctuations for sunspots and faculae with PSI and PFI have correlation coefficients of 0.949 and 0.707, respectively, which are significant at below the 10-3 level. From these and the other regres sions that were made, there is evidence that the total energy may be balanced in an active region.