NEW OBSERVATIONS OF SUBARCSECOND PHOTOSPHERIC BRIGHT POINTS

We have used an interference filter centered at 4305 Angstrom within t he bandhead of the CH radical (the ''G band'') and real-time image sel ection at the Swedish Vacuum Solar Telescope on La Palma to produce ve ry high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 1993 Septe mber 15-20 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on September 20. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measur ed FWHM distribution of the bright points in the image is lognormal wi th a modal value of 220 km(0 ''.30) and an average value of 250 km (0 ''.35). The smallest measured bright point diameter is 120 km (0 ''.17 ) and the largest is 600 km (0 ''.69). Approximately 60% of the measur ed bright points are circular (eccentricity similar to 1.0), the avera ge eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged '' quiet-Sun'' area in the image, the modal contrast is 29% and the maxim um value is 75%; when referenced to an average intergranular lane brig htness in the image, the distribution has a modal value of 61% and a m aximum of 119%. The bin-averaged contrast of G-band bright points is c onstant across the entire measured size range. The measured area of th e bright points, corrected for pixelation and selection effects, cover s about 1.8% of the total image area. Large pores and micropores occup y an additional 2% of the image area, implying a total area fraction o f magnetic proxy features in the image of 3.8%. We discuss the implica tions of this area fraction measurement in the context of previously p ublished measurements which show that typical active region plage has a magnetic filling factor on the order of 10% or greater. The results suggest that in the active region analyzed here, less than 50% of the small-scale magnetic flux tubes are demarcated by visible proxies such as bright points or pores.