Spatial distribution and temporal evolution of coronal bright points

We present a statistical study of the spatial distribution and temporal evo lution of coronal bright Faints (BPs) by analyzing a continuous set of obse rvations of a quiet-Sun region of size 780 " a 780 " over a period of 55 ho urs. The main data set consists of observations taken by EIT (the Extreme-u ltraviolet Imaging Telescope on board the SOHO spacecraft) in its Fe XII 19 5 Angstrom channel which is sensitive to coronal plasma of temperature simi lar to 1.5 MK; we also use soft X-ray observations by SXT (Soft X-ray Teles cope on the Yohkoh spacecraft) which is sensitive to coronal plasma of temp erature > 2.5 MK. The flux histogram for all pixels in EIT 195 Angstrom ima ges indicates that BPs have a power law flux distribution extending down to a level of 3 sigma (sigma, root mean square deviation) above the average B ur of the quiet Sun, while the hulk quiet Sun has a Gaussian-like flux dist ribution. Using a 3 sigma intensity threshold, we find a spatial density of one BP per 90 Mm x 90 Mm area, or equivalently 800 BPs for the entire sola r surface at any moment. The average size of a BP is 110 Mm(2). About 1.4% of the quiet-Sun ar ea is covered by bright points and the radiation from a ll BPs is only about 5% of that from the whole quiet Sun, Thus, the atmosph ere above quiet-Sun regions is not energetically dominated by BPs. During t he 55-hour period of EIT observational we identify 48 full-life-cycle BPs w hich can be tracked from their initial appearance to final disappearance. T he average lifetime of these BPs is 20 hours, which is much longer than the previously reported 8 hours based on Skylab X-ray observations (Golub et a l., 1974). We also see shorter life times and smaller numbers of BPs in the soft X-ray images than in the EIT 195 Angstrom observations, suggesting th at the temperature of BPs is generally below 2 MK.