Morphological properties and origin of the photospheric facular granules

Abstract

From time series of high resolution photographs, morphological properties of the photospheric facular granules were derived. The facular granules are cells of the common granular pattern, brighter than the normal granules when seen between cos θ = 0.6 and the limb. Their apparent diameter, which decreases towards the limb, is smaller than that of the normal granules: 0″.65 and 1″.25 respectively at cos θ = 0.55; their lifetime is 25 min but their ‘bright stage’ lifetime is only 15 min; they are visible closer to the limb than the normal granules: 1″.2 compared to 2″–5″; the brightening of the facular granules occurs at a faster rate than their fading. From the great similitude of both morphological properties and temperature models of facular and normal granules, it appears possible that the photospheric facular granules are convective cells modified by the presence of a magnetic field of some hundreds Gauss.