Large-scale structure of a sunspot and its surrounding photosphere

Abstract

Preliminary results of a study of photographic and photometric properties of the large-scale (≈ 3″) structure of a sunspot and its surrounding photosphere are given. Stratospheric direct frames of the solar photosphere were used in the study. Isophotes located immediately beyond the outer edge of the penumbra were of an irregular form and reflected bright and dark regions. No presence of either a sunspot bright outer ring or inner ring was detected. The photospheric structure and its behaviour with time were, in fact, unchanged up to the very boundary of the penumbra. A distribution of the smeared intensity in a sunspot has been derived. The mean brightness of the penumbra is I PU ≈ 0.62 I ⊙ and umbra I U < 0.15 I ⊙. An analysis of the obtained results allowed us to make a conclusion that the area of the dark penumbral regions exceeds that of the bright penumbral regions, and the condition S BR/S DR < 1 should be fulfilled in the penumbrae of sunspots.