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On the width distribution of penumbral filaments in sunspots

“…We have done a total of 2732 estimations of the width obtaining a mean value of 0.37 arc sec. This number agrees with the result obtained by Muller (1973) 0.36 arc sec and it is appreciably lower than the width measured by Danielson (1961) 0.4 arc sec analysing the observational material of the Stratoscope Project; our result is in agreement with Danielson's assumption stating that the actual width of the filaments may be possibly smaller than the value he obtained, due to the limit of resolution of his telescope (12 inches). This remark can be maintained here because the mean size that we have estimated is possibly biased by the resolving power of our telescope (0.35").…”

“…The lack of knowledge on the physical nature of the structure of penumbral filaments (Muller, 1973;Grossmann-Doerth and Schmidt, 1981) makes difficult to get a reliable definition of their width. On the basis of our observations we have adopted a parameter referred as filament width, as follows.…”

“…Fine photometrical studies on the sunspot penumbra are not very abundant, and even less are those where the author estimates the filament width (Bray and Longhhead, 1964;Danielson, 1961;Muller, 1973). The observational material used in our analysis has two important advantages: It was obtained under good seeing conditions and during the exceptional circumstance of a solar eclipse, what allows an estimation of both atmospheric effects and instrumental perturbation.…”

Properties of Umbral Dots as Measured From the New Solar Telescope Data and MHD Simulations

“…We found a strong anti-correlation between UD lifetimes and their velocities. Muller (1973) reported an anti-correlation between the velocity and the lifetime for UDs of penumbral origin. Watanabe et al (2010) analyzed a rapidly moving UD, whose lifetime was much shorter (8.7 min) than the generally reported value (~15 min), while its size was nearly the same as the average size of UDs (240 km).…”