Free Access

Fig. 2

image

Continuum images of the sunspot in NOAA active region 11899. Left image: a single continuum image near the central meridian passage on Nov. 18, 2013. Middle image: an average of the continuum images for the ten days analyzed (Nov. 14–23, 2013). For the left, and middle images: the horizontal size is the same as that of the eventual travel time maps. To identify the umbral–penumbral boundary, a contour of the ten-day average intensity at the level of 0.4 is plotted (red). The penumbral–photospheric boundary is represented from the contour at 0.85 (blue). To derive the intensities, a fit to limb darkening is done with the sunspot excluded and the intensity is normalized to unity for the background photosphere. Right image: also the ten-day average of the continuum intensity, but showing the entire field used to derive the travel-time maps. The locations A and B from Fig. 1 are shown.

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.