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Astron. Astrophys. 336, 367-370 (1998)

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Temperature mapping of sunspots and pores from speckle reconstructed three colour photometry

P. Sütterlin and E. Wiehr

Universitäts-Sternwarte, Geismarlandstrasse 11, D-37083 Göttingen, Germany

Received 4 March 1998 / Accepted 13 May 1998


The two-dimensional temperature distribution in a highly structured sunspot and in two small umbrae is determined from a three-colour photometry in narrow spectral continua. Disturbing influences from the earth's atmosphere are removed by speckle masking techniques, yielding a spatial resolution limited by the telescope's aperture. The corresponding colour temperatures are consistent over a range of more than 2000 K, although the numerical correction introduced by the reconstruction differs largely for the three colours.

Part of the scatter in the temperature relation disappears when convoluting the final images with artificial PSFs that compensate for the different, colour dependent spatial resolution. The remaining spread in the scatter plots does not reflect noise, but is related to local variations of the temperature difference between the continuum emitting layers. This is most obvious for a small umbra which yields `branches' in the scatter plots the `bluer' of which corresponding to the limb-side umbral border. Here, the `hot rim' of a Wilson depressed umbra becomes visible.

The temperature map of the large spot shows that the bright umbral dots do not reach the temperature of the non-spot surroundings. Instead, they exceed the 2000 K cooler umbral temperature minimum by 900-1300 K. The filamentary structure of the surrounding penumbra has spatial temperature fluctuations of typically 700 K, a value which fits earlier observed contrasts. However, the mean temperatures of 5650 K in the dark and 6250 K in the bright penumbral fine structures exceed former findings. Exceptionally bright penumbral grains are 250 K hotter than the mean solar surface and thus exceed even brightest granules.

Key words: sunspots – techniques: interferometric

© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998