EDP Sciences
Free access
Volume 382, Number 3, February II 2002
Page(s) 1093 - 1105
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20011639

A&A 382, 1093-1105 (2002)
DOI: 10.1051/0004-6361:20011639

Sunspot photometry with phase diversity

I. Methods and global sunspot parameters
A. Tritschler and W. Schmidt

Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
    e-mail: ali,wolfgang@kis.uni-freiburg.de

(Received 8 May 2001 / Accepted 19 November 2001 )

The global brightness structure of a small sunspot is investigated. Seeing and instrumental effects are compensated by application of the phase-diversity technique and a conventional deconvolution method. We calculate brightness temperatures for the reconstructed data in three simultaneously observed continuum bands of the solar spectrum (402.1 nm, 569.5 nm, 709.1 nm). The darkest umbral regions are on average 0.17 $I^{\odot}$, 0.27 $I^{\odot}$ and 0.32 $I^{\odot}$ bright. The corresponding temperatures lie in the range around 4790 K, 4600 K and 4460 K. The spatially averaged penumbral brightness amounts to 0.72 $I^{\odot}$, 0.81 $I^{\odot}$ and 0.85 $I^{\odot}$, which corresponds to 5910 K, 5750 K and 5640 K, respectively. Although the spectral distribution of the umbral and penumbral intensities is consistent with former measurements, the derived values support the idea that there exist a real difference in the thermal properties between the umbrae of small and large sunspots.

Key words: Sun: sunspots -- techniques: image processing

Offprint request: A. Tritschler, ali@kis.uni-freiburg.de

© ESO 2002