Title: Effective Sunspot Temperatures Derived from VIRGO Data: Applying a Starspot Modeling Approach to the Sun
Author: W. Otruba
Affil: Kanzelhoehe Solar Observatory
Email: otruba@solobskh.ac.at
Authors: Z. Eker, P. Brandt, A. Hanslmeier, C. Wehrli
Affils: King Saud Univ., KIS Freiburg, PMOD Davos
Abstract: Sunspots, faculae, and the network contribute to solar irradiance variations. For a quantitative assessment of their relative contributions we seek to analyze the sunspot contribution, as a first step, by deriving reliable mean sunspot temperatures and contrasts from VIRGO data using a starspot modeling formalism.
Unlike in the stellar case, where only the light curves can be measured, for the Sun we know additionally the area and position of the spots and reduce therefore the number of free parameters.
The passage of a single activity region during low activity in July/August 1996 is investigated. Light curves are given by the total and spectral irradiance measurements of VIRGO onboard SOHO, area and positions (but no intensity information) of the spots are taken from MDI WL images. We derive spatially averaged effective spot temperatures in three steps: a) for the total spot, b) for umbra and penumbra separately, c) for various intensity levels.