SIMULATION OF SEEING INFLUENCES ON THE PHOTOMETRIC DETERMINATION OF SUNSPOT AREAS

Various methods for measuring areas of sunspots and umbrae are compared to test their robustness against changing seeing conditions. The influence of the seeing is simulated by artificially degrading high-resolution sunspot images. A new procedure – the so-called inflexion point method – for area determinations is described. It is based on the calculation of the inflexion point contours of the two-dimensional sunspot intensity distribution. The areas derived with this method are much more stable against seeing influences than those obtained by the other procedures tested. The effect of the seeing on the measurements of the bolometric sunspot contrast and irradiance deficit produced by a sunspot is also studied.