Coronal Oscillations above Sunspots?

Abstract

Observational data clearly indicate the presence of 3-min oscillations in sunspots in spectral lines covering a vast temperature range from the low chromosphere to those lines normally associated with coronal temperatures. We show that after folding in the sunspot plume emission measure distribution, the contribution functions for lines normally formed just below 1×10⁶ K are shifted to lower temperatures. For example, the Fe ix 171 Å line is shifted to 6×10⁵ K for a Maxwellian distribution and to less than 5×10⁵ K with a non-Maxwellian distribution. Other lines such as Mg ix 368 Å will also be affected. This then questions some previous work regarding the suggested detection of 3-min oscillations in the corona above sunspots.