Eberhard Wiehr (Göttingen)

Line Profiles of Ionized and Neutral Helium in Solar Prominences
When Apr 24, 2012 from 04:00 PM to 05:00 PM
What
  • Special Seminar
Where SH, Seminar room
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He II and He I lines are observed in aiescent prominences using NaD2 as a tracer for prominence candidates of sufficient He II emission strength. The low scattering in the Gregory Coud\'e telescope at the IRSOL observatory in Locarno allows an accuracy near 10-6 of the disk center intensity. Sufficiently bright He II emissions occurred in only 4 among dozens of prominences and are characterized by very small non-thermal line broadening and velocity shifts, yielding narrow line profiles without wiggles. Considering the fine-structure boadening, He II 4686 is 1.5 times broader than He I 4472 triplet line which, in turn, is 1.1 times braoder than the He I 5015 singlet line. Possible scenarios to explain this finding will be discussed.