Eberhard Wiehr (Göttingen)

Line Profiles of Ionized and Neutral Helium in Solar Prominences
Wann Am 24.04.2012 von 16:00 bis 17:00
  • Special Seminar
Wo SH, Seminarraum
Termin übernehmen vCal / iCal

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.