SOHO/SUMER observations and analysis of hydrogen Lyman lines in a quiescent prominence

TitreSOHO/SUMER observations and analysis of hydrogen Lyman lines in a quiescent prominence
Type de publicationJournal Article
Year of Publication1999
AuteursSchmieder, B., Heinzel P., Vial J. C., and Rudawy P.
JournalSolar Physics
Date PublishedOct

A quiescent prominence was observed in June 1997 by instruments onboard the SOHO spacecraft: the Solar Ultraviolet Measurements of Emitted Radiation (SUMER), Coronal Diagnostic Spectrometer (CDS) and Extreme-Ultraviolet Imaging Telescope (EIT), along with the coronagraph of the Wrocław University Observatory at Bialków and the spectrograph of the Ondřejov Observatory. We present prominence observations in higher lines of the hydrogen Lyman series (from Lδ to L-9), together with some other UV lines obtained by SUMER. We extract the basic characteristics of the calibrated line profiles of these Lyman lines and compare them with the theoretical profiles computed from three kinds of NLTE models which also include prominence filamentation. Our principal result is that the current NLTE models are in principle capable of explaining the SUMER calibrated intensities in the observed Lyman lines. We also find that in order to fit all these lines, one has to consider a prominence-corona transition region (PCTR) with a temperature gradient. At low pressures, higher Lyman lines are still rather sensitive to the incident radiation which must be carefully taken into account in the modeling. From PCTR models, which also take into account the effect of ambipolar diffusion on the heating, we have derived the formation depths for the Lyman series lines. High Lyman lines seem to be formed just at the base of the PCTR.