FILAMENT OBSERVATIONS WITH SOHO SUMER/CDS: THE BEHAVIOUR OF HYDROGEN LYMAN LINES B. SCHMIEDER 1,2 , P. HEINZEL 3 , T. KUCERA 4,5 and J.-C. VIAL 6 1 Observatoire de Paris, Section Meudon, URA 2080, F-92195 Meudon, France 2 Institute of Theoretical Astrophysics, P.O. Box 1029, Blindern, N-0315 Oslo, Norway 3 Astronomical Institute, CZ-25165, Ondˇ rejov, Czech Republic 4 Code 682.3, NASA/GSFC, MD 20771, U.S.A. 5 Space Applications Corp., 901 Follin Ln., Suite 400, Vienna, VA, 22180, U.S.A. 6 Institut d’Astrophysique Spatiale, Université Paris XI-CNRS, Bât. 121, F-91405 Orsay Cedex, France (Received 31 December 1997; accepted 3 March 1998) Abstract. On 21 September 1996, a filament close to an area of enhanced network was observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer and Coronal Diagnostic Spectrometer (CDS). CDS provided intensity, Doppler shift and linewidth maps of the region in six lines whose temperature range covers 10 4 to 10 6 K. SUMER observations consisted of maps of the region in four hydrogen Lyman lines (Lδ,Lǫ , L-6, L-7) and a S VI line (944 Å). In all the Lyman lines we detect a central absorption and an asymmetry in the intensity of the two peaks. First NLTE computations indicate that such reversed Lyman profiles and their absolute intensities can be reproduced with the existing filament models provided that we take into account a prominence- corona transition region (PCTR). We discuss the Lyman lines’ asymmetry in terms of macroscopic flows by comparison with the He I line Doppler shifts observed with CDS. 1. Introduction In the case of quiescent prominences, the diagnostic potential of hydrogen Lyman lines has been proven in the works of Gouttebroze, Heinzel, and Vial (1993) and Heinzel, Gouttebroze, and Vial (1994). These authors have shown, for instance, how the Lα and Lβ lines (differently formed) could be indicators of temperature and pressure. It was also demonstrated that in order to explain the formation of these lines, one has to use rather sophisticated partial-redistribution (PRD) scatter- ing physics in the context of NLTE modeling. Going towards higher members of the Lyman series, we expect that the shapes and intensities of these optically thick lines will provide us with information on the temperature, density and thus pressure and on the flow velocity across the prominence body. For example, a temperature gradient inside the prominence – corona transition region (PCTR) should be de- tectable using the Lyman series lines formed at successive depths. The same applies to filaments observed on the disk, although the geometry is different. NLTE mod- eling of filaments and the spectral synthesis of hydrogen Lyman lines is described by Heinzel, Schmieder, and Vial (1997). Solar Physics 181: 309–326, 1998. © 1998 Kluwer Academic Publishers. Printed in Belgium.