The Lyα and Lyβ Profiles in Solar Prominences and Prominence Fine Structure

Lyα and Lyβ line profiles in a solar prominence were observed with high spatial and spectral resolution with SOHO/SUMER. Within a 60 arcsec scan, we measure a very large variety of profiles: not only reversed and non-reversed profiles but also red-peaked and blue-peaked ones in both lines. Such a spatial variability is probably related to both the fine structure in prominences and the different orientations of mass motions. The usage of integrated-intensity cuts along the SUMER slit, allowed us to categorize the prominence in three regions. We computed average profiles and integrated intensities in these lines which are in the range (2.36 – 42.3) W m sr for Lyα and (0.027 – 0.237) W m sr for Lyβ. As shown by theoretical modeling, the Lyα/Lyβ ratio is very sensitive to geometrical and thermodynamic properties of fine structure in prominences. For some pixels, and in both lines, we found agreement between observed intensities and those predicted by onedimensional models. But a close examination of the profiles indicated a rather systematic disagreement concerning their detailed shapes. The disagreement between observations and thread models (with ambipolar diffusion) leads us to speculate about the importance of the temperature gradient between the cool and coronal regions. This gradient could depend on the orientation of field lines as proposed by Heinzel, Anzer, and Gunár (2005).