Temperature et microturbulence dans les regions externes des protuberances

Abstract

A spectroscopic investigation of a quiescent prominence has been performed: the line profiles of the Hα and K lines have been carefully determined in all regions of the prominence where these emissions are likely to originate in optically thin layers. Therefore we have been able to study the electron temperature T _e and the microturbulent velocity ξ in the outer parts of the prominence. We find that on the average, T _e = 5700 K (Figure 1) and ξ = 6.7 km s^-1 (Figure 2) which are in very good agreement with classical data. Figure 3 represents the radial velocity measurements and Figure 4 the ratio of the total intensity of Hα to K lines. Thus the prominence we have observed does not show for T _e and ξ the regular increase outward which has been described by Hirayama (1971). On the other hand ξ increases towards the Equator, in the dynamically active part of the prominence, which could indicate that ξ represents the effect of macroturbulence rather than microturbulence (Kawaguchi, 1966). In this part of the prominence only the K line is in emission and the average value of the microturbulence is 9.4 km s^-1, the radial velocity is also generally increasing. At last, according to the absolute intensities of the Hα and K lines, the electron density in the outer layers of the prominence is no more than 1 × 10¹⁰ cm^-3.