Dynamical fine structure of a quiescent prominence

✍ Scribed by P. Mein; N. Mein

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 931 KB
• Volume: 136
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00146539

✦ Synopsis

A quiescent prominence has been observed with the MSDP spectrograph at the Pic du Midi Observatory. He profiles are obtained simultaneously in a 2D field, allowing a statistical analysis. The standard deviations of Doppler shifts and line widths are investigated as functions of the line intensity. The observations are compared with numerical simulations assuming that the prominence is made of identical 'threads', the velocity of which is distributed according to gaussian functions. The processing of simulations is very close to the processing of observations. The mixing by seeing effects and the transfer of radiation across several threads along the line of sight are considered. The results are consistent with the values derived by and Zirker and Koutchmy (1989.

The best fits are obtained with the following conditions. The temperature is -~ 8500 K. In the middle range of intensities, each pixel results typically from the mixing of 6 velocity threads, the optical thickness of which is roughly 0.2 at He center, and the geometrical thickness larger than 1000 kin. It is likely that the 'velocity threads' have larger sizes than the 'density threads'. The fit of the results is improved by taking into account a slight scatter of source functions throughout the prominence.

In the centralparts of the prominence, the fit is obtained by assuming that the line-of-sight velocities of the threads have a gaussian probability function (standard deviation _~ 7 km s ~).

In the edges, we suggest larger scatter of velocities, and two combined dispersions. The 'velocity threads' observed along a given line of sight are supposed to have neighbouring velocities (dispersion -~ 7 km s -1) around a mean value taken at random inside another distribution function (dispersion -~ 7 km s-1).