EDP Sciences
Free Access
Issue
A&A
Volume 443, Number 3, December I 2005
Page(s) 1055 - 1059
Section The Sun
DOI https://doi.org/10.1051/0004-6361:20053341


A&A 443, 1055-1059 (2005)
DOI: 10.1051/0004-6361:20053341

The HeI abundance in Solar filaments

F. Chiuderi Drago

Department of Astronomy and Space Science, University of Florence, Italy

(Received 29 April 2005 / Accepted 29 July 2005 )

Abstract
Three filaments observed with the CDS instrument on the SOHO satellite are analysed to determine the HeI/HI ratio. The HI and Hel bound-free absorptions are the major processes responsible for the lower intensity of transition region (TR) lines observed above filaments. One of the filaments was also observed by SUMER at $\lambda > 912$ Å, thus supplying the unabsorbed background intensity. The HI and Hel column densities are derived from several TR lines using a least squares method applied to two different models. The resulting HeI/HI ratio is independent of the model, while the column densities are different by about a factor of two. This difference enables us to discriminate between the two models by comparing the resulting value of the optical depth at the Lyman continuum limit, $\tau_{912}$, with previous observations and models.


Key words: Sun: filaments -- Sun: UV radiation




© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.