Determination of the 3D structure of an EUV-filament observed by SoHO/CDS, SoHO/SUMER and VTT/MSDP

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic e-mail: pheinzel@asu.cas.cz
² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching, Germany e-mail: ula@mpa-garching.mpg.de
³ Observatoire de Paris, Section Meudon, LESIA, 92195 Meudon Principal Cedex, France e-mail: brigitte.schmieder@obspm.fr
⁴ Institute of Theoretical Astrophysics, University of Oslo, Blindern, 0315 Oslo, Norway

Corresponding author: P. Schwartz, schwartz@asu.cas.cz

Received: 15 August 2003
Accepted: 14 February 2004

Abstract

Heinzel et al. ([CITE]) found that filaments seem to be much more extended in EUV spectral lines than in . In this paper we reconstruct the 3D structure of the extensions of the EUV-filament observed on 15 October 1999 by SoHO/CDS and SoHO/SUMER. Small structures were observed by VTT/MSDP. We computed the bottom and top heights of the EUV-filament extensions for several values of the hydrogen Lyman-continuum optical thickness using the spectroscopic model of Heinzel et al. ([CITE]). For this we used CDS observations of the two coronal lines  624.94 Å and  520.60 Å. Further, we develop a new method for estimating using the  line measured by CDS and the  measured by SUMER onboard SoHO. The latter line is used as a proxy to deduce the intensity variations of underneath the filament. This method also takes into account the presence of prominence-corona transition regions. 
Resulting heights of the EUV-filament extensions are around 15 000 km for the bottom and around 40 000 km for the top boundaries. However, there are significant variations around these representative values and we show that in about half of observed pixels the Lyman-continuum absorption dominates in the coronal-line depression, while in the other half it is the volume blocking effect. The latter situation corresponds to a large (larger than 30 000 km) geometrical thickness of the EUV-filament extension. From the heights of the boundaries of the EUV-filament the geometrical thickness can be computed and used to estimate the total mass loading which was found to be comparable to that of typical CMEs.