EDP Sciences
Free access
Volume 401, Number 1, April I 2003
Page(s) 361 - 375
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20030126

A&A 401, 361-375 (2003)
DOI: 10.1051/0004-6361:20030126

Spectroscopic diagnostics of an H $\alpha$ and EUV filament observed with THEMIS and SOHO

B. Schmieder1, 2, K. Tziotziou1 and P. Heinzel3

1  Observatoire de Paris, Section de Meudon, LESIA, 92195 Meudon Principal Cedex, France
    e-mail: Brigitte.Schmieder@obspm.fr; Kostas.Tziotziou@obspm.fr
2  Institute of Theoretical Astrophysics (ITA), University of Oslo, Blindern, 0315 Oslo, Norway
3  Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondrejov, Czech Republic
    e-mail: pheinzel@asu.cas.cz

(Received 27 February 2002 / Accepted 17 January 2003)

A long filament has been observed with THEMIS/MSDP and SOHO/CDS - SUMER, during a coordinated campaign (JOPs 131/95) on May 5, 2000. The data were (a) 2-D H $\alpha$ spectra, observed using THEMIS, (b) Lyman series spectra and Lyman continuum, observed using SOHO/SUMER, and (c) EUV spectra (in $\ion{O}{v}$ 629 Å, $\ion{Mg}{x}$ 624 Å, $\ion{Si}{xii}$ 520 Å, $\ion{Ca}{x}$ 557 Å and $\ion{He}{i}$ 584 Å) observed using SOHO/CDS. A large depression of the line emissions in CDS images represents the EUV filament. A computed model shows that the EUV filament consists of an extended in height cloud of low gas pressure at an altitude lower than the top of the H $\alpha$ filament, volume-blocking and absorbing coronal emission and absorbing transition region line emission. The optical thickness of the Lyman continuum is estimated by using the ratio of $\ion{O}{v}$ intensity inside and outside the EUV filament, while the optical thickness of H $\alpha$ is computed from the H $\alpha$ line profile by using an inversion technique. Using simultaneous H $\alpha$, Lyman lines and Lyman continuum spectroscopic data, we performed detailed, non-LTE radiative transfer diagnostics of the filament plasma conditions. The optical thickness of the Lyman continuum is larger than that of the H $\alpha$ line by one to two orders of magnitude. This could be of a great importance for filament formation modeling, if we consider that more cool material exists in filament channels but is optically too thin to be visible in H $\alpha$ images.

Key words: Sun: filaments -- line: profiles -- radiative transfer -- techniques: spectroscopic -- methods: data analysis

Offprint request: B. Schmieder, Brigitte.Schmieder@obspm.fr

© ESO 2003