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Astron. Astrophys. 347, 676-683 (1999)

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Proton and hydrogen temperatures at the base of the solar polar corona

E. Marsch 1, C.-Y. Tu 1,2, P. Heinzel 3, K. Wilhelm 1 and W. Curdt 1

1 Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany
2 Department of Geophysics, Peking University, Beijing, 100871, P.R. China
3 Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-25165 Ondejov, Czech Republic

Received 11 February 1999 / Accepted 19 May 1999


The SUMER (Solar Ultraviolet Measurements of Emitted Radiation) Spectrometer on SOHO (Solar and Heliospheric Observatory) has been used to observe the lines of the Lyman series (up to quantum numbers larger than 20) of hydrogen emitted in the solar atmosphere. The line shapes and intensities versus height are obtained near the limb from about -10" to 70". The lines are broad and show the typical self-absorption reversal near the limb, where the emission comes from optically thick material, and change systematically with increasing height. The H I Ly6, Ly7 and Ly9 lines attain a Gaussian shape at heights above the visible limb between about 19" and 22", where the emission comes from an optically thin plasma. The line shapes and intensities can be fitted well by model profiles obtained from multilevel NLTE (Non Local-Thermodynamic-Equilibrium) radiative transfer calculations which allow us, assuming excitation and ionization equilibrium, to derive consistently the temperatures and densities of the hydrogen atoms and, with additional assumptions, of the protons. Temperature values range between 1 [FORMULA] K to 2 [FORMULA] K. We present the systematics of the line shapes as observed in different emission regions and discuss briefly the relevance of these results for the solar wind acceleration and coronal heating.

Key words: line: profiles – Sun: corona – Sun: UV radiation

Send offprint requests to: E. Marsch (marsch@linmpi.mpg.de)

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© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999