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

The SUMER (Solar Ultraviolet Measurements of Emitted Radiation) Spectromete r 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 hydrog en 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 bro ad and show the typical self-absorption reversal near the limb, where the e mission 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 emis sion comes from an optically thin plasma. The line shapes and intensities c an be fitted well by model profiles obtained from multilevel NLTE (Non Loca l-Thermodynamic-Equilibrium) radiative transfer calculations which allow us , assuming excitation and ionization equilibrium, to derive consistently th e temperatures and densities of the hydrogen atoms and, with additional ass umptions, of the protons. Temperature values range between 1 10(5) K to 2 1 0(5) K. We present the systematics of the line shapes as observed in differ ent emission regions and discuss briefly the relevance of these results for the solar wind acceleration and coronal heating.