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

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

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...347..676m&link_type=abstract

Astronomy and Astrophysics, v.347, p.676-683 (1999)

Astronomy and Astrophysics

Astrophysics

15

Line: Profiles, Sun: Corona, Sun: Uv Radiation

Scientific paper

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\arcsec to 70\arcsec. 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\arcsec and 22\arcsec, 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 10(5) K to 2 10(5) 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.

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