Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011sf2a.conf..203b&link_type=abstract
SF2A-2011: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics Eds.: G. Alecian, K. Belkacem,
Astronomy and Astrophysics
Astrophysics
Ionized Helium He Ii 4686, Total Solar Eclipses, Flash Spectra, Helium Shells, Solar Transition Region, Intensity Profiles, Layers, Faint Emission Lines
Scientific paper
Flash spectra taken at high frame rate during the total solar eclipse of August 1st 2008 in Siberia and during the July 11th 2010 in French Polynesia are compared in the context of the quiet Sun near the minimum of activity. They both reveal the weak Paschen α 468.6 nm ionized helium line, seen as a helium shell in layers up to the 8 Mm heights. The preliminary evaluated effective height of the He I 4713 shell is 1.8 Mm and it is approximately 2.0 Mm for the He II 4686 emissions outside polar regions. These lines can be measured only in eclipse conditions, when the parasitic scattered light is negligible for very low solar fluxes corresponding to the coronal levels. Many faint lines are also seen in emission such as Ba +, Ti +, Fe +, but with a much lower radial extension. They were observed to be superposed to F-lines when defining the solar limb using the continuum background. A cartoon is proposed to describe the structuration of these low layers and to illustrate the contribution of the magnetic field. These observations are important new insights for understanding (i) the magnetic field inference in the very low layers of the solar transition region and (ii) the ionisation mechanisms producing the big jump of the temperature towards the corona, including the source of heating.
Bazin Cyril
Koutchmy Serge
Lamy Philippe
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