Abstract
A study of the solar spectrum near helium 10 830 Å has shown that, where the line is very weak, the anomalous ratio of the two components is due almost certainly to faint blends. The centre-limb intensity variation over supergranule centres is in good agreement with an optically-thin law. The line is stronger over supergranule boundaries, and the ratio of the two components can be understood only if the absorbing elements have been resolved incompletely (as is probable); using centre-limb intensity variations, we have been unable to distinguish between unresolved horizontal platelets or inclined slabs.
The integrated absorption in 10 830 Å over supergranule centres is double that at the boundaries. An analysis of the extension of 10 830 Å beyond the limb has failed to reveal the relative contributions from these two regions or their variations with height (though the supergranule-centre emission should be located relatively low). Line profiles in 10 830 Å, hydrogen Paγ and Caii 8542 Å indicate that, out to at least 5000 km, line broadening is effectively non-thermal, with horizontal rms velocities of about 20 km s−1.
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Giovanelli, R.G., Hall, D. The helium 10830 Å line in the undisturbed chromosphere. Sol Phys 52, 211–228 (1977). https://doi.org/10.1007/BF00935803
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DOI: https://doi.org/10.1007/BF00935803