Formation of the Calcium H, K, and Subordinate Lines in the Solar Chromosphere

Details Formation of the Calcium H, K, and Subordinate Lines in the Solar Chromosphere Formation of the Calcium H, K, and Subordinate Lines in the Solar Chromosphere

May 1968

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1968saosr.274.....l&link_type=abstract

SAO Special Report #274 (1968)

Astronomy and Astrophysics

Astrophysics

20

Scientific paper

Two important problems of astrophysics are the structure of the solar chromosphere and the study of spectral line formation without the assumption of local thermodynamic equilibrium (LTE). In this research we combine the two problems in the process of analyzing the Ca II resonance and subordinate lines in terms of self-consistent model chromospheres. We develop an approach for obtaining line source functions when the lines are coupled together in a four level representation of the calcium ion and when the ionization equilibrium is governed by the solar ultraviolet radiation field. By considering a number of cases in which we alter the complexity of the model ion, we determine the accuracy with which we can apply simpler representation to understanding the solar chromosphere. We compute several models of the solar chromosphere that assume hydrostatic equilibrium, an LTE representation of metal ionization, and a non-LTE formulation for the ionization equilibrium of hydrogen. The temperature distributions are adjusted to produce H and K line profiles similar to observations. A general feature of these models is a minimum temperature of ~ 4200° K in the region 3 X 10-4 < τ5000 < 3 X 10-5 corresponding to 470-650 km above the photosphere. Above the minimum we find a shallow thermal gradient followed by a steep gradient beginning at 1400-1700 km. The general features of this description persist even though we vary the calcium abundance, hydrogen ionization equilibrium, turbulent velocities, He/H ratio, and include "turbulent" pressure, although the position of the steep gradient is affected by these changes.

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