Emission Cores in the CA II Lines in Plages.

The purpose of this paper is to present some of the observed characteristics of the emission cores, which any theory of the line formation of the H and K lines must account for. The several correlations found from the data are summarized in Table 1. A range of a factor of 3 in the emission-line width occurs on the sun between such different features as sunspots and plages near the limb. The relevance to the Wilson-Bappu effect is discussed. Another parameter investigated is the separation of the emission peaks. This is not uniquely related to the width and, in fact, behaves differently in certain respects. Whereas, for instance, the emission-line width in plages exceeds that of the neighboring quiet disk, the separation of the peaks is less in plages than on the normal disk. The separation is inversely proportional to the intensity of either K3 or K2. The width, on the other hand, behaves in a more complex fashion. There exists a very high correlation between the K, and K2 intensities. The intensity of the K1 absorption just beyond the emission core depends somewhat on the intensity of the emission, though the variation within a single plage and from plage to plage is very much less. This fact, as well as tbe center-to4imb variations of their profiles, suggests that plages are restricted to a thin layer in the chromosphere with little effect on the temperature structure of the underlying photosphere.