From a study of the intensity fluctuations in the continuum as well as in the lines H and K of Ca It, b~ ofMg I and Hfl, Evans and Catalano (1972) find that the correlation between the continuum structures and those in the inner wings of the lines of K and bl assumes negative values. Thomas (1972) has suggested an explanation based on the source functions. In this note, we offer an interpretation derived from a study of the intensity oscillations in the continuum and in the Fe I 6358.695 line completed at Kodaikanal from an excellent time sequence around this region. The Rowland intensity of this line is 6 and the lower excitation potential is 0.855 eV. The intensity fluctuations were measured both in the line wings and in the line core. In the line wings the intensity measures are those averaged from the tracings at +A2 and -A2, to avoid the disturbing effects of the local Doppler shifts. The value of A2 is 0.0659 A and represents the region at which the velocities were also measured on the line to correlate the velocity oscillations with the intensity oscillations. These have been discussed in detail in a separate paper Sivaraman (1973). A cross-spectral analysJis is then carried out between intensity fluctuations (1) in the continuum and in the line wings and (2) in the continuum and in the line core.
The contribution functions show that the line wings have a mean depth of formation at logrsooo = -1.2 and the line core at logrso00 = -1.6 or -1.8.
The line wing and the continuum show a high coherence reaching a value of 0.95. The wing brightness lags behind the continuum by about 14 ~ or 12 s in the frequency range v=2.0 to 4.0 x 10 -3 Hz. Between the line core and the continuum brightness, the coherence has an average value of 0.65. The core brightness, however, is seen to lead the continuum over the entire frequency range of analysis (v = 2 to 6 x 10-a Hz) by 57 ~ .
It is this phase reversal that manifests itself as a negative correlation coefficient in the analysis of Evans and Catalano. In a collision-controlled line, at the lower levels, i.e. outside the line core, the temperature fluctuations are controlled by the local fluctuations in T e. This local thermal field is in turn assumed to be coupled to the radiation field of the continuum through collisions. This is confirmed by the observations by the high correlation coefficient of 0.95, if we interpret the brightness