Flux Measurements at the Centers of Stellar H- and K-Lines

The coudé scanner of the 100-inch telescope has been used as a two-channel photometer to measure the fluxes at the centers of stellar H- and K-lines, for the purpose of initiating a search for stellar ana- logue~ of the solar cycle. From the Stromgren-Perry catalogue 139 stars previously observed at 10 A mm1 dispersion were selected for this purpose and included most of those in which H-K emission had been seen on the spectrograms. Reasonable agreement between eye-estimated intensities and the photometric results shows that the procedure adopted is suitable for specifying chromospheric activity, but with an accuracy much improved over eye estimates. The probable error of a single measurement of a line is a little less than 2 per cent. No undoubted variations have been observed during a year's observation. However, the measures are discussed in connection with the Stromgren-Perry photometric parameters b - y, in1, C1. In this way it is possible to trace in some detail the course of chromospheric evolution as stars begin to move off the zero-age main sequence (ZAMS) toward the giant region. Doublet ratios of the chromospheric compo- nents of H and K are one of the by-products of the observations. They show that, in general, the optical thickness of the gas masses involved cannot be very great