Photoelectric Studies. I. Color-Luminosity Array for Members of the Hyades Cluster.

Observations of 64 Hyades cluster stars have been made with photomultiplier photometers on the Washburn 15-inch and the Lick 12-inch refractors. The magnitudes and colors have been reduced to no atmosphere with the use of extinction factors determined each night. The dependence of the extinction factors upon the color of the star has also been determined nightly; the results for a typical night have been described to illustrate the procedure. The color system has a baseline slightly longer and shifted to the viofrt of the International System. Both the colors and the magnitudes have been reduced to the International System, Pg and Cp, by comparisons with the North Polar Sequence. The observed magnitudes have been converted to absolute magnitudes by the use of an unpublished value for the convergent of the cluster, A = 94?0, D = + 7?6, derived by R. E. Wilson. The resulting color-luminosity array, consisting of dwarf, , subdwarf, and giant sequences, satisfies the observations of 52 of the 64 stars observed, within the uncertainties of the proper motions and colors. This result indicates that there is inappreciable "cosmical" dispersion in luminosity for the various sequences of the color-luminosity array. Of the remaining 12 stars, 9 are known, or probable, binaries, 2 stars populate an additional sequence to be described in a later paper, and 1 star is possibly a nonmember of the cluster. It is shown that the stars with high rotational velocities populate mainly the brightdwarf sequence.