Four-color observations of early-type stars. I. Standards and secondary standards

Four-color observations have been made of 39 standard and 42 secondary standard stars of spectral types O9 to K3. Each standard has been observed an average of 34 times, each secondary standard an average of 32 times. The zero point errors of the indices b - y, c1, and m1 are + 0.001, -0.002, and 0.000 mag, respectively, relative to the published values of Crawford and 13arnes. Most of the secondary standards are fainter than V = 6.0 mag and are intended for use with large telescopes. Subject headings: early-type stars - horizontal-branch stars - photometry