Secondary Standard Stars in the Four-Color System

Abstract

Now that larger telescopes are being used to make photometric measures of very faint stars, fainter standard stars are needed. Most of the stars listed in the standard star list of Crawford and Barnes (1970) are too bright, even for a 1.5 m telescope. Over the past two decades observations have been made of B, A and F-type stars in the magnitude range V = 6 to 13 in the northern and southern hemispheres in a program of four-color photometry of field and blue horizontal-branch stars. An earlier list of secondary standards was published in Philip and Philip (1973). The present paper reports on over twice as many standard stars and the secondary standards are increased by about 20%. The number of observations per star is substantially increased.