A new four-color intermediate-band photometric system.

A four-color UVGR intermediate-band photometric system is discussed which was developed to avoid several pitfalls of the standard UBV system. The bands are essentially nonoverlapping and are designed to exclude the strongest night-sky lines at most sites. The ultraviolet band (u) is not open at the short-wavelength end, is narrow enough that second-order extinction coefficients are not necessary, and its response is entirely shortward of the Balmer jump, making the (u-v) color index a sensitive measure of the Balmer discontinuity. The filters employed are described, the magnitude and extinction equations are given, and a list of standard stars defining the photometric system is provided. It is noted that the characteristics of the present system should make it far more powerful than the UBV system for the study of stellar temperatures, gravities in early-type stars, and metallicity in middle to late-type stars.