A four-color photometric system applied to line blanketing of subdwarfs.

Photoelectric observations made with a multialkali RCA C7237 photomultiplier (S20 surface) are reported for 96 stars. The usual U, B V band passes were measured, plus an r point at = 6700 A. Conventional U, B, V values were available for nearly all 96 stars, and comparison with our S20 system reduced by linear transformation to U - B, B - V colors, shows that multialkali cathodes can reproduce B - V colors with good accuracy and U - B colors with moderate accuracy. The subdwarfs observed on the program are shown to be separated from strong-lined, Hyades4ike stars in both the U - B, v - r and the B - V, v - r two-color diagrams The blanketing theory, extended to the v - r color, shows that the color changes A(U - B), A(B - V), and A(v - r) predicted for each program star completely eliminates the separation of the subdwarfs from the Hyades-like stars in the two-color diagrams. Previous results, together with the present study, show that the observed colors of a typical globular cluster subdwarf at the main-sequence termination point must be made redder by A(U - B) = 0w40. A(B - V) = Owt8, A(v - r) = 0W()4, and A(G - I) of the Stebbins-Whitford six-color system = 0W()(), before comparison with Hyades4ike stars can be made, which emphasizes the well-known result that broad-band photometry should be done in the red to minimize the effects of Fraunhofer-line blanketing.