The UBVr20 photometric system

Basic Reference

Sandage A., Smith L.L. 1963, ApJ 137, 1057


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 lambda = 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 Hyades-like stars in both the U-B, v-r and the B-V, two color diagrams. The blanketing theory, extended to the v-r color, shows that the color changes delta(U-B), and delta(B-V), and (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 delta(U-B) = 0.40, delta(B-V) = 0.18 delta (v-r) = 0.04, and delta(G -I) of the Stebbins-Whitford six color system = 0.00, before comparison with Hyades-like 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.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

U-B, B-V, V-r20, V


Transmission curves


RCA C7237


We have looked for cross-identifications with HD and DM catalogues.


This link presents comments on the data and coding of the identifications.

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Last update: 21 May 1996