html> GCPD: The ubygri photometric system

The ubygri photometric system

Basic Reference

Bahng J.D.R. 1958, ApJ 128, 572


Multicolor observations of stars with composite spectra have been analyzed to determine the individual characteristics of the separate components. Observations of fifty normal stars representing a considerable range in spectral types and luminosity classes were used to establish a set of standard colors. For unreddened stars of population I these colors furnish definite classification criteria for the spectral type and luminosity class and thus are capable of classifying stars in two dimensions. The colors in the red region are the best temperature indicators, while the ultraviolet color is most sensitive to the luminosity effect. In the case of early-type stars the effect of interstellar reddening can be sepatated from temperature reddening and the luminosity effect. In the case of late-type stars, however, the separation cannot be made from the photoelectric colors alone. Observations of two population II stars -one a K giant and the other a subdwarf- confirmed the ultraviolet excess found by other investigators and indicated a temperature lower than that normally found for population I stars of the same spectral type.

Observed colors of thirty stars with known or suspected composite spectra were compared with artificial colors calculated from selected combinations of two standard stars. The selection was guided by the spectroscopic results and such other information on reddening, parallax, and the like as was available. In most cases it was found that a unique classification could be made by the present method with the information on hand. This ability to interpret the colors and spectra of unresolved binary stars indiates that the multicolor method may be useful in identifying the components of a stellar population in much more complex composite sources.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

u-g, b-g, r-y, i-y


3.5 mm Schott RG10
2 mm Schott RG2 + interference filter G125
2 mm Corning 3385 + 2.5 mm Corning 9788, cemented
3 mm Corning 3384
2 mm Schott BG12 + 2 mm Schott GG13, cemented
3 mm Corning + 1 mm clear glass, cemented

Transmission curves



(B-V) values in the Johnson system are computed with the relation:

(B-V) = 0.834 (b-g) +0.585

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Last update: 21 May 1996