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GCPD: The ubygri photometric system
The ubygri photometric system
Basic Reference
Bahng J.D.R. 1958, ApJ 128, 572
Abstract
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.
Content
Access to the data and references
Asiago Database on Photometric System (ADPS)
Indices and Parameters
u-g, b-g, r-y, i-y
Filters
- Infrared
- 3.5 mm Schott RG10
- Red
- 2 mm Schott RG2 + interference filter G125
- Yellow
- 2 mm Corning 3385 + 2.5 mm Corning 9788, cemented
- Green
- 3 mm Corning 3384
- Blue
- 2 mm Schott BG12 + 2 mm Schott GG13, cemented
- Ultraviolet
- 3 mm Corning + 1 mm clear glass, cemented
Photomultiplier
- RCA C7160, for the Infrared, Red and Yellow colours
- RCA 1P21, for the Green, Blue and Ultraviolet colours
Transformation
(B-V) values in the Johnson system are computed with the relation:
(B-V) = 0.834 (b-g) +0.585
Please, send your
commentsto epaunzen@physics.muni.cz
epaunzen@physics.muni.cz
Last update: 21 May 1996