The Washington photometric system

Basic Reference

Canterna R. 1976, Astron. J. 81, 228


A new broad-band photometric system C, M, T1, T2 was developed specifically to obtain accurate temperatures, metal abundances, and a CN index for G and K giants. This new system is more efficient than the UBVRI system. The temperature index T1-T2 is a linear function of R-I. Metal abundances derived from the index delta (M-T1) are uncertain by a factor of 2. The system is capable of separating the effects of blanketing by the molecular CN band system from those of the metallic lines in the ultraviolet. A cyanogen band index delta I(CN) can distinguish between strong CN stars (CN +3, +2) and weak CN stars (CN -3, -2) for giants with [Fe/H] > 1.0. Delta I(CN) has been found to be linearly related to the DDO CN band strength index delta Cm.

Observations of M67 giants and several SMR giants show that (I) M67 is slightly metal deficient compared to normal and not super metal rich, and (2) the large ultraviolet deficiencies of SMR stars are a result of a slight enrichment of metals and anomalously strong CN bands. Finally, the applicability of the C, M, T1, T2, system for abundance studies of G-type dwarfs is promising. The indices delta (M-T1) and delta (C-M) are monotonically related to delta (U-B) for G-type dwarfs and the temperature index is less sensitive to blanketing than B-V or V-r. The effects of reddening and luminosity on the parameters delta (M-T1) and delta I(CN) are discussed.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

V, C-M, M-T1, V-T1, M51


C : 4 mm Corning CS-7-59 + 2.5 mm 80% CuSO4-H2O
Effective wavelength : 3910Å ; Width : 1100Å
M : 3 mm Schott GG455 + 5 mm Corning CS-4-96
Effective wavelength : 5085Å ; Width : 1050Å
T1 : 1.5 mm Schott BG38 + 3mm Schott OG 590
Effective wavelength : 6330Å ; Width : 800Å
T2 : 3 mm Schott RGN 9
Effective wavelength : 7885Å ; Width : 1400Å


RCA C31034 Ga-As


The calibrations have been revised recently.

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Last update: 13 September 2002