The 12-colour photometric system

Basic Reference

Wood D.B. 1969, AJ 74, 177

Abstract

A wide-baseline color system designed primarily for studying galaxy synthesis is described, which utilizes seven filters placed in continuum regions, and five filters placed on certain absorption features. Observations of 93 standard stars later than B7, and of all luminosity classes are presented and the relationship of the observations with temperature, luminosity, and metal abudance investigated. A color index based upon the Mgb and MgH absorption features near lambda 5175 is particularly useful for luminosity resolution for stars of spectral type G5 and later. It is also strongly sensitive to metal abundance.

Content

Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

C35, C41, C47, C55, C60, C67, C73, L52, L59, L66, L62, L71

Filters

          Effective
 Filter   wavelength   Width    Feature
              [Å]       [Å]

    u        3459       375     Balmer discontinuity
    v        4102       195     Metallic lines
    b        4667       180     Continuum
    g        5169        56     Mg, MgH
    y        5470       233     Continuum
    a        5901        64     Na D, TiO
    o        6029       145     Continuum
    t1       6220        79     TiO
    h        6571        83     Halpha
    r        6696       155     Continuum
    t2       7118        96     TiO
    i        7331       100     Continuum

Transmission curves

Parameters

Colour indices

    Mm = 1/4 (Mb + My + Mo + Mr)

    C35 = Mu - Mm          C60 = Mo - Mm
    C41 = Mv - Mm          C62 = Mt1 - Mm
    C47 = Mb - Mm          C66 = Mh - Mm
    C52 = Mg - Mm          C67 = Mr - Mm
    C55 = My - Mm          C71 = Mt2 - Mm
    C59 = Ma - Mm          C72 = Mi - Mm

Line indices

    L52 = C52 - 1/2 (C47 + C55)
    L59 = C59 - 1/2 (C55 + C60)
    L62 = C62 - 1/2 (C60 + C67)
    L66 = C66 - 1/2 (C60 + C67)
    L71 = C71 - 1/2 (C67 + C73)

Indices analogous to Strömgren m1 and c1 may be defined as

    I41 = (C41 - C47) - (C47 - C55)
    I35 = (C35 - C41) - (C41 - C47)

Photomultiplier

EMI 9558A tri-alkali
Please, send your commentsto Jean-Claude.Mermilliod@obs.unige.ch
Jean-Claude.Mermilliod@obs.unige.ch
Last update: 21 May 1996