Strömgren photometric system

Strömgren photometric system (uvby) (sometimes also referred as Strömgren - Crawford photometric system) is four-colour medium-band photometric system (plus H-beta filters) for stellar classification. It was pioneered by the Danish astronomer Bengt Strömgren in 1956 and extended by his colleague the American astronomer David L. Crawford in 1958.

b-y, m₁, c₁, β

m₁ = (v - b) - (b - y)

c₁ = (u - v) - (v - b)

β = β_narrow-β_wide

y magnitudes are well-correlated with Johnson-Morgan V magnitudes. b-y is sensitive to stellar temperature (measure of Paschen continuum). c₁ is sensitive to the surface gravity (measures Balmer discontinuity strength). m₁ is sensitive to the metallicity (measure of line blanketing).

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