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.
Indices
b-y, m1, c1, β
m1 = (v - b) - (b - y)
c1 = (u - v) - (v - b)
β = βnarrow-βwide
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).
References
Strömgren photometric system Wikipedia(Text) CC BY-SA