The Strömgren photometric system, abbreviated also as uvbyβ or simply uvby, and sometimes referred as Strömgren - Crawford photometric system, is a four-colour medium-passband photometric system plus Hβ (H-beta) filters for determining magnitudes and obtaining spectral classification of stars. Its use was pioneered by the Danish astronomer Bengt Strömgren in 1956[1] and was extended by his colleague the American astronomer David L. Crawford in 1958.[2]
It is often considered to be a powerful tool and successful investigating the brightness and effective temperature of stars. This photometric system also has a general advantage as it can be used to measure the effects of reddening and interstellar extinction.[3] This system also allows calculation of parameters from the and filters without the effects of reddening, termed and .[3]
Wavelength and half-width response functions
editThe following table shows the characteristics of each of the filters used (represented colors are only approximate):
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).[4]Strömgren photometric system filter wavelength and half-width response functions u v b y βnarrow βwide Peak wavelength (nm) 350 411 467 547 485.8 485 Half-width (nm) 30 19 18 23 2.9 12.9
Indices
editThere are four main highly applied and technical indices: ;
;
; and
.
Where;
magnitudes are well-correlated with Johnson-Morgan V magnitudes (its V band).
is sensitive to stellar temperature (measure of Paschen continuum).
is sensitive to the surface gravity (measures Balmer discontinuity strength).
is sensitive to the metallicity (measure of line blanketing).