Strömgren photometric system explained

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

b and y filters (b - y) without the effects of reddening, termed m _{1} and c _{1} .^[3]

Wavelength and half-width response functions

The following table shows the characteristics of each of the filters used (represented colors are only approximate):

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

Note: colors are only approximate and based on wavelength to sRGB representation (when possible).^[4]

Indices

There are four main highly applied and technical indices:

(b - y) ; m _{1} ; c _{1} ; and \beta .m _{1} = (v - b) - (b - y) c _{1=(u-v)} - (v - b) \beta = \beta _{narrow} - \beta _{wide}

Where;

y magnitudes are well-correlated with Johnson-Morgan V magnitudes (its V band).(b - y) is sensitive to stellar temperature (measure of Paschen continuum).c _{1} is sensitive to the surface gravity (measures Balmer discontinuity strength).m _{1} is sensitive to the metallicity (measure of line blanketing).

See also

• Photometric systems
• Stellar classification

External links

• The Asiago Database on Photometric Systems
• The uvby photometric system
• Stromgren photometric system tutorial
• SAGA: Strömgren survey for Asteroseismology and Galactic Archaeology

Notes and References

1. Strömgren. Bengt. Two-dimensional spectral classification of F stars through photoelectric photometry with interference filters. 1956. Vistas in Astronomy. 2. 1. 1336–1346. 10.1016/0083-6656(56)90060-5. 1956VA......2.1336S.
2. Crawford. D. L.. Two-Dimensional Spectral Classification by Narrow-Band Photometry for B Stars in Clusters and Associations. 1958. Astrophysical Journal. 128. 185–206. 10.1086/146536. 1958ApJ...128..185C.
3. Paunzen. E.. A new catalogue of Strömgren-Crawford uvbyβ photometry. 2015 . Astronomy and Astrophysics. 580 . A23. 10.1051/0004-6361/201526413. 2015A&A...580A..23P. 1506.04568.
4. Web site: Light wavelength to RGB Converter . 2023-07-28 . www.johndcook.com.