TheStrömgren photometric system, abbreviated also asuvbyβ or simplyuvby, and sometimes referred asStrömgren - Crawfordphotometric system, is a four-colour medium-passbandphotometric system plus Hβ (H-beta) filters for determining magnitudes and obtainingspectral classification of stars. Its use was pioneered by the Danish astronomerBengt Strömgren in 1956^[1] and was extended by his colleague the American astronomerDavid 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 andinterstellar extinction.^[3] This system also allows calculation of parameters from the${\displaystyle b}$ and${\displaystyle y}$ filters${\displaystyle (b-y)}$ without the effects of reddening, termed${\displaystyle m_1}$ and${\displaystyle c_1}$.^[3]

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]

There are four main highly applied and technical indices:${\displaystyle (b-y)}$;${\displaystyle m_1}$;${\displaystyle c_1}$; and${\displaystyle \beta }$.

• ${\displaystyle m_1=(v-b)-(b-y)}$
• ${\displaystyle c_1=(u-v)-(v-b)}$
• ${\displaystyle \beta ={\beta }_{narrow}-{\beta }_{wide}}$

Where;

• ${\displaystyle y}$ magnitudes are well-correlated withJohnson-MorganV magnitudes (its V band).
• ${\displaystyle (b-y)}$ is sensitive to stellartemperature (measure ofPaschen continuum).
• ${\displaystyle c_1}$ is sensitive to thesurface gravity (measuresBalmer discontinuity strength).
• ${\displaystyle m_1}$ is sensitive to themetallicity (measure ofline blanketing).

• Photometric systems
• Stellar classification

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

• Photometric systems