Strömgren Photometric System

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 ${\displaystyle b}$ 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	style="background-color: Template:Wavelength color; color:#ffffff; text-align:center;" | 411	style="background-color: Template:Wavelength color; color:#ffffff; text-align:center;" | 467	style="background-color: Template:Wavelength color; color:#000000; text-align:center;" | 547	style="background-color: Template:Wavelength color; color:#000000; text-align:center;"| 485.8	style="background-color: Template:Wavelength color; color:#000000; text-align:center;" | 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 with Johnson-Morgan V magnitudes (its V band).
• ${\displaystyle (b-y)}$ is sensitive to stellar temperature (measure of Paschen continuum).
• ${\displaystyle c_1}$ is sensitive to the surface gravity (measures Balmer discontinuity strength).
• ${\displaystyle m_1}$ is sensitive to the metallicity (measure of line 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

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