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 b and y filters (b−y) without the effects of reddening, termed m1 and c1.[3]

## Contents

* 1 Wavelength and half-width response functions
* 2 Indices
* 3 See also
* 4 References
* 5 External links

## 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

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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]

## Indices

There are four main highly applied and technical indices: (b−y); m1; c1; and β.

* m1=(v−b)−(b−y)
* c1=(u−v)−(v−b)
* β=βnarrow−βwide

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).
* c1 is sensitive to the surface gravity (measures Balmer discontinuity strength).
* m1 is sensitive to the metallicity (measure of line blanketing).

## See also

* Photometric systems
* Stellar classification

## References

1. ↑ Strömgren, Bengt (1956). "Two-dimensional spectral classification of F stars through photoelectric photometry with interference filters". Vistas in Astronomy 2 (1): 1336–1346. doi:10.1016/0083-6656(56)90060-5. Bibcode: 1956VA......2.1336S.
2. ↑ Crawford, D. L. (1958). "Two-Dimensional Spectral Classification by Narrow-Band Photometry for B Stars in Clusters and Associations". Astrophysical Journal 128: 185–206. doi:10.1086/146536. Bibcode: 1958ApJ...128..185C.
3. ↑ 3.0 3.1 Paunzen, E. (2015). "A new catalogue of Strömgren-Crawford uvbyβ photometry". Astronomy and Astrophysics 580: A23. doi:10.1051/0004-6361/201526413. Bibcode: 2015A&A...580A..23P.
4. ↑ "Light wavelength to RGB Converter". https://www.johndcook.com/wavelength_to_RGB.html.

## External links

* 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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