Astronomy: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 [math]\displaystyle{ b }[/math] and [math]\displaystyle{ y }[/math] filters [math]\displaystyle{ (b-y) }[/math] without the effects of reddening, termed [math]\displaystyle{ m_1 }[/math] and [math]\displaystyle{ c_1 }[/math].[3]
Wavelength and half-width response functions
The 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
There are four main highly applied and technical indices: [math]\displaystyle{ (b-y) }[/math]; [math]\displaystyle{ m_1 }[/math]; [math]\displaystyle{ c_1 }[/math]; and [math]\displaystyle{ \beta }[/math].
- [math]\displaystyle{ m_1 = (v-b) - (b-y) }[/math]
- [math]\displaystyle{ c_1=(u-v) - (v-b) }[/math]
- [math]\displaystyle{ \beta = \beta_{narrow} - \beta_{wide} }[/math]
Where;
- [math]\displaystyle{ y }[/math] magnitudes are well-correlated with Johnson-Morgan V magnitudes (its V band).
- [math]\displaystyle{ (b-y) }[/math] is sensitive to stellar temperature (measure of Paschen continuum).
- [math]\displaystyle{ c_1 }[/math] is sensitive to the surface gravity (measures Balmer discontinuity strength).
- [math]\displaystyle{ m_1 }[/math] is sensitive to the metallicity (measure of line blanketing).
See also
References
- ↑ 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.
- ↑ 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.
- ↑ 3.0 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.
- ↑ "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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