Strömgren photometric system

The photometric system by Strömgren, 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
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 indices : (b−y), m1, c1, 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.

(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).

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See also

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. Bibcode:1956VA......2.1336S. doi:10.1016/0083-6656(56)90060-5.
  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. Bibcode:1958ApJ...128..185C. doi:10.1086/146536.
  3. Paunzen, E. (2015). "A new catalogue of Strömgren-Crawford uvbyβ photometry". Astronomy and Astrophysics. 580: A23. arXiv:1506.04568. Bibcode:2015A&A...580A..23P. doi:10.1051/0004-6361/201526413.


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