The K-line photometric system

Basic Reference

Henry R.C. 1969, Astrophys. J. Suppl. 18, 47


A narrow-band spectrometer, compensated for seeing and transparency variations, has been constructed and used to measure the strength of the calcium K-line in 146 A-type stars. The K-line strength was found to be a reddening-independent temperature parameter in A stars, with an rms errors of +- 0.012 mag in the derived b-y color. Abnormal stars usually could be excluded using four-color and HBeta photometry. Additional scatter present in the K-line strength was found to be due to calcium abundance variations, and a correlation was obtained with deviations from the normal value of StrÖmgren's [m1] metal-abundance index. Line-strength calculations showed that the relative abundance of calcium in low-velocity, main-sequence A stars varies by a factor 2. A systematic overabundance of about a factor of 2 for these stars, relative to the Sun, is suggested by the calculations. A substantial fraction of the Am stars observed were found, surprisingly, to have normal K-line strengths. Several new low-velocity, low-metal-abundance stars and K-line variables were discovered.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

V, K

Narrow-band spectrometer

Wavelength : 3933.68 Å ; Width : 8.50 Å
Wavelength : 3915.3 Å ; Width : 8.23 Å


EMR 641-A
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Last update: 21 May 1996