The CaII HK photometric system

Basic Reference

Anthony-Twarog B.J., Laird J.B., Payne D., Twarog B.A. (1991) Astron. J. 101, 1902


A fifth filter (fwhm = 90 Å) centered on CaII H and K has been developed for use with the standard uvby system. The filter, called Ca, is designed primarily for applications to metal-poor dwrafs and red giants, regions where the uvby metallicity index, m1, loses some sensitivity. An index, hk, is defined by replacing v in m1 by Ca. The effects of interstellar extinction on the index are modeled and demonstrated to be modest and relatively insensitive to spectral type. Observations of V, (b-y), and hk for 163 primary standards are dtailed and transformed to the standard V and (b-y) system. A qualitative analysis using only the primary standards indicates that hk is more sensitive than m1 over the regions of interest by about a factor of 3.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

V, b-y, hk

hk = (Ca - b) - (b - y) is intended to be a metallicity index.


Ca : narrow band filter, with half width of 90 Å

Transmission curve

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Last update: 13 September 2002