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Published online by Cambridge University Press: 14 August 2015
In the preceeding paper of this Symposium by Cayrel and Perrin (1978), HR diagrams have been discussed, in which the [Fe/H] ratio and effective temperatures are derived from model atmosphere analyses and absolute bolometric magnitude from apparent visual magnitude, parallax and bolometric correction. The use of parallaxes imposes a very severe restriction on the number of objects, as parallaxes of at least 0″.050 are needed to have an absolute magnitude good to ±0m.4.