Calibration in Temperature of Photometric Parameters

It is very easy to use a Planck distribution to show that a color index is a temperature parameter, but it is more difficult to calibrate such a color index in terms of temperature because only a few Teff values are determined. A pioneering work is that of Kuiper (1938), who derived a temperature scale according to spectral type (from A0 to M2 for dwarfs and from G0 to M8 for giants) and a Becker index. The first study giving a relation between Teff and a photoelectric color index is that of Popper (1959) in which the author derives a relation between Teff and B-V for the A and F stars and for G8 to K5 (dwarf and giant) stars. On this occasion, Popper shows the relation between temperature parameters of two photometric systems, R-I from the six-color system of Stebbins and Whitford, and B-V. This work was followed by a quantity of others from numerous authors in various systems, one of the most important being that of Johnson (1966). The purpose of the present study is not to review all the relations to be found in the literature but to define a set of stars which can be used to determine a calibration of a photometric parameter in terms of Teff.