INTRINSIC IR COLORS OF NORMAL B-TYPE STARS USING THE GENEVA VISUAL AND ESO IR PHOTOMETRIC SYSTEMS

We present analysis of IR and visual observations of bright, normal B- type stars to derive colour-colour relationships between the visual an d IR wavelength regions. The reddening-free parameters X and Y of the Geneva photometric system (Cramer & Maeder 1979) allow the calculation of precise colour excesses at visual wavelengths and de-reddened obse rvations. We find well-defined linear relationships between the intrin sic [B - V], and [V - m(lambda)]o colours, where m(lambda) is the intr insic near-IR magnitude at the ESO IR J, H, K, L passbands and the IRA S 12 mum passband. We show that the derived visual-IR colour-colour re lationships are in good agreement with those of Johnson (1966) yet are bluer than the relationships derived by Koornneef (1983b). We attribu te this to the fact that Koornneef did not account for interstellar re ddening. The [V - 12mu] colour relationship is also in good agreement with that of Waters et al. (1987). Theoretical colours derived from Ku rucz (1979) model atmospheres of B-type stars are also in good agreeme nt with the near-IR passbands. However, the Kurucz models fail to repr oduce the L band and 12 mum magnitudes of B stars by about 8 - 12% as also found by previous authors. The results of this work will be used in a study of the properties of the near-IR excess emission in Be star s.