Calibration of photometric absolute magnitudes for subdwarfs with Hipparcos

In order to obtain better photometric distances for high-velocity stars in the Carney et al. (1994) sample, we have undertaken a calibration of photometric absolute magnitudes. From the intersection between this sample and the Hipparcos catalogue (770 common stars), we keep only single stars with the most reliable parallaxes ((sigma pi/pi)(HIP) less than or equal to 0.15). Metallicities, colours and absolute magnitudes of these stars are used with VandenBerg et al. (1998) isochrones in a colour-magnitude diagram. This set of isochrones allows us to derive photometric absolute magnitudes for the highest velocity stars. This photometric parallax calibration is discussed.