Unbiased Luminosity Calibrations For Hipparcos Data

One of the main uses of the Hipparcos astrometric parameters is the calibration of stellar luminosities against colour indices. The high quality of Hipparcos parameters would however be useless if selection biases were not taken into account. Using parametrical probability density functions, a maximum likelihood algorithm has been developed. It takes into account limiting magnitude or limiting parallax in order to compute unbiased estimates of various parameters: absolute magnitude (as a function of colour indices, metallicity, v sin i), galactic scale height, and first- and second-order moment of the velocity ellipsoid. As a by-product, improved estimates of distances can be obtained. A multi-platform, tcl/tk based user interface has been built which allows to determine the relevant parameters using Hipparcos data. The algorithm is described, together with the adopted parametrical models, and several applications are given. Key words: Luminosity calibration. 1. INTRODUCTION The Hippar..