COMPARISON OF 2 DIFFERENT EXTINCTION LAWS WITH HIPPARCOS OBSERVATIONS

Interstellar absorption in the galactic plane is highly variable from one direction to another. In this paper colour excesses and distances from a new open cluster sample are used to investigate the spatial dis tribution of the interstellar extinction. An inverse method (Tarantola & Valette, 1982) is used to construct the extinction map in the galac tic plane below \b\ < 10 degrees. The A(upsilon)(r, l) diagrams are co mpared with those derived from individual stars (Arenou et al. 1992, N eckel & Klare 1980). An analytic expression for the interstellar extin ction as a function of galactic longitude and distance in the solar ne ighborhood is given. The comparison of the model predictions with Hipp arcos observations in the 4-dimensional space of (V, B - V, H-upsilon, r) shows that our extinction model provides a better fit to the data. However, a new and more detailed extinction model is still lacking.