A STATISTICAL STUDY OF THE DISTRIBUTION OF STARS IN THE LOG T(EFF) LOG GN PLANE

A statistical study is made of the distribution of stars in the log T( eff)-log g(N) plane based on the photometric data set of the Geneva sy stem. To that end we made an analysis of the methods for deriving the atmospheric parameters T(eff) (effective temperature) and log g(N) (th e Newtonian acceleration of gravity) from different sets of photometri c data, corrected for the influence of extinction. We found, using the Geneva photometric system, that the Newtonian gravity can only be det ermined with good accuracy for stars with effective temperatures below 10000 K. We show the relations between luminosity class and gravity f or stars with T(eff)-values of 3.75 to 3.94, and compare these with th e theoretically predicted radiative instability line of Gustafsson & P lez (1992).