Determination of the optical or physical nature of wird visual binaries by means of two-dimensional conditional probabilities

A sample consisting of 888 wide visual double stars with known relative proper motions has been processed for the HIPPARCOS input catalogue. Brosche et al. (1992) applied two separate criteria on this list to discriminate statistically between physical and optical pairs. The first of these criteria uses the number density constrast, the second the ratio of the tangential velocity to an estimate of the orbital velocity, assuming the pair to be physical. Here we combine these two separate criteria into a single criterion based on a probability depending on two arguments, i.e. on a conditional probability. Statistically, we are thus led to the conclusion that the sample comprises 545 physical and 343 optical pairs.