The spatial distribution of O-B5 stars in the solar neighborhood as measured by Hipparcos

We have developed a method to calculate the fundamental parameters of the v ertical structure of the Galaxy in the solar neighborhood from trigonometri c parallaxes alone. The method takes into account Lutz-Kelker-type biases i n a self-consistent way and has been applied to a sample of O-B5 stars obta ined from the Hipparcos catalog. We find that the Sun is located 24.2 +/- 1 .7 (random) +/- 0.4 (systematic) pc above the Galactic plane and that the d isk O-B5 stellar population is distributed with a scale height of 34.2 +/- 0.8 (random) +/- 2.5 (systematic) pc and an integrated surface density of [ 1.62 +/- 0.04 (random) +/- 0.14 (systematic)] x 10(-3) stars pc(-2). A halo component is also detected in the distribution and constitutes at least ap proximate to5% of the total O-B5 population. The O-B5 stellar population wi thin similar to 100 pc of the Sun has an anomalous spatial distribution, wi th a less than average number density. This local disturbance is probably a ssociated with the expansion of the Gould Belt.