Local complex of O and B stars. I. Distribution of stars and interstellar dust

The O-B5 stars, supergiants, young clusters, and associations within 1 kpc of the Sun populate two flat systems inclined to each other by 19'-22'. The present paper discusses the historical background, statistical significance, composition, spatial arrangement of the contents, and interstellar extinction in the two belts. A more or less random distribution in space and in age characterizes the O-B5 stars of the "galactic belt," which is aligned nearly along the Milky Way. The "Gould belt" is inclined to the Milky Way (north in Sco-Oph and south in Orion), and exhibits a projected distribution of O-B5 stars in its mean plane that resembles a "dragonfly," with five major features defining it. A crude "diameter" of the system is pc, and the Sun's position is eccentric, lying toward Ophiuchus. The nuclear age of the system, while not unique, may be characterized as 3 X l0 yr from the spectral type of the broad main-sequence turnup near B2.5. Most of the O-B2 stars and youngest stellar groups near the Sun belong the Gould belt, but both belts have approximately equal space densities of B3-B5 stars and similar average values of interstellar extinction. Although the Gould belt is about three times as compressed vertically as is the galactic belt, each belt shows the same increasing concentration to a plane for the following objects: stars, interstellar dust, and centers of star groups. A small "h6le" around the Sun occurs in the distribution of dust and O-B5 stars.