Photometric study of faint early-type stars in the southern Milky Way

UBV photoelectric observations are presented for 101 faint early-type (mainly OB) stars in four regions of the southern Milky Way: two in Vela, one in Centaurus, and one in Circinus; H-beta data are also given for the brightest stars. Objective-prism plates showing the H-alpha region of the spectrum are used, together with published results from other authors, to recognize Be stars in the sample. A new young open cluster related to the H II region RCW 38 in Vela is found at 1.7 kpc from the sun, and the existence of at least a spur in the local arm towards galactic longitude of about 270 deg is favored; whether such a feature extends beyond that distance cannot be decided from the data. Most of the stars studied in the Centaurus region seem to belong to the Centaurus OB 1 association, at 2.4 kpc from the sun, and lie in the Sagittarius-Carina arm. It is not clear if the stars observed in the Circinus region are physically related to each other, but their distances to the sun also place most of them in the Sagittarius-Carina arm.