Kinematics of nearby OB3 stars with interstellar Ca II line distances

We tested distances derived from the equivalent widths of interstellar Ca II spectral lines by Megier et al. (2009). To this end, we used a sample of nearby 126 young OB3 stars (r < 1 kpc) with known proper motions and line-of-site velocities. We shown that these stars are closely associated with the Gould Belt structure. The bulk of the sample (about 100 stars) shows the same kinematics as the sample of distant OB3 stars. Their galactocentric radial velocities agree well with the following spiral density wave parameters: the amplitude of radial perturbations f_R ≈ 12 km s^–1, wavelength λ ≈ 2.3 kpc, and phase of the Sun in spiral wave χ⊙ ≈ –90°. However, we revealed 20 stars with absolutely unusual kinematical features. Their galactocentric radial velocities show a wave shifted by ≈180° with respect to the wave found from the entire sample. The superposition of two spiral patterns seems to be a likely explanation. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)