Kinematics of nearby OB3 stars with interstellar CaII line distances

Abstract

We tested the distances derived from the equivalent widths of interstellar CaII 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. It is shown that these stars are tightly bounded with the Gould Belt structure. Most part of this sample (about 100 stars) show the same kinematics as the sample of distant OB3 stars. Their galactocentric radial velocities are in good agreement with the following spiral density wave parameters: amplitude of radial perturbations $f_R\approx$12 km/s, wavelength $\lambda\approx2.3$ kpc and phase of the Sun in spiral wave $\chi_\odot\approx-90^\circ$. But we revealed 20 stars with absolutely unusual kinematical features. Their galactocentric radial velocities show a wave, biased on $\approx180^\circ$ with respect to the wave, found from the whole sample. The idea of superposition of two spiral patterns seems to be probable.