Kinematics of nearby OB3 stars with interstellar CaII line distances

TL;DR

This study evaluates the accuracy of CaII line-based distance estimates for nearby OB3 stars and explores their kinematic properties, revealing potential superposition of two spiral patterns in the Milky Way.

Contribution

It provides an empirical validation of CaII line distances and uncovers evidence for multiple spiral wave patterns affecting star kinematics.

Findings

Most stars align with known spiral density wave parameters.

Approximately 20 stars show unusual kinematic features.

Evidence suggests superposition of two spiral patterns.

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.