Rapidly oscillating Ap stars versus non-oscillating Ap stars

The positions in the HR diagram and the kinematic characteristics of rapidly oscillating and non-oscillating chemically peculiar stars are obtained using new Hipparcos proper motions and parallaxes, and our own radial velocity measurements. We find that rapidly oscillating stars, as a group, are (−0.47±0.34) mag above the zero-age main sequence (ZAMS), while the non-oscillating stars are (−1.20±0.65) mag above the ZAMS and so appear slightly more evolved on average. From the comparison of the kinematical characteristics, we conclude that both groups are very similar. The results of radial velocity measurements indicate that there is a real deficiency of binaries among rapidly oscillating stars. Presently, no such star is known to be a spectroscopic binary.