On the formation and evolution of magnetic chemically peculiar stars in the solar neighborhood

Abstract

In order to put strict observational constraints on the evolutionary status of the magnetic chemically peculiar stars (CP2) of the upper main sequence, we have investigated a well established sample of galactic field CP2 objects within a radius of 200pc from the Sun in the (X,Y) plane. In total, 182 stars with accurate parallax measurements from the Hipparcos satellite were divided into Si, SiCr and SrCrEu subgroups based on classification resolution data from the literature. Primarily, it was investigated if the CP2 phenomenon occurs at very early stages of the stellar evolution, significantly before these stars reach 30% of their life-time on the main sequence. This result is especially important for theories dealing with stellar dynamos, angular momentum loss during the pre- as well as main sequence and stellar evolutionary codes for CP2 stars. For the calibration of the chosen sample, the well-developed framework of the Geneva 7-color and Stromgren uvbybeta photometric system was used. We are able to show that the CP2 phenomenon occurs continuously at the zero age main sequence for masses between 1.5 and 4.5M(sun}. The magnetic field strengths do not vary significantly during the evolution towards the terminal age main sequence. Only the effective temperature and magnetic field strength seem to determine the kind of peculiarity for those stars. We found several effects during the evolution of CP2 stars at the main sequence, i.e. there are two "critical" temperatures where severe changes take place. There is a transition between Si, SiCr and SrCrEu stars at 10000K whereas a significant decrease to almost zero of evolved SrCrEu objects with masses below 2.25M(sun) at 8000K occurs.