Physical properties of a complete volume-limited sample of Ap/Bp stars: Magnetic. rotational, multiplicity, and evolutionary properties of magnetic intermediate-mass stars within 100 pc of the sun

Abstract

The population of all magnetic chemically peculiar stars (Ap stars) within 100 parsecs of the sun has been identified and investigated, determining fundamental parameters, rotational properties, and magnetic field characteristics.

Using the HIPPARCOS Catalogue all intermediate mass stars within 100 pc of the sun have been identified. From published catalogues and other literature sources, we have identified 57 bona fide magnetic Ap/Bp stars in this distance-selected sample. Effective temperature, luminosity, radius, and mass were determined for each of the sample stars using published photometry and photometric calibrations, energy distributions, and HIPPARCOS parallaxes. Using the MuSiCoS spectropolarimeter at the Pic du Midi Observatory and the Least Squares Deconvolution procedure, Stokes I and V profiles were obtained for 26 of the 57 Ap sample stars. These observations were used in combination with previously published data to refine rotation periods, to determine projected rotational velocities, and to determine magnetic field strengths and geometries.

Using the mass statistics of the sample Ap and non-Ap stars, the mass incidence distribution of magnetic intermediate mass stars in the solar neighbourhood has been derived. The Ap stars make up 1.7 to 2.8% (57 Ap stars out of 3904 intermediate mass stars) of all intermediate mass stars within 100 parsecs of the sun, and appear uniformly distributed across the main sequence. Statistical distributions of various properties, including distributions of the surface dipole field strength, rotational axis inclination, magnetic obliquity angle, and rotational period were analyzed. The rotation period distribution peaks at $2.1\pm1.1$ days, and displays an extended tail to very long periods. The majority of Ap stars in the sample have rotational velocities below 70 km/s, although some exhibit v sin i as large as 169 km/s. The histogram of obliquity angles shows a bimodal distribution, with a strong preference for beta angles near 0 and 90 degrees. The derived distribution of inclination angles agrees with that found by Abt (2001) for randomly-oriented rotation axes. The distribution of surface dipole field strengths exhibits a plateau at 2.5+/-0.5 kG, dropping off to higher and lower field strengths. The results obtained agree with those obtained by Auriere et al. (2007), who reported a lower surface field limit at 300 G, proposing a lower limit critical field strength necessary for stable magnetic configurations to exist.