SIMBAD references

We reveal sufficient evidence that the physical characteristics of Ap stars are related to binarity. The Ap star peculiarity [represented by the Δ(V1-G) value and magnetic field strength] diminishes with eccentricity, and it may also increase with orbital period (P_orb). This pattern, however, does not hold for large orbital periods. A striking gap that occurs in the orbital period distribution of Ap binaries at 160-600d might well mark a discontinuity in the above-mentioned behaviour. There is also an interesting indication that the Ap star eccentricities are relatively lower than those of corresponding B9-A2 normal binaries for P_orb>10d. All this gives serious support to the pioneering idea of Abt & Snowden concerning a possible interplay between the magnetism of Ap stars and their binarity. Nevertheless, we argue instead in favour of another mechanism, namely that it is binarity that affects magnetism and not the opposite, and suggest the presence of a new magnetohydrodynamical mechanism induced by the stellar companion and stretching to surprisingly large P_orb.