The long-term behavior of the magnetic field of β Coronae Borealis

Because of conflicting interpretations of its magnetic field variations, we have examined all of the Zeeman analyzed plates of p CrB in the files of the Hale Observatories. We measured all of the plates not previously measured and also all of the plates taken close to south polarity extremum. Our measurements confirm some of the small values of H, at the south polarity extremum reported by Babcock. However, we find some observational evidence that at south polarity extremum there is a correlation between measured field strength and photographic density of the spectroscopic plate. Numerical models show that the effect should be present in an oblique-rotator model with a displaced dipole configuration of the magnetic field. This effect could be responsible for the small fields reported by Babcock and casts further doubts on the reality of nonperiodic variations in p CrB. Subject headings: magnetic stars - peculiar A stars - stars, individual