1996A&A...313..209W

We present a magnetic model for the A2pCr star HD 192678 based upon modeling of new and previously published longitudinal magnetic field measurements, surface field measurements, broadband linear polarimetry and unpolarized high-resolution spectra. The limitations of the classical dipole oblique rotator model are clearly detectable in the case of HD 192678. An oblique rotating dipole is not capable of simultaneously reproducing the surface field variations and the broadband linear polarization variations. Line profile variations of the Fe II λ6149.2 Zeeman doublet may be consistent with a dipole field whose pole-to-equator modulus ratio has been decreased by about 20%. However, this is uncertain since it relies critically on the amount of microturbulence present, about which we have little information. Excess broadening of Fe II λ6149.2 is apparent which appears to be neither rotational nor microturbulent in origin, and may be indicative of small photospheric regions of high field strength. Our magnetic model for HD 192678 consists of an oblique rotating dipole with modified field line inclinations. The polar field strength of the dipole is 6.8±0.2kG, with i=173±5deg and β=120±7deg. This model contains a region of open field lines near the magnetic equator, a recurring feature in magnetic models of a number of Ap stars (Leroy et al. 1995b).