Extremely asymmetric bipolar magnetic field of the Bp star HD 57372 (2504.06098v1)

Abstract: Fossil magnetic fields of early-type stars are typically characterised by symmetric or slightly distorted oblique dipolar surface geometries. Contrary to this trend, the late-B magnetic chemically peculiar star HD 57372 exhibits an unusually large rotational variation of its mean magnetic field modulus, suggesting a highly atypical field configuration. In this study, we present a Zeeman Doppler imaging analysis of HD 57372, revealing an exceptionally asymmetric bipolar magnetic topology, rarely observed in early-type stars. According to our magnetic field maps, reconstructed from the intensity and circular polarisation profiles of Fe, Cr, and Ti lines, approximately 66 per cent of the stellar surface is covered by a diffuse outward-directed radial field, with local field strengths reaching 11.6 kG, while the remaining 34 per cent hosts a highly concentrated inward-directed field with a strong horizontal component and a peak strength of 17.8 kG. These unusual surface magnetic field characteristics make HD 57372 a notable object for testing fossil-field theories and interpreting phase-resolved spectropolarimetric observations of early-type stars.