Magnetic Doppler imaging of the chemically peculiar star HD 125248 (1601.00349v2)

Abstract: Intermediate-mass, chemically peculiar stars with strong magnetic fields give us an excellent opportunity to study the topology of their surface magnetic fields and the interplay between magnetic geometries and abundance inhomogeneities in their atmospheres. We reconstruct detailed maps of the surface magnetic field and abundance distributions for the magnetic Ap star HD 125248. We performed the analysis based on phase-resolved, four Stokes parameter spectropolarimetric observations obtained with the HARPSpol instrument. These data were interpreted with the magnetic Doppler imaging technique. We improved the atmospheric parameters of the star, T_eff = 9850K +/- 250K and logg = 4.05 +/- 0.10. We performed detailed abundance analysis and discovered vertical stratification effects for the FeII and CrII ions. We computed LSD Stokes profiles and studied their behavior with rotational phase. We improved the rotational period of the star P_rot = 9.29558(6)d. Magnetic Doppler imaging of HD 125248 showed that its magnetic field is mostly poloidal and quasi-dipolar with two large spots of different polarity and field strength. The chemical maps of Fe, Cr, Ce, Nd, Gd, and Ti show abundance contrasts of 0.9-3.5 dex. Among these elements, the Fe abundance map does not show high-contrast features. Cr is overabundant around the negative magnetic pole and has 3.5 dex abundance range. The rare earth elements and Ti are overabundant near the positive magnetic pole. The magnetic field of HD 125248 has strong deviations from the classical axisymmetric dipole field geometry. The comparison to results derived for other stars using four Stokes magnetic Doppler imaging suggests evidence that the field topology becomes simpler with increasing age. The abundance maps show weak correlation with the magnetic field geometry, but they do not agree with the atomic diffusion calculations.