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Paper: The Cause of Surface Abundance Inhomogeneities in the Ap Star 78 Vir
Volume: 518, Physics of Magnetic Stars
Page: 173
Authors: Romanovskaya, A.; Ryabchikova, T.; Shulyak, D.
Abstract: We have investigated the vertical abundance distribution of Cr and Fe at different rotational phases in the magnetic Ap star 78 Vir (HD 118022) using high-resolution high-S/N spectra. The spectra were analysed at 8 phases of rotation. For each phase we derived the chemical composition and performed a stratification analysis for Fe and Cr elements. The comparison of the vertical element distributions at different phases showed that at all rotational phases Cr and Fe have sharp abundance gradients with abundance jumps at optical depths –1.5≤logτ5000≤–1.0. The position of the abundance jumps slightly varies with phase, moving towards the upper atmospheric layers in the phases of increased surface abundance of the element. Rotational variations of the abundance jump positions as well as the surface abundances seem to correlate with the magnetic field variations. Our results suggest that the movement of abundance jumps towards the uppermost layers of the atmosphere may be the main reason for the observed surface inhomogeneities of Cr and Fe: higher surface abundance corresponds to a transition region that occurs higher in the atmosphere, and vice versa.
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