Doppler imaging of a southern ApSi star HD 152564

Abstract

We present the results of the spectroscopic study of a chemically peculiar star HD 152564. Using medium-resolution ($R=37000$) observations obtained with the HRS spectrograph mounted on the South African Large Telescope we determined atmospheric parameters T${}_{eff}$=11950$\pm 200$ K and log g=3.6$\pm 0.2$ dex. Abundance analysis revealed mild deficiency of the light elements and an overabundance of up to $\sim$2 dex of metals with greatest excess for the silicon. With these characteristics HD 152564 is a typical member of the silicon subgroup of Ap stars. Rotational modulation of the light curve and line profiles of HD 152564 are typical for inhomogeneous surface distribution of elements in its atmosphere. We performed multi-element Doppler imaging of the HD 152564 surface. Abundance maps constructed for He, O, Mg, Si, and Fe revealed concentration of these elements in a sequence of equatorial spots as well as in the circumpolar rings. The photometric maximum of the light curve coincided with the visibility of two most overabundant silicon spots. Abundances determined from the different ionisation stages of Fe and Si show clear evidence for vertical stratification of these elements in HD 152564 atmosphere. Meanwhile, the horizontal distribution of silicon reconstructed from the lines of different ionisation stages and excitation energies appeared to be identical with increasing average abundance deeper in atmosphere.

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