Surface abundances of light elements for a large sample of early B-type stars – IV. The magnesium abundance in 52 stars – a test of metallicity

From high-resolution spectra a non-local thermodynamic equilibrium analysis of the Mgii 4481.2-Åfeature is implemented for 52 early and medium local B stars on the main sequence (MS). The influence of the neighbouring line Aliii 4479.9-Åis considered. The magnesium abundance is determined; it is found that logɛ(Mg) = 7.67 ± 0.21 on average. It is shown that uncertainties in the microturbulent parameter Vt are the main source of errors in logɛ(Mg). When using 36 stars with the most reliable Vt values derived from Oii and Nii lines, we obtain the mean abundance logɛ(Mg) = 7.59 ± 0.15. The latter value is precisely confirmed for several hot B stars from an analysis of the Mgii 7877-Åweak line. The derived abundance logɛ(Mg) = 7.59 ± 0.15 is in excellent agreement with the solar magnesium abundance logɛ⊙ (Mg) = 7.55 ± 0.02, as well as with the proto-Sun abundance logɛps(Mg) = 7.62 ± 0.02. Thus, it is confirmed that the Sun and the B-type MS stars in our neighbourhood have the same metallicity.