Non-LTE Abundances of Helium, Magnesium, and Silicon in the Atmosphere of the Bp He-weak Star HD 175156

The synthesis of the spectral range 4400-4600 Å in UVES spectra of HD 175156 allows to estimate NLTE abundances of helium, nitrogen, oxygen, magnesium and silicon for this evolved B subgiant. The NLTE models used are published models from the BSTAR grid. Compared to the solar abundances, helium and magnesium are found to be overabundant by a factor of 2.0, oxygen and silicon underabundant by a factor of 0.75. Nitrogen has a solar abundance. The overabundances of helium and magnesium are reduced compared to their determinations in Local Thermodynamical Equilibrium.