2000A&A...355..308A

We determined effective temperatures and surface gravities for 17 magnetic Chemically Peculiar (mCP) stars by comparing optical region spectrophotometry and Hγ profiles with the predictions of ATLAS9 model atmospheres. Although solar composition models can fit the energy distributions of the normal and many Mercury-Manganese stars, they cannot match the optical energy distributions of the mCP stars, especially the λ5200 broad, continuum regions. The role of metallicity and microturbulence to provide appropriate energy distributions which fit those observed for the mCP stars is investigated. Using metal-rich models with the opacity distribution functions for microturbulent velocities of 4 and 8 km.s^–1, their λ5200 broad, continuum features are often fit as part of this process. For some stars it is impossible to fit simultaneously both this feature and the line blanketing in the Hγ region. This suggests that this continuum feature is produced by elements other than those which contribute most of the general line blanketing. A systematic difference in the temperatures found by the photometric and spectrophotometric approaches is discovered for the hotter mCP stars. An investigation of 10 Mercury-Manganese stars shows a similar effect. This may be due to the photospheric compositions becoming less solar with increasing temperature.