Modélisation d'étoiles naines blanches magnétiques éléments lourds
We present, for the first time, detailed analyses of white dwarf stars showing heavy metal lines and large magnetic fields. These analyses are carried out with a new atmosphere code able to compute the position and strength of lines for all elements (from carbon to copper) in the Paschen-Back regime for an arbitrary geometry. Firstly, we describe the effect of a magnetic field on the atomic energy levels, first with the Zeeman effect for weak fields then in the Paschen-Back regime when the pertubative approach is no longer valid. We then explore the effect of the magnetic field geometry, especially the differences between models calculated assuming a constant field and those with a dipolar geometry. Some studies recently suggested that in the presence of an intense magnetic field, the convective movement is strongly inhibited, renderingthe atmosphere mostly radiative (Tremblay et al., 2015). We briefly explore the impact the suppression of the convective energy transport can have on the analyses' results of magnetic stars. In order to carry out a thorough analysis of some magnetic stars, we have applied changes to the atmospheric models used, for example by adding magnetic treatment of metallic lines. With these new tools, we analyse for the first time, in a rigorous manner, the stars G165-7, J2105+0900 and LHS 2534, three magnetic stars showing heavy elements. We study their atmospheric parameters such as the effective temperature, surface gravity and metal abundances, and then explore the possibility of having pure radiative atmospheres, where the convection would be inhibited by intense magnetic fields. We find that hydrogen rich models cannot reproduce observations, unlike those rich in helium where the convective movement takes place out of the line forming region. We finally note that a centered dipolar magnetic field is not able to reproduce the line profiles of a given multiplet, since the sigma components (those to the left and the right of the central line) predicted are too broad. Spectroscopic observations are better reproduced with constant magnetic field models, or with a strongly offset dipole in the -z axis, indicating that the actual field geometry probably is more complex than a simple dipole.
Atmospheric parameters White dwarfs Magnetic fields