Abstract

Model atmosphere analysis of the magnetic field in cool, hydrogen-line white dwarfs

Benoit Rolland (Université de Montréal)

Pierre Bergeron Université de Montréal

We present a detailed model atmosphere analysis of the strength and geometry of the magnetic field in cool, hydrogen-line (DA) white dwarfs using offset dipole models. The atmospheric parameters of each star are obtained from fits to the observed photometric energy distribution, while the topology and strength of the magnetic field are determined using spectroscopic fits to the observed Zeeman absorption features at Halpha. We show in particular that most stars in our sample can only be accounted for if they are unresolved double white dwarf systems, one of which even consists of two magnetic DA stars. Our results also suggest that the magnetic field in these cool white dwarfs cannot have a fossil origin, and must be somehow generated by some mechanism that remains unexplained at this stage.

Mode of presentation: poster