Strong Magnetic Fields in Nova Systems

Extract

The discovery of variable circular polarization in V1500 Cygni (the remnant of Nova Cygni 1975) is the strongest evidence for the presence of highly magnetic white dwarfs in nova systems. If interpreted in terms of diluted cyclotron emission from a hot accretion shock, the recent observations of Schmidt and Stockman (1990 preprint, Ap. J. 1991) of the color dependence of the circular polarization can provide a empirical lower-limit to the primary’s magnetic field strength of B > 25 × 10⁶ gauss. Such a field strength is comparable to those observed in other magnetic variables, thus providing support for the general picture of the current and pre-nova system and the explanation for the observed search-light and period changes following the eruption. Schmidt and Stockman have also measured lengthening of the polarimetric period indicating that the system will be resynchronized within a few centuries and well before the next nova eruption. This is an independent confirmation of a significant magnetic moment for the white dwarf primary.