Upper Limits for Magnetic Fields on Pulsating White Dwarfs

A sensitive spectropolarimetric search for magnetic fields has been carried out on a selection of pulsating white dwarfs of both DAV and DBV spectral types. Despite multiple epochs and uncertainties as low as σ B e =1 kG, the observations succeed only in setting upper limits for the fields present on G22629, GD 385, ZZ Ceti, and GD 358. The results are inconsistent with a global magnetic field of the strength suggested by the pulsation spectrum of ZZ Ceti, and they approach in sensitivity the field inferred as existing on GD 358. However, if, as has been proposed, magnetic fields can be generated in many white dwarfs by dynamo action, they could be so tangled in structure as to go undetected by direct observational means.