UPPER LIMITS FOR MAGNETIC-FIELDS ON PULSATING WHITE-DWARFS

A sensitive spectropolarimetric search for magnetic fields has been ca rried out on a selection of pulsating white dwarfs of both DAV and DBV spectral types. Despite multiple epochs and uncertainties as low as s igma(Be) = 1 kG, the observations succeed only in setting upper limits for the fields present on G226-29, GD 385, ZZ Ceti, and GD 358. The r esults are inconsistent with a global magnetic held of the strength su ggested by the pulsation spectrum of ZZ Ceti, and they approach in sen sitivity 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 undet ected by direct observational means.