Stationary components of He I in strong magnetic fields - a tool to identify magnetic DB white dwarfs

In only three of the 61 known magnetic white dwarfs helium has been identied unambiguously while about 20% of all non-magnetic stars of this class are known to contain He I or He II. One reason for this discrepancy is that the identication of peculiar objects as magnetic white dwarfs is based either on the presence of hydrogen line components in strong magnetic elds { for which atomic data exist since 1984 { or the polarization of the corresponding radiation which has not been measured for many objects. Until recently, data for He I data were available only for magnetic elds below 20 MG. This changed with the publication of extensive data by the group in Heidelberg. The corresponding calculations have now been completed for the energetically lowest ve states of singlet and triplet symmetry for the subspaces withjmj3; selected calculations have been performed for even higher excitations. In strongly magnetized white dwarfs only line components are visible whose wavelengths vary slowly with respect to the magnetic eld, particularly stationary components which have a wavelength minimum or maximum in the range of the magnetic elds strengths on the stellar surface. In view of the many ongoing surveys nding white dwarfs we want to provide the astronomical community with a tool to identify helium in white dwarfs for elds up to 5.3 GG. To this end we present all calculated helium line components whose wavelengths in the UV, optical, and near IR vary slowly enough with respect to the eld strength to produce visible absorption features. We also list all stationary line components in this spectral range. Finally, we nd series of minima and maxima which occur as a result of series of extremal transitions to increasingly higher excitations. We estimated the limits for 8 series which can possibly give rise to additional absorption in white dwarf spectra; one strong absorption feature in GD229 which is yet unexplained by stationary components is very close to two estimated series limits.