Studies of magnetic and suspected-magnetic southern white dwarfs

Optical spectrophotometry and circular spectropolarimetry are presented for several candidate magnetic white dwarfs that were identified during the Hamburg/ESO survey for bright quasi-stellar objects. Two objects, HE 1211-1707 and HE 1043-0502, are shown to be rare examples of white dwarfs that show neutral helium lines in a high magnetic field, in these cases ∼ 50 and ∼ 800 MG, respectively. The former is also found to be rotating with a period of ∼2h. HE 1045-0908 is a hydrogen-line star with a polar field strength of ∼ 20 MG, spinning with a period in the range ∼ 2-4 h. Attempts at modelling the limited amount of phase-resolved data that is available suggest that the field structure on this star departs substantially from a simple centred dipolar geometry. Two cool white dwarfs with unidentified broad absorption spectral features, HE 0236-2656 and HE 0330-0002, are polarimetrically confirmed to be magnetic. Line identifications for these stars are not yet possible, but the atmospheres are probably helium-rich, with spectral features formed by trace compounds of hydrogen, carbon, and perhaps other metals. HE 0003-5701 and HE 0338-3853 were proposed by Reimers et al. alongside two similar objects to be magnetic DB white dwarfs, with Zeeman-split lines of helium in magnetic fields all near 20 MG. However, our observations show that the first two, and by extension all four, are non-magnetic white dwarf + cool dwarf pairs. They deserve to be studied in their own right as possible close binaries. Finally, a lack of circular polarization suggests that HE 0000-3430 and HE 0127-3110 are also non-magnetic. HE 0000-3430 appears to be a featureless DC white dwarf over the spectral range observed here, while the sole absorption line near 5890 Å in HE 0127-3110 could be either He I λ5876 or the Na I D doublet, but there are difficulties with either interpretation.