Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-07-26
Mon.Not.Roy.Astron.Soc. 328 (2001) 203
Astronomy and Astrophysics
Astrophysics
Accepted for MNRAS, 10 pages, 9 figures
Scientific paper
10.1046/j.1365-8711.2001.04853.x
Optical spectrophotometry and circular spectropolarimetry are presented for several candidate magnetic white dwarfs that were identified during the Hamburg/ESO survey for bright QSOs. HE 1211-1707 and HE 1043-0502 are rare examples of white dwarfs that show neutral helium lines in a high magnetic field, in these cases ~50 MG and ~800 MG, respectively. The former is also found to be rotating with a period of ~2 hr. HE 1045-0908 is a hydrogen-line star at ~20 MG, spinning with a period in the range ~2-4 hr. Attempts at modeling the limited amount of phase-resolved data that is available suggest that the field structure departs substantially from a simple centered dipolar geometry. Two rather cool white dwarfs with unidentified broad absorption spectral features, HE 0236-2656 and HE 0330-0002, are 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. (1996) alongside two similar objects to be magnetic DB white dwarfs, with magnetic fields all near 20 MG. However, our observations show that the first two, and by extension all four, are nonmagnetic white dwarf + cool dwarf pairs, deserving of study in their own right as possible close binaries. Finally, a lack of circular polarisation suggests that HE 0000-3430 and HE 0127-3110 are also nonmagnetic. HE 0000-3430 appears to be a featureless DC white dwarf over the spectral range observed here, while the sole absorption line near 5890A in HE 0127-3110 could be either He I 5876A or the Na I D doublet, but there are difficulties with either interpretation.
Ferrario Lilia
Schmidt Gary D.
Vennes Stephane
Wickramasinghe Dayal T.
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