Astron. Astrophys. 336, L33-L36 (1998)

Astron. Astrophys. 336, L33-L36 (1998)

4. Discussion and future prospects

For the first time we have been able to prove that GD 229 is indeed a helium rich (DB) white dwarf at a rather high magnetic field strength. From the magnetic field strengths corresponding to the extrema of the wavelengths of the line components we conclude that the range of magnetic fields is about 300-700 MG, so that it would be compatible with a dipole field with a polar field strength between 600 and 700 MG. With our analysis we could reject previous ideas that the atmosphere is hydrogen rich.

In the near future the rest of the line data for He I will be calculated. We expect that some of the missing line components will have wavelength extrema near the strong features at about 4100 and 5300 Å.

A detailed modelling of the spectrum and polarization of GD 229 will be possible as soon as oscillator strengths become available; this will enable us to determine the magnetic field structure which is impossible by our wavelength analysis.

With the new line data for He I we will also try to interpret other magnetic white dwarfs with unexplained features: e.g. HE 1211-1707 (Reimers et al. 1994, Jordan 1997), and four other newly discovered objects from the Hamburg ESO Survey (Reimers et al. 1998).

Another good candidate for such an analysis is LB 11146B for which a convincing analysis of the spectrum with hydrogen line components arrived at an approximate field strength of about 670 MG (Liebert et al. 1993, Glenn et al. 1994). Additionally a very strong and broad feature at about 5600 Å was present in the spectrum which cannot be due to hydrogen. Therefore Glenn et al. speculated that helium might be responsible. However, in our current set of line data no stationary line component of He I was found at about 670 MG.

Online publication: July 20, 1998
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