. Magnetic field , rotation and spectrum of 40 Eri B

This paper describes results of magnetic field measurements of white dwarfs carried out on the 6–m telescope for the last years. A magnetic field of about Be ≈ 28 kG has been discovered in the degenerate star WD1953–011 which has been selected from high–resolution spectroscopy of non–LTE Hα core by Koester et al. (1998). A rotational period of WD0009+501, 1.83 hours, has been discovered, the average magnetic field of the star is < Be >= −42.3±5.4 kG and its semi–amplitude of the rotational variability is 32.0± 6.8 kG. The variable magnetic field of the bright normal (non–magnetic) degenerate star 40 Eridani B was confirmed in January 1999 by Zeeman time–resolved spectroscopy. Both the Hα and the Hβ lines give about the same results, we have selected two best periods in the magnetic field variability, 2 25 and 5 17. The semi–amplitude of the rotational variations Bmax ≈ 4000÷ 5000 G and the average field is about zero ±500 G. If the magnetic field of 40 Eridani B is a central dipole, then the rotational axis inclination to the line of sight is i ∼ 90, and the magnetic axis inclination to the rotational axis is about the same, β ∼ 90. For the first time an ultra–high signal–to–noise spectrum of the white dwarf has been obtained (S/N > 1000). We have found in this hydrogen–rich DA white dwarf 40 Eridani B (16500 K) that helium abundance is low (N(He)/N(H) < 10), but the spectrum is rich in ultra–weak absorption lines of metals in low ionization states. It was proposed that these lines were produced in both circumstellar and interstellar gas. The gas may be supplied by accretion from interstellar medium and from the dM4e companion 40 Eridani C with an accretion rate Ṁa ∼ 10 −19 M⊙/y. The accreting gas may form a circumstellar rotating envelope in the magnetosphere at a distance of ∼ 4 · 10 cm.