Discovery of a Magnetic/Nonmagnetic Double-degenerate Binary System

We report the discovery of an unresolved binary system consisting of two degenerate stars: one a polarized object with an inferred magnetic field among the largest yet found on a white dwarf; the other a normal DA with no detectable field. We have deconvolved the composite 1250 Å-2.2 microns energy distribution into individual spectra and find that, with the exception of the graphic difference in magnetic field strength, the two stars are remarkably similar. For the normal DA, Teff ≈ 14,500 K, log g ≈ 8.5, and M = 0.91±0.07 Msun, while the magnetic component has Teff ≈ 16,000 K, log g ≈ 8.5, and 0.76 ≤ M/Msun At a distance of about 40 pc, the projected separation of the stellar components could be as large as 20 AU. The binary might therefore be a wide pair in which two stars of similar initial mass evolved into two very different end states. On the other hand, it could be an unusual product of close binary evolution, in which case this would be the first such example whose combined mass appears to exceed the Chandrasekhar limit. Potential implications and future observations to clarify the evolutionary and magnetic status of the system are suggested.