Astron. Astrophys. 346, L13-L16 (1999)

Letter to the Editor

On the ultimate fate of AM Her stars

F. Meyer and E. Meyer-Hofmeister

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching, Germany

Received 12 April 1999 / Accepted 1 May 1999

Abstract

We suggest, that the magnetic field of the white dwarf in AM Her systems loses coupling to the secondary star when the latter becomes non-magnetic at the transition from a late main sequence star to a cool degenerate brown dwarf. This leads to spin-up of the primary white dwarf. After synchronous rotation is lost the systems do not appear as AM Her stars anymore. We discuss the further evolution of such systems.

Key words: stars: novae, cataclysmic variables stars: magnetic fields stars: low-mass, brown dwarfs stars: white dwarfs

Send offprint requests to: Emmi Meyer-Hofmeister

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Contents

• 1. Introduction
• 2. Magnetic coupling
  • 2.1. Disappearance of the secondary's magnetic field
  • 2.2. Loss of coupling
• 3. The spin-up phase
• 4. The propeller phase
• 5. Further evolution
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999
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