Polar (star)

For other uses, see Polar (disambiguation).
Polar variables are magnetic white dwarfs accreting material from a low mass donor, with no accretion disk due to the intense magnetic field

In astronomy, a polar is a highly magnetic type of cataclysmic variable (CV) binary star system, originally known as an AM Herculis star after the prototype member AM Herculis. Like other CVs, polars contain two stars: an accreting white dwarf (WD), and a low-mass donor star (usually a red dwarf) which is transferring mass to the WD as a result of the WD's gravitational pull, overflowing its Roche lobe.[1] Polars are distinguished from other CVs by the presence of a very strong magnetic field in the WD. Typical magnetic field strengths of polar systems are 10 million to 80 million gauss (1000–8000 teslas).[2] The WD in the polar AN Ursae Majoris has the strongest known magnetic field among cataclysmic variables, with a field strength of 230 million gauss (23 kT).[3]

  1. ^ Hellier, Coel (2001). Cataclysmic Variable Stars. Springer.
  2. ^ Cropper, Mark (1990-12-01). "The polars". Space Science Reviews. 54 (3–4): 195–295. Bibcode:1990SSRv...54..195C. doi:10.1007/BF00177799. ISSN 0038-6308. S2CID 189786424.
  3. ^ Krzeminski, W. & Serkowski, K. (August 1977). "Extremely high circular polarization of AN Ursae Majoris". The Astrophysical Journal Letters. 216: L45. Bibcode:1977ApJ...216L..45K. doi:10.1086/182506.