Skip to main content

Astronomy (thesaurus)

Search from vocabulary

align
annotate
download

Concept information

... > stellar astronomy > stellar type > multiple star > binary star > cataclysmic star > AM Herculis binary
stellar astronomy > stellar type > variable star > cataclysmic star > AM Herculis binary
stellar astronomy > stellar remnant > AM Herculis binary

Preferred term

AM Herculis binary  

Definition

  • An AM Herculis star is a type of magnetic cataclysmic binary that consists of a closely-orbiting dwarf M star or K star and a super-strong magnetic white dwarf primary, in which the magnetic field of the primary not only prevents the formation of an accretion disk but also synchronizes the primary's rotation with its orbital period. Such systems are the most extremely polarized objects known (hence their alternative name polars), exhibiting both strong linear and, more significantly, circular polarization. The powerful (10 to 100 megagauss) magnetic field of the white dwarf captures infalling material from the red dwarf before it can form an accretion disk and forces it instead into an accretion stream or funnel, one part of which heads for the star's north magnetic pole and the other for the south pole. As the field lines, like those around a bar magnet, converge, they channel the streams of matter onto tiny polar accretion spots. The streams slam into the white dwarf at some 3,000 km/s and have their kinetic energy converted primarily into X-rays. The white dwarf's magnetic field also locks the spin of the two stars so that they always present the same face to each other (though in about one-tenth of AM Her stars, the white dwarf's axial and orbital rotations are off by about 1%). Furthermore, the magnetic field of the white dwarf often tilts over, so that one magnetic pole points toward the direction from which the stream comes (this being the lowest-energy configuration). As a result, material flows preferentially onto that pole. (Encyclopedia of Science, by David Darling, https://www.daviddarling.info/encyclopedia/A/AM_Herculis_star.html)

Broader concept

Entry terms

  • AM Her binary
  • AM Herculis binary star
  • AM Herculis star
  • AM Herculis system
  • AM Her star
  • AM Her system

In other languages

URI

http://data.loterre.fr/ark:/67375/MDL-M2F7Q5FV-M

Download this concept:

RDF/XML TURTLE JSON-LD Last modified 10/6/22