|
An Intermediate Polar (also DQ Herculis Star) is a type of cataclysmic variable binary star system. In most cataclysmic variables, matter from a main-sequence companion star is gravitationally stripped by a white dwarf star in the form of an accretion disk. In intermediate polar systems, the accretion disk is disrupted by the magnetic field of its white dwarf star. Infalling gas from the companion star will form a disk when the matter is still far from the white dwarf, but will follow magnetic field lines in ''accretion streams'' when the matter falls closer to the white dwarf. In the transition region between the accretion disk and the accretion stream, infalling gas may also fall as curved sheets called ''accretion curtains''. The name "intermediate polar" is derived from the strength of the white dwarf's magnetic field, which is between that of non-magnetic cataclysmic variable systems and strongly magnetic systems. Non-magnetic systems exhibit full accretion disks, while strongly magnetic systems (called polars, or AM Herculis systems) exhibit only accretion streams. There are (26 confirmed intermediate polar systems ) as of 14 April 2006. This represents about 1% of the 1,830 total cataclysmic variable systems presented by Downes et al. (2006) in the (Catalog of Cataclysmic Variables ). ==Physical Properties== Intermediate polar systems are strong x-ray emitters. The x-rays are generated by high velocity particles from the accretion stream forming a shock as they fall onto the surface of the white dwarf star. As particles decelerate and cool before hitting the white dwarf surface, bremsstrahlung x-rays are produced and may subsequently be absorbed by gas surrounding the shock region. The magnetic field strength of white dwarfs in intermediate polar systems are typically 1 million to 10 million gauss (100–1000 teslas). This is about a million times stronger than the Earth's magnetic field and towards the upper limit of magnetic field strengths that can be produced in a laboratory on Earth, but is much less than the magnetic field strength of neutron stars. At the intersection of the accretion stream and the surface of the white dwarf, a hot spot is produced. Because the white dwarf has a dipole magnetic field, it will have one hot spot at each of its magnetic poles. As the white dwarf and its dipole magnetic field spin, the hot spots will spin also. Other defining characteristics of intermediate polars include a strong Helium II emission line at 468.1 nm and circular polarization, in addition to the light curve periodicities described below. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intermediate polar」の詳細全文を読む スポンサード リンク
|