Rotationally variable star

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In rotating stars , the change in brightness is modulated by the rotation of a star or the period of revolution in a binary star system .

Reasons for the changes in brightness can either be ellipsoidally deformed components of close binary stars or the occurrence of an uneven brightness distribution on the star's surface . This can be caused by

  • Star spots like the sun spots
  • different temperature distribution
  • different chemical distribution

Subgroups

  • In ellipsoidal variable is close binary systems in which the components due to their proximity under gravitational influence ellipsoid have deformed. Because of the orbital movement of the binary star system, we see differently large areas of the stars from the earth and this leads to a slight change in light of less than 0.1 mag .
  • Variable reflection stars are also binary star systems in which the change in light is mainly a result of the warming of the star hemispheres facing each other .
  • Alpha 2 -Canum Venaticorum variables are main sequence stars with the spectral types B8p-A7p. They show a strong magnetic field of a few thousand Gauss , which varies as the star rotates from the Earth's perspective. The slight change in light of a maximum of 0.1 mag is a result of a chemical accumulation of silicon , chromium and rare earths around the poles of the magnetic field.
  • BY Draconis stars are late dwarfs with emission lines with a spectral type from dKe to dMe. They show quasi-periodic light changes with cycle lengths of 0.2 to 100 days with an amplitude of up to 0.5 mag. The variability is a consequence of star spots and chromospheric activity due to rapid rotation. In BY-Draconis stars, flares like the UV-Ceti stars have also been observed.
  • The FK-Comae-Berenices stars are rapidly rotating variables with uneven surface brightness and a spectral type from G to K. The spectrum is dominated by calcium and hydrogen lines in emission. They are probably single stars that have recently emerged from a merger of a close binary star system and where the magnetic field has not yet had time to slow down the rotation. The rotation duration and the period of the changes in brightness are less than 5 days.
  • Pulsars are rapidly rotating neutron stars with a strong magnetic field. The rotation time is between 0.01 and a few seconds. In young pulsars, the magnetic field is sufficient to tear electrons from the crust of the neutron star and accelerate them along the magnetic field lines. In this case, synchrotron radiation emitted in the direction of movement of the electrons and the observer assumes a 'pulsed' with radiation of half the period of the rotation period of the neutron star true.
  • The SX Arietis stars are early main sequence stars with a spectral class from B0p to B9p. The stars, also known as helium-variable stars, show a variable intensity in the spectral lines of helium and silicon. It is probably a continuation of the Alpha-2-Canum-Venaticorum stars at higher temperatures, since the same mechanism is used to explain the change in light for both star classes.

See also

Individual evidence

  1. ^ Definition of variable stars in the GCVS
  2. ^ John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .