RS Canum Venaticorum variable

RS Canum - Venaticorum stars are a class of discrete binary stars consisting of more massive primary giants or sub- giants with the spectral type GK and a companion who is a subgiant or main-sequence star with a G to M. RS CVn stars show outside a possible eclipsing change a modulation of the light curve with an amplitude of up to 0.6 like in V, which is interpreted as a rotation of star spots on the surface of the star. The strong magnetic activity of these stars is shown by a hot corona in the field of X-ray radiation as well as the observations of flares.

Definition

There are several definitions of the RS Canum - Venaticorum stars that are working side by side. The first definition of the criteria included Hall

  • Photometric variability
  • The calcium K & H lines in emission
  • Under a giant within the Roche limit
  • Fast rotation of the star, which is almost synchronized with the orbital period of the binary system
  • The orbital period is itself changeable

In addition to this definition, RS CVn stars not as close binary systems with stars with nearly the same mass, in which the component with higher temperature, the spectral type FK shows and orbital period of between one day and two weeks is. In the broadest sense RS CVNs are described as interacting close binary systems with at least one cool star, and at best very low mass transfer.

Related classes of stars

To the stars with magnetic activity include not only the RS Canum - Venaticorum - stars the

  • Red dwarfs of class UV Ceti star, show the flares
  • BY Draconis stars whose light curves are modulated by star spots
  • Rapidly rotating giant FK Comae Berenices - star
  • Young T Tauri stars
  • Close eclipsing binary W - Ursae Majoris stars whose light curves can be modeled only by the assumption of star spots
  • Algolsterne
  • The Sun-like star

Cause of magnetic activity

All the related classes of stars and the RS Canum - Venaticorum - stars have a convective energy transport in the photosphere in combination with a high rotational speed. The speed of rotation is the result of a bound rotation in the double star system in the RS - CVNs. The magnetic field is likely to arise as the sun in the tachocline region in the RS - Canum - Venaticorum stars. The MGD describes the formation of a magnetic field when an electric current flows in the form of a plasma due to the differential rotation inside a star. Because of the coupling of the rotational period of the train orbital period in this class of stars, the magnetic field strength exceeds by orders of magnitude that of the sun. The signs of the magnetic activity but are the same:

  • Star spots that can occupy up to 50 % of the visible surface
  • A heated several million K corona, which may be observed in the field of X-ray
  • The detection of flare in X-ray, radio, and ultraviolet radiation
  • Emission lines from a chromosphere as the calcium and magnesium lines

RS Canum - Venaticorum star rather than single stars

A K- supergiant with stellar magnetic activity is counted even if no signs of a companion to be found to the RS Canum - Venaticorum stars. In most cases, the companion is likely to be too faint to be detected. But there are to be transformed into an active K subgiant also a development path for rapidly rotating single stars. These stars with spectral type early F on the main sequence form in the phase of central hydrogen burning only a convection zone with a shallow depth in the photosphere. The tachocline region generates only a weak magnetic field and the rotation speed to remain high. When developing these stars after exhausting the hydrogen supply in the core of the main series continued to cross the Hertzsprung gap as an active K subgiant with a 1.25 - to 1.5 times the solar mass. Since the Hertzsprung- gap but through within a few 10,000 years the Steren are very rare. Massive stars through the Hertzsprung gap too fast to be observed and massenärme stars evolve such a powerful magnetic field during their main sequence phase to rotate later too slow to show a K- subgiant signs of stellar activity.

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