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An RS Canum Venaticorum variable is a type of
/ref> The RS CVn systems are divided into five separate subgroups: *Regular systems. Orbital periods are between 1 and 14 days. The hotter component is of the spectral type F or G and luminosity class V or IV. Strong Ca II H and K emission is seen outside eclipse. *Short period systems. Components are detached and orbital periods are less than 1 day. The hotter component is of the spectral type F or G and luminosity class V or IV. Ca II H and K emission is displayed in one or both components. * Long period systems. Orbital periods is greater than 14 days. Either component is of the spectral type G through K and luminosity class II through IV. Strong Ca II H and K emission is seen outside eclipse. *Flare star systems. In this case the hotter component is of the spectral type dKe or dMe, where the emission refers to strong Ca II H and K. * V471 Tau type systems. The hotter component is a
The light curves of RS CVn type systems show a peculiar semiperiodic structure outside eclipse. This structure has been referred to as a distortion wave in the light curve. Eaton and Hall (1979) determined that the simplest mechanism for the creation of the distortion wave was "starspots", which, in analogy to sunspots, are large, cool active regions on the photosphere. Such spots have since been observed indirectly on many systems.
Chromospheric activity is signaled by the presence of emission cores in the Ca II H and K resonance lines. Balmer emission, or Hα, is also associated with active chromospheres. X-ray emission is known as a tracer for active coronal regions, and ultraviolet (UV) emission and flaring are, by solar analogy, known to be associated with stellar active and transition regions. These areas on the Sun are associated with intense magnetic fields, and sunspot activity is enhanced in and around these magnetically active regions.
Some RS CVn type stars are known X-ray and radio emitters. The radio emission is nonthermal in origin (gyrosynchrotron) and is one of the few direct indicators of magnetic fields. The X-ray luminosities are on the order of Lx >> 1024 watts. This emission has been interpreted, in solar analogy, as being caused by a hot, T ~ 107 K, corona.
Another subgroup of RS CVns is known to have infrared excess emission, seen by the Spitzer Space TelescopeMatranga, M., Drake, J.J., Kashyap, V.L., Marengo, M., & Kuchner, M.J. 2010,'' Astrophysical Journal''
OGLE Atlas of Variable Star Light Curves - RS Canum Venaticorum variables
{{Variable star topics *
variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...
. The variable type consists of close binary stars
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
having active chromosphere
A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...
s which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity
Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
. Systems can exhibit variations on timescales of years due to variation in the spot surface coverage fraction, as well as periodic variations which are, in general, close to the orbital period of the binary system. Some systems exhibit variations in luminosity due to their being eclipsing binaries. Typical brightness fluctuation is around 0.2 magnitudes. They take their name from the star RS Canum Venaticorum (abbreviated RS CVn).
Otto Struve (1946) first called attention to the group, but it was Oliver (1974) who was the first to formally propose a set of observational characteristics to define the RS CVn criteria. The working definition, as it is used today, was that set down by Hall (1976). Berdyuginabr>2.4 RS CVn stars/ref> The RS CVn systems are divided into five separate subgroups: *Regular systems. Orbital periods are between 1 and 14 days. The hotter component is of the spectral type F or G and luminosity class V or IV. Strong Ca II H and K emission is seen outside eclipse. *Short period systems. Components are detached and orbital periods are less than 1 day. The hotter component is of the spectral type F or G and luminosity class V or IV. Ca II H and K emission is displayed in one or both components. * Long period systems. Orbital periods is greater than 14 days. Either component is of the spectral type G through K and luminosity class II through IV. Strong Ca II H and K emission is seen outside eclipse. *Flare star systems. In this case the hotter component is of the spectral type dKe or dMe, where the emission refers to strong Ca II H and K. * V471 Tau type systems. The hotter component is a
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
. The cooler component, spectral class G through K, displays strong Ca II H and K emission.
The light curves of RS CVn type systems show a peculiar semiperiodic structure outside eclipse. This structure has been referred to as a distortion wave in the light curve. Eaton and Hall (1979) determined that the simplest mechanism for the creation of the distortion wave was "starspots", which, in analogy to sunspots, are large, cool active regions on the photosphere. Such spots have since been observed indirectly on many systems.
Chromospheric activity is signaled by the presence of emission cores in the Ca II H and K resonance lines. Balmer emission, or Hα, is also associated with active chromospheres. X-ray emission is known as a tracer for active coronal regions, and ultraviolet (UV) emission and flaring are, by solar analogy, known to be associated with stellar active and transition regions. These areas on the Sun are associated with intense magnetic fields, and sunspot activity is enhanced in and around these magnetically active regions.
Some RS CVn type stars are known X-ray and radio emitters. The radio emission is nonthermal in origin (gyrosynchrotron) and is one of the few direct indicators of magnetic fields. The X-ray luminosities are on the order of Lx >> 1024 watts. This emission has been interpreted, in solar analogy, as being caused by a hot, T ~ 107 K, corona.
Another subgroup of RS CVns is known to have infrared excess emission, seen by the Spitzer Space TelescopeMatranga, M., Drake, J.J., Kashyap, V.L., Marengo, M., & Kuchner, M.J. 2010,'' Astrophysical Journal''
Notes
References
* (explains how Doppler imaging works) *Further reading
* *Hall, D.S. 1976, in IAU Colloquium No. 29, "Multiple Periodic Variable Stars" (D. Reidel: Boston), p. 278-348. * * *External links
OGLE Atlas of Variable Star Light Curves - RS Canum Venaticorum variables
{{Variable star topics *