Type RS CVn star

Type RS CVn stars are a type of variable star. They are close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity. 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.

Subgroups

The RS CVn systems are divided into five separate subgroups:

1. (I.) Regular Systems: Orbital periods 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 of eclipse.
2. (II.) Short Period Systems: Components are detached. Orbital periods 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.
3. (III.) Long Period Systems: Orbital periods 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 of eclipse.
4. (IV.) Flare Star Systems: The hotter component is of the spectral type dKe or dMe, where the emission refers to strong Ca II H and K.
5. (V.) V471 Tau Type Systems: The hotter component is a white dwarf. 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 of eclipse. This structure has been referred to as a distortion wave in the light curve. Chromospheric activity is signaled by the presence of emission cores in the Ca II H and K resonance lines. Hα emission 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 known to be associated with stellar active and transition regions. These areas are associated with intense magnetic fields, and sunspot activity is enhanced in and around these magnetically active regions.

Some RS CVn's 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. Another subgroup of RS CVNs is known to have infrared excess emission.