RS Canum Venaticorum variable
Close binary stars with starspots causing brightness variations.
An RS Canum Venaticorum variable is a type of variable star consisting of close binary stars with active chromospheres that can cause large stellar spots. These spots are believed to cause variations in observed luminosity, with typical brightness fluctuations around 0.2 magnitudes. Systems can exhibit variations on timescales of years due to changes in spot surface coverage, as well as periodic variations generally close to the orbital period. Some systems also show variations due to being eclipsing binaries. The class takes its name from the star RS Canum Venaticorum (abbreviated RS CVn).
- Typical brightness fluctuation
- 0.2 magnitudes
- Orbital period range regular systems
- 1 to 14 days
- Short period systems orbital period
- less than 1 day
- Long period systems orbital period
- greater than 14 days
- Nearby example
- χ1 Orionis, at 28 light years
- X ray luminosity order
- Lx >> 10^24 watts
- Coronal temperature estimate
- T ~ 10^7 K
Lore & Background
Otto Struve first called attention to the group in 1946, but it was Oliver in 1974 who formally proposed a set of observational characteristics to define the RS CVn criteria. The working definition used today was set down by Hall in 1976. The systems are divided into five subgroups: regular systems (orbital periods 1–14 days, hotter component spectral type F or G, luminosity class V or IV, strong Ca II H and K emission outside eclipse); short period systems (detached components, orbital periods less than 1 day, hotter component F or G, luminosity class V or IV, Ca II H and K emission in one or both components); long period systems (orbital periods greater than 14 days, either component G through K, luminosity class II through IV, strong Ca II H and K emission outside eclipse); flare star systems (hotter component spectral type dKe or dMe); and V471 Tau type systems (hotter component a white dwarf, cooler component G through K with strong Ca II H and K emission).
Reader's Guide
The light curves of RS CVn type systems show a peculiar semiperiodic structure outside eclipse, called a distortion wave. Eaton and Hall in 1979 determined that the simplest mechanism for this distortion wave was starspots—large, cool active regions on the photosphere, analogous to sunspots. Such spots have since been observed indirectly on many systems. Chromospheric activity is signaled by emission cores in the Ca II H and K resonance lines, and Balmer emission (Hα) is also associated with active chromospheres. X-ray emission is a tracer for active coronal regions, and ultraviolet emission and flaring are 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 (gyrosynchrotron) and is one of the few direct indicators of magnetic fields. X-ray luminosities are on the order of Lx >> 10^24 watts, interpreted as caused by a hot corona at about 10^7 K. Another subgroup shows infrared excess emission, seen by the Spitzer Space Telescope.
Did You Know?
- The class is named after the star RS Canum Venaticorum.
- Typical brightness fluctuation is around 0.2 magnitudes.
- A nearby example is χ1 Orionis, at only 28 light years away.
- Some RS CVn systems exhibit variations due to being eclipsing binaries.
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