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RS CVn

RS CVn (rscvn)

Classification and numbers

  • Supertypes
  • variable
  • periodic
  • binary
  • Occurrence rate: common, about 105 expected in ZTF data

ZTF light curves

ZTF rscvn ZTF rscvn flaring

Description

RS Canum Venaticorum stars are binary systems in which one or both stars are chromospherically active. The surface of the star (typically F or G main-sequence or subgiant) is covered with groups of spots, which makes the surface brightness inhomogeneous. These spots rotate with a period close to the orbital period. However, the spot rotation period can differ slightly from the orbital period, which causes the light curve shape to change over timescales of years. The variability of the wave's amplitude is explained by the existence of a long-period stellar activity cycle similar to the 11-year solar activity cycle, during which the number and total area of spots on the star's surface vary. Small amplitude flares, another signature of chromospheric activity, can also be observed in some cases.

Other types of variable stars with chromospheric activity (which we do not consider of the RS CVn type): - white dwarf or hot subdwarf stars with a chromospherically active companion - BY Dra variables (single rotating star, typically K or M type) - UV Cet variables (flaring low mass main sequence stars) - single solar-type stars with active chromospheres - T Tau variables (young chromospherically active stars) - W UMa binaries (overcontact binaries) - FK Com stars (rapidly rotating single stars) - single giants with active chromospheres

Light curve characteristics

  • periodic variable
  • period range: 0.5-50 days
  • amplitude: 0.01 up to 0.6 mag
  • light curve shape:
    • sinusoidal; or with two maxima and minima of different heights and depths
    • the shape can change over timescales of years (modulation)
    • they can show eclipses, but this is not required
    • can show stellar flares

Other characteristics and selection methods

  • the chromospherically active star is a F or G main-sequence star
  • often show Ca-II emission lines

HR diagram of RS CVn

RA/Dec diagram of RS CVn

References and further reading:

  • VSX: https://www.aavso.org/vsx/index.php?view=about.vartypes
  • Sterken & Jasschek: Light curves of variable stars