Star system
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A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems, which include planets and similar bodies.
The Algol three-star system imaged in the near-infrared by the CHARA interferometer with 0.5 mas resolution in 2009. The shape of Algol C is an artifact.[citation needed]
Artist's impression of the orbits of HD 188753, a triple star system.
Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.
Sirius A (center), with its white dwarf companion, Sirius B (lower left) taken by the Hubble Space Telescope.
Delta Cephei
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Delta Cephei is a quadruple star system located approximately 887 light-years away in the northern constellation of Cepheus, the King. At this distance, the visual magnitude of the star is diminished by 0.23 as a result of extinction caused by gas and dust along the line of sight. It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity.
Image of Delta Cephei, in the center
Hermes Radial Velocity Curve of Delta Cephei A. The offset between points of identical color is due to the spectroscopic companion, Delta Cephei B.
Bow shock around Delta Cephei