Castor system

Castor (α Gem, α Geminorum, Alpha Geminorum) is a quadruple star system. Castor has a faint companion with the same parallax and proper motion; this companion is an eclipsing binary system with a period slightly less than 1 day, and it is one of only a few known eclipsing binary systems where both companions are class M dwarf stars. Castor can thus be considered to be a sextuple star system, with six individual stars gravitationally bound together. Component C has the variable star designation YY Geminorum.

Overview

Parameter Star Component Aa Ab Ba Bb Ca Cb Spectral type A1 V Unknown (probably M5 V) A2 Vm M2 V M0.5 Ve M0.5 Ve