Alpha Centauri

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Abstract
The nearest star α Centauri is a triple system. The star α Cen, one of the pointers to the Southern Cross, is itself a −0.3 mag visual binary consisting of a α Cen A, a G2V star popularly considered to resemble the Sun, and α Cen B, a KOV star. The orbital period is 80.089 years, the semimajor axis is 23.5 AU, the distance 1.34 pc, the masses are 1.11 and 0.92 (±0.03) M⊙ (Kamper & Wesselink 1977). The third star, Proxima Cen (V645 Cen) is a faint common proper-motion companion separated from α Cen AB by about 2°. It is known to most people only by virtue of being slightly closer to the Sun than is α Cen A, and therefore actually the closest star.. This 11th mag flare star is undoubtedly coeval with a α Cen AB, but being the least massive by a considerable margin, may have been ejected from the system shortly after formation.