Gamma Arietis

Gamma Arietis (γ Ari, γ Arietis) is the Bayer designation for a binary star system in the northern constellation of Aries. It has the traditional name Mesarthim, which is of obscure origin. The combined apparent visual magnitude of the two stars is 3.86, which is readily visible to the naked eye and makes this the fourth brightest member of Aries. Based upon an annual parallax shift of 19.88 mas, the distance to Gamma Arietis is approximately 164 light-years (50 parsecs).

The double star nature of this system was discovered by Robert Hooke in 1664. The two components have an angular separation of 7.606 arcseconds, which can be resolved with a small telescope. The orbital period of the pair is greater than 5000 years. The brighter component, γ¹ Arietis, is a magnitude 4.58 B-type main sequence star with a stellar classification of B9 V. The secondary, γ² Arietis, is a Lambda Boötis (chemically peculiar) star with a stellar classification of A1p Si and a magnitude of 4.64. It is classified as an α2 CVn type variable star and its brightness varies by 0.04 magnitudes with a period of 2.61 days.