It is a cluster of Trumpler type I1p or II3p, with few members with large brightness range and a slight concentration toward its center.[3] Klarchenko et al. mention 53 possible members within the angular diametre of the cluster. The tidal radius of the cluster is 1.4 – 5.5 parsecs (4.5 – 18 light years) and represents the average outer limit of NGC 3228, beyond which a star is unlikely to remain gravitationally bound to the cluster core.[2] The brightest member is of mag. 7.9 and the hottest star is of spectral type B9.[3] One member, HD 89856 (mag. 9.04, spectral type B9), is a variable star with period 4.556 days.[5]
