Claim: Eta Orionis is a multiple star that is assigned to the oldest and closest part of the association, OB1a which is  a group of massive stars that includes most of the bright stars of Orion.
Evidence: Eta Orionis (η Orionis) is a multiple star in the constellation Orion. It is assigned to the oldest and closest part of the association, known as OB1a. The system lies within the Orion OB1 association, a group of massive stars that includes most of the bright stars of Orion.