Theta² Orionis (θ² Ori) is a multiple star system in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster, also known as θ¹ Orionis.

θ² Orionis consists of three stars in a line, each about an arc-minute from the next. In addition to the well-known three stars, the Washington Double Star Catalog confusingly lists a component D which is actually θ¹ Orionis C.^[16]

There is one other star brighter than 10th magnitude in the region. V1073 Orionis is a B9.5 Orion variable that forms an equilateral triangle with θ² Ori B and C.

Bizarrely, θ² Orionis C has a second entry in the Washington Double Star Catalog under the name S490. The companion is 10th magnitude and actually lies between θ² Ori B and V1073 Ori.^[16]

θ¹ Orionis, the well known Trapezium cluster, is only 2 arc minutes away from θ² Orionis A. Despite the names, θ² Orionis A is marginally brighter than the brightest star in the Trapezium. The Catalog of Components of Double and Multiple Stars includes the stars of θ¹ and θ² Ori within the same system of 13 components.

There are dozens of much fainter stars in the same field, many of them pre-main-sequence stars still forming from the Orion molecular cloud complex.

The primary component A appears as a 5th magnitude O class subgiant over 100,000 times as luminous as the sun. The spectral type suggests it is evolving away from the main sequence, although it is thought to be less than 2 million years old. The spectral peculiarities may be related to close companions or could be caused by the extreme youth of the star.

The 6th magnitude component B is an early B main sequence star nearly 30,000 K and over 10,000 times the luminosity of the sun.

Component C is another B class main sequence star, but cooler and less than a thousand times the luminosity of the sun.

θ² Orionis A is itself a triple star system. Its spectral lines were seen to change position periodically, indicating orbital motion. The first orbit was derived in 1924, indicating a period of 21 days. and a rather eccentric orbit.^[17]

Speckle interferometry has resolved a companion about 0.3" away, around 147 AU. High resolution spectroscopy shows that there is an even closer companion, only about 0.47 AU from the primary, for a total of three stars. Both companions are thought to be early A or late B with masses of 7-9 M_☉. This helps to explain the high mass and visual luminosity for an O9.5 star at this distance. The three stars together have nearly the same mass as the O5.5 θ¹ Orionis C and visually are even brighter.^[18]

θ² Orionis A also shows unexplained rapidly variable x-ray emission. The x-rays cannot be explained standard mechanisms such as colliding winds or coronal emissions from an unseen companion.^[13]