Theta1 Orionis A

Theta1 Orionis A (θ1 Ori A) is a variable trinary star in the constellation Orion.

It is one of the main stars in The Trapezium in Orion, along with B, C, and D, as well as the fainter E. θ1 Orionis A varies in brightness, showing dips from magnitude 6.72 to 7.65 every 65.432 days.

θ1 Orionis A1 is an eclipsing binary but the secondary is not detected in the spectrum and is far less luminous than the primary.

[10] The relative motion of the two stars has been measured and they are slowly getting closer together but it has not been possible to derive an orbit.

The relative motion of the two stars could simply be a straight line, but it is calculated that they are gravitationally bound.

A visual band light curve for V1016 Orionis, plotted from AAVSO data. [ 7 ] The inset plot, adapted from Lloyd and Stickland (1999), [ 8 ] shows the time around the eclipse minimum with an expanded scale.