Optical long-baseline interferometers are now being built which extend over an area several hundreds of meters across. While the primary shines at magnitude 2, the secondary is only 2 magnitudes fainter and would be easily visible to the naked eye if it weren't so close to its brilliant neighbor. NPOI has already detected relative motion of the two stars, most likely due to their being gravitationaly bound with an orbital period of a few years. In amateur telescopes it appears as an optical double star, with a 4th magnitude companion, Zeta Orionis B, lying 2.3 arcseconds to the southeast of Zeta Orionis A. Zeta Orionis A's primary component is a supergiant star of spectral type O9.5, which also shows peculiar emission lines. Type O stars are the hottest stars in the spectral sequence, and the supergiants show strong stellar winds that produce optical spectral emission lines, thermal radio, and X-ray emission.
Shock waves created in the turbulent stellar wind flow are one ingredient of current theories.
NPOI is routinely observing double stars as well as single giant and supergiant stars near Flagstaff, Arizona. It is a joint project of the U. S. Naval Observatory and the Naval Research Laboratory in Washington, DC, in association with the Lowell Observatory in Flagstaff. An arcsecond is a unit of angular measure on the plane of the sky. At the position of the primary, where all three colors, i.e. images coincide, the result is a white colored image. At the position of the secondary, a band of colors appears, indicating motion of the secondary with respect to the primary.