Zeta Opihuchi
Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is an enormous star of spectral class O9.5 V, with the luminosity class of V indicating that it is generating energy in its core by the nuclear fusion of hydrogen. This energy is being emitted from the outer envelope at an effective temperature of 34,000K, giving the star the blue hue of an O-type star. It is rotating rapidly and may be close to the velocity at which it would begin to break up. The projected rotational velocity may be as high as 400 km/s–1 and it may be rotating at a rate of once per day.
This is a young star with an age of only three million years. Its luminosity is varying in a periodic manner similar to a Beta Cephei variable. This periodicity has a dozen or more frequencies ranging between 1–10 cycles per day.
This star is roughly half way through the initial phase of its stellar evolution and will, within the next few million years, expand into a red supergiant star before ending its life in a supernova explosion leaving behind a Neutron Star or Pulsar.
X-ray emissions have been detected from Zeta Ophiuchi that vary periodically. The net X-ray flux is estimated at 1.2 × 1031 erg/s−1. In the energy range of 0.5–10 keV, this flux varies by about 20% over a period of 0.77 days. This behavior may be the result of a magnetic field in the star. The measured average strength of the longitudinal field is about 141 ± 45 G.
ζ Ophiuchi is moving through space with a peculiar velocity of 30 km/s−1. Based upon the age and direction of motion of this star, it is a member of the Upper Scorpius sub-group of the Scorpius-Centaurus Association of stars that share a common origin and space velocity. Such runaway stars may be ejected by dynamic interactions between three or four stars. However, in this case the star may be a former component of a binary star system in which the more massive primary was destroyed in a Type II supernova explosion. The pulsar PSR B1929+10 may be the leftover remnant of this supernova, as it too was ejected from the association with a velocity vector that fits the scenario.
Due to the high space velocity of Zeta Ophiuchi, in combination with high intrinsic brightness and its current location in a dust-rich area of the galaxy, the star is creating a bow-shock in the direction of motion.
