A blue star, also called HD 149757 and HR 6175, which is the nearest,
and probably the most widely studied, → massive star.
It is variable in several wavelength bands and has a mean visual magnitude
of V = 2.58, B - V = 0.01. It lies ~ 222 pc away and has
a formal spectral type of O9.5 Ve and a luminosity of 105 Lsun.
ζ Ophiuchi is a very rapid rotator with a v sin i
~ 400 km s-1, i.e.
~ 85% of the → break-up velocity. It is one of
the earliest prototypes of the → Be phenomenon.
Moreover, it shows episodes of Hα emission variability, a common feature of Be/Oe stars.
It also shows periodic non-radial pulsations and UV
→ P Cygni profile variability, as is evident in the periodic behavior of
→ discrete absorption components (DACs).
It has a → mass loss rate of 10-7 Msun yr-1
and a → terminal velocity of wind
v∞ = 1550 km s-1.
ζ Ophiuchi is a well-known → runaway star with a
velocity of 30 km s-1.
The interstellar → CH molecule and
→ CN molecule were first detected toward ζ Ophiuchi.
It has been recognized for some time that this star lies close to the
blue edge of the → beta Cephei instability strip.
See also: Zeta (ζ), according to the → variable star designation
system; Ophiuchi, → Ophiuchus.
