  HD 148937 is a peculiar massive star (Of?p) with a strong magnetic field
(1kG). The hourglass-shaped emission nebula NGC 6164/5 surrounds this star.
This nebula is presumed to originate from episodic mass-loss events of the
central O-type star, but the detailed formation mechanism is not yet well
understood. Grasping its three-dimensional structure is essential to uncover
the origin of this nebula. Here we report the high-resolution multi-object
spectroscopic observation of NGC 6164/5 using the GIRAFFE on the 8.2m Very
Large Telescope. Integrated intensity maps constructed from several spectral
lines delineate well the overall shape of this nebula, such as the two bright
lobes and the inner gas region. The position-velocity diagrams show that the
two bright lobes are found to be redshifted and blueshifted, respectively,
while the inner region has multiple layers. We consider a geometric model
composed of a bilateral outflow harboring nitrogen-enriched knots and expanding
inner shells. Its spectral features are then simulated by using a Monte-Carlo
radiative transfer technique for different sets of velocities. Some
position-velocity diagrams from simulations are very similar to the observed
ones. According to the model that best reproduces the observational data, the
two bright lobes and the nitrogen-enriched knots are moving away from HD 148937
at about 120 km s$^{-1}$. Their minimum kinematic age is estimated to be about
7,500 years. We discuss possible formation mechanisms of this nebula in the
context of binary interaction.
