  We describe the results of a long-slit spectroscopic study of an unusual star
complex in the nearby spiral galaxy NGC 6946 using the SAO 6-m telescope and
the Keck 10-m telescope. The complex resembles a circular bubble 600 pc in
diameter with a young super star cluster (SSC) near the center. The kinematics
of ionized gas is studied through Ha emission with several slit positions.
Position-velocity diagrams show two distinct features with high speed motions.
One is an irregularly shaped region to the east of the SSC, 270 pc in size, in
which most of the Ha emission is blue shifted by 120 km/s, and another is a 350
pc shell centered on the SSC with positive and negative velocity shifts of 60
km/s. Balmer and HeI absorption lines in the SSC give an age of 12-13 Myr,
which is consistent with the photometric age but significantly older than the
kinematic ages of the high speed regions. The energetics of the SSC and its
interaction with the environment are considered. The expansion energies exceed
10^52 ergs, but the power outputs from winds and supernova in the SSC are large
enough to account for this. The intensities of Balmer, [NII], and [SII]
emission lines within and around the complex indicate that shock excitation
makes a significant contribution to the emission from the most energetic
region.

Astrophysics