  The 2008 optical transient in NGC 300 is one of a growing class of
intermediate-luminosity transients that brighten several orders of magnitude
from a previously optically obscured state. The origin of their eruptions is
not understood. Our multi-wavelength photometry and spectroscopy from maximum
light to more than a year later provide a record of its post-eruption behavior.
We describe its changing spectral-energy distribution, the evolution of its
absorption- and emission line-spectrum, the development ofa bipolar outflow,
and the rapid transition from a dense wind to an optically thin ionized wind.
In addition to strong, narrow hydrogen lines, the F-type absorption-line
spectrum of the transient is characterized by strong Ca II and [Ca II]
emission. The very broad wings of the Ca II triplet and the asymmetric [Ca II]
emission lines are due to strong Thomson scattering in the expanding ejecta.
Post-maximum, the hydrogen and Ca II lines developed double-peaked emission
profiles that we attribute to a bipolar outflow. Between approximately 60 and
100 days after maximum, the F-type absorption spectrum, formed in its dense
wind, weakened and the wind became transparent to ionizing radiation. We
discuss the probable evolutionary state of the transient and similar objects
such as SN 2008S, and conclude thatthey were most likely post-red supergiants
or post-AGB stars on a blue loop to warmer temperatures when the eruption
occurred. These objects are not LBVs.
