  (Abridged) We use optical spectroscopy to investigate the disk, wind, and
accretion during the 2008 ZCMa NW outburst. Over 1000 optical emission lines
reveal accretion, a variable, multi-component wind, and double-peaked lines of
disk origin. The variable, non-axisymmetric, accretion-powered wind has slow
($\sim $0 km s$^{-1}$), intermediate ($\sim -$100 km s$^{-1}$) and fast ($\geq
-$400 km s$^{-1}$) components. The fast components are of stellar origin and
disappear in quiescence, while the slow component is less variable and could be
related to a disk wind. The changes in the optical depth of the lines between
outburst and quiescence are consistent with increased accretion being
responsible for the observed outburst. We derive an accretion rate of 10$^{-4}$
M$_\odot$/yr in outburst. The Fe I and weak Fe II lines arise from an
irradiated, flared disk at $\sim$0.5-3 $\times$M$_*$/16M$_\odot$ au with
asymmetric upper layers, revealing that the energy from the accretion burst is
deposited at scales below 0.5 au. Some line profiles have redshifted
asymmetries, but the system is unlikely sustained by magnetospheric accretion,
especially in outburst. The accretion-related structures extend over several
stellar radii and, like the wind, are likely non-axisymmetric. The stellar mass
may be $\sim$6-8 M$_\odot$, lower than previously thought ($\sim$16 M$_\odot$).
Emission line analysis is found to be a powerful tool to study the innermost
regions and accretion in stars within a very large range of effective
temperatures. The density ranges in the disk and accretion structures are
higher than in late-type stars, but the overall behavior, including the
innermost disk emission and variable wind, is very similar independently of the
spectral type. Our work suggests a common outburst behavior for stars with
spectral types ranging from M-type to intermediate-mass stars.

Solar and Stellar Astrophysics