  We study the effects of current systematic errors in Type Ia supernova (SN
Ia) measurements on dark energy (DE) constraints using current data from the
Supernova Legacy Survey (SNLS). We consider how SN systematic errors affect
constraints from combined SN Ia, baryon acoustic oscillations (BAO), and cosmic
microwave background (CMB) data, given that SNe Ia still provide the strongest
constraints on DE but are arguably subject to more significant systematics than
the latter two probes. We focus our attention on the temporal evolution of DE
described in terms of principal components (PCs) of the equation of state,
though we examine a few of the more common, simpler parametrizations as well.
We find that the SN Ia systematics degrade the total generalized figure of
merit (FoM), which characterizes constraints in multi-dimensional DE parameter
space, by a factor of two to three. Nevertheless, overall constraints obtained
on more than five PCs are very good even with current data and systematics. We
further show that current constraints are robust to allowing for the finite
detection significance of the BAO feature in galaxy surveys.
