  Once thought to be devoid of warm and cold interstellar matter, elliptical
galaxies are now commonly observed to host extended regions of neutral and
ionized gas. Outside of the innermost nuclear regions of these galaxies, the
favoured candidate ionizing source remains some component of the stellar
population, with mounting evidence suggesting post-asymptotic-giant-branch
stars (pAGBs). In a recent paper, we demonstrated that observations of
recombination lines of He II (or upper limits thereof) may provide a strong
constraint on the presence of any other, higher temperature ionizing sources,
in particular nuclear-burning white dwarfs in the context of the single
degenerate (SD) scenario for type Ia supernovae. The sensitivity of the HeII
test is greatest for WD effective temperatures ~ 2 x 10^5 K. Here we extend our
analysis to include predictions for all of the "classical" strong optical
lines, as well as UV, optical, and infra-red lines of neutral Oxygen, Nitrogen,
and singly-ionized Carbon. This allows us to extend the temperature range over
which we can meaningfully constrain the collective luminosity of
nuclear-burning WDs to 10^5 K <~ T <~ 10^6 K. We then demonstrate how
observations of nearby early-type and post-starburst galaxies can place strong
limits on the origin of type Ia supernovae.
