Planetary Nebulae and How to Find Them: Color Identification in Big
  Broadband Surveys
  Planetary nebulae (PNe) provide tests of stellar evolution, can serve as
tracers of chemical evolution in the Milky Way and other galaxies, and are also
used as a calibrator of the cosmological distance ladder. Current and upcoming
large scale photometric surveys have the potential to complete the census of
PNe in our galaxy and beyond, but it is a challenge to disambiguate partially
or fully unresolved PNe from the myriad other sources observed in these
surveys. Here we carry out synthetic observations of nebular models to
determine $ugrizy$ color-color spaces that can successfully identify PNe among
billions of other sources. As a primary result we present a grid of synthetic
absolute magnitudes for PNe at various stages of their evolution, and we make
comparisons with real PNe colors from the Sloan Digital Sky Survey. We find
that the $r-i$ versus $g-r$, and the $r-i$ versus $u-g$, color-color diagrams
show the greatest promise for cleanly separating PNe from stars, background
galaxies, and quasars. Finally, we consider the potential harvest of PNe from
upcoming large surveys. For example, for typical progenitor host star masses of
$\sim$3 M$_\odot$, we find that the Large Synoptic Survey Telescope (LSST)
should be sensitive to virtually all PNe in the Magellanic Clouds with
extinction up to $A_{\rm V}$ of $\sim$5 mag; out to the distance of Andromeda,
LSST would be sensitive to the youngest PNe (age less than $\sim$6800 yr) and
with $A_{\rm V}$ up to 1 mag.
