  A prevailing open problem in planetary nebulae research, and photoionized
gaseous nebulae research at large, is the systematic discrepancies in electron
temperatures and ionic abundances as derived from recombination and
collisionally excited lines. Peimbert (1967) proposed the presence of
'temperature fluctuations' in these nebulae, but the apparent amplitude of such
fluctuations, as deduced from spectral diagnostics and/or abundance discrepancy
factors, remain unexplained by standard photoionization modeling. While this
and other alternative models to explain the temperature and abundance
discrepancies remain inconclusive, recent observations seem to point at a
connection between nebular abundance discrepancy factors and a binary nature of
photoionizing stars. In this paper we show that large amplitude temperature
fluctuations are expected to form in planetary nebulae photoionized by
short-period binary stars. Resonant temperature fluctuations are first formed
along the orbital disk around the binary stars, as the periodically varying
ionizing radiation field induces periodic oscillations in the
heating-minus-cooling function. Then, the temperatures fluctuations propagate
vertically to the disk as thermal waves that later steepen into radiative
shocks. The binary period of the ionizing stars is determinant in the formation
and propagation of temperature fluctuations, as well as in associated density
fluctuations. Fluctuations propagate efficiently only in systems with binary
periods significantly shorter than the gas thermalization time, of the order of
10 days.
  Further, we propose temperature diagnostic line ratios that combine [O III]
collisionally excited lines and O II recombination lines to determine the
equilibrium temperature and the magnitude of resonant temperature fluctuations
in nebulae.
