  A present prevailing open problem planetary nebulae research, and
photoionized gaseous nebulae research at large, is the systematic discrepancies
in ionic abundances derived from recombination and collisionally excited lines
in many H II regions and planetary nebulae. Peimbert (1967) proposed that these
discrepancies were due to 'temperature fluctuations' in the plasma, but the
amplitude of such fluctuations remain unexplained by standard phtoionization
modeling. In this letter we show that large amplitude temperature oscillations
are expected to form in gaseous nebulae photoionized by short-period binary
stars. Such stars yield periodically varying ionizing radiation fields, which
induce periodic oscilla- tions in the heating-minus-cooling function across the
nebula. For flux oscillation periods of a few days any temperature
perturbations in the gas with frequencies similar to those of the ionizing
source will undergo resonant amplification. In this case, the rate of growth of
the perturbations increases with the amplitude of the variations of the
ionizing flux and with decreasing nebular equilibrium temperature. We also
present a line ratios diagnostic plot that combines [O III] collisional lines
and O II recombination lines for diagnosing equilibrium and fluctuation am-
plitude temperatures in gaseous nebulae. When applying this diagnostic to the
planetary nebula M 1-42 we find an equilibrium temperature of ~6000 K and a
resonant temperature fluctuation amplitude (Trtf ) of ~4000 K. This equilibrium
temperature is significantly lower than the temperature estimated when
temperature perturbations are ignored.
