Diffuse Galactic Light in the Field of the Translucent High Galactic
  Latitude Cloud MBM32
  We have conducted B, g, V, and R-band imaging in a 45x40 arcmin^2 field
containing part of the high Galactic latitude translucent cloud MBM32, and
correlated the intensity of diffuse optical light S_\nu(\lambda) with that of
100 micron emission S_\nu(100um). A chi^2 minimum analysis is applied to fit a
linear function to the measured correlation and derive the slope parameter
b(\lambda)= \Delta S_\nu(\lambda) / \Delta S_\nu(100um) of the best-fit linear
function. Compiling a sample by combining our b(\lambda) and published ones, we
show that the b(\lambda) strength varies from cloud to cloud by a factor of 4.
Finding that b(\lambda) decreases as S_\nu(100um) increases in the sample, we
suggest that a non-linear correlation including a quadratic term of
S_\nu(100um)^2 should be fitted to the measured correlation. The variation of
optical depth, which is A_V = 0.16 - 2.0 in the sample, can change b(\lambda)
by a factor of 2 - 3. There would be some contribution to the large b(\lambda)
variation from the forward-scattering characteristic of dust grains which is
coupled to the non-isotropic interstellar radiation field (ISRF). Models of the
scattering of diffuse Galactic light (DGL) underestimate the b(\lambda) values
by a factor of 2. This could be reconciled by deficiency in UV photons in the
ISRF or by a moderate increase in dust albedo. Our b(\lambda) spectrum favors a
contribution from extended red emission (ERE) to the diffuse optical light;
b(\lambda) rises from B to V faster than the models, seems to peak around 6000
\AA, and decreases towards long wavelengths. Such a characteristic is expected
from the models in which the DGL is combined with ERE.
