  Optical spectropolarimetry carried out by Kishimoto et al. (2004) has shown
that several luminous type 1 quasars show a strong decrease of the polarized
continuum flux in the rest-frame near-UV wavelengths of $\lambda<4000$\AA. In
the literature, this spectral feature is interpreted as evidence of the
broadened hydrogen Balmer absorption edge imprinted in the accretion disk
thermal emission due to the disk atmospheric opacity effect. On the other hand,
the quasar flux variability studies have shown that the variable continuum
component in UV-optical spectra of quasars, which is considered to be a good
indicator of the intrinsic spectral shape of the accretion disk emission,
generally have significantly flat spectral shape throughout the near-UV to
optical spectral range. To examine whether the disk continuum spectral shapes
revealed as the polarized flux and as the variable component spectra are
consistent with each other, we carry out multi-band photometric monitoring
observations for a sample of four polarization-decreasing quasars of Kishimoto
et al. (2004) (4C09.72, 3C323.1, Ton 202, and B2 1208+32) to derive the
variable component spectra and compare the spectral shape of them with that of
the polarized flux spectra. Contrary to expectation, we confirm that the two
spectral components of these quasars have totally different spectral shape in
that the variable component spectra are significantly bluer compared to the
polarized flux spectra. This discrepancy in the spectral shape may imply either
(1) the decrease of polarization degree in the rest-frame UV wavelengths is not
indicating the Balmer absorption edge feature but is induced by some unknown
(de)polarization mechanisms, or (2) the UV-optical flux variability is
occurring preferentially at the hot inner radii of the accretion disk and thus
the variable component spectra do not reflect the whole accretion disk
emission.
