  We have used the Keck I telescope to resolve at mid-infrared wavelengths the
dust emission from HD 56126 (IRAS 07134+1005), a post-Asymptotic Giant Branch
carbon star with a detached dust shell. The gross morphology of the image can
be explained by a strong wind which started to die about 1500 years ago. If the
star had an effective temperature near 2600 K when it was losing a large amount
of mass, then during the past 1500 years, the average value of dT/dt has been
+2.2 K/yr. With such a time variation of the effective temperture of the star,
the 11.7 micron image can be approximately reproduced if the mass loss rate
varied as T^(-8.26), as proposed in recent models for dust-driven winds. Since
the mass loss rate appears to be very sensitive to the effective temperature of
the star, we speculate that the observed deviations from spherical symmetry of
the dust shell can be explained by plausible variations in the surface
temperature of the mass-losing star caused by rotation and/or magnetic fields.
