Variability in C-rich proto-PNe.

The light and color curves display variability in all of them. The light curves are complex and suggest multiple periods, changing periods, and/or changing amplitudes, which are attributed to pulsation.

A dominant period has been determined for each and found to be in the range of ~150 days for the coolest (G8) to 35-40 days for the warmest (F3). A clear, linear inverse relationship has been found in the sample between the pulsation period and the effective temperature and also an inverse relationship between the amplitude of light variation and the effective temperature. These are consistent with the expectation for a pulsating post-asymptotic giant branch (post-AGB) star evolving toward higher temperature at constant luminosity.