The Search for Periodicity in Light Variations in a Sample of Proto-planetary Nebulae Candidates

We are analyzing light curves of several potential proto-planetary nebulae (PPNe), which are stars in the late stages of their lives, in search of periodic light variability that would give us insight into the inner mechanisms and properties of these late stage stars. Significant periods in these stars are from pulsational variations in the outer layers of the star. Instability between the shell and the core star causes oscillatory behavior from over-correctional contraction and expansion of the shell. This oscillation causes observable changes in brightness which is then predicted to be periodic on a timescale of about 50-100 days. Using the Valparaiso University Observatory, we have compiled several years of data and created light curves for each star using data collected over 7 years for a majority. A Fourier analysis is then implemented in search of significant periodicity in the light variations. Here, we display newly discovered significant periods of a few confirmed PPNe and PPNe candidates. Out of 7 stars analyzed, all of them varied in brightness but only 4 of them varied periodically. These periods range from 15 days to 300 days. This research is supported by funding from the Indiana Space Grant Consortium and the National Science Foundation