Searching for Periodicity in a Sample of Evolved Stars

We are studying the light variations in a sample of post-AGB stars. The majority are likely proto-planetary nebulae, objects surrounded by expanding circumstellar envelopes of gas and dust and in the process of evolving to become planetary nebulae. Others do not show such evidence of a circumstellar envelope, but rather seem to possess a circumstellar or a circumbinary disk. We used primarily publicly-available data from the All-Sky Automated Survey for Supernovae. Observations were made in the V and g filters, and typically cover 3-4 years in each, with one year of overlap. We present the results for seven objects. Five show clear periodicity, with periods ranging from 60 to 100 days. Several also show evidence of longer-term trends or periodicities, but the observations do not cover a long enough time interval to determine these. We show the fits to the light curves, typically with two periods each. This research is supported by the National Science Foundation (1413660) and the Indiana Space Grant Consortium.