Presentation #314.01 in the session “Variable Stars I”.
We have carried out a long-term study of a sample of nine proto-planetary nebulae (PPNe), objects in the rapid transition between the asymptotic giant branch (AGB) and planetary nebula phases in the evolution of intermediate- and low-mass stars. We observed the stars from 2010-2018 using the SARA telescope at CTIO. These observations were supplemented with the high-density ASAS-SN observations from 2016-2020 and the lower-precision ASAS-3 data from 2000-2009. Dominant periods of variation were found in seven of them, ranging from 24 to 73 days and with ranges in brightness of ~0.3 mag peak-to-peak. These are due to pulsation. Spectral types of the stars range from late-A to late-F. These properties fit with the previously found relationships between period, amplitude, and Teff in this class of objects, with shorter periods and smaller amplitudes for hotter (and thus more evolved) objects (Hrivnak et al. 2010, ApJ 709, 1042; 2015, AJ, 149, 184). However, the periods are about twice that predicted by present pulsation models. Period and amplitude data have now been obtained for about 25 PPNe, and these provide a good motivation for new pulsation models. They have the potential of determining empirical masses, which are not known for any of these PPNe. Masses, combined with good Gaia distances, can provide important constraints on models of post-AGB stellar evolution. Three of these PPNe also have long-term (5-19 yr) light variations, suggesting binary or disk interactions. This research has been supported by grants from the National Science Foundation (most recently AST 1413660).