Pulsational Variability in Proto-Planetary Nebulae and Other Post-AGB Objects

Bruce Hrivnak

Valparaiso University, USA

Pulsational variability has been observed for several centuries in Miras and other AGB stars. These have large amplitudes (> 1 mag) and long periods (> 1 year). However, we find that pulsational variability carries on in the post-AGB phase, albeit with smaller amplitude and shorter periods. Many such objects have been identified in the past three decades based on their infrared excesses. These objects have been studied photometrically. Those with F-G spectral types are found to have periods or "quasi-periods" in the range of 35-160 days, and those with hotter central stars vary on even shorter timescales. For a subset of the brightest ones, contemporaneous light, color, and velocity curves have been used to document the variability. Based on these results, we will discuss what they tell us about the central stars.

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