  We have obtained contemporaneous light, color, and radial velocity data for
three proto-planetary nebulae (PPNe) over the years 2007 to 2015. The light and
velocity curves of each show similar periods of pulsation, with photometric
periods of 42 and 50 days for IRAS 17436+5003, 102 days for IRAS 18095+2704,
and 35 days for IRAS 19475+3119. The light and velocity curves are complex with
multiple periods and small, variable amplitudes. Nevertheless, at least over
limited time intervals, we were able to identify dominant periods in the light,
color, and velocity curves and compare the phasing of each. The color curves
appear to peak with or slightly after the light curves while the radial
velocity curves peak about a quarter of a cycle before the light curves.
Similar results were found previously for two other PPNe, although for them the
light and color appeared to be in phase. Thus it appears that PPNe are
brightest when smallest and hottest. These phase results differ from those
found for classical Cepheid variables, where the light and velocity differ by
half a cycle, and are hottest at about average size and expanding. However,
they do appear to have similar phasing to the larger amplitude pulsations seen
in RV Tauri variables. Presently, few pulsation models exist for PPNe, and
these do not fit the observations well, especially the longer periods observed.
Model fits to these new light and velocity curves would allow masses to be
determined for these post-AGB objects, and thereby provide important
constraints to post-AGB stellar evolution models of low and intermediate-mass
stars.

Solar and Stellar Astrophysics