Variability in Proto-Planetary Nebulae: V. Velocity and Light Curve Analyses of IRAS 17436+5003, 18095+2704, and 19475+3119

TL;DR

This study analyzes light, color, and radial velocity data of three proto-planetary nebulae over several years, revealing complex pulsation patterns and phase relationships that differ from classical Cepheids, providing insights into stellar evolution.

Contribution

It provides detailed observational analysis of PPNe pulsations, identifying dominant periods and phase relationships, and highlights the need for improved pulsation models for these objects.

Findings

PPNe show multiple pulsation periods with complex light and velocity curves.

Color peaks occur near or after light peaks, while velocity peaks precede light peaks by a quarter cycle.

Results differ from classical Cepheids but resemble RV Tauri variables.

Abstract

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.