The Bizarre Spectral Variability of Central Stars of Planetary Nebulae

TL;DR

This study investigates spectral variability in central stars of planetary nebulae, finding that wind variability and pulsations complicate binary detection, and suggesting faint stars are better candidates for binary surveys.

Contribution

It provides detailed analysis of spectral variability causes in central stars, highlighting the challenges in detecting binaries due to stellar winds and pulsations.

Findings

RV variability confirmed in four stars but not due to binarity

Wind variability explains most spectral changes in IC4593

Irregular variables show complex RV and line shape variability

Abstract

A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2002 and 2004. De Marco et al. (2004) reported that 10 out of 11 monitored stars exhibited strong RV variability, but periods were not detected. Since other mechanisms, such as wind variability, can cause apparent RV variations, we monitored 4 of the 10 RV-variable stars at echelle resolutions to determine the origin of the variability. Although RV changes are confirmed for all four stars, none of them can be ascribed to binarity at this time. However, only for IC4593 is wind variability able to explain most (though not all) spectral variability. For BD+332642, no wind and no pulsations appear to be the origin of the RV changes. Finally, M1-77 and M2-54, both known to be irregular photometric variables, exhibit dramatic RV and line shape variability of the hydrogen and HeI absorption lines, as well as large RV variability of weaker lines, which do not change in shape. There is no satisfactory explanation of this variability, though a combination of wind variability and pulsations is still the best guess at what makes these stars so variable. We suggest that luminous central stars are ill suited to detect spectroscopic binaries, because winds (and possibly pulsations) are pervasive and would mask even strong periodicities. It it likely that a sample of intrinsically faint central stars would more readily yield binary information.