Binary Central Stars of Planetary Nebulae Discovered Through Photometric Variability V: The Central Stars of HaTr 7 and ESO 330-9

TL;DR

This study identifies and characterizes close binary central stars in planetary nebulae HaTr 7 and ESO 330-9, revealing their orbital parameters, stellar properties, and implications for post-RGB evolution.

Contribution

The paper provides detailed observational data and binary modeling for two new close binary central stars, including system parameters and spectral analysis, expanding knowledge of post-RGB stellar evolution.

Findings

Both systems have orbital periods less than half a day.

The hot central star in ESO 330-9 is likely a post-RGB star.

Binary modeling reveals unique limb-darkening and stellar parameters.

Abstract

We find the central stars of the planetary nebulae (PNe) HaTr 7 and ESO 330-9 to be close binary systems. Both have orbital periods of less than half a day and contain an irradiated cool companion to the hot central star. We provide light curves, spectra, radial velocity curves, orbital periods, and binary modeling results for both systems. The binary modeling leads to system parameters, or ranges of allowed parameters for each system. We find that for the CS of HaTr 7 we need to use limb-darkening values for the cool companion that are different than the expected values for an isolated star. We also fit the central star spectrum to determine $\log g$ and temperature values independent of the binary modeling. For ESO 330-9 we find that based on our binary modeling the hot central star is most likely a post-RGB star with a mass of around 0.4 M$_\odot$. We discuss our derived stellar and nebular parameters in the broader context of close binary central stars and their surrounding PNe. We also discuss the present status of known or suspected post-RGB stars in PNe.