# The planetary nebula IC 4776 and its post-common-envelope binary central star

## TL;DR

This paper analyzes the planetary nebula IC 4776 and its binary central star, revealing morphological features, binary characteristics, chemical abundances, and implications for post-common-envelope evolution.

## Contribution

It provides the first detailed analysis of IC 4776's morphology, binarity, and chemical abundances, highlighting the potential for undetected intermediate-period binaries.

## Key findings

- Binary central star with periodic radial velocity variability
- Chemical abundance analysis suggests truncated AGB evolution
- Discrepancies in abundance measurements from different methods

## Abstract

We present a detailed analysis of IC 4776, a planetary nebula displaying a morphology believed to be typical of central star binarity. The nebula is shown to comprise a compact hourglass-shaped central region and a pair of precessing jet-like structures. Time-resolved spectroscopy of its central star reveals periodic radial velocity variability consistent with a binary system. While the data are insufficient to accurately determine the parameters of the binary, the most likely solutions indicate that the secondary is probably a low-mass main sequence star. An empirical analysis of the chemical abundances in IC 4776 indicates that the common-envelope phase may have cut short the AGB evolution of the progenitor. Abundances calculated from recombination lines are found to be discrepant by a factor of approximately two relative to those calculated using collisionally excited lines, suggesting a possible correlation between low abundance discrepancy factors and intermediate-period post-common-envelope central stars and/or Wolf-Rayet central stars. The detection of a radial velocity variability associated with binarity in the central star of IC 4776 may be indicative of a significant population of (intermediate-period) post-common-envelope binary central stars which would be undetected by classic photometric monitoring techniques.