A Survey for Planetary Nebulae in M31 Globular Clusters

TL;DR

This survey investigates planetary nebulae in M31 globular clusters using spectroscopy, identifying a few candidates and exploring their potential formation mechanisms, but with limited conclusive evidence due to small sample size.

Contribution

First spectroscopic survey of PNe in M31 globular clusters, providing candidate identifications and analyzing their properties and possible formation channels.

Findings

Identified 3 PN candidates in globular clusters

Candidates are faint with high excitation ratios

Data suggest possible link between PNe formation and binary interactions

Abstract

We report the results of an [O III] 5007 spectroscopic survey for planetary nebulae (PNe) located within the star clusters of M31. By examining R ~ 5000 spectra taken with the WIYN+Hydra spectrograph, we identify 3 PN candidates in a sample of 274 likely globular clusters, 2 candidates in objects which may be globular clusters, and 5 candidates in a set of 85 younger systems. The possible PNe are all faint, between ~2.5 and ~6.8 mag down the PN luminosity function, and, partly as a consequence of our selection criteria, have high excitation, with [O III] 5007 to H-beta ratios ranging from 2 to ~12. We discuss the individual candidates, their likelihood of cluster membership, and the possibility that they were formed via binary interactions within the clusters. Our data are consistent with the suggestion that PN formation within globular clusters correlates with binary encounter frequency, though, due to the small numbers and large uncertainties in the candidate list, this study does not provide sufficient evidence to confirm the hypothesis.