The enigmatic central star of the planetary nebula PRTM 1

TL;DR

This study monitored the central star of planetary nebula PRTM 1 to investigate its variability, finding minimal evidence for binarity and suggesting it is likely a single star, though further high-resolution observations are needed.

Contribution

First spectroscopic and photometric monitoring of PRTM 1's central star, providing evidence against binarity and revealing the nebula's spherical morphology.

Findings

Minimal radial velocity variability (<10 km/s)

Minimal photometric variability (< 0.2 mag)

Spherical nebula morphology

Abstract

The central star of the planetary nebula PRTM 1 (PN G243.8-37.1) was previously found to be variable by M. Pena and colleagues. As part of a larger programme aimed towards finding post common-envelope binary central stars we have monitored the central star of PRTM 1 spectroscopically and photometrically for signs of variability. Over a period of ~3 months we find minimal radial velocity (<10 km/s) and photometric (< 0.2 mag) variability. The data suggest a close binary nucleus can be ruled out at all but the lowest orbital inclinations, especially considering the spherical morphology of the nebula which we reveal for the first time. Although the current data strongly support the single star hypothesis, the true nature of the central star of PRTM 1 remains enigmatic and will require further radial velocity monitoring at higher resolution to rule out a close binary. If in the odd case that it is a close binary, it would be the first such case in a spherical planetary nebula, in contradiction to current thinking.