The enigmatic central star of the planetary nebula PRTM 1^⋆

¹ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile
e-mail: djones@eso.org; djones@eso.org
² South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
³ Southern African Large Telescope Foundation, PO Box 9, 7935 Observatory, South Africa

Received: 31 January 2012
Accepted: 13 August 2012

Abstract

The central star of the planetary nebula PRTM 1 (PN G243.8−37.1) has previously been found to be variable by Peña and colleagues. As part of a larger programme aimed at finding post common-envelope binary central stars, we 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^-1) 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, contradicting current thinking.