Kinematics of the ring-like nebula SuWt 2

TL;DR

This study provides the first detailed kinematic analysis of the planetary nebula SuWt 2, revealing its complex structure and challenging existing theories of nebula formation due to the absence of a known central progenitor star.

Contribution

It offers the first spatio-kinematical model of SuWt 2, including measurements of its inclination, expansion velocity, and systemic velocity, and discusses implications for its formation scenario.

Findings

Nebula has a bright torus and bipolar lobes.

Inclination of the ring is approximately 68 degrees.

Systemic velocity is about -25 km/s, inconsistent with the binary's velocity.

Abstract

We present the first detailed spatio-kinematical analysis and modelling of the Southern planetary nebula SuWt 2. This object presents a problem for current theories of planetary nebula formation and evolution, as it is not known to contain a central post-main sequence star. Deep narrowband [NII]6584 images reveal the presence of faint bipolar lobes emanating fromthe edges of the nebular ring. Longslit observations of the H-alpha and [NII]6584 emission lines were obtained using EMMI on the 3.6-m ESO-NTT. The spectra reveal the nebular morphology as a bright torus encircling the waist of an extended bipolar structure. By deprojection, the inclination of the ring is found to be 68$\degr$ $\pm$ 2$\degr$ (c.f. ~90$\degr$ for the double A-type binary believed to lie at the centre of the nebula), and the ring expansion velocity is found to be 28 km/s. Our findings are discussed with relation to possible formation scenarios for SuWt 2. Through comparison of the nebular heliocentric systemic velocity, found here to be -25 $\pm$ 5 km/s, and the heliocentric systemic velocity of the double A-type binary, we conclude that neither component of the binary could have been the nebular progenitor. However, we are unable to rule out the presence of a third component to the system, which would have been the nebula progenitor.