History of the mass ejection in K 4-37: from the AGB to the evolved planetary nebula phase

TL;DR

This study analyzes the complex morphology and chemical composition of planetary nebula K 4-37, revealing multiple bipolar outflows, a large detached shell from the AGB phase, and insights into its progenitor star's mass and evolution.

Contribution

It provides the first detailed morphokinematical analysis of K 4-37, identifying multiple axes and outflows, and links its structure to progenitor properties and evolution.

Findings

K 4-37 is a multi-axis planetary nebula with several bipolar outflows.

The nebula is surrounded by a large detached shell likely from the AGB phase.

K 4-37's properties suggest a highly evolved nebula at ~14 kpc distance.

Abstract

We present narrow-, broad-band, and WISE archive images, and high- and intermediate-resolution long-slit spectra of K 4-37, a planetary nebula that has never been analyzed in detail. Although K 4-37 appears bipolar, the morphokinematical analysis discloses the existence of three distinct axes and additional particular directions in the object, indicating that K 4-37 is a multi-axis planetary nebula that has probably been shaped by several bipolar outflows at different directions. A 4-6 M$_{\odot}$ main-sequence progenitor is estimated from the derived high nebular He and N abundances, and very high N/O abundance ratio ($\sim$2.32). The general properties are compatible with K 4-37 being a highly evolved planetary nebula located at $\sim$14 kpc. The WISE image at 22 $\mu$m reveals K 4-37 to be surrounded by a large ($\sim$13$\times$8 pc$^2$) elliptical detached shell probably related to material ejected from the AGB progenitor. The observed elliptical morphology suggests deformation of an originally spherical AGB shell by the ISM magnetic field or by the influence of a companion. We compare K 4-37 and NGC 6309 and found remarkable similarities in their physical structure but noticeably different chemical abundances that indicate very different progenitor mass. This strongly suggests that, irrespective of the initial mass, their (presumably binary) central stars have shared a very similar mass ejection history.