K 1-6: an asymmetric planetary nebula with a binary central star

TL;DR

This study presents multiwavelength observations of the asymmetric planetary nebula K 1-6, revealing a binary central star system with a hot subdwarf or white dwarf and a variable cool star, suggesting complex stellar interactions.

Contribution

First detailed multiwavelength analysis of K 1-6, identifying its binary central star and confirming its status as an old planetary nebula interacting with the interstellar medium.

Findings

K 1-6 is an asymmetric planetary nebula at ~1.0 kpc.

Central star is a binary or ternary system with a hot subdwarf/white dwarf and a variable cool star.

The cool star shows activity consistent with RS CVn or FK Com classification.

Abstract

We present new imaging data and archival multiwavelength observations of the little studied emission nebula K 1-6 and its central star. Narrow-band images in H-alpha (+ [NII]) and [OIII] taken with the Faulkes Telescope North reveal a stratified, asymmetric, elliptical nebula surrounding a central star which has the colours of a late G- or early K-type subgiant or giant. GALEX ultraviolet images reveal a very hot subdwarf or white dwarf coincident in position with this star. The cooler, optically dominant star is strongly variable with a period of 21.312 +/- 0.008 days, and is possibly a high amplitude member of the RS CVn class, although an FK Com classification is also possible. Archival ROSAT data provide good evidence that the cool star has an active corona. We conclude that K 1-6 is most likely an old bona fide planetary nebula at a distance of ~1.0 kpc, interacting with the interstellar medium, and containing a binary or ternary central star. The observations and data analyses reported in this paper were conducted in conjunction with Year 11 high school students as part of an Australian Research Council Linkage Grant science education project, denoted Space To Grow, conducted jointly by professional astronomers, educational researchers, teachers, and high-school students.