Physics & Astronomy Faculty Publications
Document Type
Article
Publication Date
9-23-2026
Abstract
Aims. K 1-6 has long been classified as a planetary nebula (PN) hosting a binary central star; however, it has remained poorly studied due to its faintness. The central star exhibits pronounced photometric variability whose origin is still unclear. We present a comprehensive characterisation of the K 1-6 system, including the physical properties of its stellar components and the nature of the surrounding nebulosity.
Methods. We conducted a multi-wavelength analysis combining optical and UV spectroscopy obtained with the Gran Telescopio Canarias, the Telescopio Nazionale Galileo, the Nordic Optical Telescope, and the Hubble Space Telescope. We also present long-term multi-band ground- and space-based photometry, including high-cadence data from the Transiting Exoplanet Survey Satellite, narrowband imaging, and the latest astrometric constraints from Gaia.
Results. Our results show that the nebula is not a remnant PN, but instead consists of interstellar medium photoionised by a hot white dwarf, which is relatively evolved. It has a cooling age of 1–2 Myr, implying that any original PN has long since dissipated. We further find that the central object is a hierarchical triple system, comprising an inner binary with an orbital period likely of the order of thousands of days and a distant tertiary companion orbiting on a timescale of tens of thousands of years. The optically dominant cool component of the inner binary is an inflated K-type star displaying extreme magnetic activity, including large-amplitude variability and flaring. Its properties resemble those of BY Dra-type binaries and Abell 35-type systems, and are difficult to reconcile with single-star evolution, pointing instead to a history of binary interaction.
Recommended Citation
Merc, Jaroslav, David Jones, Ana Escorza, Henri MJ Boffin, Nicole Reindl, Michael Abdul-Masih, Thomas Masseron et al. "K 1-6 is a photoionised interstellar medium nebula shaped by a fast-moving hot white dwarf in a triple system." Astronomy & Astrophysics 713 (2026): A283. https://doi.org/10.1051/0004-6361/202661227
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Publication Title
Astronomy & Astrophysics
DOI
10.1051/0004-6361/202661227
Comments
© The Authors 2026
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.