Evolutionary Map of the Universe: Detection and Analysis of the Shell Surrounding the Runaway Wolf-Rayet Star WR16

Bradley AC, Filipović MD, Smeaton ZJ, Sano H, Fukui Y, Bordiu C, Cichowolski S, Tothill NF, Alsaberi RZ, Bufano F, Dai S, Gordon YA, Hopkins AM, Jarrett TH, Koribalski BS, Lazarević S, Riseley CJ, Rowell G, Sasaki M, Urošević D, Vernstrom T (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Publications of the Astronomical Society of Australia Commonwealth Scientific and Industrial Research Organization Publishing

DOI: 10.1017/pasa.2025.10070

Abstract

We present the first radio–continuum detection of the circumstellar shell around the well-known WN8 type Wolf-Rayet star WR16 at 943.5 MHz using the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey. At this frequency, the shell has a measured flux density of 72.2±7.2 mJy. Using previous Australia Telescope Compact Array (ATCA) measurements at 2.4, 4.8, and 8.64 GHz, as well as the EMU observations of the star itself, we determine a spectral index of α = +0.74 ± 0.02, indicating thermal emission. We propose that the shell and star both exhibit thermal emission, supported by the its appearance in near-infrared and Hα observations. The latest Gaia parallax is used to determine a distance of 2.28±0.09 kpc. This star is well-known for its surrounding circular nebulosity, and using the distance and an angular diameter of 8.′42, we determine the shell size to be 5.57±0.22 pc. We use the Gaia proper motions (PMs) of WR16 to determine peculiar velocities of the star as Vα(pec) = –45.3±5.4 km s–1 and Vδ(pec) = 22.8±4.7 km s–1, which indicates that the star is moving in a north-west direction, and translates to a peculiar tangential velocity to be 50.7±6.9 km s–1. We also use these PMs to determine the shell’s origin, estimate an age of ∼ 9500 ± 1300 yr, and determine its average expansion velocity to be 280 ± 40 km s–1. This average expansion velocity suggests that the previous transitional phase is a Luminous Blue Variable (LBV) phase, rather than a Red Super Giant (RSG) phase. We also use the measured flux at 943.5 MHz to determine a mass-loss rate of 1.753 × 10–5 M☉ yr–1, and use this to determine a lower-limit on ionising photons of NUV > 1.406 × 1047 s–1

Authors with CRIS profile

Manami Sasaki Professur für Multiwellenlängenastronomie

Involved external institutions

University of Western Sydney AU Australia (AU) Ruhr-Universität Bochum (RUB) DE Germany (DE) University of Adelaide AU Australia (AU) Macquarie University AU Australia (AU) University of Belgrade / Универзитет у Београду RS Serbia (RS) Commonwealth Scientific and Industrial Research Organisation (CSIRO) AU Australia (AU) Gifu University / 岐阜大学 JP Japan (JP) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) IT Italy (IT) Instituto de Astronomía y Física del Espacio (IAFE) AR Argentina (AR) University of Wisconsin - Madison US United States (USA) (US)

How to cite

APA:

Bradley, A.C., Filipović, M.D., Smeaton, Z.J., Sano, H., Fukui, Y., Bordiu, C.,... Vernstrom, T. (2025). Evolutionary Map of the Universe: Detection and Analysis of the Shell Surrounding the Runaway Wolf-Rayet Star WR16. Publications of the Astronomical Society of Australia. https://doi.org/10.1017/pasa.2025.10070

MLA:

Bradley, A. C., et al. "Evolutionary Map of the Universe: Detection and Analysis of the Shell Surrounding the Runaway Wolf-Rayet Star WR16." Publications of the Astronomical Society of Australia (2025).

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