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Accepted manuscript

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

Published online by Cambridge University Press:  10 July 2025

A. C. Bradley*
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
M. D. Filipović
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
Z. J. Smeaton
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
H. Sano
Affiliation:
Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
Y. Fukui
Affiliation:
Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
C. Bordiu
Affiliation:
INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123, Catania, Italy
S. Cichowolski
Affiliation:
Instituto de Astronomía y Física del Espacio (UBA, CONICET), CC 67, Suc. 28, 1428 Buenos Aires, Argentina
N. F. H. Tothill
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
R. Z. E. Alsaberi
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
F. Bufano
Affiliation:
INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123, Catania, Italy
S. Dai
Affiliation:
Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, Epping, NSW 1710, Australia
Y. A. Gordon
Affiliation:
Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706, USA
A. M. Hopkins
Affiliation:
School of Mathematical and Physical Sciences, 12 Wally’s Walk, Macquarie University, NSW 2109, Australia
T. H. Jarrett
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
B. S. Koribalski
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, Epping, NSW 1710, Australia
S. Lazarević
Affiliation:
Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, Epping, NSW 1710, Australia Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
C. J. Riseley
Affiliation:
Astronomisches Institut der Ruhr-Universität Bochum (AIRUB), Universitätsstraße 150, 44801 Bochum, Germany
G. Rowell
Affiliation:
School of Physical Sciences, The University of Adelaide, Adelaide 5005, Australia
M. Sasaki
Affiliation:
Dr Karl Remeis Observatory, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
D. Urošević
Affiliation:
Department of Astronomy, Faculty of Mathematics, University of Belgrade, Studentski trg 16, 11000 Belgrade, Serbia
T. Vernstrom
Affiliation:
CSIRO Space and Astronomy, PO Box 1130, Bentley, WA 6102, Australia ICRAR, The University of Western Australia, 35 Stirling Hw, 6009 Crawley, Australia
*
Author for correspondence: A. C. Bradley, Email: 20295208@student.westernsydney.edu.au.
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Abstract

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We present the first radio–continuum detection of the circumstellar shell around the well-known WN8 type Wolf-Rayet star WR16 at 943.5MHz 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 kms–1 and Vδ(pec) = 22.8±4.7 kms–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 kms–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.

Information

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Astronomical Society of Australia

Footnotes

Deceased on 3rd July 2024