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Evolutionary Map of the Universe: Detection of the Wolf-Rayet Star WR40

A. C. Bradley, Z. J. Smeaton, M. D. Filipovic, N. F. H. Tothill, R. Z. E. Alsaberi, J. D. Collier, Y. A. Gordon, A. M. Hopkins, H. Zakir

TL;DR

We present the first EMU 943.5 MHz radio-continuum detection of WR40 and its RCW 58 shell. Using Gaia DR3 distances and archival ATCA data, we derive a distance of $2.79 ± 0.13$ kpc and a shell size of $7.32(±0.34) × 4.89(±0.23)$ pc, with shell flux $158.9 ± 15.8$ mJy and WR40 flux $0.41 ± 0.04$ mJy at 943.5 MHz. The star’s spectral index, from ATCA measurements, is $α = 0.80 ± 0.11$, consistent with thermal emission via $S ∝ ν^α$, while RCW 58’s spectral index remains unconstrained due to low surface brightness and archival inconsistencies. The results demonstrate EMU’s capability to map WR shells and motivate deeper follow-up (e.g., MeerKAT) to resolve RCW 58 emission and spectral properties. These findings refine the understanding of wind–ISM interactions around WR stars and provide a framework for studying similar shells with upcoming radio surveys.

Abstract

We present a radio-continuum detection of the well-known Wolf-Rayet star WR40 at 943.5 MHz using observations from the EMU survey. We find that the shell surrounding WR40, known as RCW 58, has a flux density of 158.9+/-15.8 mJy and the star itself is 0.41+/-0.04 mJy. The shell size is found to be 9' x 6', which matches well with the shell in Halpha and is similarly matched to the shell at 22 um in infrared. Using Gaia data, we derive a linear size of 7.32(+/-0.34) x 4.89(+/-0.23) pc at a distance of 2.79+/-0.13 kpc. We use previous ATCA observations at 8.64, 4.80, and 2.4 GHz to determine a spectral index of WR40, which is estimated to be alpha = 0.80+/-0.11, indicating that the emission from the star is thermal.

Evolutionary Map of the Universe: Detection of the Wolf-Rayet Star WR40

TL;DR

We present the first EMU 943.5 MHz radio-continuum detection of WR40 and its RCW 58 shell. Using Gaia DR3 distances and archival ATCA data, we derive a distance of kpc and a shell size of pc, with shell flux mJy and WR40 flux mJy at 943.5 MHz. The star’s spectral index, from ATCA measurements, is , consistent with thermal emission via , while RCW 58’s spectral index remains unconstrained due to low surface brightness and archival inconsistencies. The results demonstrate EMU’s capability to map WR shells and motivate deeper follow-up (e.g., MeerKAT) to resolve RCW 58 emission and spectral properties. These findings refine the understanding of wind–ISM interactions around WR stars and provide a framework for studying similar shells with upcoming radio surveys.

Abstract

We present a radio-continuum detection of the well-known Wolf-Rayet star WR40 at 943.5 MHz using observations from the EMU survey. We find that the shell surrounding WR40, known as RCW 58, has a flux density of 158.9+/-15.8 mJy and the star itself is 0.41+/-0.04 mJy. The shell size is found to be 9' x 6', which matches well with the shell in Halpha and is similarly matched to the shell at 22 um in infrared. Using Gaia data, we derive a linear size of 7.32(+/-0.34) x 4.89(+/-0.23) pc at a distance of 2.79+/-0.13 kpc. We use previous ATCA observations at 8.64, 4.80, and 2.4 GHz to determine a spectral index of WR40, which is estimated to be alpha = 0.80+/-0.11, indicating that the emission from the star is thermal.

Paper Structure

This paper contains 6 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Data
  3. ASKAP EMU
  4. Other Data
  5. Results and Discussion
  6. Conclusion

Figures (3)

  • Figure 1: EMU 943.5 MHz radio-continuum image of WR40 and its surrounding shell RCW 58 at 15$^{\prime\prime}$ resolution. Image is linearly scaled.
  • Figure 2: WR40 and its surrounding shell RCW 58, both images are linearly scaled. -- Left: WISE infrared image in the W4 band at 22 $\mu$m. -- Right: SuperCOSMOS H$\alpha$ (656.281 nm) image.
  • Figure 3: Four-colour composite image of WR40 and RCW 58. Red is WISE 22 $\mu$m, yellow is SuperCOSMOS H$\alpha$, green is the EMU observation, and blue is the DSS2 red plate provided from 1996ASPC..101...88L.