WISE morphological study of Wolf-Rayet nebulae

TL;DR

This study uses optical and infrared imaging to classify the diverse morphologies of Wolf-Rayet nebulae, revealing their structures, dust emission characteristics, and a new obscured shell around WR35, highlighting complex nebular evolution.

Contribution

It provides a detailed morphological classification of WR nebulae using multi-wavelength data and identifies a new obscured shell around WR35, enhancing understanding of their structure and evolution.

Findings

WR nebulae are detected in WISE W4 band at 22 μm.

Morphologies classified into bubbles, clumpy/disrupted shells, and mixed types.

Discovery of an infrared-only obscured shell around WR35.

Abstract

We present a morphological study of nebulae around Wolf-Rayet (WR) stars using archival narrow-band optical and Wide-field Infrared Survey Explorer (WISE) infrared images. The comparison among WISE images in different bands and optical images proves to be a very efficient procedure to identify the nebular emission from WR nebulae, and to disentangle it from that of the ISM material along the line of sight. In particular, WR nebulae are clearly detected in the WISE W4 band at 22 $\mu$m. Analysis of available mid-IR Spitzer spectra shows that the emission in this band is dominated by thermal emission from dust spatially coincident with the thin nebular shell or most likely with the leading edge of the nebula. The WR nebulae in our sample present different morphologies that we classified into well defined WR bubbles (bubble ${\cal B}$-type nebulae), clumpy and/or disrupted shells (clumpy/disrupted ${\cal C}$-type nebulae), and material mixed with the diffuse medium (mixed ${\cal M}$-type nebulae). The variety of morphologies presented by WR nebulae shows a loose correlation with the central star spectral type, implying that the nebular and stellar evolutions are not simple and may proceed according to different sequences and time-lapses. We report the discovery of an obscured shell around WR35 only detected in the infrared.