Dust In Rcw58: Clues To Common Envelope Channel Formation?

We present a characterization of the dust in the Wolf-Rayet (WR) nebula RCW58 around the WN8h star WR 40 using archival infrared (IR) observations from WISE and Herschel and radio observations from ATCA. We selected two clumps, free from contamination from material along the line of sight and located towards southern regions in RCW58, as representative of the general properties of this WR nebula. Their optical, IR, and radio properties are then modelled using the photoionization code CLOUDY, which calculates a self-consistent spatial distribution of dust and gas properties. Two populations of dust grains are required to model the IR SED: a population of small grains with sizes 0.002-0.01 mu m, which is found throughout the clumps, and a population of large grains, with sizes up to 0.9 mu m, located further from the star. Moreover, the clumps have very high dust-to-gas ratios, which present a challenge for their origin. Our model supports the hypothesis that RCW58 is distributed in a ring-like structure rather than a shell, and we estimate a mass of similar to 2.5M(circle dot). This suggests that the mass of the progenitor of WR40 was about approximate to 40(-3)(+2) M-circle dot. The ring morphology, low nebular mass, large dust grain size, and high dust-to-gas ratio lead us to propose that RCW58 has formed through a common envelope channel, similar to what has been proposed for M1-67.