Far-infrared observations and the structure of Wolf-Rayet ring nebulae

Detailed IRAS images of three WR ring nebulae, NGC 2359, RCW 58, and NGC 6888, are analyzed to obtain information on dust and associated gas masses within these nebulae, and these data are used together with kinematical data to derive the form and the structure of the nebulae. The IRAS maps show the presence of FIR emission that appears closely related to the optical shell structures. Calculations of forbidden line emission in the FIR associated with these nebulae suggest that only 8 to 20 percent of the observed FIR emission is due to these lines; the remaining emission is from heated dust. Dust temperatures are typically 33 K, although some high-temperature dust regions were found in the areas of greatest FIR emission. From continuum flux data, it was found that 0.25-1.3 solar mass is associated with the shells as dust, suggesting that their origins must be in the swept-up ISM near the WR stars, which has produced the ring nebulae. 33 refs