Nitrogen and helium enrichment in four Wolf-Rayet ring nebulae

Abstract

Spectrophotometry is reported of four additional ring nebulae around Population I Wolf-Rayet stars: S308 (HD 50896, WN5), NGC 3199 (HD 89358, WN5), Anon (HD 191765 = MR 100, WN6), and RCW 58 (HD 96548, WN8). The nitrogen to helium abundance ratio in each nebula is combined with corresponding data for the central star and the general Interstellar Medium (ISM) to estimate the fractional contribution that the nitrogen and helium-rich stellar wind has made to the mass of each nebula. The fractional contribution is independently estimated from the dynamical age of each nebula and the mass loss rate of its central star. The results from these methods agree within experimental errors, and for three of the objects are consistent with enrichment by the stellar wind over the nebular lifetimes. Coupled with the estimated total of Wolf-Rayet population in the Galaxy, it is concluded that such enrichment of the ISM is Galaxy-wide.