Chemical abundances of the WR-ring nebulae NGC 2359 and RCW 78

Esteban, C.; Vilchez, J. M.; Manchado, A.; Edmunds, M. G.
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(Instituto de Astrofisica de Canarias and Comision Interministerial de Ciencia y Tecnologia, Summer School on Evolutionary Phenomena in Galaxies, Puerto de la Cruz, Spain, July 4-15, 1988) Astrophysics and Space Science (ISSN 0004-640X), vol. 157, no. 1-2, July 1989, p. 3-7.

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This paper reports on extensive spectroscopic observations of the WR-ring nebulae NGC 2359 and RCW 78, respectively, excited by the WN5 stars HD 56925 and WN8 HD 117688. For the first object, abundances were determined for O/H, Ne/H, N/H, and He/H in many different positions, including the ionized gas in the bubble, inside the optical shell structure, and the outermost zones associated with the S 298 H II region. No significant difference in the N/H and O/H abundances was found over the entire nebula. The O/H and N/H abundances expected are close to those for a normal H II region located at similar distance. In the case of He/H, indication is found of local enhancements which sum to the abundance of metal-rich galactic H II regions like M17. RCW 78 appears to show slight overabundances of He/H and N/H in the two observed positions. The ionizing temperature for the WN central star (HD 56925) of NGC 2359 is determined from the observed H II region spectrum giving a value of 50,000 K, appropriate to its spectral type.