Do chemical abundances in HII regions and their ionizing stars agree?

02/12/2014

The atmospheres of main-sequence massive stars should have the same chemical composition as the interstellar material from which they formed. The SO Postdocs Jorge García-Rojas and Sergio Simón-Díaz, and César Esteban, researchers of the IAC and the ULL, have investigated the chemical abundances of the Cocoon nebula, a close-by Galactic H II region, and its ionizing star, a main-sequence B-type star, using spectra obtained with the William Herschel Telescope in the Roque de los Muchachos Observatory. The results of this study indicate that the Oxygen and Nitrogen nebular abundance values, obtained from relatively bright emission lines, are different to those derived for the star and agree better with them assuming small temperature fluctuations in the nebula, of the order of those found in other Galactic HII regions. The presence of such temperature fluctuations in the gas, make the real abundances in the nebula to be underestimated if they are not taken into account. More information: García-Rojas et al. 2014, A&A 571, A93