Photoionization Models of Metal-poor Extragalactic HII Regions and the Primordial Helium Abundance

Details Photoionization Models of Metal-poor Extragalactic HII Regions and the Primordial Helium Abundance Photoionization Models of Metal-poor Extragalactic HII Regions and the Primordial Helium Abundance

2003-02-28

arxiv.org/abs/astro-ph/0302612v1

Astronomy and Astrophysics

Astrophysics

5 pages, 5 figures. RMAA Latex. Proceedings of 'The Eighth Texas-Mexico Conference on Astrophysics: Energetics of Cosmic Plasm

Scientific paper

We discuss the effects of collisional enhancement of Balmer lines on the determination of the primordial helium abundance. To this aim, we present a photoionization model of the metal-poor extragalactic HII region SBS 0335--052. We show that the derived helium abundance (Y) of this HII region depends on the amount of collisional excitation affecting the Balmer lines, both directly (through an underestimation of the actual He/H ratio) and indirectly (through an overestimation of the interstellar reddening). We detail how each of these effects affects the derived value of Y.

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