Photoionization Models of Metal-poor Extragalactic H Ii Regions and the Primordial Helium Abundance
نویسنده
چکیده
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 H II region SBS 0335–052. We show that the derived helium abundance (Y ) of this H II 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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تاریخ انتشار 2003