Cosmic Chemical Evolution with an Early Population of Intermediate Mass Stars

Understand

We explore the consequences of an early population of intermediate mass stars in the 2 - 8 M\odot range on cosmic chemical evolution.

• We discuss the implications of this population as it pertains to several cosmological and astrophysical observables.
• For example, some very metal-poor galactic stars show large enhancements of carbon, typical of the C-rich ejecta of low-mass stars but not of supernovae; moreover, halo star carbon and oxygen abundances show wide scatter, which imply a wide range of star-formation and nucleosynthetic histories contributed to the first generations of stars.
• Also, recent analyses of the 4He abundance in metal-poor extragalactic H II regions suggest an elevated abundance Yp \simeq 0.256 by mass, higher than the predicted result from big bang nucleosynthesis assuming the baryon density determined by WMAP, Yp = 0.249.