American Astronomical Society, Astrophysical Journal, 2(788), p. 131, 2014
DOI: 10.1088/0004-637x/788/2/131
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We present a comparison of the frequencies of carbon-enhanced metal-poor (CEMP) giant and main-sequence turnoff stars, selected from the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration, with predictions from asymptotic giant-branch (AGB) mass-transfer models. We consider two initial mass functions (IMFs)-a Salpeter IMF, and a mass function with a characteristic mass of 10 solar mass. These comparisons indicate good agreement between the observed CEMP frequencies for stars with [Fe/H] > -1.5 and a Salpeter IMF, but not with an IMF having a higher characteristic mass. Thus, while the adopted AGB model works well for low-mass progenitor stars, it does not do so for high-mass progenitors. Our results imply that the IMF shifted from high- to low-mass dominated in the early history of the Milky Way, which appears to have occurred at a "chemical time" between [Fe/H] = -2.5 and [Fe/H] = -1.5. The corrected CEMP frequency for the turnoff stars with [Fe/H]