Chemical Composition of the Carbon-rich, Extremely Metal-Poor Star CS 29498–043: A New Class of Extremely Metal-Poor Stars with Excesses of Magnesium and Silicon

We analyze a high-resolution, high signal-to-noise spectrum of the carbon-rich, extremely metal-poor star CS 29498–043, obtained with the Subaru Telescope High Dispersion Spectrograph. We find its iron abundance is extremely low ([Fe/H] = −3.7), placing it among the few stars known with [Fe/H] ≤ −3.5, while Mg and Si are significantly overabundant ([Mg/Fe] = +1.8, and [Si/Fe] = +1.1) compared with stars of similar metallicity without carbon excess. Overabundances of N and Al were also found. These characteristics are similar to the carbon-rich, extremely metal-poor star CS 22949–037. Though the sample is small, our discovery of CS 29498–043 suggests the existence of a class of extremely metal-poor stars with large excesses of C, N, Mg, and Si. Subject headings: nuclear reactions, nucleosynthesis – stars: abundances – stars: individual(CS 29498–043) – stars: carbon – stars: Population II