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 ratio 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. Although 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.