Chemical abundance analysis of Kapteyn's Star

We report spectral chemical abundances for 12 elements in Kapteyn's Star (HD 33793), a subdwarf M star. We use stellar temperature and gravity parameters derived using the recent interferometric measurement of its radius. We find [Fe/H]=−1.13 ± 0.01, [Ti/H]=−0.90 ± 0.03, and a weighted mean metallicity [M/H]=−0.98 ± 0.10, where the uncertainties in temperature, gravity and microturbulence are included in the latter. This value falls about mid-way between the metallicity found in the only previous high-resolution analysis, [M/H]=−0.55 ± 0.15, and the value derived from low-resolution spectra of TiO and CaH features, [M/H]=−1.5 ± 0.5. It is essentially identical to that found using low-resolution infrared spectra of water lines, [M/H]=−1.0 ± 0.3. This abundance determination for a nearby subdwarf M star using well-determined stellar parameters and a spectrum with a high signal-to-noise ratio will provide an anchor point for abundance studies of similar stars where the situation is not so favourable.