Aberration-corrected echelle spectrometer for measuring ultraviolet branching fractions of iron-group ions.

A high-resolution echelle spectrometer with broad wavelength coverage from the UV to the IR and high sensitivity to weak lines is described. Total instrument astigmatism is suppressed through rotation of the order separation system into an orthogonal plane. A suitable choice of mirror angles avoids increased coma. This spectrometer is used to record UV through IR spectra of Fe-group ions to measure improved branching fractions. These new results reduce transition probability uncertainties and yield more accurate derived stellar abundances. Instrument design and performance, including aberration compensation, are presented.