We are developing a prototype instrument for McDonald Observatory designed to measure stellar radial velocity variations to a precision of a few meters per second. The instrument will be used to study low amplitude stellar oscillations, to search for binary stellar systems with large mass ratios, and possibly to search for extra-solar planetary systems. A fixed gap Fabry-Perot etalon, used in reflection, imposes a set of fixed reference absorption lines on the stellar spectrum before it enters the McDonald Observatory 2.7m coudé spectrograph. The spectrum, covering 1500 Å at 0.13 Å resolution, is recorded on a set of eight Reticon arrays, placed end-to-end. Doppler shifts of the stellar spectral lines with respect to the fixed Fabry-Perot orders are measured by cross-correlation techniques. Calibration methods have been developed to measure any long-term drifts within the system.
