HERCULES: A high-resolution spectrograph for small to medium-sized telescopes

The High Efficiency and Resolution Canterbury University Large Echelle Spectrograph (HERCULES) is a fibre-fed echelle spectrograph that has been in operation at the Mount John University Observatory for just over one year. HERCULES can capture the spectrum from 380nm to 880nm on a single 50-mm square CCD. Resolving powers of 40 000 to 80 000 are possible using different fibres. The spectrograph is designed to achieve high efficiency when the seeing is well matched to the image scale on the fibre input (up to 20% in 1 arcsec seeing), and high stability is achieved by having the spectrograph installed inside a vacuum tank in a thermally isolated environment. Radial velocities with a precision of less than or equal to 10 ms(-1) are routinely possible.