Lucifers, a photoelectric radial-velocity spectrometer

Abstract

A spectrometer dedicated to the measurement of stellar radial velocities has been developed at the University of Canterbury and the Mt John University Observatory. The spectrometer scans a spectrum from the Observatory's 1-metre McLellan reflecting telescope and fibre-fed echelle with an oscillating mask having 2447 rectangular slots representing absorption lines in the spectrum of the starα Centauri A covered by the wavelength range 397 to 570 nm in orders 40 to 58 of the spectrograph and measures the light passing through the mask as a function of mask position. A dedicated computer constructs a cross-correlation function to which a Gaussian distribution function is fitted. The difference between the radial velocities of a star and a zero-velocity reference spectrum provided by a hollow-cathode iron emission lamp is calculated from the Gaussian parameters. The sources of random error in the system are discussed and its magnitude for stars of spectral types F0 to M3.5 is estimated. Systematic errors in the system are also discussed.