Absolute radial velocities by cross-correlation with synthetic spectra

Precise absolute radial velocities have been measured for several hundred late-type stars at Mt John University Observatory with the 1-m telescope, fiber-fed echelle spectrograph, and Thomson CCD. Six echelle orders in the green (5000-5600 Angstrom) are used. Many delicate steps have been undertaken in order to maintain exactly the same conditions, both in recording and reducing the spectra, over a period of 18 months. A cross-correlation technique with theoretical spectra computed by R. L. Kurucz has been chosen to determine the absolute radial velocities. Blue sky spectra have been used to monitor systematic zero-point fluctuations from one observing run to another. An additional correlation between the measured velocities and average number of A/D units in the continuum has been discovered and used for fine adjustments, significantly improving the results. A random uncertainty of 10-20 ms(-1) has been achieved for stellar spectra having intrinsically constant radial velocities.