Application of the Telluric - Line Technique to StudyLate - Type Stars for Radial - Velocity

Although the use of telluric lines as wavelength ducials to measure radial velocities does not achieve as high precision as other ducial-imposition techniques, this very convenient technique can be used concurrent with other observing programmes to increase the temporal sampling of target stars. We have been carrying out a programme to monitor the line-proole variations of early-type non-radial pulsators at the H-alpha and He 667.8nm region. With the rather modest reciprocal dispersion of 1nm/mm and the use of a 4096-element CCD, the telluric lines in the 630nm region are also available in the observed spectra. We decided to use these telluric lines as wavelength ducials to monitor bright, late-type stars for radial-velocity variations. As an experiment, we have also decided to reduce the spectra using available simple IRAF tasks to see how high a velocity precision can be achieved with only minor tweak-ing. The precision certainly would not rival other precise techniques, but the convenience in both the observing and reduction procedure may enable more target stars to be monitored by more observers. Moreover, interesting results can still be obtained with a mere 100 m/s precision. The result for a few late-type stars which also have prior HF velocities will be presented.