Autoguider locked on a fiber input for precision stellar radial velocities

Measurement of stellar radial velocities (RV) is one acknowledged approach for planetary-search and asteroseismology programs. We study the incomplete scrambling action of a fiber feeding a spectrograph, which leaves RV error s at a level of few m/s. Observations realised with the ELODIE fiber-fed cr ossed-dispersion spectrograph at the 193-cm telescope of Observatoire de Ha ute-Provence (OHP) are presented. A fiber-locked autoguider (called FLAG) h as been specifically built to reduce the stellar-beam geometrical fluctuati ons within the spectrograph. With FLAG, the fiber-input plays the role of g uiding detector. Automatic focusing is also accomplished by the system. The design and performance characteristics of the instrument tested at the 152 -cm telescope of OHP are reviewed here.