AAS 201st Meeting, January, 2003
Session 18. Instrumentation for Infrared and Optical Observing
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[18.15] The radial velocity precision possible with a fiber-fed spectrograph

G. Walker, E. Shkolnik (UBC), D. Bohlender (HIA), S. Yang (UVic)

The best radial velocity precision possible in conventional coudé spectroscopy used to be several hundreds of m/s. Guiding and collimation errors contributing the major uncertainties. As a by-product of Ca II H&K spectroscopy of certain 51~Peg-type stars, we regularly measure differential radial velocities between nights to a precision of 20 m/s - this allows us to update and improve the ephemerides of their planetary companions. The spectra are of high signal to noise (~500/pixel) and high resolution (~ 110,000) taken with the fiber-fed Gecko echellette spectrograph on the Canada France Hawaii 3.6-m Telescope. The fiber is continuously agitated and comparison arcs are taken before and after each stellar exposure. The arcs are sufficient to track spectrograph drift and the agitated fiber eliminates collimation and guiding errors. While we are not advocating this combination for Doppler planet searches, the precision is more than adequate for other programs. This research was supported by the Canadian NSERC.

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