Development of iodine cells for Subaru HDS and Okayama HIDES. III. An improvement on the radial-velocity measurement technique

An improvement of the radial-velocity measurement accuracy is crucial for the detection of tiny stellar oscillations and exoplanets. Through the analysis of week-long extensive observations of solar-type stars (Procyon in 2000, 2002, and 2006/2007 and tau Cet in 2002 and 2006/2007), we have carefully examined, revised, and finely tuned the widely used multiple Gaussian IP fitting method for the spectrograph, HIDES. By determining a necessary and sufficient number of free parameters in the model as well as introducing an iterative process in the radial-velocity analysis, we can reach a precision of below 3 m s(-1), which is much smaller than the precision of 6 m s(-1) officially announced so far for HIDES. We also make our technique refined for the 2002 McDonald Procyon data. Even with our revised method, slow radial velocity variations with an amplitude of about 10 m s(-1) are left in the Procyon data. We emphasize that it is neither due to particular observing instruments nor radial-velocity analysis, and thus could be due to stellar origin. The analysis presented here makes the foundations of our next scientific analysis of the radial-velocity variations of Procyon, which will be presented in our forthcoming papers.