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The Echelle spectrograph operating at Vainu Bappu Telescope (VBT) is ageneral purpose instrument designed for high resolution spectroscopy. It isbeing considered for precision Doppler measurements without altering theexisting design and basic usage. However, the design level limitations andenvironmental perturbations are a major source of instability and systematicerrors. As a result, a small Doppler signal in the stellar spectra iscompletely swamped by the large and uncontrolled instrumental drift. In thispaper, we discuss some of the remedial measures we took to improve the radialvelocity performance of the spectrograph. We show that a new auto-guiderassembly has greatly reduced the mechanical jitter of the star image at thefibre input, making the illumination of the spectrograph slit at the other endstable. We have also installed an iodine absorption cell to track and eliminatethe instrumental drifts to facilitate precision radial velocity observations.Furthermore, we have developed a generic algorithm that uses iodine exposuresto extract the stellar radial velocities without the need for the complexforward modeling. Our algorithm is not accurate to the level of traditionaliodine technique. However it is convenient to use on a low-cost general-purposespectrograph targeting a moderate Radial Velocity (RV) precision at a few10-100~$\textrm{ms}^{-1}$ level. Finally, we have demonstrated the usefulnessof our approach by measuring the RV signal of a well known short-period,planet-hosting star.

Toward precision radial velocity measurements using Echelle spectrograph at Vainu Bappu Telescope