Charge Transfer Inefficiency (CTI) is a well known effect of charge-coupled
devices (CCD). The charge transfer from one pixel to the next is not perfect
and is quantified by the fraction of charge successfully moved (clocked) between
adjacent pixels. The amplitude of this effect depends on the signal level
inside the pixel. In the context of high-precision radial velocity measurements
using cross-dispersed echelle spectrograph, this CTI effect on a CCD
recording spectral orders may introduce associated spectral lines shifts.
Indeed if the signal level recorded on the spectra is changing, the CTI amplitude
will change affecting the associated centroid of all spectral lines.
Such effect may introduced radial velocity shifts of several m s-1.
We describe here CTI effect which is affecting the SOPHIE spectrograph installed on
the 1.93-m telescope of Observatoire de Haute Provence (OHP). We calibrated the
effect thanks to the Thorium-Argon
lines and we applied a software correction on the spectra in order to assess
the charge lost during the readout process on all pixels.