Radial Velocity Accuracy Prediction of the GREGOR At Night Spectrograph Based on Simulated Spectra

The Gregor At Night Spectrograph (GANS) is a new instrument currently being built for the GREGOR solar telescope at Izana observatory on Tenerife. Its primary science case will be the follow up of planetary candidates detected by upcoming surveys focussing on bright targets (TESS, PLATO2). Therefore it will be optimised for precise radial velocity determination and long term stability. We have developed a ZEMAX based software package to create simulated spectra, which are reduced using standard IRAF tasks. We used a solar model spectrum to determine the influence of S/N ratio, wavelength coverage, pixel sampling and telluric lines on the extracted radial velocities. Furthermore we derived the effect of an asymmetric spectrograph illumination on the measured radial velocity.