Research on the influence factors of radial velocity based on a coherent-dispersion spectrometer

High precision extrasolar planet detection based on the radial velocity (RV) method has important scientific significance for studying planet formation, galaxy evolution, and exploring the origin of life and extraterrestrial civilizations. The asymmetric common-path coherent-dispersion spectrometer (CODES) has great potential in the field of exoplanet detection due to its high stability and high throughput. However, the non-ideal characteristics of the telescope and limitation of the detector resolution will cause the problem of uneven distribution of received starlight intensity and the sub-pixel Doppler shift. These problems will affect the inversion precision of the RV. To solve these problems effectively, this paper first determines the optimal optical path difference (OPD) and detector sampling of the optical system through theoretical simulation. Then, based on these parameters, the influence of interference envelope caused by uneven distribution of intensity and sub-pixel Doppler shift on RV are discussed. A method of alleviating sub-pixel Doppler shift by extracting interference information of absorption/emission line based on the 3σ rule with small sampling is also studied. Finally, an improved empirical mode decomposition (EMD) interference envelope removal method based on extrapolation interpolation is proposed. The simulation results indicate that the absolute errors of the RV obtained based on the absorption line and emission line are 0.32 m/s and 0.24 m/s, and the root mean squared error (RMSE) is 0.56 m/s and 0.14 m/s, respectively. This method effectively solves the problems caused by sub-pixel Doppler shift and uneven distribution of intensity, and significantly improves the accuracy of RV. Furthermore, it establishes a crucial foundation for investigating galaxy evolution and exploring the origin of life.