A. M. Silva, D. Doshi, K. Al Moulla, E. A. S. Cristo, E. Artigau, P. T. P. Viana, N. C. Santos, J. H. C. Martins, C. M. J. Marques, S. G. Sousa, C. San Nicolas Martinez, T. L. Campante, A. Cabral, S. Cristiani
Abstract
Aims. We explore the impact that spectral interpolation introduces in radial velocity (RV) time-series that are extracted using templatebased methods, in particular systematic biases induced in this process. Methods. We generate synthetic datasets with Gaussian profiles to evaluate the flux residuals and line asymmetry that are the result of changing the sampling location of the lines, induced by barycentric motion and instrumental drifts. We generate synthetic spectra as the sum of Gaussian functions whose parameters were determined through an observed spectrum. The s-BART pipeline was applied to such datasets, allowing us to evaluate any biases in RV extraction that are introduced by its internal and implicit assumptions in line shape. Lastly, we apply the s-BART pipeline to ESPRESSO observations of four stars, with different observation strategies: two that use high-cadence observations over a single night and two that have observations spread over multiple nights. When extracting RVs from stellar spectra, we change the interpolation algorithm used in the process of constructing the stellar template and, afterwards, during RV extraction. They are then compared with RVs extracted whilst using the widely used cubic-spline interpolation. Results. We find that the synthetic datasets reveal systematic biases with the largest peak-to-peak amplitudes reaching ~20 m s-1 in low S/N cases, with the amplitude decreasing as the S/N of the spectra increases. In the extreme case of noise-free data, we still recover a systematic bias, albeit at the mm s-1 level, significantly smaller than the RV precision of state-of-the-art instruments. When using real observations, we find that RV time series that use high-cadence observations with small BERV variation (barycentric motion comparable to the pixel size of the instrument) are impacted by the choice of the interpolation algorithm. This impact is smaller in cases of higher S/N, where the peak-to-peak amplitude reaches ~1 m s-1. In the comparatively lower S/N case we find peak-to-peak residuals as large as ~25 m s-1. In cases where the observations are spread over a larger BERV window, we find an upper limit of 20 cm s-1 of RV scatter for this systematic signal. Conclusions. We conclude that diverse science cases are affected by the results presented in this manuscript, as the interpolation of stellar spectra is present in all of them to place observations in a common wavelength grid. This will impact not only the detection and characterization of exoplanets, but also atmosphere studies, asteroseismic analysis, and even cosmological red-shift determination.
Keywords
methods: data analysis / techniques: radial velocities / techniques: spectroscopic
Astronomy & Astrophysics
Volume 712, Article Number A159, Number of pages 13
2026 August
