Impact of Spectral Resolution on <i>S</i>-index and Its Application to Spectroscopic Surveys

Abstract Utilizing the PHOENIX synthetic spectra, we investigated the impact of spectral resolution on the calculation of S -indices. We found that for spectra with a resolution lower than ≈30,000, it is crucial to calibrate S -indices for accurate estimations. This is especially essential for low-resolution spectral observations. We provided calibrations for several ongoing or upcoming spectroscopic surveys such as the LAMOST low-resolution survey, the SEGUE survey, the Sloan Digital Sky Survey-V/BOSS survey, the DESI survey, the Maunakea Spectroscopic Explorer survey, and the MUST survey. Using common targets between the HARPS and Mount Wilson Observatory (MWO) observations, we established conversions from spectral S -indices to the well-known S MWO values, applicable to stars with [Fe/H] values greater than −1. These calibrations offer a reliable approach to converting S -indices obtained from various spectroscopic surveys into S MWO values and can be widely applied in studies on chromospheric activity.