Empirically Predicted Absolute Magnitudes for Red Clump Stars in Mephisto and CSST Filters

Abstract Red clump (RC) stars are reliable standard candles for studying the structure and evolution of the Milky Way. In this study, we present empirical calibrations of RC absolute magnitudes in the Mephisto ( v , g , r , i ) and CSST ( g , r , i ) photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra. Through synthetic photometry and polynomial fitting, we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity, with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths. In particular, the Mephisto v band exhibits the highest sensitivity, with variations reaching up to 2.0 mag across the metallicity range (−1.0 dex <[Fe/H] < 0.5 dex) and the temperature range (4500–5200 K). The calibrations achieve high precision for all bands, enabling accurate determination of RC absolute magnitudes and distances. Furthermore, we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method, achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties (≤0.01 mag). These results provide robust tools for distance and metallicity determinations, supporting future Galactic structure studies with Mephisto and CSST data.