Calibration of Complementary Metal-oxide-semiconductor Sensor-based Photometry to a Few-millimagnitude Precision: The Case of the Mini-SiTian Array

We present a pioneering achievement in the high-precision photometric calibration of CMOS-based photometry, by application of the Gaia BP/RP (XP) spectra-based synthetic photometry (XPSP) method to the mini-SiTian array (MST) photometry. Through 79 repeated observations of the $\texttt{f02}$ field on the night, we find good internal consistency in the calibrated MST $G_{\rm MST}$-band magnitudes for relatively bright stars, with a precision of about 4\,mmag for $G_{\rm MST}\sim 13$. Results from more than 30 different nights (over 3100 observations) further confirm this internal consistency, indicating that the 4\,mmag precision is stable and achievable over timescales of months. An independent external validation using spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR10 and high-precision photometric data using CCDs from Gaia DR3 reveals a zero-point consistency better than 1\,mmag. Our results clearly demonstrate that CMOS photometry is on par with CCD photometry for high-precision results, highlighting the significant capabilities of CMOS cameras in astronomical observations, especially for large-scale telescope survey arrays.