Recalibration of the Landolt <i>UBVRI</i> Standard Stars and the Generation of 5.4 Million New <i>UBVRI</i> Standard Stars Using LAMOST and Gaia

Abstract We present an independent validation and recalibration of the Landolt 2013 (celestial equator and δ ∼ −50 ∘ ) and 2016 ( δ ∼ −50 ∘ ) standard stars in the Johnson UBV and Kron–Cousins RI systems, using tens of thousands of XP spectra-based synthetic photometry (XPSP) data from the BEst STar (BEST) database. Our analysis reveals an overall zero-point offset between the 2016 and 2013 datasets. We further identify zero-point offsets for each standard field, ranging from 5 to 14 mmag across all UBVRI bands, with correlations between offsets in different bands. Additionally, we confirm the spatial structures up to 7–10 mmag in the BVRI bands. We also find that spatial structures are similar across bands for the same field, and similar across different fields for the same band. These similarities may arise from the averaged flat fields from each observing run. The recalibrated results are consistent with the XPSP data within 48 mmag in the U band, 11 mmag in the B band, and 5–6 mmag in the VRI bands in the brightness G < 16. Furthermore, based on stellar atmospheric parameters from LAMOST DR12 and Gaia DR3 photometry, along with the XPSP data, we derive temperature- and extinction-dependent extinction coefficients for the UBVRI bands as well as a LAMOST- and Gaia-based catalog of 5.4 million standard stars in the UBVRI bands, for which the U -band photometry of the vast majority of sources exhibits significantly higher precision than XPSP. The recalibrated Landolt standard stars and LAMOST- and Gaia-based standard stars will be available on the BEST website ( https://nadc.china-vo.org/data/best/ ) and on Zenodo at doi: 10.12149/101704 .