Homogenization of the Stetson Photometry with the BEST Database

Abstract

As one of the most widely recognized high-quality standard stars, the Stetson standards have been extensively used as a photometric reference for calibrating other surveys. In this work, we present an independent validation and re-calibration of the Stetson standard star photometry using the BEST database. Based on typically 30,000-70,000 calibration stars per band, we find that the original Stetson photometry achieves field-to-field zero-point precisions of approximately 10--40\,mmag in the $UBVRI$-band. In addition, significant spatially dependent magnitude offsets are detected within individual Stetson fields for all bands, with magnitudes exceeding 1\%, probably caused by the calibration errors in the Stetson photometry. After correcting those systematic errors, the agreement between the Stetson and BEST photometry is improved to $\sim$5\,mmag for individual fields for $BVRI$-band. The re-calibrated photometry is further validated using the SCR standards, yielding agreement better than 10\,mmag for individual stars in the $BVRI$ bands and confirming zero-point precisions of 2--4\,mmag in the $BVI$ band. The precisions is further confirmed by checks using Gaia DR3 broad band colors. These results highlight the power of the BEST database for improving photometric calibration and suggest that, if feasible, it be incorporated into the calibration process of future releases of the Stetson standard catalog.

Figures (7)

• Figure 1: Histograms of the distributions of magnitudes, magnitude errors, and numbers of observations for all S24 sources, shown on linear (top panels) and logarithmic (bottom) scales from left to right. Colors denote different photometric bands, and the legends are shown in the upper-right corner of the top-right panel.
• Figure 2: Spatial distributions of S24 source number (top), calibration star number (middle), and the zero-point offsets (bottom) for the $UBVRI$ bands from left to right. Each point denotes a S24 field, with color bars shown on the right.
• Figure 3: Magnitude difference between BEST and S24 as function of Gaia $G$ magnitude, Gaia $G_{\rm BP}-G_{\rm RP}$ color, and $E(B-V)$ extinction Wang2025. Panels from left to right correspond to $U$, $B$, $V$, $R$, and $I$ bands, with colors indicating density.
• Figure 4: Spatial distribution of the magnitude differences between the BEST and S24 for individual fields. A color bars is shown on the right. It should be noted that in certain fields (e.g., Ru149), the calibration stars do not cover the entire area, primarily because the S24 catalog itself does not extend to those regions.
• Figure 5: Same as Figure \ref{['fig:f4']}, but for the re-calibrated photometry.