Homogenization of the Stetson Photometry with the BEST Database

TL;DR

This study validates and improves the calibration of the Stetson standard star photometry using the BEST database, reducing systematic errors and achieving higher zero-point precision across multiple bands.

Contribution

It provides an independent re-calibration of the Stetson standards with the BEST database, correcting systematic offsets and enhancing photometric accuracy.

Findings

Original Stetson photometry has 10-40 mmag zero-point precision.

Systematic spatial offsets exceeding 1% are detected and corrected.

Re-calibrated photometry achieves 5 mmag precision in BVRI bands.

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.