APASS DR9 Calibration Input Sample for Empirical Transformation Formulae from APASS DR9 to Johnson–Kron–Cousins BVRcIc

This dataset contains the input photometric data from APASS DR9 (Henden et al. 2016) used to derive the empirical transformation formulae from the APASS DR9 photometric system to the Johnson-Kron-Cousins BVRcIc system, presented in:

Montigiani, N. (2026), "Empirical Transformation Formulae from APASS DR9 to the Johnson-Kron-Cousins BVRcIc Photometric System", Journal of the American Association of Variable Star Observers (JAAVSO).

This dataset constitutes the raw input to the calibration workflow. The complete file contains 51,347 APASS DR9 entries from sky regions covered by Landolt (1992, 2009) photometric standard fields. The final calibration sample of 41,311 stars used in the published transformation fit is obtained by applying the quality cuts described in Section 2.1 of the paper, plus iterative 3.5 sigma-MAD outlier rejection during the Orthogonal Distance Regression (ODR) fitting procedure.

The B and V magnitudes are not direct measurements of Landolt standards: they are APASS DR9 photometric values calibrated onto the Landolt (1992) photometric system through the APASS pipeline, which uses primary Landolt equatorial standards together with SDSS standards in nightly all-sky solutions (Henden et al. 2016; Munari et al. 2014).

A comprehensive README file is included in this deposit, describing column definitions, data provenance, reproducibility instructions, and citation details.

The companion software pipeline is available at:- GitHub: https://github.com/Goldrake71/apass2johnson- Zenodo (software): doi:10.5281/zenodo.19153359