The calibration of <i>Gaia</i> DR3 synthetic Strömgren–Crawford photometry
Abstract
ABSTRACT The superiority of narrow-band photometric systems over the nowadays commonly used broad-band ones is indisputable. The latter cannot probe characteristics such as metallicity with a high accuracy. Also, some basic properties, like interstellar reddening, are difficult to estimate. The presented Strömgren–Crawford $uvby\beta$ photometric system is ideally suited to study individual stars, clusters, and galaxies. The $Gaia$ consortium presented calibrated synthetic Strömgren $vby$ photometry and noted that the standard indices could not be reproduced. Besides the missing standard u and H$\beta$ magnitudes, the published status is unsatisfactory. Therefore, a new calibration of the complete Strömgren–Crawford filter set is presented. The mean photoelectric and CCD photometry of 33 465 stars were used to calibrate the synthetic ones. No constraints about the luminosity and metallicity were made. No offset for the y magnitude was found. Depending on the filter, a correlation with the effective temperature (colour) was detected and corrected. The statistical errors less than 0.05 mag allow one to use synthetic photometry for many purposes. The flux-calibrated low-resolution spectrophotometry (BP/RP spectra) of the $Gaia$ mission are well suited for synthesize narrow-band photometry. There is great potential in the future.