Photonic Passbands and Zeropoints for the Stromgren uvby system

TL;DR

This paper derives new photonic passbands for the Strömgren uvby system, enabling accurate synthetic photometry from spectrophotometric data, and compares these with observed indices to validate their effectiveness.

Contribution

It introduces updated passbands for the uvby system and provides transformation equations for synthetic photometry, improving consistency between models and observations.

Findings

Excellent agreement between synthetic and observed photometry.

Better fits achieved when considering different b-y color ranges.

Systematic differences explored between various instrumental systems.

Abstract

Photonic passbands have been derived for the uvby standard system by convolving the original filter passbands of Str\"omgren and Perry with atmospheric extinction and the QE of a cooled 1P21 photomultiplier tube. Using these new passbands, synthetic photometry was calculated for all the stars in the extensive NGSL and MILES spectrophotometric libraries and compared with the homogenised b-y, m1 and c1 indices in the Hauck-Mermilliod 1998 catalog and the derived u - v and v - b colors. Excellent agreement between observed and synthetic photometry was achieved with regression slopes near unity. Slightly better fits were obtained by considering stars with b-y < 0.5 and b-y > 0.5, separately. It is recommended that these new passbands be used together with the provided transformation equations to generate synthetic photometry from model atmosphere fluxes and observed spectrophotometry. Synthetic photometry was also carried out using the natural system of the 4-channel spectrograph-photometers and those of Cousins and Eggen in order to explore the systematic dfferences that could be expected between their instrumental systems and the standard system.