Revised Filter Profiles and Zero Points for Broadband Photometry

TL;DR

This paper improves broadband photometric filter profiles and zero points for bright stars by empirically calibrating them against flux-calibrated spectra, reducing systematic errors in flux estimation.

Contribution

It introduces an empirical method to refine filter profiles and zero points using spectroscopic data, enhancing flux accuracy for bright star photometry.

Findings

Most zero points change by less than 5%.

Some systems show zero point changes of 10-15%.

Estimated accuracy of zero points is 0.5-1%.

Abstract

Estimating accurate bolometric fluxes for stars requires reliable photometry to absolutely flux calibrate the spectra. This is a significant problem for studies of very bright stars, which are generally saturated in modern photometric surveys. Instead we must rely on photometry with less precise calibration. We utilize precisely flux-calibrated spectra to derive improved filter bandpasses and zero points for the most common sources of photometry for bright stars. In total we test 40 different filters in the General Catalog of Photometric Data as well as those from Tycho-2 and Hipparcos. We show that utilizing inaccurate filter profiles from the literature can create significant color terms resulting in fluxes that deviate by >10% from actual values. To remedy this we employ an empirical approach; we iteratively adjust the literature filter profile and zero point, convolve it with catalog spectra, and compare to the corresponding flux from the photometry. We adopt the passband values that produces the best agreement between photometry and spectroscopy and is independent of stellar color. We find that while most zero points change by <5%, a few systems change by 10-15%. Our final profiles and zero points are similar to recent estimates from the literature. Based on determinations of systematic errors in our selected spectroscopic libraries, we estimate that most of our improved zero points are accurate to 0.5-1% or better.