Photometric Flux Calibration Free from the Pitfalls of Spectroscopic Fits

From supernovae and exoplanets to fundamental stellar and galactic astronomy, deriving accurate astrophysical parameters often depends on accurate photometric flux calibration. In the ultraviolet, optical, and infrared, this flux calibration generally depends on the comparison between observations and models of just a few (3) white dwarf stars, where the model deemed to give the true flux is chosen by fits to observed Balmer lines. This makes the results subject to inaccuracies in the underlying line broadening physics and also to the details of the line fitting procedure. The method is also not robust against possible peculiarities in the few fundamental standards. The abundant photometric and astrometric data now available allows an alternative calibration procedure that uses many white dwarf stars instead of just a few. Using SDSS and Pan-STARRS photometry and Gaia astrometry, we demonstrate such a method. Because it does not rely on spectroscopic fits, it is not subject to the uncertainties of Balmer line fitting and is also largely independent of inaccuracies in the input line profiles. We also discuss these uncertainties in the model input physics in the context of our spectroscopic measurements of white dwarf photospheres in the lab, which we kindle with the world’s most powerful x-ray source, the Sandia National Labs Z Machine.