Speaker
Description
We present a study that calibrates the Galactic Leavitt law to the highest available accuracy using Cepheids residing in open star clusters. We developed a method for detecting open clusters near Cepheids. This has allowed us to discover 2 new host clusters and update the parameters of 31 previously discovered ones. Cluster member stars span a similar magnitude and color range as the quasars used by Lindegren et al. (2021) (hereafter L21) to determine Gaia parallax systematics, are non-variable, and are not subject to other complicating factors of Gaia data processing, such as the gating mechanism to avoid saturation of stars brighter than G ⼠12. Using this approach, we find an average uncertainty in the cluster parallaxes of 7 μas, an improvement of a factor of three over the uncertainties in the Cepheid parallaxes used to calibrate the distance ladder. Using the known distance to the Large Magellanic Cloud based on detached eclipsing binaries as a reference, we find that the L21 corrections accurately describe the parallax offset for this sample of clusters to within -3 +/- 6 μas. In a combined fit using cluster parallaxes and Cepheid parallaxes simultaneously, we find excellent agreement with the Cepheid parallax zero-point offset determined by Riess, and confirm that cluster parallaxes and Cepheid parallaxes have different zero-point offsets. Lastly, we simultaneously calibrate the Leavitt law in several photometric bands while solving for the parallax offset, and obtain a 1.7% LL calibration for MW Cepheids.
