The Valuable Long-period Cluster Cepheid KQ Scorpii and other Calibration Candidates

The classical Cepheid KQ Sco is a valuable anchor for the distance scale because of its long pulsation period (28.ͩ7) and evidence implying membership in the open cluster UBC 1558. Analyses tied to Gaia DR3 astrometry, photometry, spectroscopy, radial velocities, and 2MASS-VVV photometry indicate a common distance of 2.15 ± 0.15 kpc (L21 DR3 corrections applied). Additional cluster Cepheid candidates requiring follow-up are identified, and it is suggested that a team of international researchers could maintain a cluster Cepheid database to guide the broader community to cases where consensus exists.