Pre-Gaia distances for the open cluster Pismis 19 disagree with Gaia parallaxes. A 2MASS JKs red clump distance was therefore established for Pismis 19 (2.90±0.15 kpc), which reaffirms that zero-point corrections for Gaia are required (e.g., Lindegren et al.~2021). OGLE GD-CEP-1864 is confirmed as a member of Pismis 19 on the basis of DR3 proper motions, and its 2MASS+VVV color-magnitude position near the tip of the turnoff. That 0d.3 variable star is likely a δ Scuti rather than a classical Cepheid. The case revealed a pertinent criterion to segregate those two populations in tandem with the break in the Wesenheit Leavitt Law (≃0d.5). Just shortward of that period discontinuity are δ Scutis, whereas beyond the break lie first overtone classical Cepheids mostly observed beyond the first crossing of the instability strip.
Cite
@article{arxiv.2502.06930,
title = {The Gaia parallax discrepancy for the cluster Pismis 19, and separating $\delta$ Scutis from Cepheids},
author = {Daniel Majaess and Charles J. Bonatto and David G. Turner and Roberto K. Saito and Dante Minniti and Christian Moni Bidin and Danilo González-Díaz and Javier Alonso-Garcia and Giuseppe Bono and Vittorio F. Braga and Maria G. Navarro and Giovanni Carraro and Matias Gomez},
journal= {arXiv preprint arXiv:2502.06930},
year = {2025}
}