The pre-main-sequence evolution of the chemically peculiar (CP) stars on the upper main sequence is still a vast mystery and not well understood. Our analysis of young associations and open clusters aims to find (very) young CP stars to try to put a lower boundary on the age of such objects. Using three catalogues of open clusters and associations, we determined membership probabilities using HDBSCAN. The hot stars from this selection were submitted to synthetic Δa photometry, spectral, and light curve classification to determine which ones are CP stars and candidates. Subsequently, we used spectral energy distribution fitting and emission line analysis to check for possible PMS CP stars. The results were compared to the literature. We detected 971 CP stars and candidates {in 217 clusters and associations}. A relatively large fraction, ∼10\% of those, show characteristics of PMS CP stars. This significantly expands the known list of candidate PMS CP stars, bringing us closer to solving the mystery of their origin.
@article{arxiv.2510.19810,
title = {A Census of Chemically Peculiar Stars in Stellar Associations},
author = {Lukas Kueß and Ernst Paunzen},
journal= {arXiv preprint arXiv:2510.19810},
year = {2025}
}