The evolutionary state of the chemically peculiar members of the open cluster NGC2516

TL;DR

This study assesses the membership and evolutionary status of 11 chemically peculiar stars in NGC2516 using Gaia data, revealing that only some are true cluster members and providing insights into their magnetic and evolutionary properties.

Contribution

It provides a detailed membership analysis of CP stars in NGC2516 and clarifies their evolutionary states using Gaia data and Padova isochrones, including the identification of a unique blue straggler.

Findings

Only 5 of 11 CP stars are probable cluster members.

HD65987 and HD65712 are confirmed magnetic cluster members.

HD66318 is a non-member despite previous low fractional age reports.

Abstract

We aim at establishing safe membership and evolutionary status of 11 chemically peculiar (CP) stars that are residing in the domain of the open cluster NGC2516 and are frequently referred to as cluster members. We queried the Gaia EDR3 catalogue in an area with a radius of 1deg and selected 37508 stars brighter than G=19mag. The cluster membership was determined in parallax-proper motion-space and 719 probable and 764 possible members were found. The obtained average astrometric and photometric parameters of the cluster are in good agreement with the most recent literature data. The evolutionary status of the target stars was determined with respect to Padova isochrones. After minor adjustments including the metallicity, the reddening, and the transformation scale variation, a perfect fit of the model to the observations over the whole observed magnitude range was achieved. Only 5 of the 11 considered CP stars could be classified as highly probable cluster members. Among the Ap/Bp stars with previously detected magnetic fields HD65987 and HD65712 have a high membership probability and the magnetic star CPD-60 944B is a possible cluster member. Further we discuss the blue straggler nature of HD66194 and the magnetic star HD65987. To our knowledge, HD65987 is currently the only known blue straggler, with a field of the order of a few hundred Gauss. The most striking result of our study is that the strongly magnetic A0p star HD66318 with previously reported very low fractional age does not belong to the NGC2516 cluster at a high level of confidence.