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arXiv · 2601.21059

A rotation-based census of blue lurker candidates in open clusters

Vikrant V. Jadhav·Khushboo K. Rao·Elisabetta Reggiani
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Abstract

Blue lurkers (BLs) are rejuvenated main-sequence stars hidden among normal main-sequence stars on color-magnitude diagrams of star clusters. In comparison, the blue straggler stars, formed via similar mass transfers or mergers, occupy a distinct space in the color-magnitude diagrams. We compile a list of BL candidates in open clusters using available rotation catalogs. BLs can be identified using either unusually faster rotation compared to similar mass stars, which is a signature of recent accretion, or the presence of a companion, which can only be formed by mass donation, e.g., an extremely low mass white dwarf. Here, we searched for fast-rotating stars on the main sequence of open clusters using Kepler, TESS, and spectroscopic rotation indicators, such as rotation periods and $v\sin i$ measurements. We identified 97 new BL candidates across 35 open clusters, almost tripling the previously known sample of 36. Based on the estimated completeness of $\approx$3\%, thousands of BLs are likely hidden within the cluster population. Detailed spectroscopic and time-series analyses will be essential to confirm their mass-transfer histories.

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Vikrant V. Jadhav, Khushboo K. Rao, Elisabetta Reggiani. 2026-01-28. A rotation-based census of blue lurker candidates in open clusters. https://doi.org/10.1051/0004-6361/202558188

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