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arXiv · 2509.02304

The incidence of magnetism in blue and yellow straggler stars

S. Hubrig·S. P. Järvinen·I. Ilyin·M. Schöller
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Abstract

Our understanding of the generation of magnetic fields in intermediate-mass and massive OBA stars remains limited. Some theories have proposed that their magnetic fields could be a result of strong binary interactions, including stellar mergers. Blue stragglers, which lie well beyond the main sequence turn-off point on the colour-magnitude diagram of stellar clusters, are widely theorised to be merger products or interacting binaries and therefore can be considered excellent test targets to get insights into the origin of magnetic fields in stars with radiative envelopes. We search for the presence of magnetic fields in a sample of blue and yellow stragglers listed in the Gaia DR2-based catalogue of blue stragglers in open clusters. We measured the mean longitudinal magnetic field from HARPSpol spectra of five blue stragglers and three yellow stragglers using the least-squares deconvolution technique. We present the first observational evidence that blue and yellow stragglers possess magnetic fields of the order of a hundred to a few hundred Gauss. The targets in our sample belong to open clusters of very different ages and metallicities, but we do not detect any relationship between the presence or strength of the detected magnetic field and the cluster characteristics. For the first time, using high-resolution spectropolarimetric observations, a definite detection of a magnetic field is achieved in a Be-shell star, HD61954. The two yellow stragglers, HD62329 and HD65032, appear to be members in binary systems, whereas the blue straggler HD62775 is possibly a triple system. HD62329 and HD65032 exhibit in their spectra weak Nd III 6145 lines, which are usually prominent in magnetic Ap and Bp stars.

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S. Hubrig, S. P. Järvinen, I. Ilyin, M. Schöller. 2025-09-02. The incidence of magnetism in blue and yellow straggler stars. https://arxiv.org/abs/2509.02304

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