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arXiv · 2606.05321

Hot Degenerate Components in Blue Stragglers: A Multi-Wavelength SED Analysis of Nine Open Clusters with Swift/UVOT

Deniz Cennet Çınar·D. Bisht·Selçuk Bilir·Songmei Qin·Leila Saker
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Abstract

We present a homogeneous multi-wavelength analysis of 35 blue straggler star (BSS) candidates in nine open clusters, combining Swift/UVOT near-ultraviolet data with Gaia DR3 astrometry and optical-to-infrared photometry. We construct spectral energy distributions (SEDs) to search for signatures of hot companions associated with past mass transfer. Among the sample, 15 BSSs (~43%) show ultraviolet excesses that are better described by two-component SED fits. The inferred companions are consistent with hot white dwarfs and pre-extremely low-mass (pre-ELM) white dwarf candidates, suggesting systems observed at different stages following mass transfer. We examine the radial distribution of the BSSs and find evidence for mass segregation in dynamically evolved clusters, a result that is broadly consistent with the estimated half-mass relaxation timescales of the host systems. To place the clusters in a Galactic context, we compute their orbits using galpy, obtaining low eccentricities (e <= 0.1) and disk-like trajectories. We also find a positive relation between the half-number radius of the BSS population (r50) and the total number of BSSs. Overall, our results are consistent with a scenario in which the BSS population in these clusters is dominated by binary evolution. The systems identified here provide observational constraints on post-mass-transfer evolutionary phases. While the number of robust detections is limited and intrinsic degeneracies remain in SED-based decomposition, these results provide a useful foundation for future spectroscopic confirmation.

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Deniz Cennet Çınar, D. Bisht, Selçuk Bilir, Songmei Qin, Leila Saker. 2026-06-03. Hot Degenerate Components in Blue Stragglers: A Multi-Wavelength SED Analysis of Nine Open Clusters with Swift/UVOT. https://arxiv.org/abs/2606.05321

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