Barium Surface Abundances of Blue Stragglers in the Open Cluster NGC 6819

Abstract

We present the barium surface abundance of 12 blue stragglers (BSs) and 18 main-sequence (MS) stars in the intermediate-age open cluster NGC 6819 (2.5 Gyr) based on spectra obtained from the Hydra Multi-object Spectrograph on the WIYN 3.5 m telescope. For the MS stars we find [Fe/H] = $+$0.05 $\pm$ 0.04 and [Ba/Fe] = $-$0.01 $\pm$ 0.10. The majority of the BS stars are consistent with these values. We identify five BSs with significant barium enhancement. These stars most likely formed through mass transfer from an asymptotic giant branch star that polluted the surface of the BS with the nucleosynthesis products generated during thermal pulsations. This conclusion aligns with the results from the substantial work done on the BSs in old open cluster NGC 188 that identifies mass transfer as the dominant mechanism for BS formation in that open cluster. However, four of the BSs with enhanced barium show no radial-velocity evidence for a companion. The one star that is in a binary is a double-lined system, meaning the companion is not a white dwarf and not the remnant of a prior AGB star. In this paper we attempt to develop a consistent scenario to explain the origin of these five BSs.

11 pages, 6 figures

References in corpus (10)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
• WIYN Open Cluster Study XXXII: Stellar Radial Velocities in the Old Open Cluster NGC 188
• Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae: the chemical signature of a mass-transfer formation process
• Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars
• CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star
• WIYN Open Cluster Study. LX. Spectroscopic Binary Orbits in NGC 6819
• Spectroscopic Abundances in the Open Cluster, NGC 6819
• The Puzzling Li-rich Red Giant Associated with NGC 6819
• The Blue Stragglers of the Old Open Cluster NGC 188

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