Authors:

Gabriela Escobedo

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About Paper:

Blue straggler stars (BSSs) present a challenge to traditional models of stellar evolution due to their unexpected location in the color-magnitude diagrams (CMDs) of star clusters. Their position, bluer and brighter than the main sequence turnoff, cannot be explained by standard single-star evolution. One channel of BSS formation involves mass transfer in binary systems. In this process, a donor star in a binary loses material that is accreted by its companion star, which becomes a rejuvenated, more luminous BSS. In this work, we used the Bayesian analysis code BASE-9 combined with archival photometric and spectroscopic measurements to constrain the mass and time since formation of the BSSs in the rich, intermediate-age, open cluster NGC 6819. We used photometric data from Gaia DR3, 2MASS, and Pan-STARSS to construct a CMD of the cluster, and employed MIST stellar evolution models to determine preliminary by-eye masses for 19 BSSs in the cluster. We then applied a modified version of the Bayesian cluster analysis software package, BASE-9, to derive more robust posterior distributions for the masses and transformational ages for these BSSs based on photometric information from Gaia DR3, 2MASS, and Pan-STARRS. Using archival data collected from the WIYN Open Cluster Study, we also matched each BSS to radial velocity and barium abundance measurements. As barium is an s-process element that is enhanced during asymptotic giant branch (AGB) evolution, these abundances allow us to identify binary BSSs and which systems may have evolved through mass transfer from an AGB star. By combining these measurements, we can identify specific formation channels for these BSSs and place new limits on the amount of mass accreted during binary mass transfer. With this work, we have established a methodology to evaluate BSS masses, ages, and formation channels, which we can extend to more open clusters in the future.

Source:

Illinois Institute of Technology

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Co-authors:

Gabriela Escobedo