Stellar encounter driven red-giant star mass loss in globular clusters

Mario Pasquato, Andrea De Luca, Gabriella Raimondo, Roberta Carini, Anthony Moraghan, Chul Chung, Enzo Brocato, Young Wook Lee

    Research output: Contribution to journalArticlepeer-review


    Globular cluster (GC) color-magnitude diagrams (CMDs) are reasonably well understood in terms of standard stellar evolution. However, there are still some open issues, such as fully accounting for the horizontal branch (HB) morphology in terms of chemical and dynamical parameters. Mass loss on the red giant branch (RGB) shapes the mass distribution of the HB stars, and the color distribution in turn. The physical mechanisms driving mass loss are still unclear, as direct observations fail to reveal a clear correlation between mass-loss rate and stellar properties. The HB mass distribution is further complicated by helium-enhanced multiple stellar populations due to differences in the evolving mass along the HB. We present a simple analytical mass-loss model based on tidal stripping through Roche-Lobe overflow during stellar encounters. Our model naturally results in a non-Gaussian mass-loss distribution with high skewness and contains only two free parameters. We fit it to the HB mass distribution of four Galactic GCs, as obtained from fitting the CMD with zero age HB models. The best-fit model accurately reproduces the observed mass distribution. If confirmed on a wider sample of GCs, our results would account for the effects of dynamics in RGB mass-loss processes and provide a physically motivated procedure for synthetic CMDs of GCs. Our physical modeling of mass loss may result in the ability to disentangle the effects of dynamics and helium-enhanced multiple populations on the HB morphology and is instrumental in making HB morphology a probe of the dynamical state of GCs, leading to an improved understanding of their evolution.

    Original languageEnglish (US)
    Article number28
    JournalAstrophysical Journal
    Issue number1
    StatePublished - Jul 1 2014


    • globular clusters: general
    • globular clusters: individual (NGC 5904, NGC 6093, NGC 6266, NGC 6752)
    • stars: horizontal-branch
    • stars: kinematics and dynamics
    • stars: mass-loss

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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