On the internal pollution mechanisms in the globular cluster NGC 6121(M4): Heavy-element abundances and AGB models

D’Orazi, V.; Campbell, S. W.; Lugaro, M.; Lattanzio, J. C.; Pignatari, M.; Carretta, E.

Abstract

Globular clusters display significant variations in their light-element content, pointing to the existence of a second stellar generation formed from the ejecta of an earlier generation. The nature of these internal polluters is still a matter of debate: the two most popular scenarios indicate intermediate-mass asymptotic giant branch (IM-AGB) stars and fast rotating massive stars. Abundances determination for some key elements can help distinguish between these competitor candidates. We present in this paper Y abundances for a sample of 103 red giant branch stars in NGC 6121. Within measurement errors, we find that the [Y/Fe] is constant in this cluster contrary to a recent suggestion. For a subsample of six stars we also find [Rb/Fe] to be constant, consistent with previous studies showing no variation in other s-process elements. We also present a new set of stellar yields for IM-AGB stellar models of 5 and 6M⊙, including heavy element s-process abundances. The uncertainties on the mass-loss rate, the mixing length parameter and the nuclear reaction rates have a major impact on the stellar abundances. Within the IM-AGB pollution scenario, the constant abundance of heavy elements inside the cluster requires a marginal s-process efficiency in IM-AGB stars. Such a constrain could still be satisfied by the present models assuming a stronger mass-loss rate. The uncertainties mentioned above are limiting the predictive power of IM-AGB models. For these reasons, at the moment we are not able to clearly rule out their role as main polluters of the second population stars in globular clusters. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Citation

D’Orazi, V., Campbell, S. W., Lugaro, M., Lattanzio, J. C., Pignatari, M., & Carretta, E. (2013). On the internal pollution mechanisms in the globular cluster NGC 6121(M4): Heavy-element abundances and AGB models. Monthly notices of the Royal Astronomical Society, 433(1), 366-381. https://doi.org/10.1093/mnras/stt728

• Journal Article Type: Article
• Acceptance Date: Apr 25, 2013
• Online Publication Date: May 21, 2013
• Publication Date: Jul 21, 2013
• Deposit Date: Jul 30, 2018
• Publicly Available Date: Jul 30, 2018
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 433
• Issue: 1
• Pages: 366-381
• DOI: https://doi.org/10.1093/mnras/stt728
• Keywords: Stars: abundances; Stars: AGB and post-AGB; Globular clusters: individual: NGC 6121
• Public URL: https://hull-repository.worktribe.com/output/561783
• Publisher URL: https://academic.oup.com/mnras/article/433/1/366/1032563