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http://hdl.handle.net/20.500.12386/26487
Titolo: | Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters | Autori: | Angelou, George C. D'ORAZI, VALENTINA Constantino, Thomas N. Church, Ross P. Stancliffe, Richard J. Lattanzio, John C. |
Data pubblicazione: | 2015 | Rivista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Numero: | 450 | Fascicolo: | 3 | Da pagina:: | 2423 | Abstract: | We conduct a series of comparisons between spectroscopic and photometric observations of globular clusters and stellar models to examine their predictive power. Data from medium-to-high resolution spectroscopic surveys of lithium allow us to investigate first dredge-up and extra mixing in two clusters well separated in metallicity. Abundances at first dredge-up are satisfactorily reproduced but there is preliminary evidence to suggest that the models overestimate the luminosity at which the surface composition first changes in the lowest metallicity system. Our models also begin extra mixing at luminosities that are too high, demonstrating a significant discrepancy with observations at low metallicity. We model the abundance changes during extra mixing as a thermohaline process and determine that the usual diffusive form of this mechanism cannot simultaneously reproduce both the carbon and lithium observations. Hubble Space Telescope photometry provides turn-off and bump magnitudes in a large number of globular clusters and offers the opportunity to better test stellar modelling as function of metallicity. We directly compare the predicted main-sequence turn-off and bump magnitudes as well as the distance-independent parameter ∆ M_V ^{MSTO}_{bump}. We require 15 Gyr isochrones to match the main-sequence turn-off magnitude in some clusters and cannot match the bump in low-metallicity systems. Changes to the distance modulus, metallicity scale and bolometric corrections may impact on the direct comparisons but ∆ M_V ^{MSTO}_{bump}, which is also underestimated from the models, can only be improved through changes to the input physics. Overshooting at the base of the convective envelope with an efficiency that is metallicity dependent is required to reproduce the empirically determined value of ∆ M_V ^{MSTO}_{bump}. | Acknowledgments: | We warmly thank our anonymous referee whose comments significantly improved this paper. The authors would like to thank Carolyn Doherty, Simon Campbell, Luca Casagrande and Warrick Ball for useful discussions. We also thank David Nataf and Alessio Mucciarelli for providing us with their data tables. GCA would like to thank the staff at MoCA for their help and support through the duration of his PhD part of the research leading to the presented results has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 338251 (StellarAges). VD'O is partially supported by an ARC grant (Super Science Fellow 2011). RPC is supported by the Swedish Research Council (grants 2012-2254 and 2012-5807). RJS is a recipient of a Sofja Kovalevskaja Award from the Alexander von Humboldt Foundation, by ARC DP1095368 and Discovery Grant. This work was supported in part by ARC DP1095368 and Discovery Grant DP120101815 (PI: J. Lattanzio) at Monash University, Clayton, Australia. | URI: | http://hdl.handle.net/20.500.12386/26487 | URL: | https://academic.oup.com/mnras/article/450/3/2423/1063506 | ISSN: | 0035-8711 | DOI: | 10.1093/mnras/stv770 | Bibcode ADS: | 2015MNRAS.450.2423A | Fulltext: | open |
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