The Gaia-ESO Survey: evidence of atomic diffusion in M67?

Investigating the chemical homogeneity of stars born from the same molecular cloud at virtually the same time is very important for our understanding of the chemical enrichment of the interstellar medium and with it the chemical evolution of the Galaxy. One major cause of inhomogeneities in the abundances of open clusters is stellar evolution of the cluster members. In this work, we investigate variations in the surface chemical composition of member stars of the old open clusterM67 as a possible consequence of atomic diffusion effects taking place during the main-sequence phase. The abundances used are obtained from high-resolution UVES/FLAMES spectra within the framework of the Gaia-ESO Survey. We find that the surface abundances of stars on the main sequence decrease with increasing mass reaching a minimum at the turn-off. After deepening of the convective envelope in subgiant branch stars, the initial surface abundances are restored.We found themeasured abundances to be consistent with the predictions of stellar evolutionary models for a cluster with the age and metallicity of M67. Our findings indicate that atomic diffusion poses a non-negligible constraint on the achievable precision of chemical tagging methods.© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
This work was supported by Sonderforschungsbereich SFB 881 'The Milky Way System' (subproject B5) of the German Research Foundation (DFG). AB acknowledges support from the SFB 881 visitor program. CBM thanks Elisabetta Caffau for fruitful discussions and Don VandenBerg for providing the isochrones shown in Fig 1. The authors would like to thank the anonymous referee for the constructive comments that helped in improving the present work.r MTC acknowledges the financial support from the Spanish Ministerio de Economia y Competitividad, through grant AYA2016-75931. AD and GT acknowledge support by the Research Council of Lithuania (MIP-082/2015). UH acknowledges support from the Swedish National Space Board (SNSB/Rymdstyrelsen). TB was supported by the project grant 'The New Milky' from the Knut and Alice Wallenberg foundation. RS acknowledges support from the Polish Ministry of Science and Higher Education. SGS and VA acknowledge the support by Fundacao para a Ciencia e Tecnologia (FCT) through national funds and a research grant (project ref. UID/FIS/04434/2013, and PTDC/FISAST/7073/2014). SGS also acknowledges the support from FCT through Investigador FCT contract of reference IF/00028/2014 and POPH/FSE (EC) by FEDER funding through the program 'Programa Operacional de Factores de Competitividade - COMPETE'. VA acknowledges the support from FCT through Investigador FCT contract IF/00650/2015/CP1273/CT0001. EJA acknowledges partial support from the Spanish Ministry for Economy and Competitiveness and FEDER funds through grant AYA2013-40611-P. ARC is supported through an Australian Research Council Discovery Project under grant DP160100637. CL thanks the Swiss National Science Foundation for supporting this research through the Ambizione grant number PZ00P2 168065. AK acknowledges support from the Swedish National Space Board (SNSB). XF acknowledges financial support from Premiale 2015 MITiC (PI B/Garilli). SLM acknowledges support from the Australian Research Council through grant DE140100598. AB acknowledges support from the Millennium Science Initiative (Chilean Ministry of Economy).r Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant 'Premiale VLT 2012', and through PRIN-INAF 2014 'The Gaia-ESO Survey'. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France and NASA's Astrophysics Data System.