The GALAH survey: verifying abundance trends in the open cluster M67 using non-LTE modelling

Gao, Xudong and Lind, Karin and Amarsi, Anish M. and Buder, Sven and Dotter, Aaron and Nordlander, Thomas and Asplund, Martin and Bland-Hawthorn, Joss and de Silva, Gayandhi M. and D'Orazi, Valentina and Freeman, Ken C. and Kos, Janez and Lewis, Geraint F. and Lin, Jane and Martell, Sarah L. and Schlesinger, Katharine J. and Sharma, Sanjib and Simpson, Jeffrey D. and Zucker, Daniel B. and Zwitter, Tomaz and Da Costa, Gary and Anguiano, Borja and Horner, Jonathan and Hyde, Elaina A. and Kafle, Prajwal R. and Nataf, David M. and Reid, Warren and Stello, Dennis and Ting, Yuan-Sen (2018) The GALAH survey: verifying abundance trends in the open cluster M67 using non-LTE modelling. Monthly Notices of the Royal Astronomical Society, 481 (2). pp. 2666-2684. ISSN 0035-8711

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Open cluster members are coeval and share the same initial bulk chemical composition. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer. From the non-LTE analysis, we find a typical star-to-star scatter in the abundance ratios of around 0.05 dex. We find trends in the abundance ratios with effective temperature, indicating systematic differences in the surface abundances between turn-off and giant stars; these trends are more pronounced when LTE is assumed. However, trends with effective temperature remain significant for Al and Si also in non-LTE. Finally, we compare the derived abundances with prediction from stellar evolution models including effects of atomic diffusion. We find overall good agreement for the abundance patterns of dwarfs and sub-giant stars, but the abundances of cool giants are lower relative to less evolved stars than predicted by the diffusion models, in particular for Mg.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version deposited in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 14 Feb 2019 04:47
Last Modified: 17 Feb 2019 23:11
Uncontrolled Keywords: radiative transfer; stars; abundances; atmospheres; late-type; astrophysics; stellar astrophysics
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Identification Number or DOI: 10.1093/mnras/sty2414

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