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Extended Main Sequence Turnoffs in Open Clusters as Seen by Gaia: I. NGC 2818 and the Role of Stellar Rotation

Bastian, N, Kamann, S, Cabrera-Ziri, I, Georgy, C, Ekström, S, Charbonnel, C, de Juan Ovelar, MDJ and Usher, CG (2018) Extended Main Sequence Turnoffs in Open Clusters as Seen by Gaia: I. NGC 2818 and the Role of Stellar Rotation. Monthly Notices of the Royal Astronomical Society, 480 (3). pp. 3739-3746. ISSN 0035-8711

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We present an analysis of the relatively low mass ($\sim2400$~M$_{\odot}$), $\sim800$~Myr, Galactic open cluster, NGC~2818, using Gaia DR2 results combined with VLT/FLAMES spectroscopy. Using Gaia DR2 proper motions and parallax measurements we are able to select a clean sample of cluster members. This cluster displays a clear extended main sequence turn-off (eMSTO), a phenomenon previously studied mainly in young and intermediate age massive clusters in the Magellanic clouds. The main sequence of NGC~2818 is extremely narrow, with a width of $\sim0.01$ magnitudes (G$_{\rm BP} - $ G$_{\rm RP}$), suggesting very low levels of differential extinction. Using VLT/FLAMES spectroscopy of 60 cluster members to measure the rotational velocity of the stars (Vsini) we find that stars on the red side of the eMSTO have high Vsini ($>160$~km/s) while stars on the blue side have low Vsini ($<160$~km/s), in agreement with model predictions. The cluster also follows the previously discovered trend between the age of the cluster and the extent of the eMSTO. We conclude that stellar rotation is the likely cause of the eMSTO phenomenon.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: astro-ph.SR; astro-ph.SR; astro-ph.GA
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 05 Nov 2018 10:32
Last Modified: 04 Sep 2021 02:16
DOI or ID number: 10.1093/mnras/sty2100
URI: https://researchonline.ljmu.ac.uk/id/eprint/9607
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