Study of color-magnitude diagram of star cluster SL 506
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ORIGINAL ARTICLE
Study of color-magnitude diagram of star cluster SL 506 Zhongmu Li1 · Jing Chen1
· Su Zhang1 · Yangyang Deng1,2 · Wenchang Zhao1
Received: 26 November 2019 / Accepted: 24 July 2020 / Published online: 5 August 2020 © Springer Nature B.V. 2020
Abstract We report a study of the color-magnitude diagram (CMD) of globular cluster SL 506, which shows extended main sequence turn-off (eMSTO). The CMD is derived from deep F450W (B) and F555W (V) images of Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2). We reproduce the CMD via simple stellar population including the combination of rotational stars and binaries, and composite stellar population of non-rotating single stars. We derive the parameters of the star cluster, including age, age spread, metallicity, color excess, distance modulus, binary fraction, and rotating star fraction, by comparing the observed and synthetic CMDs. The results show that the eMSTO region of the cluster can be reproduced by both age spread and a combination of rotating and binary stars, but the blue stragglers, color and magnitude distributions can not be reproduced well by age spread. This implies that SL 506 is a simple population with rotating, single and binary stars. Keywords Stars: Hertzsprung- Russell and C-M diagrams · Galaxy: globular clusters: general · Individual: globular clusters: SL 506
1 Introduction Star cluster SL 506 is located in the Large Magellanic Cloud (LMC) at RA = 05:28:47.33, DEC = −73:37:50.7, J2000. The data of a high-quality color-magnitude diagram (CMD)
B J. Chen
[email protected]
1
Institute for Astronomy, Dali University, Dali 671003, China
2
Shanghai Key Lab for Astrophysics, Shanghai Normal University, Shanghai 200234, China
of SL 506 have been obtained by the Hubble Space Telescope (HST). The CMD shows some interesting structures including broad main sequence, extended main sequence turn-off (eMSTO), blue stragglers and red giant clump (RC). The eMSTO is a common phenomenon in the intermediateage clusters. In the LMC and Small Magellanic Cloud (SMC), many clusters have features similar to this star cluster, e.g., NGC 1651 (Li et al. 2015), NGC 6362, NGC 6652, NGC 6838 and M67 (Li et al. 2017). There are many possible causes for the eMSTO phenomenon, e.g., the spread of chemical abundance (Piotto et al. 2005; Piotto et al. 2007; Mackey et al. 2008; Goudfrooij et al. 2009), star formation history (Goudfrooij et al. 2009), stellar rotation (Bastian and de Mink 2009; Brandt and Huang 2015) and the combination of binaries and stellar rotation (Li et al. 2012), early escape velocity (Goudfrooij et al. 2014). Recently, the composite stellar population models that contain age spread (Girardi et al. 2011; Girardi et al. 2009; Milone et al. 2017; Niederhofer et al. 2015; Richer et al. 2013), binaries (Li and Deng 2018; Luo and Li 2018) and stellar rotation (Bastian and de Mink 2009; Brandt and Huang 2015) are considered to be the most possible reasons of eMSTO. However, there is no certain answer yet. It is therefore
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