Author:
Alonso-Santiago J.,Negueruela I.,Marco A.,Tabernero H. M.,González-Fernández C.,Castro N.
Abstract
Context. NGC 2345 is a young open cluster that hosts seven blue and red supergiants, low metallicity, and a high fraction of Be stars, which makes it a privileged laboratory to study stellar evolution.
Aims. We aim to improve the determination of the cluster parameters and study the Be phenomenon. Our objective is also to characterise the seven evolved stars found in NGC 2345 by deriving their atmospheric parameters and chemical abundances.
Methods. We performed a complete analysis combining for the first time ubvy photometry with spectroscopy as well as the Gaia Data Release 2. We obtained spectra with classification purposes for 76 stars and high-resolution spectroscopy for an in-depth analysis of the blue and red evolved stars.
Results. We identify a new red supergiant and 145 B-type likely members within a radius of 18.7 ± 1.2 arcmin, which implies an initial mass, Mcl ≈ 5200 M⊙. We find a distance of 2.5 ± 0.2 kpc for NGC 2345, placing it at RGC = 10.2 ± 0.2 kpc. Isochrone fitting supports an age of 56 ± 13 Ma, implying masses around 6.5 M⊙ for the supergiants. A high fraction of Be stars (≈10%) is found. From the spectral analysis we estimate an average vrad = +58.6 ± 0.5 km s−1 and a low metallicity, [Fe/H] = −0.28 ± 0.07, for the cluster. We also determine chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. One of the K supergiants, S50, is a Li-rich star, presenting an A(Li) ≈ 2.1. An overabundance of Ba is found, supporting the enhanced s-process.
Conclusions. NGC 2345 has a low metallicity for its Galactocentric distance, which is comparable to typical Large Magellanic Cloud stars. It is massive enough to serve as a test bed for theoretical evolutionary models for massive intermediate-mass stars.
Subject
Space and Planetary Science,Astronomy and Astrophysics
Reference95 articles.
1. Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program
2. ON LITHIUM-RICH RED GIANTS. I. ENGULFMENT OF SUBSTELLAR COMPANIONS
3. NGC 6067: a young and massive open cluster with high metallicity
4. NGC 3105: a young open cluster with low metallicity
5. Alonso-Santiago J., Negueruela I., Marco A., & Tabernero H. M. 2019, in Highlights on Spanish Astrophysics X, Proceedings of the XIII Scientific Meeting of the Spanish Astronomical Society held on July 16–20, 2018, in Salamanca, Spain, eds. Montesinos B., Asensio Ramos A., Buitrago F., et al., 261
Cited by
17 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献