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Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

Schneider, F. R. N. and Izzard, R. G. and de Mink, S. E. and Langer, N. and Stolte, A. and de Koter, A. and Gvaramadze, V. V. and Hußmann, B. and Liermann, A. and Sana, H. (2014) Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions. Astrophysical Journal, 780 (2). Art. No. 117. ISSN 0004-637X. doi:10.1088/0004-637X/780/2/117.

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Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ☉ limit and observations of four stars with initial masses of 165-320 M_☉ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M_☉ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M_☉.

Item Type:Article
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URLURL TypeDescription Paper
de Mink, S. E.0000-0001-9336-2825
Additional Information:© 2014 American Astronomical Society. Received 2013 September 15; accepted 2013 November 13; published 2013 December 16. We thank the referee, Dany Vanbeveren, for carefully reading our manuscript and constructive suggestions. F.R.N.S. acknowledges the fellowships awarded by the German National Academic Foundation (Studienstiftung) and the Bonn-Cologne Graduate School of Physics and Astronomy. R.G.I. thanks the Alexander von Humboldt foundation. S.d.M. acknowledges support by NASA through Hubble Fellowship grant HST-HF-51270.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555, and the Einstein Fellowship program through grant PF3-140105 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. B.H. and A.S. acknowledge funding from the German science foundation (DFG) Emmy Noether program under grant STO 496-3/1.
Funding AgencyGrant Number
Deutscher Akademischer Austauschdienst (DAAD)UNSPECIFIED
Bonn-Cologne Graduate School of Physics and AstronomyUNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
NASA Hubble FellowshipHST-HF- 51270.01-A
NASANAS 5-26555
NASA Einstein FellowshipPF3-140105
Deutsche Forschungsgemeinschaft (DFG)STO 496-3/1
Subject Keywords:binaries: general; blue stragglers; open clusters and associations: individual (Arches, Quintuplet); stars: luminosity function, mass function; stars: mass-loss
Issue or Number:2
Record Number:CaltechAUTHORS:20140225-071027535
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Official Citation:Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions F. R. N. Schneider et al. 2014 ApJ 780 117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43965
Deposited By: Ruth Sustaita
Deposited On:25 Feb 2014 15:43
Last Modified:10 Nov 2021 16:45

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