The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit

Abstract

Spectroscopic analyses of H-rich WN5-6 stars within the young star clusters NGC 3603 and R136 are presented, using archival HST & VLT spectroscopy, & high spatial resolution near-IR photometry. We derive high T* for the WN stars in NGC 3603 (T*~42+/-2 kK) & R136 (T*~53+/-3 kK) plus clumping-corrected dM/dt ~ 2-5x10^-5 Msun/yr which closely agree with theoretical predictions. These stars make a disproportionate contribution to the global budget of their host clusters. R136a1 alone supplies ~7% of N(LyC) of the entire 30 Dor region. Comparisons with stellar models calculated for the main-sequence evolution of 85-500 Msun suggest ages of ~1.5 Myr & M_init in the range 105 - 170 Msun for 3 systems in NGC 3603, plus 165-320 Msun for 4 stars in R136. Our high stellar masses are supported by dynamical mass determinations for the components of NGC 3603 A1. We consider the predicted L_X of the R136 stars if they were close, colliding wind binaries. R136c is consistent with a colliding wind binary system. However, short period, colliding wind systems are excluded for R136a WN stars if mass ratios are of order unity. Widely separated systems would have been expected to harden owing to early dynamical encounters with other massive stars in such a dense environment. From simulated star clusters, whose constituents are randomly sampled from the Kroupa IMF, both clusters are consistent with a tentative upper mass limit of ~300 Msun. The Arches cluster is either too old, exhibits a deficiency of very massive stars, or more likely stellar masses have been underestimated - M_init for the most luminous stars in the Arches cluster approach 200 Msun according to contemporary stellar & photometric results. The potential for stars greatly exceeding 150 Msun within metal-poor galaxies suggests that such pair-instability SNe could occur within the local universe, as has been claimed for SN 2007bi (abridged).

20 pages, 14 figures, accepted for MNRAS. Version with higher resolution figures is available from http://pacrowther.staff.shef.ac.uk/R136.pdf See also http://www.eso.org/public/news/eso1030/ from Wed 21 from noon (CEST)

References in corpus (24)

• Physical Properties of Wolf-Rayet Stars
• Mass loss from hot massive stars
• SN 2006gy: An extremely luminous supernova in the galaxy NGC 1260
• Binary star progenitors of long gamma-ray bursts
• A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
• The VLT-FLAMES survey of massive stars: rotation and nitrogen enrichment as the key to understanding massive star evolution
• The most massive stars in the Arches cluster
• The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics observations
• The VLT-FLAMES survey of massive stars: Wind properties and evolution of hot massive stars in the LMC
• Pair creation supernovae at low and high redshift
• Do O-stars form in isolation?
• Radio, X-ray, and gamma-ray Emission Models of the Colliding Winds Binary WR 140
• A Spectroscopic Survey of WNL Stars in the LMC: General Properties and Binary Status
• The Arches Cluster Mass Function
• The Interplay between Star Formation and the Nuclear Environment of our Galaxy: Deep X-ray Observations of the Galactic Center Arches and Quintuplet Clusters
• The very massive binary NGC3603-A1
• The Massive Star Content of NGC 3603
• The Physical Properties and Effective Temperature Scale of O-type Stars as a Function of Metallicity. III. More Results from the Magellanic Clouds
• Chemical composition and mixing in giant HII regions: NGC3603, 30Doradus, and N66
• Maximum stellar mass versus cluster membership number revisited
• An X-ray Survey of Wolf-Rayet Stars in the Magellanic Clouds. I. The Chandra ACIS Dataset
• Biases on initial mass function determinations. II. Real multiple systems and chance superpositions
• The very massive X-ray bright binary system Wack 2134 (= WR 21a)
• 3D numerical model of the Omega Nebula (M17): simulated thermal X-ray emission

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• The VLT-FLAMES Tarantula Survey III: A very massive star in apparent isolation from the massive cluster R136
• Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2
• Photon Dominated Regions in NGC 3603