We report the discovery of additional hot and massive stars in the cluster surrounding the soft gamma repeater SGR 1806−20, based upon UKIRT and Keck near-infrared spectroscopy. Of the newly identified stars, three are Wolf-Rayet stars of types WC8, WN6, and WN7, and a fourth star is an OB supergiant. These three stars, along with four previously discovered, imply a cluster age of ~3.0- 4.5 Myr, based on the presence of WC stars and the absence of red supergiants. Assuming coevality, this age suggests that the progenitor of SGR 1806−20 had an initial mass greater than ~50 M⊙. This is consistent with the suggestion that SGRs are post-supernovae end states of massive progenitors, and may suggest that only massive stars evolve into magnetars that produce SGRs. It also suggests that very massive stars can evolve into neutron stars, not just black holes, as recently predicted by theory. The cluster age also provides constraints on the very high mass object, LBV 1806−20. (Refer to PDF file for exact formulas).

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Also archived in: arXiv:astro-ph/0501560 v3 30 Jan 2005 AND [ST]ScI Eprint #1640 F. N. acknowledges grants AYA2003-02785-E and ESP2002-01627. Finally, we acknowledge a similar result, by independent means, in Gaensler et al. (2005).ISSN:1538-4357 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

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Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus