The location of the oxygen sequence Wolf-Rayet star DR1 in the Hertzsprung-Russel Diagram.

The most massive stars end are believed to end their lives as Wolf-Rayet stars, very hot and luminous. In this study the spectrum of an extremely hot and bright ionizing Wolf-Rayet star, DR1, is analyzed. The star is embedded in the hottest known HII region known and located in the metal-poor local group galaxy IC 1613.

The star is of the rare oxygen sequence subtype (WO). Only 8 of such stars are known, but they may have been more common in the earlier metal poor universe. Detailed analysis of the spectrum provides evidence that WO stars do not form an evolutionary sequence with carbon rich Wolf-Rayet stars (WC) as was previously thought.

On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613? by  Tramper, Grafener, Hartoog, Sana, de Koter, Vink, Ellerbroek, Langer, Garcia, Kaper, and de Mink, A&A 2013 in press.



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