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On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613

Tramper, F. and Gräfener, G. and Hartoog, O. E. and Sana, H. and de Koter, A. and Vink, J. S. and Ellerbroek, L. E. and Langer, N. and Garcia, M. and Kaper, L. and de Mink, S. E. (2013) On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613. Astronomy and Astrophysics, 559 . Art. No. A72. ISSN 0004-6361.

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Context. Oxygen sequence Wolf-Rayet (WO) stars are thought to represent the final evolutionary stage of the most massive stars. The characteristic strong O _(VI) emission possibly originates from an enhanced oxygen abundance in the stellar wind. Alternatively, the O _(VI) emission can be caused by the high temperature of these stars, in which case the WO stars are the high-temperature extension of the more common carbon sequence Wolf-Rayet (WC) stars. Aims. By constraining the physical properties and evolutionary status of DR1, a WO star in the low-metallicity Local Group dwarf galaxy IC 1613 and one of only two objects of its class known in a SMC-like metallicity environment, we aim to investigate the nature of WO stars and their evolutionary connection with WC stars. Methods. We use the non-local thermodynamic equilibrium atmosphere code CMFGEN to model the observed spectrum of DR1 and to derive its stellar and wind parameters. We compare our values with other studies of WC and WO stars, as well as with the predictions of evolutionary models. We also model the surrounding nebula using the photo-ionization code CLOUDY. Results. The oxygen and carbon abundances that we obtain are comparable to values found for WC stars. The temperature and luminosity are, however, higher than those of WC stars. DR1 is embedded in the hottest known H _(II) region in the Local Group. The nebular properties can be consistently reproduced by CLOUDY models adopting DR1 as central ionizing source. Conclusions. Comparison of the abundances and temperature of DR1 with core helium-burning models show that DR1 is currently well into the second half of helium burning. If the properties of DR1 are representative for the WO class, it would imply that WO stars are the high-temperature and high-luminosity extension of the WC stars, and do not necessarily represent a later evolutionary stage.

Item Type:Article
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URLURL TypeDescription Paper
de Mink, S. E.0000-0001-9336-2825
Additional Information:© 2013 ESO. Received 27 June 2013; Accepted 8 October 2013. Published online 18 November 2013. S.d.M. acknowledges support through a Hubble Fellowship grant HST-HF-51270.01-A awarded by the STScI, operated by AURA, Inc., under contract NAS 5-26555 and a Einstein Fellowship grant PF3-140105 awarded by the Chandra X-ray Center, operated SAO under the contract NAS8-03060.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF-51270.01-A
NASANAS 5-26555
NASA Einstein FellowshipPF3-140105
Subject Keywords:stars: Wolf-Rayet; stars: massive; stars: individual: DR1; galaxies: individual: IC 1613; HII regions
Record Number:CaltechAUTHORS:20140211-090028753
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Official Citation:Tramper, F., Gräfener, G., Hartoog, O. E., Sana, H., de Koter, A., Vink, J. S.,... de Mink, S. E. (2013). On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613⋆. A&A, 559, A72.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43765
Deposited By: Aucoeur Ngo
Deposited On:11 Feb 2014 17:29
Last Modified:09 Mar 2020 13:19

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