Volume 560, December 2013
|Number of page(s)||12|
|Section||Stellar structure and evolution|
|Published online||02 December 2013|
Institut d’Astrophysique et de Géophysique, Université de
Liège, Bât. B5c, Allée du 6 Août
2 Departamento de Astronomia, Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, GTO, Mexico
Received: 28 June 2013
Accepted: 8 October 2013
Context. Massive-binary evolution models predict that some systems will go through an evolutionary phase where the original primary has become a supernova and left a compact object behind that then orbits a Wolf-Rayet (WR) star. WR 138 is an X-ray bright WR star that has been described as a triple system, including a compact companion in a short-period orbit.
Aims. Our goal is to search for spectroscopic evidence of a compact companion around WR 138.
Methods. We used optical and X-ray spectra to search for signatures of a compact companion, which can be revealed by systematic variations in WR optical spectral lines induced by orbital motion of the compact companion or by hard, luminous X-rays from accretion onto this companion.
Results. The optical spectra display emission-line profile variations that are most probably caused by clumps inside the stellar winds. The radial velocities do not vary on a short time-scale compatible with the suggested orbital period of a putative compact companion. The X-ray spectra are found to be normal for a WN5-6+OB system with no indication of accretion by a compact companion.
Conclusions. There is no evidence for the presence of a compact companion, and we therefore conclude that WR 138 is a normal long-period (P ~ 1521 d) eccentric WR+OB system.
Key words: stars: early-type / stars: Wolf-Rayet / stars: massive / stars: individual: WR 138 (HD 193077) / X-rays: stars
Based on observations collected at the Observatoire de Haute-Provence (France), the San Pedro Mártir observatory (Mexico), and with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA).
Tables 2–5 are available in electronic form at http://www.aanda.org
© ESO, 2013
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