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Astron. Astrophys. 349, 457-466 (1999)


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An investigation of the large-scale variability of the apparently single Wolf-Rayet star WR 1

T. Morel 1, L.N. Georgiev 2, Y. Grosdidier 1,3, N. St-Louis 1, T. Eversberg 1 and G.M. Hill 4

1 Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec, H3C 3J7, Canada and Observatoire du Mont Mégantic (morel, yves, stlouis, eversber@astro.umontreal.ca)
2 Instituto de Astronomía, UNAM, Apdo. Postal 70-264, México D.F. 04510, México (georgiev@astroscu.unam.mx)
3 Observatoire Astronomique de Strasbourg, UMR 7550, 11 rue de l'Université, F-67000 Strasbourg, France
4 McDonald Observatory, HET, P.O. Box 1337, Fort Davis, TX, USA (grant@astro.as.utexas.edu)

Received 3 July 1998 / Accepted 23 July 1999

Abstract

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with the existence of an unseen (collapsed?) companion or of spatially extended wind structures as potential candidates. We present observations of WR 1 which highlight the unusual character of the variations in this object. Our narrowband photometric observations reveal a gradual increase of the stellar continuum flux amounting to [FORMULA] [FORMULA] 0.09 mag followed by a decline on about the same timescale (3-4 days). Only marginal evidence for variability is found during the 11 following nights. Strong, daily line-profile variations are also observed but they cannot be easily linked to the photometric variations. Similarly to the continuum flux variations, coherent time-dependent changes are observed in 1996 in the centroid, equivalent width, and skewness of HeII [FORMULA]4686. Despite the generally coherent nature of the variations, we do not find evidence in our data for the periods claimed in previous studies. While the issue of a cyclical pattern of variability in WR 1 is still controversial, it is clear that this object might constitute in the future a cornerstone for our understanding of the mechanisms leading to the formation of largely anisotropic outflows in Wolf-Rayet stars.

Key words: stars: individual: WR 1 – stars: mass-loss – stars: Wolf-Rayet

Present address: Astrophysics Group, Imperial College of Science, Technology and Medicine, Blackett Laboratory, Prince Consort Road, London, SW7 2BZ, UK (t.morel@ic.ac.uk)

Present address: Feinfocus Medizintechnik GmbH, Im Bahlbrink 11-13, 30827, Garbsen, Germany (t_eversberg@feinfocus.com)

Send offprint requests to: T. Morel

Correspondence to: t.morel@ic.ac.uk

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999

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