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

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 <sup>4

1</sup> 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 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 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

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and reduction procedure
  • 2.1. Photometry
  • 2.2. Spectroscopy
    • 2.2.1. Long-slit and Reticon spectra
    • 2.2.2. Echelle spectra
• 3. Results
  • 3.1. Photometric variations
  • 3.2. An overview of the line-profile variations
  • 3.3. Temporal Variance Spectrum Analysis
  • 3.4. The P Cygni profile variability
  • 3.5. Correlated line-profile variations in different lines?
  • 3.6. Centroid, FWHM, EW, and Skewness variations
• 4. Comparison with previous studies
• 5. On the presence of a companion
  • 5.1. A non-degenerate companion?
  • 5.2. A collapsed companion?
• 6. Concluding remarks
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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