Volume 575, March 2015
|Number of page(s)||7|
|Published online||24 February 2015|
Search for magnetic fields in particle-accelerating colliding-wind binaries⋆
LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris
5 place Jules Janssen,
2 European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
3 Department of Astrophysics, Geophysics and Oceanography, University of Liège, 17 Allée du 6 Août, B5c, 4000 Sart Tilman, Belgium
Received: 20 October 2014
Accepted: 15 December 2014
Context. Some colliding-wind massive binaries, called particle-accelerating colliding-wind binaries (PACWB), exhibit synchrotron radio emission, which is assumed to be generated by a stellar magnetic field. However, no measurement of magnetic fields in these stars has ever been performed.
Aims. We aim at quantifying the possible stellar magnetic fields present in PACWB to provide constraints for models.
Methods. We gathered 21 high-resolution spectropolarimetric observations of 9 PACWB available in the ESPaDOnS, Narval and HarpsPol archives. We analysed these observations with the least squares deconvolution method. We separated the binary spectral components when possible.
Results. No magnetic signature is detected in any of the 9 PACWB stars and all longitudinal field measurements are compatible with 0 G. We derived the upper field strength of a possible field that could have remained hidden in the noise of the data. While the data are not very constraining for some stars, for several stars we could derive an upper limit of the polar field strength of the order of 200 G.
Conclusions. We can therefore exclude the presence of strong or moderate stellar magnetic fields in PACWB, typical of the ones present in magnetic massive stars. Weak magnetic fields could however be present in these objects. These observational results provide the first quantitative constraints for future models of PACWB.
Key words: stars: magnetic field / stars: early-type / binaries: spectroscopic / stars: general
Based on archival observations obtained at the Télescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique (CNRS) of France, at the Canada-France-Hawaii Telescope (CFHT) operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the CNRS of France, and the University of Hawaii, and at the European Southern Observatory (ESO), Chile.
© ESO, 2015
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