Preprint Logo P109 November

To be published in:
Monthly Notices of the Royal Astronomical Society

Towards an understanding of the Of?p star HD191612: Phase-resolved multiwavelength observations+

Y. Nazé1,*, G. Rauw1,**, A.M.T. Pollock2, N.R. Walborn3 and I.D. Howarth4

1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
2 European Space Agency, XMM-Newton Science Operations Centre, European Space Astronomy Centre, Apartado 50727, Villafranca del Castillo, 28080 Madrid, Spain
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4 Department of Physics and Astronomy, University College London, Gower Street, London WC1E6BT, UK

* Postdoctoral Researcher FNRS, Belgium
** Research Associate FNRS, Belgium

+ Based on observations collected at the Haute-Provence Observatory (France) and with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and The USA (NASA).


     We present the analysis of phase-resolved X-ray and optical observations of the peculiar hot star HD191612 (Of?p). This star is known to display line-profile variations that are recurrent with a period of 538d and its spectrum was found to present the signature of a magnetic field. In the X-rays, it is slightly overluminous compared to the canonical LX/LBOL relation and appears brighter when the optical lines are strongest. Our XMM-Newton observations further reveal that the X-ray spectrum of HD191612 exhibits rather broad lines and is dominated by a 'cool' (0.2-0.6 keV) thermal component, two characteristics at odds with the proposed magnetic rotator model. We also report for the first time the low-level variability of the metallic (abs/em) lines and HeII absorptions that appear to be associated with radial-velocity shifts. Finally, we compare our results with observations of the early-type stars and discuss several possible scenarios.

Key words
stars: individual: HD 191612 -- stars: early-type -- X-rays: stars -- X-rays: individual: HD 191612


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