New findings on the prototypical Of?p stars

Y. Nazé, A. Ud-Doula, M. Spano, G. Rauw, M. De Becker, N. R. Walborn

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Abstract

Aims. In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X-rays as well as in the optical): magnetic fields, periodic line profile variations, recurrent photometric changes. However, many questions remain unsolved. Methods. To clarify some of the properties of the Of?p stars, we have continued their monitoring. A new xmm-Newton observation and two new optical datasets were obtained. Results. Additional information about the prototypical Of?p trio has been found. HD 108 has now reached its quiescent, minimum-emission state for the first time in 50-60 yr. The échelle spectra of HD 148937 confirm the presence of the 7d variations in the Balmer lines and reveal similar periodic variations (though of lower amplitudes) in the He i λ 5876 and He ii λ 4686 lines, underlining its similarities with the other two prototypical Of?p stars. The new xmm-Newton observation of HD 191612 was taken at the same phase in the line modulation cycle, but at a different orbital phase from previous data. It clearly shows that the X-ray emission of HD 191612 is modulated by the 538d period and not by the orbital period of 1542d - it is thus not of colliding-wind origin. The phenomenon responsible for the optical changes appears also at work in the high-energy domain. There are problems however: our MHD simulations of the wind magnetic confinement predict both a harder X-ray flux of a much larger strength than what is observed (the modelled differential emission measure peaks at 30-40 MK, whereas the observed one peaks at 2 MK) and narrow lines (hot gas moving with velocities of 100-200 km s -1, whereas the observed full width at half maximum is ∼2000 km s-1).

Original languageEnglish (US)
Article numberA59
JournalAstronomy and Astrophysics
Volume520
Issue number9
DOIs
StatePublished - Oct 4 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Nazé, Y., Ud-Doula, A., Spano, M., Rauw, G., De Becker, M., & Walborn, N. R. (2010). New findings on the prototypical Of?p stars. Astronomy and Astrophysics, 520(9), [A59]. https://doi.org/10.1051/0004-6361/201014333