Active OB stars: structure, evolution, mass loss and critical limits
[en] Proceedings IAU Symposium no. 272
IAU Symposium no. 272
19-23 July 2010
[en] X-rays: stars ; stars: early-type ; stars: individual (HD 108 ; HD 148937 ; HD 191612) ; stars: emission-line
[en] In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our monitoring of the prototypical Of?p trio. HD 108 has now reached its quiescent, minimum-emission state, for the first time in 50-60yrs, while new echelle spectra of HD 148937 confirm the presence in several H and He lines of the 7d variations detected previously only in the Hα line. A new XMM observation of HD 191612 clearly shows that its X-ray emission is not modulated by the orbital period of 1542d, but the high-energy variations are rather compatible with the 538d period of the optical changes - it is thus not of colliding-wind origin but linked to the phenomena responsible for the spectral/photometric variations, though our current MHD simulations remain at odds with the observational properties.