To be published in:
Monthly Notices of the Royal Astronomical Society
The XMM-Newton view of Plaskett's star and its surroundings.+
A. M. T. Pollock2 and
I. R. Stevens3
1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
2 ESA XMM-Newton Science Operations Centre, ESAC, Apartado 50727, 28080 Madrid, Spain
3 School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
* Research Associate FNRS, Belgium
+ Based on observations obtained with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member states and the USA (NASA).
XMM-Newton data of Plaskett's star (HD 47129) are used in order to analyse
its X-ray spectrum and variability and hence to derive further constraints
on the wind interaction in this early-type binary (O6 I + O7.5 I) system.
Conventional models fail to provide a consistent fit of the EPIC and RGS
spectra. The lines seen in the RGS spectrum have a temperature of maximum
emissivity between 0.18 and 1.4 keV. The EPIC and RGS spectra are best
fitted by a non-equilibrium model consisting of a bremsstrahlung continuum
at 2.2 ± 0.1 keV and a number of independent emission lines.
Our tests also suggest that an overabundance in nitrogen by a factor ~6
might be indicated to best represent the RGS spectrum. On the other hand,
a short term variability study of the light curves of the system indicates
that the X-ray flux of Plaskett's star did not display any significant
variability during our observation. This result holds for all time scales
investigated here (from a few minutes to about one hour). Combining our
XMM-Newton data with ROSAT archival observations, we find however a
significant variability on the orbital time scale. If this behaviour is
indeed phase-locked, it suggests a minimum in the X-ray flux when the
primary star is in front. This might be attributed to an occultation of
the colliding wind region by the body of the primary. Finally, 71 other
X-ray sources have been detected in the field around Plaskett's star and
most of them have a near-IR counterpart with colours that are consistent
with those of slightly reddened main-sequence objects. Actually, a sizeable
fraction of the X-ray sources in the EPIC images could be either foreground
or background sources with no direct connection to HD 47129.
stars: early-type -- stars: individual (HD 47129) -- X-rays: stars.