Open AccessThe XMM–Newton view of Plaskett's star and its surroundings ★
Author(s) -
Linder N.,
Rauw G.,
Pollock A. M. T.,
Stevens I. R.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10611.x
Subject(s) - physics , star (game theory) , astrophysics , binary number , astronomy , binary star , order (exchange) , spectrum (functional analysis) , stars , arithmetic , mathematics , finance , quantum mechanics , economics
ABSTRACT 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 European Photon Imaging Camera (EPIC) and Reflexion Grating Spectrometer (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 of ∼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‐infrared (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.