Astronomy and Astrophysics, volume 490, 801-806 (2008/11-1)
High-resolution X-ray spectroscopy of θ Carinae.
NAZE Y. and RAUW G.
Abstract (from CDS):
The peculiar hot star θCar in the open cluster IC2602 is a blue straggler as well as a single-line binary with a short period (2.2d). Its high-energy properties are not well known, though X-rays can provide useful constraints on the energetic processes at work in binaries as well as in peculiar, single objects. We present the analysis of a 50ks exposure taken with the XMM-Newton observatory. It provides medium as well as high-resolution spectroscopy. Our high-resolution spectroscopy analysis reveals a very soft spectrum with multiple temperature components (1-6MK) and an X-ray flux slightly below the `canonical' value (log[LX(0.1-10.)/LBOL]~-7). The X-ray lines appear surprisingly narrow and unshifted, reminiscent of those of βCru and τSco. Their relative intensities confirm the anomalous abundances detected in the optical domain (C strongly depleted, N strongly enriched, O slightly depleted). In addition, the X-ray data favor a slight depletion in neon and iron, but they are less conclusive for the magnesium abundance, which may be solar-like. While no significant changes occur during the XMM-Newton observation, variability in the X-ray domain is detected in the long-term range. The formation radius of the X-ray emission is loosely constrained to <5R☉, which allows for a range of models (wind-shock, corona, magnetic confinement, ...) though not all of them can be reconciled with the softness of the spectrum and the narrowness of the lines.