XMM-Newton observations of ζ Orionis (O9.7 Ib): a collisional ionization equilibrium model

A. J. J. Raassen; K. A. van der Hucht; N. A. Miller; J. P. Cassinelli

doi:10.1051/0004-6361:20077891

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Volume 478 / No 2 (February I 2008)

A&A, 478 2 (2008) 513-520

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Issue		A&A Volume 478, Number 2, February I 2008


Page(s)		513 - 520
Section		Stellar structure and evolution
DOI		https://doi.org/10.1051/0004-6361:20077891
Published online		04 December 2007

A&A 478, 513-520 (2008)

XMM-Newton observations of ζ Orionis (O9.7 Ib): a collisional ionization equilibrium model^*

A. J. J. Raassen¹^,2, K. A. van der Hucht¹^,2, N. A. Miller³ and J. P. Cassinelli⁴

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: a.j.j.raassen@sron.nl
² Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
³ Dept. of Physics & Astronomy, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire WI 54702, USA
⁴ Dept. of Astronomy, University of Wisconsin at Madison, 6251 Sterling Hall, North Charter Str., Madison, WI 53706, USA

Received: 15 May 2007
Accepted: 18 November 2007

Abstract

We present XMM-Newton observations of the O supergiant ζ Orionis (O9.7 Ib). The spectra are rich in emission lines over a wide range of ionization stages. The rgs spectra show for the first time lines of low ion stages such as $\ion{C}{\sc vi}$ , $\ion{N}{\sc vi}$ , $\ion{N}{\sc vii}$ , and $\ion{O}{\sc vii}$ . The line profiles are symmetric and rather broad ( ${\it {\it FWHM}}\approx 1500$ km s^-1) and show only a slight blue shift. With the XMM-epic spectrometer several high ions are detected in this star for the first time including $\ion{Ar}{\sc xvii}$ and $\ion{S}{\sc xv}$ . Simultaneous multi-temperature fits and DEM-modeling were applied to the rgs and epic spectra to obtain emission measures, elemental abundances and plasma temperatures. The calculations show temperatures in the range ≈0.07-0.6 keV. According to the derived models the intrinsic source X-ray luminosity at a distance of 251 pc is L_x = 1.37(.03) $\times$ 10³² erg s^-1 in the energy range 0.3-10 keV. In the best multi-temperature model fit, the abundances of C, N, O, and Fe are near their solar values, while the abundances of Ne, Mg, and Si appear somewhat enhanced. The sensitivity of the He-like forbidden and intercombination lines to ζ Ori's strong radiation field is used to derive the radial distances at which lines are formed. Values of 34 $R_*$ for $\ion{N}{\sc vi}$ , 12.5 $R_*$ for $\ion{O}{\sc vii}$ , 4.8 $R_*$ for $\ion{Ne}{\sc ix}$ , and 3.9 $R_*$ for $\ion{Mg}{\sc xi}$ are obtained.

Key words: stars: early-type / stars: winds, outflows / X-rays: individual: ζ Orionis / X-rays: stars

^*

Appendix A is only available in electronic form at http://www.aanda.org

© ESO, 2008

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XMM-Newton observations of ζ Orionis (O9.7 Ib): a collisional ionization equilibrium model*

XMM-Newton observations of ζ Orionis (O9.7 Ib): a collisional ionization equilibrium model^*