High resolution X-ray spectroscopy of ζ Puppis with the XMM-Newton reflection grating spectrometer

¹ Department of Physics and Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
² Institut d'Astrophysique et de Géophysique de l'Université de Liège, 5 avenue de Cointe, 4000 Liège, Belgium
³ Space Research Organization of The Netherlands, Sorbonnelaan 2, 3548 CA, Utrecht, The Netherlands
⁴ Laboratory for Astrophysics, Paul Scherrer Institute, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland

Corresponding author: S. M. Kahn, skahn@astro.columbia.edu

Received: 2 October 2000
Accepted: 2 November 2000

Abstract

We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star ζ Puppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright emission lines of hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon, as well as neon-like ions of iron. The lines are all significantly resolved, with characteristic velocity widths of order 1000-1500 km s^-1. The nitrogen lines are especially strong, and indicate that the shocked gas in the wind is mixed with CNO-burned material, as has been previously inferred for the atmosphere of this star from ultraviolet spectra. We find that the forbidden to intercombination line ratios within the helium-like triplets are anomalously low for N VI, O VII, and Ne IX. While this is sometimes indicative of high electron density, we show that in this case, it is instead caused by the intense ultraviolet radiation field of the star. We use this interpretation to derive constraints on the location of the X-ray emitting shocks within the wind that are consistent with current theoretical models for this system.