X-ray, UV and optical analysis of supergiants: $\epsilon$ Ori

Abstract

We present a multi-wavelength (X-ray to optical) analysis, based on non-local thermodynamic equilibrium photospheric+wind models, of the B0 Ia-supergiant: $\epsilon$~Ori. The aim is to test the consistency of physical parameters, such as the mass-loss rate and CNO abundances, derived from different spectral bands. The derived mass-loss rate is $\dot{M}/\sqrt{f_{\infty }}\sim$1.6$\times$10${}^{-6}$ M${}_{\odot }$ yr${}^{-1}$ where $f_{\infty }$ is the volume filling factor. However, the S IV $\lambda \lambda$1062,1073 profiles are too strong in the models; to fit the observed profiles it is necessary to use $f_{\infty }<$0.01. This value is a factor of 5 to 10 lower than inferred from other diagnostics, and implies $\dot{M}\lesssim 1\times 10^{-7}$ M${}_{\odot }$ yr${}^{-1}$. The discrepancy could be related to porosity-vorosity effects or a problem with the ionization of sulfur in the wind. To fit the UV profiles of N V and O VI it was necessary to include emission from an interclump medium with a density contrast (${\rho }_{cl}/{\rho }_{ICM}$) of $\sim$100. X-ray emission in H-He like and Fe L lines was modeled using four plasma components located within the wind. We derive plasma temperatures from $1\times 10^6$ to $7\times 10^6$ K, with lower temperatures starting in the outer regions (R${}_0\sim$3-6 R${}_{\ast }$), and a hot component starting closer to the star (R${}_0\lesssim$2.9 R${}_{\ast }$). From X-ray line profiles we infer $\dot{M}<4.9\times 10^{-7}$ M${}_{\odot }$ yr${}^{-1}$. The X-ray spectrum ($\ge$0.1 kev) yields an X-ray luminosity $L_{\mathrm{X}}\sim 2.0\times 10^{-7}{L}_{\mathrm{bol}}$, consistent with the superion line profiles. X-ray abundances are in agreement with those derived from the UV and optical analysis: $\epsilon$ Ori is slightly enhanced in nitrogen and depleted in carbon and oxygen, evidence for CNO processed material.

33 pages, 25 figures. Accepted for publication in MNRAS

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