Document Type

Article

Publication Date

3-1-2016

Published In

Monthly Notices Of The Royal Astronomical Society

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: ϵ 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 M˙/f∞−−−√∼ 1.6 × 10−6 M⊙ yr−1 where f∞ is the volume filling factor. However, the S iv λλ1062,1073 profiles are too strong in the models; to fit the observed profiles it is necessary to use f∞ <0.01. This value is a factor of 5 to 10 lower than inferred from other diagnostics, and implies M˙≲1×10−7 M⊙ yr−1. The discrepancy could be related to porosity–vorosity effects or a problem with the ionization of sulphur 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 (ρcl/ρICM) of ∼100. X-ray emission in H/He like and Fe L lines was modelled using four plasma components located within the wind. We derive plasma temperatures from 1 × 106 to 7 × 106 K, with lower temperatures starting in the outer regions (R0 ∼ 3–6 R*), and a hot component starting closer to the star (R0 ≲ 2.9 R*). From X-ray line profiles we infer M˙<4.9 × 10−7 M⊙ yr−1. The X-ray spectrum (≥0.1 kev) yields an X-ray luminosity LX ∼ 2.0 × 10−7Lbol, consistent with the superion line profiles. X-ray abundances are in agreement with those derived from the UV and optical analysis: ϵ Ori is slightly enhanced in nitrogen and depleted in carbon and oxygen, evidence for CNO processed material.

Keywords

techniques: spectroscopic; stars: abundances; stars: individual: ϵ Ori; stars: massive; stars: mass-loss; supergiants

Comments

This work is freely available courtesy of Oxford University Press and the Royal Astronomical Society.

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