Regresar

X-ray, UV and optical analysis of supergiants: ε 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: 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 NV and OVI 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.