Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004a%26a...423..693d&link_type=abstract
Astronomy and Astrophysics, v.423, p.693-704 (2004)
Astronomy and Astrophysics
Astrophysics
7
Hydrodynamics, Stars: Early-Type, Stars: Mass-Loss
Scientific paper
I present radiation hydrodynamics simulations of rotating line-driven O-star winds subject to surface variations taking the shape of localized bright Gaussian spots. Following the original work of Cranmer & Owocki, I investigate the influence on resulting corotating interaction regions (CIRs) of 1) extending the simulation domain from 2D (equatorial plane) to 3D (octant of a sphere) and 2) explicitly account for the lateral components of the radiative acceleration, computed using a multiple-ray quadrature of the visible stellar disk at all wind locations. I identify the wind spin down effect of Gayley & Owocki, present in unperturbed rotating hot star winds. In 2D simulations, the perturbed azimuthal component of the radiative acceleration does not change the gross properties of CIRs. However, the resulting perturbed azimuthal velocity extrema are enhanced by a factor of 50 compared to unperturbed models, so that its magnitude is now a few times greater than the adopted isothermal sound speed. This lateral broadening of wind material at the vertical of a spot leads to an overall weakening of the CIR compression compared to Cranmer & Owocki. In 3D, the extra dimension weakens further the CIR compression and associated velocity kink compared to equivalent 2D simulations. 3D simulations confirm the assumption of Cranmer & Owocki that the angular extent of a surface spot influence is similar in the azimuthal and latitudinal directions. 3D simulations for off-equatorial spots reveal the presence of CIRs advecting out along a fixed latitude, i.e. centred on the spot latitude and contained within a conic shell whose latitudinal thickness is of the order of the full-width-half-maximum of the Gaussian spot. Thus, the CIR properties are essentially independent of the latitude of base perturbations. These results suggest that the key properties of a line-driven wind subject to base brightness variations are well described by considering only the perturbation on the radial radiative acceleration, with, for a Gaussian spot, an angular modulation solely dependent on the distance to the spot location, irrespective of the latitudinal or azimuthal direction. Following the technique of Cranmer & Owocki, I have performed spectroscopic line synthesis computations based on 2D hydrodynamical inputs obtained using the multi-ray computation of the multi-component perturbed radiative acceleration or its perturbed radial component. For both P-Cygni and emission line profiles, the differences in hydrodynamical inputs have unnoticeable effects on profile shapes. The method developed in Cranmer & Owocki is therefore adequate for extensive investigations of the large-amplitude long-term line profile variability identified in many O-star spectra.
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