Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.8003c&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #80.03; Bulletin of the American Astronomical Society, Vol. 26, p.1446
Astronomy and Astrophysics
Astronomy
3
Scientific paper
We present 2D hydrodynamical simulations of co-rotating stream structure in the winds from rotating O-stars, together with resulting synthetic line profiles showing discrete absorption components (DAC's). The azimuthal variation is induced by a local increase or decrease in the radiative driving force, as would arise from a ``star spot'' in the equatorial plane. Since much of the emergent wind structure seems independent of the exact method of perturbation, we expect similar morphology in winds perturbed by localized magnetic fields or non-radial pulsations. Because the radiative force depends on the local rate of mass loss, bright spots with enhanced driving generate high-density, low-velocity streams, while dark spots generate low-density, high-velocity streams. Co-rotating interaction regions (CIR's) form where fast material collides with slow material -- e.g. at the leading (trailing) edge of a stream from a dark (bright) spot, often steepening into shocks. The asymmetric wind also generates sharp propagating discontinuities (``kinks'') in the radial velocity gradient, which travel inward in the co-moving frame at the radiative-acoustic characteristic speed, and slowly outward in the star's frame. We find that these slow kinks, rather than the CIR's themselves, are more likely to result in high-opacity DAC's in the absorption troughs of unsaturated P Cygni line profiles. Because the hydrodynamic structure settles to a steady state in a frame co-rotating with the star, the more tightly-spiraled kinks sweep by an observer on a longer timescale than material moving with the wind itself. This is in general accord with observations showing slow apparent accelerations for DAC's.
Cranmer Steven R.
Owocki Stanley P.
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