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Velocity Density The effect of clumping on predictions of the mass-loss rate of early-type stars Lianne Muijres 1 , Jiri Krticka 2 , Alex de Koter 1 , Jorick Vink 3 , Joachim Puls 4 , Ines Brott 5 , Norbert Langer 5
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The effect of clumping on predictions of the mass-loss rate of early-type stars
Lianne Muijres1, Jiri Krticka2, Alex de Koter1, Jorick Vink3, Joachim Puls4, Ines Brott5, Norbert Langer5
1) Universiteit van Amsterdam, 2) Masaryk University, 3) Armagh Observatory , 4) Universitäts-Sternwarte München, 5) Universiteit Utrecht
Fig.1: Hubble image of Wolf-Rayet star WR 124; providing an observational motivation for studying density inhomogeneities in stellar winds.
Fig.2: Time snap shot of line driven instability; density and velocity pattern are shown. The blue dotted and red dotted line show the stationary, smooth (from modified CAK-theory) density and velocity (resp.) profile of the wind (Owocki, 1994).
Up to now, we assumed a smooth flow in our mass-loss predictions (de Koter et al. 1997, Vink et al. 2000). To deal with inhomogeneities in the flow, we introduced clumps described by a constant volume filling factor (fv). This means that each volume element is only filled for a fraction fv , and that the density in this part is enhanced by a factor 1/fv. The rest of the volume, i.e. the inter-clump matter, is assumed to be void (see Fig. 2). We calculated the ionization structure of the clumpy wind and then computed the mass-loss rate. We looked at optically thin clumps for continuum processes, but the clumps might be optically thick in lines. Line absorption is treated purely locally, within the Sobolev approximation.
We also investigated the case in which only the ionization is affected by the presence of clumps, but the effects of a clumpy medium on the effectiveness of the line driving is ignored.
dM/dt ~ f0.74
dM/dt ~ f0.81
dM/dt ~ f1.06
Fig.4: The effect of the changed ionization structure on the mass-loss rate of a star of 20 Msun and 2.09∙105 Lsun. The mass-loss rate increases with decreasing volume filling factor.
Fig.3: The effect of clumping on the mass-loss rate for three stars of M = 20 Msun , Teff= 30000 K with different luminosities. The red circles belong to a star with L = 5.01∙105 Lsun, the green circles to L = 2.09∙105 Lsun, and the blue triangles to L = 7.94∙104 Lsun. With decreasing volume filling factor the mass-loss rate drops.