Influence of X-ray Radiation on Wind Structure of Hot Stars

Presented at the meeting of the Working Group on Active B Stars during the
27th IAU General Assembly in Rio de Janeiro, Brazil on 2009 August 6

Jiří Krtička¹, Jiří Kubát²

¹ Ústav teoretické fyziky a astrofyziky, Masarykova univerzita, CZ-611 37 Brno, Czech Republic,
e-mail: krticka@physics.muni.cz
² Astronomický ústav AV ČR, Fričova 298, CZ-251 65 Ondřejov, Czech Republic,
email: kubat@sunstel.asu.cas.cz

Received: 2009 October 01; Accepted: 2009 October 03

We study influence of wind X-ray emission on wind structure of selected hot stars. To this end we include additional artificial source of X-rays (assumed to originate in wind shocks) into our NLTE wind code. We show that the influence of shock X-ray emission on wind mass-loss rate is relatively small. Wind terminal velocity may be slightly influenced by presence of strong X-ray sources, especially for stars cooler than T_eff < 35 000 K.

Inclusion of X-rays leads to better agreement of the model ionization structure with observations. However, we do not find any significant influence of X-rays on P V ionization fraction implying that presence of X-rays cannot explain the P V problem.

We study implications of modified ionization equilibrium due to shock emission on the line transfer in the X-ray region. We conclude that X-ray line profiles of helium-like ions may be affected by line absorption within the cool wind.

We show that the dependence of the shock cooling time on wind density could be important for explanation of observed L_x/L = 10^-7 relation. Stars with optically thin winds exhibiting the `weak wind problem' display enhanced X-ray emission. The shock cooling length in their winds could be larger than hydrodynamical length scale. We propose that this effect can explain the `weak wind problem'.

References

Krtička, J., & Kubát, J. 2009, MNRAS, 394, 2065