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Astron. Astrophys. 344, 647-654 (1999)


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On modeling radiation-driven envelopes at arbitrary optical depths

G.S. Bisnovatyi-Kogan and A.V. Dorodnitsyn

Space Research Institute, 84/32, Profsoyuznaya st., Moscow, Russia (gkogan; dora@mx.iki.rssi.ru)

Received 1 April 1998 / Accepted 14 January 1999

Abstract

We consider stationary outflowing stellar envelopes accelerated by radiation pressure. Making use of solutions of the transfer equation in the Eddington approximation, we derive relations for pressure, radiation energy density, and radiative energy flux at arbitrary optical depth [FORMULA]. These relations are used in the equations of radiative hydrodynamics, which can be solved numerically. The solution proceeds through a singular point, where the velocity is equal to the isothermal sound speed, and satisfies zero temperature and pressure boundary conditions at infinity. A sample calculation is performed for a constant opacity and molecular weight. We argue that, with realistic opacity tables and thermodynamic functions which take into account variable ionization states and in conjunction with self-consistent evolutionary calculations, our method for constructing outflowing envelopes will provide unambiguous mass-loss rates for massive stars in yellow and red supergiant stages. Advantages of this approach are discussed in comparison with previously used methods.

Key words: hydrodynamics – radiative transfer – stars: carbon – stars: mass-loss

Send offprint requests to: A.V. Dorodnitsyn

© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999

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