The theory of radiatively driven stellar winds. II - The line acceleration

Abstract

Numerical values of the radiation pressure on spectral lines are presented for the envelopes of stars having spectral type O-G and any luminosity, metallicity, or velocity structure. The line acceleration is calculated using a tabulation of atomic lines that is complete for the elements H-Zn. The acceleration is found to be remarkably constant over the temperature range 50,000-10,000 K but to drop off sharply for cooler stars. The anomalous ionization observed in OB stars decreases the acceleration by a factor of as much as 2 from radiative equilibrium values. More than half of the acceleration comes from lines whose frequencies overlap with those of neighboring lines at some point in the wind. Line blanketing of the continuum flux by the wind becomes significant for mass loss rates above 10 to the -6th solar mass/yr. The predicted and observed mass loss rates are in complete agreement for the OB stars, and it is concluded that radiation pressure is the dominant mechanism driving the winds from these stars.