Appendix A: lateral heat diffusion
Here we show that in a realistic situation the lateral temperature gradient caused by irradiating the secondary anisotropically is negligible compared to the radial temperature gradient in the subphotospheric layers and that, therefore, lateral energy transport by radiation is unimportant. We demonstrate this in the framework of the point source model. In that model we estimate the lateral gradient of to be
On the other hand, the radial temperature stratification is given by the Eddington approximation (e.g. Tout et al. 1989)
Because in the stars in question is so small, the lateral temperature gradient is always much smaller than the radial one unless and thus . However, in the range of interest of x and , i.e. where is near its maximum and to a few, (A.8) yields that the lateral temperature gradient is of order .
© European Southern Observatory (ESO) 2000
Online publication: August 23, 2000