Roche potentials including radiation effects

A modified Roche potential which incorporates the effects of radiation pressure due to one component of a binary system is mathematically explored. In some cases, the resulting potentials do not exhibit the familiar contact surfaces of the classical Roche potential. The concept of a contact surface, which has been fundamental to the investigations of close binary systems, must be used with discretion for close binaries in which one component is very luminous. A convenient criterion for the existence of a contact surface is given by (1-μ) ? 3δ_c ^3/2 \((1 - 2(\tfrac{2}{3})^4 \delta _c )\) , (δ_c?1) where μ is the mass of the very luminous star in terms of the system mass. For systems of given μ, no contact surface exists if δ is greater than δ_c where δ is the ratio of radiation pressure force to gravitational attraction. Furthermore, energy considerations of the modified Roche potential indicate that binary systems with δ < δ_c should have a greater tendency to form rings than those with δ < δ_c.