AN OBSERVATIONAL TEST OF COMMON-ENVELOPE EVOLUTION

By analysing and modelling the change in the abundance ratios of C-12/C-13 and O-16/O-17 on the surface of the lower mass star of a binary during the common-envelope (CE) phase of evolution, we propose a simple observational test of the CE scenario. The test is based on the infrared measurement of either the C-12/C-13 or the O-16/O-17 ratio of red dwarfs in post-common-envelope binaries (PCEBs). In certain cases (main-sequence red dwarf secondaries in PCEBs without planetary nebulae), as well as determining whether or not accretion has occurred during the CE phase, we can determine the amount of mass accreted during the CE phase and hence the initial mass of the red dwarf component prior to the CE phase. In the other cases considered (low-mass red dwarfs in PCEBs and red dwarfs in PCEBs with planetary nebulae), we can only say whether or not accretion has occurred during the CE phase.