Post-common-envelope binaries from SDSS - IX: Constraining the common-envelope efficiency

摘要

Context. Reconstructing the evolution ofpost-common-envelope binaries (PCEBs) consisting of a white dwarf and amain-sequence star can constrain current prescriptions ofcommon-envelope(CE) evolution. This potential could so far not befully exploited due to the small number of known systems and theinhomogeneity of the sample. Recent extensive follow-up observations ofwhite dwarf/main-sequence binaries identified by the Sloan Digital SkySurvey (SDSS) paved the way for a better understanding ofCEevolution. Aims. Analyzing the new sample of PCEBs we derive constraints onone of the most important parameters in the field of close compactbinary formation, i.e. the CE efficiency .Methods. After reconstructing the post-CE evolution and based onfits to stellar evolution calculations as well as a parametrized energyequation for CE evolution, we determine the possible evolutionaryhistories of the observed PCEBs. In contrast to most previous attemptswe incorporate realistic approximations of the binding energy parameter.Each reconstructed CE history corresponds to a certain value of themass of the white dwarf progenitor and - more importantly - the CEefficiency .We also reconstruct CEevolution replacing the classical energyequation with a scaled angular momentum equation and compare theresults obtained with both algorithms. Results. We find that all PCEBs in our sample can bereconstructed with the energy equation if the internal energy of theenvelope is included. Although most individual systems have solutionsfor a broad range of values for ,only for do we find simultaneous solutions for all PCEBs in our sample. If we adjust to this range of values, the values of the angular momentum parametercluster in a small range of values. In contrast if we fix to a small range of values that allows us to reconstruct all our systems, the possible ranges of values for remains broad for individual systems. Conclusions. The classical parametrized energy equation seems tobe an appropriate prescription of CE evolution and turns out toconstrain the outcome of the CE evolution much more than thealternative angular momentum equation. If there is a universal value ofthe CE efficiency, it should be in the range of .We do not find any indications for a dependence of on the mass of the secondary star or the final orbital period. Key words: binaries: close - stars: evolution - white dwarfs