Details

Autor(en) / Beteiligte

• Politano, Michael
• Weiler, Kevin P

Titel

Population Synthesis Studies of Close Binary Systems Using a Variable Common Envelope Efficiency Parameter. I. Dependence on Secondary Mass

Ist Teil von

• The Astrophysical journal, 2007-08, Vol.665 (1), p.663-679

Ort / Verlag

Chicago, IL: IOP Publishing

Erscheinungsjahr

2007

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• We perform population synthesis calculations of present-day post-CE binaries (PCEBs) and zero-age cataclysmic variables (ZACVs) using a common envelope (CE) efficiency parameter,, that is a function of secondary mass,. We investigate three basic possibilities: (1) a standard constant prescription, with ranging from 0.05 to 1.0, to provide a baseline for comparison; (2) a power-law dependence,, with, and 2.0; and (3) a dependence in which approaches 1 for large and below some assumed cutoff mass,, where, and 0.15. We find that if in our constant sequence, the predicted present-day ZACV population is significantly modified compared with our standard model. All prior population synthesis calculations of the formation of CVs only considered values of and found that their model populations were not strongly dependent upon the value of. Our results indicate that a much wider range of values for, including very low values, must be considered in order for a dependence to be seen. In our variable sequences for ZACVs, we find that for models in which decreases very rapidly for small, the orbital period distribution below the period gap differs significantly from our standard model. In particular, the fraction of CVs forming with hr is reduced significantly, the fraction forming in the gap is increased significantly, and both the short-period peak and the minimum period shift to considerably longer periods compared with our standard model. We suggest that the observed scarcity of CVs with minutes may possibly provide evidence that progenitor binaries with are unable to avoid merger within the CE. We also suggest that if decreases rapidly for small, it is possible that the lower edge of the period gap could be, in part, an imprint of the ZACV population.