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

摘要: 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, αCE, that is function secondary mass, Ms. investigate three basic possibilities: (1) standard constant αCE prescription, with ranging from 0.05 to 1.0, provide baseline for comparison; (2) power-law dependence, = (Ms)n, n 0.5, 2.0; (3) dependence in which approaches 1 large Ms 0 below some assumed cutoff - Mcut/Ms, where Mcut 0.0375, 0.075, 0.15 M☉. find if 0.2 our sequence, the predicted ZACV significantly modified compared model (αCE 1.0). All prior formation CVs only considered values ≥ 0.3 found their populations were not strongly dependent upon value αCE. Our results indicate much wider range including very low values, must be order seen. In variable sequences ZACVs, we models decreases rapidly small Ms, orbital period distribution gap differs model. particular, fraction forming P < 2 hr reduced significantly, increased both short-period peak minimum shift considerably longer periods suggest observed scarcity 77 minutes may possibly evidence progenitor 0.10 M☉ are unable avoid merger within CE. also it possible lower edge could be, part, an imprint population.