用一个声音说话：模拟和观察讨论常见信封$α$参数
Speaking with one voice: simulations and observations discuss the common envelope $α$ parameter
摘要：
我们提出了一个比较研究的结果之间的最流体动力学模拟的共同信封二进制相互作用的日期和后共同信封二进制的观测。我们的目标是评估这个数据集是否表明存在一个公式，该公式可以预测后共同信封系统的最终分离作为前共同信封参数的函数。我们的一些结论并不令人惊讶，而另一些则更为微妙。我们发现：（一）从共同的包络模拟得出的最终轨道分离值必须在这个时候被认为是上限。包括复合能的模拟似乎没有系统性的不同最终分离;这些和其他模拟暗示了$α_{\rm CE} < 0.6-1.0$。至少有一个模拟，{适用于双退化系统}，意味着$α_{\rm CE} < 0.2$。(ii)尽管重建误差较大，但后RGB观测重建参数与一些模拟一致。相反，AGB后的观测结果表现为$α_{\rm CE}$的值系统性降低。由于缺乏对低质量AGB恒星的共同包络模拟，我们无法深入了解为什么会出现这种情况。(iii)与中等质量巨星共同包层中存活的最小质量伴星是0.05-0.1~ \ms。(iv)观测到的双星的分离度大于$\sim$ 10~ \rs，倾向于具有高的$M_2/M_1$质量比，并且可能会经历一个相对较长的不稳定洛希瓣质量转移阶段，然后是一个减弱的共同包络（或根本没有共同包络）。(v)空间分辨率和软化长度对模拟结果的影响仍然很难量化。
英文摘要：
We present a comparative study between the results of most hydrodynamic simulations of the common envelope binary interaction to date and observations of post common envelope binaries. The goal is to evaluate whether this dataset indicates the existence of a formula that may predict final separations of post-common envelope systems as a function of pre-common envelope parameters. Some of our conclusions are not surprising while others are more subtle. We find that: (i) Values of the final orbital separation derived from common envelope simulations must at this time be considered upper limits. Simulations that include recombination energy do not seem to have systematically different final separations; these and other simulations imply $α_{\rm CE} < 0.6-1.0$. At least one simulation, {applicable to double-degenerate systems}, implies $α_{\rm CE} < 0.2$. (ii) Despite large reconstruction errors, the post-RGB observations reconstructed parameters are in agreement with some of the simulations. The post-AGB observations behave instead as if they had a systematically lower value of $α_{\rm CE}$. The lack of common envelope simulations with low mass AGB stars leaves us with no insight as to why this is the case. (iii) The smallest mass companion that survives the common envelope with intermediate mass giants is 0.05-0.1~\ms. (iv) Observations of binaries with separations larger than $\sim$10~\rs, tend to have high $M_2/M_1$ mass ratios and may go through a relatively long phase of unstable Roche lobe mass transfer followed by a weakened common envelope (or with no common envelope at all). (v) The effect of the spatial resolution and of the softening length on simulation results remains poorly quantified.
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