氦白矮星中玻色-爱因斯坦凝聚的发生和可探测性
On the occurrence and detectability of Bose-Einstein condensation in helium white dwarfs
摘要：
最近有人提出，氦白矮星可能为玻色-爱因斯坦凝聚的发生提供有希望的条件。支持这一预期的论点是，在这些物体的核心达到的某些条件下，与氦核相关的典型德布罗意波长大约是相邻核之间的平均距离。在这些条件下，系统应该偏离经典行为，表现出量子效应。由于氦核是玻色子，它们被认为是凝聚的。为了探索在氦白矮星演化过程中探测到玻色-爱因斯坦凝聚的可能性，我们计算了一组不同恒星质量和凝聚温度的模型。我们不进行详细的治疗的凝聚过程，但模仿它通过抑制核的贡献状态方程通过应用适当的功能。由于白矮星的冷却取决于整个恒星内部的平均性质，因此这种方法应该适合于探索冷却过程与标准处理所预测的冷却过程的偏离。我们发现，玻色-爱因斯坦凝聚对冷却过程的影响是显著的，但并不显著，只对质量最大的白矮星才有影响，这些白矮星的内部以氦为主（\approx 0.50 M_ \odot），光度很低（Log（L/L_ \odot）< -4.0）.这些事实使我们得出这样的结论：似乎很难找到玻色-爱因斯坦凝聚的可观测信号。最近，有人提出在球状星团NGC 6397中探测到的氦白矮星是探测玻色-爱因斯坦凝聚信号的一个很好的候选者。我们发现，这些恒星的质量太低，太亮，以至于没有一个已经凝聚的内部。
英文摘要：
It has been recently proposed that helium white dwarfs may provide promising conditions for the occurrence of the Bose-Einstein condensation. The argument supporting this expectation is that in some conditions attained in the core of these objects, the typical De Broglie wavelength associated with helium nuclei is of the order of the mean distance between neighboring nuclei. In these conditions the system should depart from classical behavior showing quantum effects. As helium nuclei are bosons, they are expected to condense. In order to explore the possibility of detecting the Bose-Einstein condensation in the evolution of helium white dwarfs we have computed a set of models for a variety of stellar masses and values of the condensation temperature. We do not perform a detailed treatment of the condensation process but mimic it by suppressing the nuclei contribution to the equation of state by applying an adequate function. As the cooling of white dwarfs depends on average properties of the whole stellar interior, this procedure should be suitable for exploring the departure of the cooling process from that predicted by the standard treatment. We find that the Bose-Einstein condensation has noticeable, but not dramatic effects on the cooling process only for the most massive white dwarfs compatible with a helium dominated interior (\approx 0.50 M_\odot) and very low luminosities (say, Log(L/L_\odot) < -4.0). These facts lead us to conclude that it seems extremely difficult to find observable signals of the Bose-Einstein condensation. Recently, it has been suggested that the population of helium white dwarfs detected in the globular cluster NGC 6397 is a good candidate for detecting signals of the Bose-Einstein condensation. We find that these stars have masses too low and are too bright to have an already condensed interior.
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