脉冲星辐照和持续磁制动导致的黑寡妇形成
Black widow formation by pulsar irradiation and sustained magnetic braking
摘要：
黑寡妇是一种毫秒级的恒星，它的伴星质量很小，只有太阳质量的百分之几，在几个小时的轨道上运行。这些伴星可能是主序星的残余，它们的质量是由主脉冲星的高能量辐射造成的罗奇瓣溢出和烧蚀共同作用的结果。虽然烧蚀本身太弱，无法显著降低伴星的质量，但烧蚀的风耦合到它的磁场，消除轨道角动量，从而保持稳定的罗氏瓣溢出。我们使用MESA恒星演化代码，辅以分析估计，跟踪最初的主要序列同伴，因为他们减少到原来的质量的一小部分，这种烧蚀驱动的磁制动。我们认为，磁制动仍然有效，即使是低质量的同伴。我们的模型的一个关键因素是，脉冲星$L_{\rm irr}$的辐射亮度在伴星的大气中沉积能量，从而减缓其开尔文-亥姆霍兹冷却。我们发现费米$L_{\rm irr}=0.1-3\,{\rm L}_\odot$测量的高能光度可以解释黑寡妇轨道周期的跨度。同样的$L_{\rm irr}$范围再现了伴星的夜侧温度，从光学光变曲线推断，它们聚集在3000 K左右。
英文摘要：
Black widows are millisecond pulsars with low-mass companions, a few per cent the mass of the sun, on orbits of several hours. These companions are presumably the remnants of main sequence stars that lost their mass through a combination of Roche-lobe overflow and ablation by the host pulsar's high-energy radiation. While ablation itself is too weak to significantly reduce the mass of the companion star, the ablated wind couples to its magnetic field, removes orbital angular momentum, and thus maintains stable Roche-lobe overflow. We use the MESA stellar evolution code, complemented by analytic estimates, to track initially main sequence companions as they are reduced to a fraction of their original mass by this ablation-driven magnetic braking. We argue that magnetic braking remains effective even for low-mass companions. A key ingredient of our model is that the irradiating luminosity of the pulsar $L_{\rm irr}$ deposits energy in the companion's atmosphere and thereby slows down its Kelvin-Helmholtz cooling. We find that the high-energy luminosities measured by Fermi $L_{\rm irr}=0.1-3\,{\rm L}_\odot$ can explain the span of black widow orbital periods. The same $L_{\rm irr}$ range reproduces the companions' night-side temperatures, which cluster around 3000 K, as inferred from optical light curves.
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