来自系外行星的无线电发射：恒星日冕密度和磁场强度的作用
Radio emission from exoplanets: the role of the stellar coronal density and magnetic field strength
摘要：
迄今为止，对太阳系外行星无线电发射的研究还没有成功。在模拟预测的排放方面，大部分工作都是基于与众所周知的木星排放的类比。然而，与木星不同的是，这些无线电搜索的许多目标非常接近它们的母星，以至于它们很可能位于恒星磁层内。对于这些近距离的行星，我们确定哪些物理过程主导无线电发射，并将我们的结果与沉浸在恒星风中的大轨道行星进行比较。我们模拟了恒星和行星磁场的重联。我们计算的行星磁层的范围，如果它是在压力平衡与周围环境，并确定条件下，重新连接的恒星和行星磁场可以提供必要的加速电子预测的无线电发射。我们表明，接收到的无线电流量的几十毫焦耳是可能的太阳附近的系外行星，接近他们的母恒星，如果他们的恒星表面场强度超过1- 10 G。我们发现，对于这些靠近的行星，射电辐射的功率主要取决于比值（Nc/B^{1/3}）^2，其中Nc是恒星日冕底部的密度，B是恒星表面的磁场强度。无线电辐射最有可能是从具有高密度日冕的恒星周围的行星上探测到的，因此它们可能是明亮的X射线源。恒星日冕密度对恒星自转速率和有效温度的依赖性在预测来自系外行星的无线电通量方面至关重要。
英文摘要：
The search for radio emission from extra-solar planets has so far been unsuccessful. Much of the effort in modelling the predicted emission has been based on the analogy with the well-known emission from Jupiter. Unlike Jupiter, however, many of the targets of these radio searches are so close to their parent stars that they may well lie inside the stellar magnetosphere. For these close-in planets we determine which physical processes dominate the radio emission and compare our results to those for large-orbit planets that are immersed in the stellar wind. We have modelled the reconnection of the stellar and planetary magnetic fields. We calculate the extent of the planetary magnetosphere if it is in pressure balance with its surroundings and determine the conditions under which reconnection of the stellar and planetary magnetic fields could provide the accelerated electrons necessary for the predicted radio emission. We show that received radio fluxes of tens of mJy are possible for exoplanets in the solar neighbourhood that are close to their parent stars if their stars have surface field strengths above 1-10G. We show that for these close-in planets, the power of the radio emission depends principally on the ratio (Nc/B^{1/3})^2 where Nc is the density at the base of the stellar corona, and B is the stellar surface magnetic field strength. Radio emission is most likely to be detected from planets around stars with high-density coronae, which are therefore likely to be bright X-ray sources. The dependence of stellar coronal density on stellar rotation rate and effective temperature is crucial in predicting radio fluxes from exoplanets.
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