SiO恒星中的旋进行星磁层？在RLeo和VCam中首次探测到准周期偏振涨落
Precessing planetary magnetospheres in SiO stars ? First detection of quasi-periodic polarization fluctuations in R Leo and V Cam
摘要：
AGB星周围的磁性起源是不确定的。如果这些恒星驱动发电机，它不足以产生强大的全球场，否则观测到的X射线光度会更高。对于大气中SiO脉泽的圆偏振，还需要其他的解释。AGB风与先前喷射的物质和行星的相互作用在短时间尺度上具有复杂的磁流体动力学现象，因此可以在局部维持强磁场。在这里，我们提供了相应的磁波动的观测证据。我们用相关旋光计跟踪了v=1，J=2-1的SiO脉泽的圆偏振磁活动。在V Cam和R Leo中，我们发现了在几个小时的时间尺度上圆偏振的伪周期波动的证据，从中我们推断出~1G的磁波动。这种现象很罕见，并且仅限于很窄的速度范围。它似乎与VLBI图所显示的行星尾流有关。虽然在扩展的恒星大气中涉及磁活动的场景有问题来解释所有观测到的特征，但岁差木星磁层预测了所有这些特征。对于狮子座R的情况下，我们约束行星的轨道（估计周期为5.2年），并估计恒星质量为0.7太阳质量。
英文摘要：
The origin of magnetism around AGB stars is uncertain. If these stars drive a dynamo, it cannot be sufficient to generate a strong global field, otherwise the observed X-ray luminosities would be higher. Other explanations for the circular polarization of SiO masers in the atmospheres are needed. The interaction of the AGB wind with previously ejected matter and with planets bears complex magneto-hydrodynamic phenomena on a short time scale, such that strong magnetic fields can be maintained locally. Here we provide observational evidence for the corresponding magnetic fluctuations. We trace magnetic activity with the circular polarization of the v=1, J=2-1 SiO masers, using a correlation polarimeter. In V Cam and R Leo, we find evidence of pseudo-periodic fluctuations of the circular polarization on a timescale of a few hours, from which we infer magnetic fluctuations of ~1G. The phenomenon is rare and restricted to a narrow range of velocities. It seems to be associated with planetary wake flows suggested by VLBI maps. While scenarios involving magnetic activity in the extended stellar atmosphere have problems to explain all observed features, precessing Jovian magnetospheres predict all of them. For the case of R Leo, we constrain the orbit of the planet (estimated period 5.2 years) and estimate a stellar mass of 0.7 solar masses.
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