L型矮星双星2 MASSW J0746425 +200032的周期性射电和H-α辐射：探索L型矮星的磁场拓扑和半径
Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf
摘要：
我们提出了一个8.5小时的同时无线电，X射线，紫外线和光学观测的L矮双星2 MASSW J 0746 +20。我们检测到强无线电发射，占主导地位的短周期脉冲在4.86 GHz的P=124.32+/-0.11分钟。脉冲轮廓和到达时间的稳定性表明，它们是由于旋转调制的B~1.7 kG磁场。一个静态的不可变的组件也被检测到，可能是由于从一个统一的大规模领域的排放。H-α发射具有相同的周期性，但与无线电脉冲不同的是，它是正弦变化的，并且正好偏移1/4的相位。正弦变化需要色球层从大尺度场结构发射，无线电脉冲可能从磁极发出。虽然两个光变曲线都可以用旋转的未对准磁场来解释，但是1/4相位滞后排除了对称偶极子拓扑，因为它将导致1/2（极向场）或零（环向场）的相位滞后。因此，我们得出结论，要么（i）场由四极配置主导，这可以自然地解释1/4相位滞后;要么（ii）H-α和/或无线电发射区域与场不平凡地对齐。不管磁场拓扑如何，我们使用测量的周期和已知的自转速度（vsini=27 km/s），以及双星轨道倾角（i=142 deg），得出主星的半径为0.078+/-0.010 R_sun。这是第一次测量L型矮星的半径，加上0.085+/-0.010 M_sun的质量，它提供了一个质量-半径关系低于0.1 M_sun的约束。我们发现，半径是约30%小于预期的理论模型，即使是几个陀螺仪的年龄。
英文摘要：
[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio emission, dominated by short-duration periodic pulses at 4.86 GHz with P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times demonstrates that they are due to the rotational modulation of a B~1.7 kG magnetic field. A quiescent non-variable component is also detected, likely due to emission from a uniform large-scale field. The H-alpha emission exhibits identical periodicity, but unlike the radio pulses it varies sinusoidally and is offset by exactly 1/4 of a phase. The sinusoidal variations require chromospheric emission from a large-scale field structure, with the radio pulses likely emanating from the magnetic poles. While both light curves can be explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out a symmetric dipole topology since it would result in a phase lag of 1/2 (poloidal field) or zero (toroidal field). We therefore conclude that either (i) the field is dominated by a quadrupole configuration, which can naturally explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions are not trivially aligned with the field. Regardless of the field topology, we use the measured period along with the known rotation velocity (vsini=27 km/s), and the binary orbital inclination (i=142 deg), to derive a radius for the primary star of 0.078+/-0.010 R_sun. This is the first measurement of the radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides a constraint on the mass-radius relation below 0.1 M_sun. We find that the radius is about 30% smaller than expected from theoretical models, even for an age of a few Gyr.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
