L型矮双星2 MASS J0746 +2000 AB的多历元VLBI：精确质量测量和两个组分射电辐射的确认
Multi-Epoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components
摘要：
调查显示，高达十分之一的超冷矮星（UCD）是可观的无线电发射体，其发射归因于回旋同步辐射和电子回旋脉泽不稳定性（ECMI）的组合。2 M J 0746 + 2000 AB是一个由L0和L1.5矮星组成的近距离双星，先前被确定为5 GHz射电辐射源。我们使用甚长基线干涉测量（VLBI）在2010-2017年的七个时期内精确跟踪无线电发射，并发现两个组件都是无线电发射器-这是第一个这样的系统-第二个组件是所有时期的主要发射源。之前确定的2.07 h周期性爆发被证实源自次要组件，尽管也从主要组件中确定了孤立的爆发。我们还拟合VLBI绝对天体测量位置与现有的相对轨道天体测量来自光学/红外观测与马尔可夫链蒙特卡罗（MCMC）方法，以确定两个组件的轨道参数。我们发现初级和次级光学组件的质量分别为0.0795 +/- 0.0003 Msun和0.0756 +/- 0.0003 Msun，这是迄今为止对任何UCD最精确的质量估计。最后，我们把一个3西格玛上限0.9兆焦耳的质量和分离的行星轨道的两个组件之一。
英文摘要：
Surveys have shown that up to one tenth of all ultracool dwarfs (UCDs) are appreciable radio emitters, with their emission attributed to a combination of gyrosynchrotron radiation and the electron cyclotron maser instability (ECMI). 2M J0746+2000AB is a close stellar binary comprised of an L0 and L1.5 dwarf that was previously identified as a source of 5 GHz radio emission. We used very-long-baseline interferometry (VLBI) to precisely track the radio emission over seven epochs in 2010-2017, and found both components to be radio emitters -- the first such system identified -- with the secondary component as the dominant source of emission in all epochs. The previously identified 2.07 h periodic bursts were confirmed to originate from the secondary component, although an isolated burst was also identified from the primary component. We additionally fitted the VLBI absolute astrometric positions jointly with existing relative orbital astrometry derived from optical/IR observations with Markov-chain Monte Carlo (MCMC) methods to determine the orbital parameters of the two components. We found the masses of the primary and secondary optical components to be 0.0795 +/- 0.0003 Msun and 0.0756 +/- 0.0003 Msun, respectively, representing the most precise mass estimates of any UCDs to date. Finally, we place a 3-sigma upper limit of 0.9 Mjup au on the mass and separation of planets orbiting either of the two components.
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