蛇夫座核心的初步VLBA距离，精确度为4%
A Preliminary VLBA Distance to the Core of Ophiuchus, with an Accuracy of 4%
摘要：
2005年6月至2006年8月，甚长基线天线阵（VLBA）分别在第6和第7历元观测到蛇夫座核心年轻恒星S1和DoAr21的非热3.6厘米射电连续辐射。连续观察之间的典型间隔为2至3个月。由于VLBA提供了非常精确的天体测量，可以非常精确地追踪两颗恒星在天空平面上的轨迹，并将其建模为三角视差和均匀自行的叠加。最佳拟合得到S1和DoAr21的距离分别为116.9 $^{+7.2}_{-6.4}$ pc和121.9 $^{+5.8}_{-5.3}$ pc。结合这些结果，我们估计蛇夫座核心的平均距离为120.0 $^{+4.5}_{-4.2}$ pc，一个值与最近的几个间接测定一致，但与4%的显着提高的准确性。S1和DoAr21都是紧双星系统的成员，但我们的观测不够频繁，无法正确地推导出相应的轨道参数。然而，这可以利用附加数据来完成，并且将导致显著提高距离确定的准确性。
英文摘要：
The non-thermal 3.6 cm radio continuum emission from the young stars S1 and DoAr21 in the core of Ophiuchus, has been observed with the Very Long Baseline Array (VLBA) at 6 and 7 epochs, respectively, between June 2005 and August 2006. The typical separation between successive observations was 2 to 3 months. Thanks to the remarkably accurate astrometry delivered by the VLBA, the trajectory described by both stars on the plane of the sky could be traced very precisely, and modeled as the superposition of their trigonometric parallax and a uniform proper motion. The best fits yield distances to S1 and DoAr21 of 116.9$^{+7.2}_{-6.4}$ pc and 121.9$^{+5.8}_{-5.3}$ pc, respectively. Combining these results, we estimate the mean distance to the Ophiuchus core to be 120.0$^{+4.5}_{-4.2}$ pc, a value consistent with several recent indirect determinations, but with a significantly improved accuracy of 4%. Both S1 and DoAr21 happen to be members of tight binary systems, but our observations are not frequent enough to properly derive the corresponding orbital parameters. This could be done with additional data, however, and would result in a significantly improved accuracy on the distance determination.
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