Very Long Baseline Interferometry (VLBI) astrometry using the phase-referencing technique remains an open issue for the quantitative characterization of the observing conditions to achieve a feasible parallax precision of 10 micro-arcseconds (μas). To address this issue, we evaluated the astrometric performance of the VLBI Exploration of Radio Astrometry (VERA) through the parallax measurements of five distant star-forming regions under good observing conditions of close separations (⁠|${0{^{\circ}_{.}}5}$|–|${1{_{.}^{\circ}}3}$|⁠) and high elevations (≥50°). Their parallaxes measured 89–200 μas, corresponding to distances of 5–11 kpc with an error of 11–20 μas. Furthermore, we investigated the contributions to the position error budget and concluded that the tropospheric residual contribution is the dominant error source. We also confirmed that the astrometric error propagation strongly depends on the term |$\Delta \sec Z$|⁠, which stands for the difference between |$\sec Z$| of the target and its reference source, where Z is the zenith angle during the observations. We found that for a source pair with a |$\Delta \sec Z$| less than 0.01 (for example, a set of a close separation of |$\le {{0{^{\circ}_{.}}5}}$| and a high elevation of ≥50°), we can achieve the parallax precision of 10 μas using a typical monitoring program comprising 10 observing epochs over a span of two years.

中文翻译：

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VERA在10微秒天文测量中的性能

使用相位参考技术的超长基线干涉术（VLBI）天文测量法，对于观测条件的定量表征，以实现10微弧秒（μas）的视差精度，仍然是一个悬而未决的问题。为解决此问题，我们通过在良好的近距离观测条件下对五个遥远的恒星形成区域进行视差测量，评估了VLBI射电占星术（VERA）的天文性能（⁠| $ {0 {^ {\ circ} _ {。}} 5} $ | – | $ {1 {_ {。} ^ {\ circ}} 3} $ |⁠）和高海拔（≥50°）。它们的视差为89–200μas，对应于5–11 kpc的距离，误差为11–20μas。此外，我们调查了对位置误差预算的贡献，并得出结论，对流层残余贡献是主要的误差源。我们还证实了天文误差传播在很大程度上取决于| $ \ Delta \ sec Z $ |⁠，它代表| $ \ sec Z $ |之间的差。目标及其参考源的角度，其中Z是观测期间的天顶角。我们发现对于| $ \ Delta \ sec Z $ |的源对。小于0.01（例如，|| \ le {{0 {^ {\ circ} _ {。}} 5}} $ |的一组紧密分隔 且高海拔（≥50°）），我们可以使用一个典型的监控程序，在10年内实现10个观测纪元，从而达到10μas的视差精度。