KVN和VERA阵列（KaVA）的首次三角视差测量
First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)
- National Astronomical Research Institute of Thailand（泰国国家天文研究所）
- Mizusawa VLBI Observatory, National Astronomical Observatory of Japan（日本国立天文台水泽VLBI观测站）
- Tokyo Electron Ltd.（东京电子株式会社）
- Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文通过KaVA阵列对W3(OH)的22 GHz水脉泽进行六历元观测，成功测量三角视差0.497毫角秒，对应距离2.01千秒差距，验证了KaVA联合阵列在天体测量中的能力。
AI中文摘要：
为展示韩国VLBI（甚长基线干涉测量）网络（KVN）与射电天体测量VLBI探测（VERA）阵列（KaVA）联合后的天体测量能力，我们对与恒星形成区W3(OH)相关的22 GHz H$_{2}$O脉泽进行了六个历元的VLBI观测。在天体测量分析中，独立应用了两种大气校准方法：（1）GPS和（2）JMA（日本气象厅）中尺度分析数据，以及两个相位参考源。所有校准策略均成功测量了W3(OH)的三角视差，包括首次使用JMA校准的成功视差测量。联合拟合视差为0.497$\pm$0.024毫角秒，对应距离为2.01$^{+0.10}_{-0.09}$千秒差距。该值与先前甚长基线阵列（VLBA）的结果0.489$\pm$0.017毫角秒一致。KaVA在相位参考图中的信噪比比VERA高55$\\%$，与理论预期高度吻合。这些结果表明，KaVA将能够对22 GHz H$_2$O脉泽进行三角视差测量，而这些脉泽由于低通量密度和/或有限的$uv$覆盖而难以仅用VERA观测。在为期一年的观测活动中，检测到W3(OH)的通量变化从510$\pm$50央斯基到3900$\pm$400央斯基，这归因于在2.01千秒差距处仅相隔约64天文单位的两个邻近脉泽特征。最亮的特征表现出线宽随峰值通量密度增加而减小的趋势，与未饱和脉泽放大一致，而另一个特征未发现类似趋势，表明它们对相同放大条件的不同响应，可能由于饱和状态和内部速度结构的差异所致。
英文摘要：
To demonstrate the astrometric capability of the combined Korean VLBI (Very Long Baseline Interferometry) Network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA), we conducted six-epoch VLBI observations of 22-GHz H$_{2}$O masers associated with the star-forming region W3(OH). Two atmospheric calibration methods, (1) GPS and (2) JMA (Japan Meteorological Agency) mesoscale analysis data, and two phase-reference sources were independently applied to the astrometric analysis. Trigonometric parallaxes of W3(OH) were successfully measured with all calibration strategies, including the first successful parallax measurement using JMA calibration. The combined-fit parallax is 0.497$\pm$0.024 mas, corresponding to a distance of 2.01$^{+0.10}_{-0.09}$ kpc. This value is consistent with the previous Very Long Baseline Array (VLBA) result of 0.489$\pm$0.017 mas. KaVA achieved a 55$\%$ higher signal-to-noise ratio in phase-referenced maps than VERA, in good agreement with theoretical expectations. These results suggest that KaVA will enable trigonometric parallax measurements of 22-GHz H$_2$O masers that are difficult to observe with VERA alone because of low flux densities and/or limited $uv$ coverage. A flux variation from 510\,$\pm$\,50 to 3900\,$\pm$\,400 Jy was detected in W3(OH) over a one-year observing campaign and is attributed to two nearby maser features separated by only $\sim$64 AU at 2.01 kpc. The brightest feature showed a decrease in linewidth with increasing peak flux density, consistent with unsaturated maser amplification, whereas no similar trend was found for the other feature, suggesting different responses to the same amplification conditions, possibly owing to differences in saturation state and internal velocity structure.
