The Thermal Radio Jet of Cepheus A HW2 and the Water Maser Distribution at 0.″08 Scale (60 AU)
The Thermal Radio Jet of Cepheus A HW2 and the Water Maser Distribution at 0.″08 Scale (60 AU)
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仙王座 A HW2 的热射电射流和 0.″08 尺度（60 天文单位）的水脉泽分布
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发表时间：
1996
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通讯作者：
G. Garay
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作者：
J. Torrelles;José F. Gómez;Luis F. Rodriguez;S. Curiel;P. Ho;G. Garay
我们报告了对仙王座 A HW2 中的热射电射流以及相关水微波激射器的观测，这些观测是在 VLA 上以迄今为止最高的 (0.″08) 角分辨率（A 配置，λ = 1.3 cm）进行的。为了校准 1.3 cm 连续发射，我们使用强 (~1000 Jy) H2O 脉泽源作为参考，从而纠正了大气引入的幅度和相位不稳定性。这项强大的技术首先应用于恒星形成区域，使我们能够实现最强微波激射器特征的 15,000:1 动态范围、射电喷流的信噪比 (S/N) 为 70:1，以及射电连续谱射流和该区域中 H2O 微波激射器之间相对位置的 1 mas 量级的精度。我们将 1.3 厘米的射流分解为两个最大值以及西南方向较弱的尾部。这两个最大值之间的间隔 (0.”14) 和射流的总尺寸 (0.”39) 都与双锥电离射流的模型一致。然而，观测到的通量密度 (39 mJy) 高于预期。我们在仙王座 A 区域检测到 39 个 H2O 脉泽点，其中 28 个与 HW2 天体相关，其中大多数分布在射电喷流的两侧。我们认为，后面这些微波激射特征可能正在追踪半径约为 300 天文单位的星周分子盘，几乎垂直于射电喷流。在沿垂直于射电射流的轴超过 600 AU 的 H2O 点中观察到的 30 ± 10 km s-1 的速度梯度可能受到 70 ± 40 M☉ 中心质量的引力约束。
We report observations of the thermal radio jet in Cepheus A HW2, and the associated water masers, carried out with the highest (0.″08) angular resolution available to date at the VLA (A configuration at λ = 1.3 cm). To calibrate the 1.3 cm continuum emission, we used the strong (~1000 Jy) H2O maser source as the reference, thus correcting the amplitude and phase instabilities introduced by the atmosphere. This powerful technique, first applied here to a star-forming region, allowed us to achieve a dynamic range of 15,000:1 for the strongest maser feature, a signal-to-noise ratio (S/N) of 70:1 for the radio jet and an accuracy of the order of 1 mas in the relative positions between the radio-continuum jet and the H2O masers in the region. We resolved the 1.3 cm jet into two maxima plus a fainter tail to the southwest. The separation between these two maxima (0.″14) and the total size of the jet (0.″39) are both consistent with models for a biconical ionized jet. The observed flux density (39 mJy) is, however, higher than expected. We detected 39 H2O maser spots toward the Cepheus A region, 28 of which are associated with the HW2 object, most of them distributed on either sides of the radio jet. We suggest that these latter maser features might be tracing a circumstellar molecular disk of radius ~300 AU, nearly perpendicular to the radio jet. The velocity gradient of 30 ± 10 km s-1 observed in the H2O spots over 600 AU along the axis perpendicular to the radio jet could be gravitationally bound by a central mass of 70 ± 40 M☉.