ALMA Long Baseline Campaigns: Phase Characteristics of Atmosphere at Long Baselines in the Millimeter and Submillimeter Wavelengths
Satoki Matsushita, Yoshiharu Asaki, Edward B. Fomalont, Koh-Ichiro Morita, Denis Barkats, Richard E. Hills, Ryohei Kawabe, Luke T. Maud, Bojan Nikolic, Remo P. … 展开作者
Satoki Matsushita, Yoshiharu Asaki, Edward B. Fomalont, Koh-Ichiro Morita, Denis Barkats, Richard E. Hills, Ryohei Kawabe, Luke T. Maud, Bojan Nikolic, Remo P. J. Tilanus, Catherine Vlahakis, Nicholas D. Whyborn
This paper presents the first detailed investigation of the characteristics of mm/submm phase fluctuation and phase correction methods obtained using ALMA with baseline lengths up to ~15 km. Most of the spatial structure functions (SSFs) show that the phase fluctuation increases as a function of baseline length, with a power-law slope of ~0.6. In many cases, we find that the slope becomes shallower (average of ~0.2-0.3) at baseline lengths longer than ~1 km, namely showing a turn-over in SSF. The phase correction method using water vapor radiometers (WVRs) works well, especially for the cases where PWV >1 mm, which reduces the degree of phase fluctuations by a factor of two in many cases. However, phase fluctuations still remain after the WVR phase correction, suggesting the existence of other turbulent constituent that cause the phase fluctuation. This is supported by occasional SSFs that do not exhibit any turn-over; these are only seen when the PWV is low or after WVR phase correction. This means that the phase fluctuation caused by this turbulent constituent is inherently smaller than that caused by water vapor. Since there is no turn-over in the SSF up to the maximum baseline length of ~15 km, this turbulent constituent must have scale height of 10 km or more, and thus cannot be water vapor, whose scale height is around 1 km. This large scale height turbulent constituent is likely to be water ice or a dry component. Excess path length fluctuation after the WVR phase correction at a baseline length of 10 km is large (>200 micron), which is significant for high frequency (>450 GHz or <700 micron) observations. These results suggest the need for an additional phase correction method, such as fast switching, in addition to the WVR phase correction. We simulated the fast switching, and the result suggests that it works well, with shorter cycle times linearly improving the coherence.
The Atacama Large Millimeter/submillimeter Array (ALMA) Band-1 Receiver
阿塔卡马大型毫米/亚毫米阵列（ALMA）频段1接收机覆盖35-50 GHz频段。原型接收机，包括关键部件和子系统的开发已经完成，并对两套原型接收机进行了全面测试。我们将提供ALMA Band 1科学目标的概述，以及在ALMA上使用的要求和设计。本文还将讨论接收机的发展现状，并将讨论完全组装的频段1接收机系统的基础设施、集成和评估。最后，将讨论所遇到的技术和管理挑战。
阿塔卡马大型毫米/亚毫米阵列（英语：Atacama Large Millimeter/Submillimeter Array，简称ALMA）是一个国际射电望远镜，位于智利北部的阿塔卡马沙漠。ALMA位于海拔5000米的干燥场地上，在仪器波长范围为0.3至10毫米的范围内具有良好的大气传输能力。其中一个是多达64个直径为12米的天线，可以在150米到15公里的范围内以多种模式重新配置。第二个阵列由一组四个12米和十二个7米天线组成，在直径约50米的两个紧密排列的配置中的一个中工作。该仪器将提供关于太阳系、银河系和附近高红移宇宙中原子、分子和电离气体和尘埃的干涉和总功率天文信息。在本文中，我们概述了ALMA的科学驱动因素，技术挑战和计划进展。
ALMA High-frequency Long-baseline Campaign in 2017: A Comparison of the Band-to-band and In-band Phase Calibration Techniques and Phase-calibrator Separation Angles
Submillimeter polarization and variability of quasar PKS 1830-211
活动星系核的偏振被解释为磁场在发射和准直相对论射电喷流中的作用的路标。在这里，我们报告了一个清晰的偏振信号的ALMA观测引力透镜类星体PKS 1830-211在亚毫米波长（波段9，650 GHz）的检测。将差分偏振测量技术应用于类星体的两张紧凑透镜图像，我们估计一张透镜图像的分数偏振约为5%，而另一张图像几乎未偏振，这意味着偏振活动在几周的时间尺度上变化。随着额外的ALMA波段7和8（300-500 GHz之间）的伴随数据，我们约束几个$10^5$ rad m $^{-2}$的法拉第旋转。我们还观察到在波段9中一小时内通量密度变化约为10%。这项工作表明，差分分析可以提取高精度的信息（通量密度比和偏振）的校准问题，从解决来源在亚毫米域。
VAPOLA -- A multi-year, multi-band polarization survey of AGN and Sgr A* at mm wavelengths with ALMA I. Survey Overview and Science-Ready Archival Products
Università degli Studi di Cagliari（卡利亚里大学）；INAF - Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；University of Balearic Islands（巴利阿里群岛大学）；Institute of the Balearic Islands (IAIB)（巴利阿里群岛研究所）；Health Research Institute of the Balearic Islands (IdISBa)（巴利阿里群岛健康研究所）；Universidade São Paulo, Instituto de Astronomia, Geofísica e Ciéencias Atmosféricas（圣保罗大学天文、地球物理与大气科学研究所）；INAF-Istituto di Radioastronomia（意大利国家天体物理研究所射电天文学研究所）；INAF–Italian Centre for Astronomical Archive（意大利天体物理研究所意大利天文档案中心）
