We present a pilot study of extragalactic HI 21-cm absorption lines using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We observed 5 continuum sources with HI absorption features firstly identified in the 40% data release of the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFA) Survey (ALFALFA), including two systems later detected by the Westerbork Synthesis Radio Telescope (WSRT). Most of our observations were carried out during the FAST commissioning phase, and we have tested different observing modes, as well as data reduction methods, to produce the best spectra. Our observations successfully confirmed the existence of HI absorption lines in all these systems, including two sources that were marginally detected by ALFALFA. We fitted the HI profiles with single or double of Gaussian functions, and calculated the HI column densities of each source. The HI absorption profiles obtained by FAST show much higher spectral resolution and higher S/N ratio than the existing data in the literature, thus demonstrating the power of FAST in revealing detailed structures of HI absorption lines. Our pilot observations and tests have enabled us to develop a strategy to search for HI absorption sources using the data from the FAST extragalactic HI survey, which is one of the key projects undertaken at FAST. We expect that over 1,500 extragalactic HI absorbing systems could be detected with survey data, based on sensitivity level we achieved in pilot observations.
Science drivers and requirements for an Advanced Technology Large Aperture Space Telescope (ATLAST): Implications for technology development and synergies with other future facilities
Scientific Objectives of the Xue-shan-mu-chang 15-meter Submillimeter Telescope
Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；School of Astronomy and Space Sciences, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）；Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences（中国科学院南京天文光学技术研究所）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）
JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5: Photometric Catalog
Department of Astronomy and Astrophysics, University of California, Santa Cruz（加州大学圣克鲁兹分校天体物理学与天文学系）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；Steward Observatory, University of Arizona（亚利桑那大学斯图德天文台）；AURA for the European Space Agency (ESA), Space Telescope Science Institute（欧洲航天局（ESA）所属美国大学研究协会（AURA）太空望远镜科学研究所）；Centro de Astrobiología (CAB), CSIC–INTA（西班牙国家航空航天技术研究所（INTA）/西班牙国家科学研究委员会（CSIC）天体生物学中心）
The Far-Ultraviolet Extragalactic Legacy (FUEL) Survey: Hubble Far-UV Images and Catalogs of the Extragalactic Legacy Fields
University of California, Riverside（加州大学河滨分校）；California Institute of Technology（加州理工学院）；Universidad Complutense de Madrid（马德里康普顿斯大学）；University of Western Australia（西澳大学）；Stockholm University（斯德哥尔摩大学）；University of California at Santa Cruz（加州大学圣克鲁兹分校）；Clemson University（克莱姆森大学）
FAST search for circumstellar atomic hydrogen--I: the young planetary nebula IC 4997
利用中国贵州的500米口径球面射电望远镜（FAST）观测到年轻行星状星云IC 4997中21厘米的中性氢原子吸收。吸收来自也与Na I D线相关的壳层。H I壳的质量为$1.46\times10^{-2}$ M $_\odot$，动态年龄为990年。H I的柱密度估计为$7.1\times10^{20}$ cm $^{-2}$，这可以很好地解释为电离星云周围的光解离区域，受到H $_2$自屏蔽的限制。我们发现，原子电离氢的比例为0.6，这表明H I大大有助于整体星云质量。
