报告题目：Prevalence of He I* Absorption Line in Mg II LoBAL quasars and an Individual Study

　　报 告 人：纪拓（中国极地研究中心）

　　Collaborators：Wenjuan Liu, Hongyan Zhou, Peng Jiang, Tinggui Wang, Jian Ge, S. Komossa, Fred Hamann and others

　　Abstract：The multiplets HeI*λλ2765,2830,2946,3189,3889,10830 are a very useful diagnostics to the geometry and physical conditions of the absorbing gas, due to their wide wavelength separations, large oscillator strength differences, and highly metastable common lower transition level 23S. So far, however, only a handful of HeI* detections have been reported. We develop a new method that can well reproduce the absorption-free spectral regions of BAL quasars, in analog to the pair-matching method tradition- ally used to recover the extinction-free stellar spectra. Using the “pair-matching method”, we detected He I*λ3889 absorption line in 101 of a well-defined sample of 285 Mg II LoBAL quasars selected from the Fifth Data Release of the Sloan Digital Sky Survey (SDSS DR5). The detection fraction of He I* BALs in Mg II BAL quasars is fr ～ 35.4% as a whole, and increases dramatically with increasing spectra signal-to-noise ratios, from fr ～ 18% for S/N ≤ 10 to fr ～ 93% for S/N ≥ 35. This suggests that He I* BALs could be detected in most Mg II LoBAL quasars, provided S/N is high enough. I illustrate the diagnostics power of He I* absorption lines in an individual SDSS J0802+5513, A few tens of absorption lines are detected, including He I*, Fe II* and Ni II* that arise from metastable or excited levels, as well as resonant lines in Mg I, Mg II, Fe II, Mn II, and Ca II. With the aid of CLOUDY, ionization parameters, density and location of the absorber can be well constrained from He I* and its accompanying absorption lines.

　　时间及地点：12月18日（周四）中午11:30，天文楼202会议室

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