Emergence of spectroscopic features of AT2018cow/ATLAS18qqn with the Xinglong-2.16m spectroscopy

ATel #11740; Dong Xu, Jing Wang, Liping Xin, Junbo Zhang, Zipei Zhu (NAOC), Sarah Antier(LAL), Jirong Mao(GMG), Damien Turpin(NAOC), Chao Wu(NAOC), Weikang Zheng(Berkeley), Nicolas Leroy(LAL), Michael Coughlin(Caltech), Xuhui Han(NAOC), Jianyan Wei(NAOC), Alain Klotz (IRAP), Michel Boër (Artemis), Xuan Zhang, Junhui Liu (XAO) report for the GRANDMA and GWFUNC teams
on 20 Jun 2018; 17:40 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Dong Xu (dxu@nao.cas.cn)

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We obtained 2x1200s spectroscopy of the bright transient AT2018cow (ATLAS18qqn; Smartt et al. ATel #11727) using the BFOSC camera on the Xinglong-2.16m telescope. Spectroscopy started at 13:25:11 UT on 2018-06-20, and the wavelength range covers 3600-9000 AA. Due to relatively low spectral resolution, we cannot confirm the presence of Ca II H&K absorption features at z=0 and at z=0.014 (likely the redshift of the transient's host galaxy CGCG 137-068), which has been claimed in Jones et al. (ATel #11736). As a whole, the Xinglong spectrum is blue and thermal-like. However, a prominent feature is evident in the blue end, more likely a bump centered on ~3960 AA than an absorption trough centered ~3790 AA, depending on the fitting of the spectral continuum. If understood as an absorption feature, it could be He I [3889]. A weak broad feature is also evident at ~5040 AA, implying very high velocity that can be seen inbroad-lined Type Ic supernovae. All the wavelengths are in the observer frame. Further spectroscopic observations are planned.