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Spectroscopic classification of transients ASSASN-17ni and AT2017hid (= Gaia17cot)

ATel #10848; M. Berton (Padova University), G. Terreran (Northwestern University), U. Munari (INAF Padova)
on 14 Oct 2017; 14:09 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Cataclysmic Variable, Transient

We have obtained low resolution, fluxed spectra of the two transients ASSASN-17ni and AT-2017hid (= Gaia17cot) with the Asiago 1.22m telescope (range 3300-8000 Ang, dispersion 2.31 Ang/pix) on 2017 Oct 13.9 UT.

ASSASN-17ni displays a template spectrum for a cataclysmic variable in outburst: blue continuum, Balmer continuum in moderate absorption, broad Balmer lines in absorptions, with an emission core that increases in intensity going from Hdelta to Hbeta. A pronounced emission is visible at Halpha, which largely overfills the underlying absorption line. HeI lines 3639, 4026, 4471, and 4922 are present in absorptions. HeI 7065 is seen in emission, while the continuum is flat around HeI 5876 and 6678, probably the result of the emission core filling just right the corresponding absorption line. CaII K line (3933 Ang) and NaI doublet (5890, 5896) are also seen in absorption. The slope of the continuum corresponds to photometric colors B-V=0.0, V-Rc=+0.08.

Our spectrum for AT2017hid has a significantly lower S/N than for ASSASN-17ni (S/N=20 and 65 at 5000 Ang, respectively). The continuum is blue (corresponding to photometric colors B-V=+0.09, V-Rc=+0.17), with a Balmer continuum in moderate absorption. Wide Balmer lines are seen in absorption up to Hbeta, which could show an emission core (at 2sigma the noise of the continuum). The spectrum is flat around Halpha, probably the result of an emission core filling just right the corresponding absorption. The spectrum suggest that also AT 2017hid is a cataclysmic variable in outburst.