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Spectroscopic confirmation and photometry of the M31 nova ASASSN-18ca (= PNV J00423439+4044255)

ATel #11349; S. Fabrika, A. F. Valeev, A. Vinokurov (SAO RAS), K. Hornoch (Ondrejov), M. Henze, A. W. Shafter (SDSU), S. C. Williams (Lancaster), M. J. Darnley (LJMU)
on 24 Feb 2018; 19:57 UT
Credential Certification: Sergei Fabrika (fabrika@sao.ru)

Subjects: Optical, Nova

We report optical spectroscopic confirmation of the recent M31 nova candidate ASASSN-18ca (= PNV J00423439+4044255), discovered independently by Koichi Itagaki (Yamagata, Japan) and by J. Brimacombe et al. (ATel #11275). Raj et al. (ATel #11292) obtained spectra of the object and have suggested that the nova belongs to the Fe II class.

We obtained additional spectroscopic observations on 2018 Feb. 17.710 UT using the Russian BTA telescope equipped with the SCORPIO spectrograph. The spectrum was taken with a resolution of 5.3 Å in the 4050 - 5840 Å range. The photometry of the nova was obtained just before the time of the BTA spectrum with the same device, and gave B = 19.1 ± 0.1, V = 19.1 ± 0.1, Rc = 18.22 ± 0.08.

The nova shows strong and broad Balmer emission lines together with many Fe II lines. In the case of the principal lines: H-delta, H-gamma, H-beta, Fe II 4923 Å, and 5018 Å we found FWHM = 2800, 2720, 2650, 2980, 2880 km/sec, respectively, with errors ± 20-30 km/sec. The widths were corrected for spectral resolution. All these lines have sharp wings with flat and structured tops. In addition to these Balmer and Fe II lines, we also see evidence for the N III, C III Bowen blend at 4640, 4650 Å along with possible N II 5679 Å and [N II] 5755 Å emission features. We conclude that ASASSN-18ca is most likely a Hybrid nova or a broad-lined Fe II (Fe IIb) nova in the classification scheme of Williams (1992, AJ, 104, 725).