Spectroscopic confirmation of M81N 2018-04b (AT2018asx) as a nova eruption
ATel #11562; S. Fabrika (SAO RAS), S. C. Williams (Lancaster), O. Sholukhova, A. Vinokurov, Yu. Solovyeva, A. Sarkisyan, A. F. Valeev (SAO RAS), K. Hornoch (Ondrejov), M. Henze (SDSU), G. Sala, J. Jose (UPC-IEEC), H. Meusinger (TLS), M. J. Darnley (LJMU), A. Kaur (PSU), D. H. Hartmann (Clemson), A. W. Shafter (SDSU)
on 22 Apr 2018; 21:18 UT
Credential Certification: Steven Williams (scw@astro.ljmu.ac.uk)
Subjects: Optical, Nova, Transient
We report optical spectroscopic confirmation of the recent M81 nova candidate M81N 2018-04b (AT2018asx = XMr5ZX = PNV J09555269+6858409), the object was first announced and designated AT2018asx by Z. Xu and X. Gao (see TNS), and independently discovered by K. Hornoch et al. in ATel #11527.
We obtained a spectrum on 2018 April 13.864 UT using the Russian BTA telescope equipped with the SCORPIO spectrograph. The spectrum was taken with a resolution of 13 Å in the 3670 - 7720 Å range. The candidate shows strong and broad Balmer absorption lines together with many Fe II absorption lines, as well as Mg II, Na I, Si II, Al II. The Hβ and Hα lines show weak emission components in a P-Cygni profile. The radial velocities in these lines correspond to the M81 galaxy. The blue edge in the absorption lines (Hδ, Hγ, Hβ, Hα) have velocities 2000 ± 100 km/s; in the blue edge of Fe II lines (4922, 5018, 5169 Å) we measure velocities of 1800 ± 100 km/s.
We also obtained a spectrum using the SPRAT spectrograph (Piascik et al. 2014) on the 2-m Liverpool Telescope (LT) on 2018 Apr 17.89 UT. The spectrum had evolved to show strong Hα emission, and we measure the FWHM of the Hα line to be ~1600 km/s. We also detect Hβ and Hγ emission, along with emission lines corresponding to the 5018 and 5169 Å lines of the Fe II 42 multiplet.
These spectra confirm that M81N 2018-04b is a luminous classical nova eruption in M81 and we classify it as a member of the Fe II spectroscopic class.
