Spectroscopic classification of AT2018bto and AT2018cmi as nova eruptions in M31
ATel #11765; M. Sitaram (University of Maryland), M. W. Healy (LJMU), M. J. Darnley (LJMU)
on 22 Jun 2018; 18:27 UT
Credential Certification: Matt Darnley (M.J.Darnley@ljmu.ac.uk)
Subjects: Optical, Nova, Transient
We obtained a spectrum of classical nova candidate AT2018cmi (see TNS) with the SPRAT spectrograph (resolution R~350; Piascik et al. 2014) on the 2-m Liverpool Telescope (Steele et al. 2004) on 2018 June 20.13 UT. A spectrum of AT2018bto/PNV J00434212+4122349/Gaia18bkp (see TNS and ATel #11656) was taken on 2018 June 21.19 UT.
The spectrum of AT2018cmi shows strong Balmer emission (Hα, Hβ, Hγ, Hδ) on top of a blue continuum. The Balmer lines exhibit a 'boxy' profile with multiple peaks. The width of the Hα and Hβ lines are around 4800 km/s. We also note tentative detections of N II 5001, 5679 and 5938 Å, and He I 5876 Å emission lines. There is no strong evidence for the presence of any Fe II or O I lines.
In conclusion, this spectrum confirms AT2018cmi is a classical nova in M31, the line profiles, line velocities, and lack of Fe II/O I lines suggests that this nova will belong to the He/N taxonomic class.
This spectrum of AT2018bto also shows strong Balmer emission (Hα, Hβ, Hγ, Hδ) on top of a blue continuum. The FWHM of these lines was measured to be about 2100 km/s. We tentatively detect emission lines from [O III] 4363, 4959, 5007 Å, along with the Bowen blend at ~4640 Å, with possible He II emission at 4686 Å, and [O I] at 6300 Å.
Therefore, we conclude the AT2018bto is a classical nova eruption in M31 and that the spectral evolution may have proceeded to the nebular phase.
Follow-up observations of both these novae are encouraged.
This summer internship project is supported by the GROWTH project funded by the National Science Foundation under Grant No 1545949.
