AT 2021rno: spectroscopic confirmation and likely third eruption of the recurrent nova M31N 1923-12c
ATel #14750; M. J. Darnley (LJMU), S. C. Williams (Turku)
on 4 Jul 2021; 09:35 UT
Credential Certification: Matt Darnley (M.J.Darnley@ljmu.ac.uk)
Subjects: Optical, Nova, Transient
Referred to by ATel #: 14755
AT 2021rno reports the discovery of a transient event coincident with the position of the known M31 recurrent nova M31N 1923-12c (also M31N 2012-01b, see ATel #3914).
A Liverpool Telescope SPRAT spectrum collected on 2021 Jul 04.16 (UT) shows strong Balmer emission lines with a FWHM of 5900 ± 300 km/s.
The spectrum also shows tentative evidence for He I emission lines. This would be consistent with the He/N designation of the 2012 eruption (ATel #3914).
The profile of the Hα and Hβ lines are highly asymmetric and may indicate that they are still optically thick.
This spectrum confirms that AT 2021rno is a nova eruption and the implication is that M31N 1923-12c has a recurrence period as short as 9 years. This would be more frequent than the Galactic recurrent U Sco and adds to the large population of 'rapid recurrent novae' (11 of 19 known M31 recurrent novae have recurrence periods ≤ 10 years) in M31 (Darnley & Henze, 2020)
