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Recurrent Nova M31N 2008-12a: spectroscopic confirmation of the 2015 eruption and additional photometry

ATel #7965; M. J. Darnley (LJMU), M. Henze (IEEC/CSIC), A. W. Shafter (SDSU), M. Kato (Keio University), for a larger collaboration
on 29 Aug 2015; 00:13 UT
Credential Certification: Matt Darnley (M.J.Darnley@ljmu.ac.uk)

Subjects: Optical, Nova

Referred to by ATel #: 7967, 7969, 7974, 7976, 7979, 7980, 7984, 8029, 8033, 8062

In ATel #7964 we reported the discovery of the 2015 eruption of the recurrent nova M31N 2008-12a (Darnley et al. 2014, 2015, Henze et al. 2014, 2015a). This recurrent nova has a remarkably short duty cycle of either 6 months or 1 year, and this is the eighth eruption detected in as many years (dating back to 2008; Henze et al. 2015b).

Here we present additional early photometry and pre-eruption limits (3 sigma) using data from the Swift satellite and the Faulkes North and Liverpool Telescopes (all times UT).

2015 Aug 28.008 uvw1 > 19.9 (Swift)
2015 Aug 28.160 r' > 21.78 (Liverpool Telescope)
2015 Aug 28.161 u' > 20.29 (Liverpool Telescope)
2015 Aug 28.406 uvw1 = 17.7 ± 0.1 (Swift)
2015 Aug 28.425 r' = 19.09 ± 0.04 (Faulkes Telescope North)
2015 Aug 28.602 uvw1 = 17.3 ± 0.1 (Swift)
2015 Aug 28.801 uvw1 = 17.2 ± 0.1 (Swift)
2015 Aug 28.964 u' = 18.5 ± 0.2 (Liverpool Telescope)
2015 Aug 28.969 B = 18.73 ± 0.02 (Liverpool Telescope)
2015 Aug 28.974 V = 18.66 ± 0.02 (Liverpool Telescope)
2015 Aug 28.979 r' = 18.50 ± 0.02 (Liverpool Telescope)
2015 Aug 28.984 i' = 18.77 ± 0.02 (Liverpool Telescope)

These data indicate that, as in 2014, the eruption has been caught on the rise at around one day before the optical peak.

The Liverpool Telescope obtained a 900s spectrum of the 2015 eruption at 2015 Aug 28.94 UT. This spectrum shows clear detection of Hα and Hβ emission lines on top of the detected continuum. Preliminary analysis also shows evidence of He I emission lines and tentative evidence of P Cygni absorption profiles associated with the Balmer lines. This spectra again confirms the nova nature of this transient.

We have triggered our pre-approved HST target of opportunity proposal. STIS UV spectroscopic visits have been scheduled for 2015 Aug 31.7, 2015 Sep 1.6 and Sep 2.6.

Any additional observations particularly blue photometric data (B- and U-band) or optical spectroscopy would be most welcome, particularly around the epochs of the HST visits.