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Spectral classification of the recurrent nova M31N 1990-10a during its 2016 eruption with WHT/ACAM

ATel #9281; A. Ederoclite (CEFCA), M. Henze (CSIC-IEEC), D. Aguado (IAC), C. Allende (IAC), S. Williams (Lancaster), M. J. Darnley (LJMU), G. Sala (UPC-IEEC), A. W. Shafter (SDSU), K. Hornoch (Ondrejov)
on 30 Jul 2016; 21:11 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: Optical, Nova, Transient

Referred to by ATel #: 9383, 9386, 9435, 10001

An optical spectrum of the fast recurrent nova candidate M31N 1990-10a (see ATels #9276,#9280) was obtained on 2016-07-30.11 UT with the ACAM instrument on the 4m William Herschel Telescope at the Roque de los Muchachos Observatory (located in La Palma, Spain). The observation was carried out with the R400 grating and 1.5-arcsec slit for a 1200 s exposure time. This is the first optical spectrum ever obtained for this object and it was taken about 3.1 d after the currently estimated eruption date.

We can confirm that M31N 1990-10a is indeed a nova in M31. The spectrum is dominated by strong Balmer (FWHM ~ 2000 km/s) and Fe II (multiplets 42, 48, 49, 74) emission features, along with other low excitation lines such as O I 7773, 8446, and the Ca II infrared triplet. A strong P Cyg feature is seen near 5880 A, which is likely Na D, but possibly He I 5876. Strong He I 7065 emission is also likely detected. We tentatively classify the spectrum as that of a broad-lined Fe II (Fe IIb) nova, but the presence of the He I 7065 emission, which is atypical of Fe II novae, complicates this simple interpretation. We also tentatively identify a broad H-alpha emission component extending to ~4450 km/s from line center that requires confirmation.