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Spectroscopy and photometry of novae M31N 2013-12a and M31N 2013-12b

ATel #5745; S. Fabrika, E. A. Barsukova, A. F. Valeev, O. Sholukhova (Special Astrophysical Observatory, Nizhnij Arkhyz), K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), A. W. Shafter (SDSU), M. Henze (ESA/ESAC, Spain)
on 9 Jan 2014; 13:17 UT
Credential Certification: Sergei Fabrika (fabrika@sao.ru)

Subjects: Optical, Nova, Transient, Variables

We report optical spectroscopy and photometry of the recent M31 nova candidates M31N 2013-12a (= Swift J004249.9+411457; ATel #5669, #5677) and M31N 2013-12b (= PNV J00425172+4118142; ATels #5671, #5723). The spectroscopy and photometry were obtained on 2013 Dec. 31.77 UT (M31N 2013-12a) and 2013 Dec. 31.73 UT (M31N 2013-12b) using the Russian BTA telescope equipped with the SCORPIO spectrograph. Spectra were taken with a spectral resolution of 13 Å in the spectral range of 3700 - 7900 Å. We suggest that both novae may belong to the He/N class (see spectra attached). Besides strong hydrogen emission lines we detect N II blends (at 4650, 4800, 5170, 5300, 5540, 6350 Å), He I lines (4922, 5015, 5876 Å), He II at 4686 Å, N III at about 4640 Å, Mg I 5172 at Å. The hydrogen lines in M31N 2013-12a show P Cyg type profiles. The Hγ, Hβ and Hα widths corrected for spectral resolution are FWHM = 1040, 850 and 1130 km/s, their equivalent widths are EW = 22, 40 and 300 Å respectively. The envelope expansion velocity measured as the distance between emission and absorption peaks is 1250 km/s in Hγ and 1330 km/s in Hβ. Photometry of M31N 2013-12a obtained prior to the spectroscopy gave V = 19.54 ± 0.06, Rc = 19.07 ± 0.05. We note that both the brightness evolution (the nova is faint at maximum and the fading is relatively slow) and the relatively narrow hydrogen lines (however the Hα line has broad wings, 2250 km/s at zero intensity) are not typical for the He/N class. M31N 2013-12a may be a member of the narrow-lined He novae (He/Nn) introduced in Shafter et al., ApJ, 734:12, 2011.

The hydrogen lines in M31N 2013-12b are relatively broad with a red asymmetry of the chamfered top. Their widths are FWHM = 3250, 2900 and 3070 km/s, equivalent widths are EW = 130, 210 and 1220 Å for Hγ, Hβ and Hα respectively. Photometry of M31N 2013-12b resulted in V = 19.99 ± 0.06, Rc = 18.60 ± 0.04. Nova M31N 2013-12b had been classified previously as a FeIIb nova (based on spectroscopy obtained four days after discovery, see ATel #5723). However, our spectrum taken 14 days after the discovery suggests a He/N classification (based on very broad hydrogen lines and the strong N III line and N II blends). This spectral evolution suggests that M31N 2013-12b is a "hybrid" object (Williams, AJ, 144, 98, 2012).

Optical spectra of M31N 2013-12ab