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

ATel #9383; S. Fabrika, O. Sholukhova, A. Valeev, A. Burenkov, D. Makarov (all SAO RAS), M. Henze (CSIC-IEEC), S. C. Williams (Lancaster), M. J. Darnley (LJMU), A. W. Shafter (SDSU), K. Hornoch (Ondrejov), A. Ederoclite (CEFCA), G. Sala (UPC-IEEC)
on 17 Aug 2016; 20:45 UT
Credential Certification: Martin Henze (henze@ice.cat)

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We report optical spectroscopy and photometry of the recurrent nova M31N 1990-10a during its 2016 eruption (see ATels #9276,#9280,#9281). We confirm the first spectrum obtained in ATel #9281 and describe the spectral evolution of the nova. We used the Russian BTA telescope equipped with the SCORPIO spectrograph.

Our first data were obtained on 2016-07-31.82 UT, about 4.8 d after the currently estimated eruption date (ATel #9281). The spectra were taken with a spectral resolution of 2.3 A in the spectral range of 4700-5500 A. Our second data set was obtained on 2016-08-02.93 UT with a spectral resolution of 13 A in the spectral range of 3500-7200 A. Photometry of the nova obtained shortly prior to the spectroscopy gave B = 19.34 ± 0.07, V = 18.88 ± 0.06, R = 18.44 ± 0.07. A third epoch of photometry only was taken on 2016-08-08.99 UT: B = 20.5 ± 0.15, V = 20.1 ± 0.2, R = 19.8 ± 0.2. Our 4th data were obtained on 2016-08-09.99 UT with a spectral resolution of 3.0 A in the spectral range of 6100-7100 A.

The optical spectra show a clear evolution: from the 1st to the 2nd observation the H-beta line has changed its width (FWHM) from 1350 to 900 km/s. From the 2nd to the 4th observation the H-alpha line width decreased from 1250 to 350 km/s (all widths were corrected for spectral resolution). In the 2nd observation, which has the largest spectral range, we found for the H-alpha, H-beta, H-gamma, and H-delta lines the following values of the FWHM / the blue edge of the P Cyg profile: 1250 / -3300, 900 / -2350, 600 / -2200, 150 / -1950 km/s, respectively.

We also found that the strong HeII 4686 A line and the [OIII] 4959, 5007 A (1st observation) nebular lines are all narrow corresponding to the spectral resolution. In the 1st and 2nd observations we observed very strong and relatively broad FeII and HeI lines without P Cyg profiles. We found the HeI 6678 A and 7065 A lines to have FWHMs of 430 km/s and 500 km/s, respectively. The NaI D_1,2 lines are blended with the HeI 5876 A line. However, because we did not observe P Cyg features in other HeI lines, only the NaI D_1,2 lines may show the P Cyg profile with a blue edge at -3700 km/s. Furthermore, we found NII lines (5667 - 5686 A and 6482 - 6492 A) in our spectra as well as suspected SiII and NIII lines. The radial velocities of the hydrogen lines from H-alpha to H-delta are in the range from -125 to -110 km/s, probably caused by the P Cyg contaminations. The HeII and [OIII] lines show radial velocities from -250 to -270 km/s while the HeI lines show velocities from -170 to -210 km/s. The FeII lines are blended; they show velocities of about -270 km/s.

We conclude that the recurrent nova envelope consists of a multi-temperature gas in which the higher ionized (excited) component has narrower line widths. This might be caused by anisotropic outflows or by material ejected in previous outbursts being illuminated by the current nova eruption.