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Additional spectroscopic observations of two luminous novae in M31

ATel #8145; E. A. Barsukova (Special Astrophysical Observatory, Russia), V. P. Goranskij (SAI, Moscow University), M. Henze (IEEC/CSIC), A. W. Shafter (SDSU), K. Hornoch (Astronomical Institute, Ondrejov, Chech Republic)
on 9 Oct 2015; 18:26 UT
Credential Certification: Barsukova E.A. (bars@sao.ru)

Subjects: Optical, Nova

We report additional spectroscopy of the two M31 novae PNV J00432114+4124597 (M31N 2015-09c, ATel#8074, #8108, #8109, #8144) and PNV J00415937+4117026 (M31N 2015-10a, ATel #8134, #8141, #8144). The observations were carried out with the 1-m telescope at the Special Astrophysical Observatory, equipped with the UAGS spectrograph at the Cassegrain focus. The spectra were taken with a spectral resolution of 3 A in the spectral range of 3850 - 5240 Å.

For the spectrum of M31N 2015-09c, a total exposure of 7.2 ks was collected between Oct 4.80 and 5.10 UT, about five days after the first spectra (ATel #8109). Despite the low signal-to-noise ratio (< 20), very strong Balmer emission lines are visible as well as broad numerous Fe II emission lines. There are two Ca II emission lines on the blue end of the spectra. The widths of the H-beta and Fe II 4924 Å lines (FWHM, corrected for spectral resolution) are 1630 and 1220 km/s respectively. The corresponding equivalent widths are 85 and 23 Å, respectively. The H-beta line has a pedestal with a width of FWHM ~ 3200 km/s. In the Fe II 5018 Å line, the P Cyg profile is clearly visible. Its absorption minimum is shifted from the emission maximum by 1050 km/s. Almost all lines of hydrogen and iron have two-peak structure. The division between the two peaks is ~750 km/s (H-beta) and ~680 km/s (Fe II 4924 Å). The H-beta line appears to show a red wing.

The spectrum of M31N 2015-10a was collected with a total exposure of 4.8 ks between Oct 6.97 and 7.05 UT. It is very similar to the spectrum of the preceding nova, only the lines are 1.6 times wider and Ca II lines are not visible. The widths of H-beta and FeII 4924 Å lines are 2680 and 2100 km/s, respectively. The equivalent widths are 45 and 23 Å, respectively. The HWZI of H-beta ~ 2100 km/s. The Fe II 5018 Å line show a P Cyg profile with the absorption minimum shifted from the emission maximum by 1800 km/s. This suggests an expansion velocity 1.7 times higher than for M31N 2015-09c. We confirm the findings reported in ATel #8141, which was based on observations on the following day.