Spectroscopic Observations of Two Recent M31 Novae: M31N 2010-09b and M31N 2010-10a

ATel #2909; A. W. Shafter (SDSU), R. Ciardullo (PSU), M. J. Darnley, M. F. Bode (Liverpool JMU, UK), K. A. Misselt (U. Arizona)
on 7 Oct 2010; 07:04 UT
Credential Certification: Allen W. Shafter (aws@nova.sdsu.edu)

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We report spectroscopic observations of the recent M31 nova M31N 2010-09b (CBET #2472; ATel #2896), and of a new M31 nova candidate, M31N 2010-10a, which was discovered by Nishiyama and Kabashima (Miyaki-Argenteus Observatory, Japan) on 2010 Oct. 05.551 UT (private communication).

A previous spectrum of M31N 2010-09b obtained by our group within a day of discovery (Shafter et al., ATel #2898) established that the nova was likely a member of the Fe II class, but the possibility that it might evolve into a hybrid nova could not be ruled out at that time. To explore this possibility further, we acquired a follow-up spectrum (410–950 nm) of M31N 2010-09b on 2010 Oct. 06.40 UT with the Marcario Low-Resolution Spectrograph on the 9.2m Hobby-Eberly Telescope (HET). Broad-band B and V photometry obtained with the Liverpool Telescope on Oct. 05.125 UT indicated that the nova had faded to V = 18.9±0.1 with B-V ~ 0 by the night preceding our latest spectroscopic observations.

Our most recent data show that the spectrum of M31N 2010-09b has changed significantly from our original spectrum obtained ~5 days earlier. The follow-up spectrum is dominated by strong Balmer emission lines that have increased in width from a FWHM Hα ~ 1600 km/s at the time of our earlier spectrum to a FWHM Hα ~ 3600 km/s, and are now superimposed on a flat continuum. Strong O I λ 777.3, 844.6 nm emission lines are now seen, along with weaker Fe II (42) and blended N III λ 464.0 nm + He II λ 468.6 nm emission features. Although the spectrum of M31N 2010-09b shares some similarities with those of hybrid novae, the latest spectrum is consistent with the identification of M31N 2010-09b as a broad-lined Fe II nova.

Just prior to our observations of M31N 2010-09b, we obtained a spectrum of the latest M31 nova candidate, M31N 2010-10a, on 2010 Oct. 06.38 UT (less than a day post discovery) using the same instrument and configuration. Our HET spectrum of M31N 2010-10a reveals narrow Balmer (FWHM Hα ~ 1100 km/s) and weak Fe II emission features with pronounced P Cgyni profiles superimposed on a blue continuum. The absorption components are displaced by ~1100 km/s to the blue of the emission peaks. Our observations confirm that M31N 2010-10a is a nova observed near maximum light, and that it appears to be a member of the Fe II spectroscopic class.

A.W.S. thanks the NSF for support through AST-0607682 and the University of Victoria for hospitality.