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Spectroscopy of M31N 2007-11g: Another Luminous Mira-like Variable in M31 Masquerading as a Nova

ATel #1851; A. W. Shafter (SDSU); R. Ciardullo (PSU); V. Burwitz, M. Henze and W. Pietsch (MPE); P. Milne, K. A. Misselt and G. Williams (U. Arizona); D. H. Hartmann and A. Updike (CU); M. F. Bode and M. J. Darnley (Liverpool JMU)
on 21 Nov 2008; 23:58 UT
Credential Certification: Allen W. Shafter (aws@nova.sdsu.edu)

Subjects: Optical, Nova, Transient, Variables

On 2008 November 17.23 UT observations made with the Livermore Optical Transient Imaging System (Super-LOTIS, located at Steward Observatory, Kitt Peak, Arizona, USA) revealed that the nova candidate M31N 2007-11g (Ovcharov et al. 2007; Atel #1312) had re-brightened to R~18.8, similar to its brightness at discovery a year earlier in November 2007. Since this behavior would be unusual for a nova (but typical of a Long-Period Variable), we decided to obtain a spectrum of M31N 2007-11g to determine its nature.

On 2008 November 18.3 UT, we observed M31N 2007-11g with the Marcario Low-Resolution Spectrograph on the 9.2-m Hobby Eberly Telescope. The spectrum reveals strong TiO absorption bands and narrow Balmer emission (H&alpha: FWHM ~ 300 km/s; EW ~ -10Å; RV ~ -275 km/s) superimposed on a red continuum. Thus, as suspected, M31N 2007-11g is not a nova; but rather appears to be a luminous long-period Mira-like variable, similar to the nova candidate M31N 1995-11e (Shafter et al. 2008; Atel #1834).