M31N 2007-11d: A slowly rising, luminous nova in M31

Abstract

We report a series of extensive photometric and spectroscopic observations of the luminous M31 nova M31N 2007-11d. Our photometric observations coupled with previous measurements show that the nova took at least 4days to reach peak brightness at R ≃ 14.9 on 2007 November 20 UT. After reaching maximum, the time for the nova to decline 2 and 3 mag from maximum light (t 2 and t 3) was 9.5 and 13 days, respectively, establishing that M31N 2007-11d was a moderately fast declining nova. During the nova's evolution, a total of three spectra were obtained. The first spectrum was obtained one day after maximum light (5 days post-discovery), followed by two additional spectra taken on the decline at two and three weeks post-maximum. The initial spectrum reveals narrow Balmer and Fe II emission with P Cygni profiles superimposed on a blue continuum. These data, along with the spectra obtained on the subsequent decline, clearly establish that M31N 2007-11d belongs to the Fe II spectroscopic class. The properties of M31N 2007-11d are discussed within the context of other luminous novae in M31, the Galaxy, and the LMC. Overall, M31N 2007-11d appears to be remarkably similar to Nova LMC 1991, which was another bright, slowly rising, Fe II nova. A comparison of the available data for luminous extragalactic novae suggests that the ≳4 day rise to maximum light seen in M31N 2007-11d may not be unusual, and that the rise times of luminous Galactic novae, usually assumed to be ≲2 days, may have been underestimated. © 2009. The American Astronomical Society. All rights reserved..