M31N 2007-11d: A Slowly-Rising, Luminous Nova in M31

TL;DR

This paper presents detailed photometric and spectroscopic observations of the luminous M31 nova M31N 2007-11d, revealing its slow rise, moderate decline, and classification as an Fe II nova, with implications for understanding luminous extragalactic novae.

Contribution

It provides the first extensive observational characterization of M31N 2007-11d, highlighting its slow rise and spectral class, and compares it with other luminous novae, challenging assumptions about rise times.

Findings

M31N 2007-11d took at least four days to reach peak brightness.

The nova was classified as an Fe II spectroscopic class.

The rise time may be longer than previously assumed for luminous novae.

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 four days to reach peak brightness at R~14.9 on 20 Nov 2007 UT. After reaching maximum, the time for the nova to decline 2 and 3 magnitudes 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 suggest 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.