On the Spectroscopic Classes of Novae in M33

TL;DR

This study presents initial spectroscopic classifications of novae in M33, revealing a higher proportion of He/N and hybrid types than in other galaxies, suggesting a link to the galaxy's younger stellar population.

Contribution

First spectroscopic survey of M33 novae showing a different class distribution, indicating possible influence of stellar population age on nova types.

Findings

Majority of M33 novae are He/N or hybrid classes.

Fewer Fe II novae observed compared to M31 and Milky Way.

Suggests younger stellar population influences nova spectroscopic types.

Abstract

We report the initial results from an ongoing multi-year spectroscopic survey of novae in M33. The survey resulted in the spectroscopic classification of six novae (M33N 2006-09a, 2007-09a, 2009-01a, 2010-10a, 2010-11a, and 2011-12a) and a determination of rates of decline (t_2 times) for four of them (2006-09a, 2007-09a, 2009-01a, and 2010-10a). When these data are combined with existing spectroscopic data for two additional M33 novae (2003-09a and 2008-02a) we find that 5 of the 8 novae with available spectroscopic class appear to be members of either the He/N or Fe IIb (hybrid) classes, with only two clear members of the Fe II spectroscopic class. This initial finding is very different from what would be expected based on the results for M31 and the Galaxy where Fe II novae dominate, and the He/N and Fe IIb classes together make up only ~20% of the total. It is plausible that the increased fraction of He/N and Fe IIb novae observed in M33 thus far may be the result of the younger stellar population that dominates this galaxy, which is expected to produce novae that harbor generally more massive white dwarfs than those typically associated with novae in M31 or the Milky Way.