tokens: This leads to a fraction of ∼30 per cent of the nova progenitor systems which harbour evolved secondaries. Given that the nova progenitor systems with evolved secondaries have relatively higher mass transfer rates compared with nova progenitor systems with MS donors, nova progenitor systems with evolved secondaries should have more frequent outbursts. Therefore, the contribution of novae with evolved donors to the total nova rate should be larger than the fraction of corresponding binary systems, 30 per cent. Recently, Williams et al. ( 2016 ) conducted a more accurate statistical analysis of their preceding results and came to the conclusion that of nova eruptions in M31 galaxy are RG-novae. 4.5 Correlation between mass-specific nova rate and morphological type of galaxy Observations give contradicting results regarding the dependence of the mass-specific nova rate on the Hubble type of the galaxy. Some observational studies (e.g. Ciardullo et al. 1990 ; Shafter et al. 2000 ; Ferrarese et al. 2003 ; Williams Shafter 2004 ) claimed that there is no strong dependence of mass-specific nova rate on the Hubble types of galaxies: the majority of galaxies have around 2 ± 1 × 10 −10 L ⊙, K −1 yr −1 . However, there are several galaxies which may have a higher mass-specific nova rate e.g. the SMC, LMC, M33 and others (Della Valle et al. 1994 ; Della Valle 2002 ; Neill Shara 2005 ; Alis Saygac 2014 ; Mróz et al. 2016 ; Shara et al. 2016 ). The mass-specific nova rate of elliptical-like galaxies at 10 Gyr in our calculation is around (1 − 2) × 10 −10 M ⊙ −1 yr −1 . This is consistent with Williams Shafter ( 2004 ), since the total stellar mass-to-light ratio M ⋆ / L K ∼ 1.0, slightly depending on the colour of the galaxy (Bell de Jong 2001 ). However, for spiral-like galaxies, we obtained a mass-specific nova rate 10–20 times larger. It would seem then that our results are inconsistent with measurements of Williams Shafter ( 2004 ). However, one crucial point to understand this discrepancy is the incompleteness of nova surveys. For example, the nova rate of M31 in the analysis of Williams Shafter ( 2004 ) is significantly lower than the nova rates of Darnley et al. ( 2006 ). As we discussed above, a more reliable value should be ≈97 yr −1 , giving a luminosity-specific nova rate ∼7.0 × 10 −10 L ⊙,K −1 yr −1 , which is a factor of 3–4 larger than the value in Williams Shafter ( 2004 ). In our model for M31, we find a mass-specific nova rate of ≈(7 − 14) × 10 −10 M ⊙ −1 yr −1 , which is consistent with the above number. In our model of spiral-like galaxies, we assume the SFR to be constant, which is almost certainly oversimplified in the general case. As shown in Figs 1 and 2 , if there was an initial spike of SFR, certain fraction of total mass of ‘realistic’ spirals sits in old population which does not contribute much to the current nova rate. This will lead to a smaller value of luminosity-specific nova rate (cf. Table 1 ). 4.6 Novae with short
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