2018ApJS..237....4H

We analyzed optical, UV, and X-ray light curves of 14 recurrent and very fast novae in our Galaxy, Magellanic Clouds, and M31, and obtained their distances and white dwarf (WD) masses. Among the 14 novae, we found that eight novae host very massive (>=1.35 M_☉) WDs and are candidates for Type Ia supernova (SN Ia) progenitors. We confirmed that the same timescaling law and time-stretching method as in galactic novae can be applied to extragalactic fast novae. We classify the four novae V745 Sco, T CrB, V838 Her, and V1534 Sco as V745 Sco type (rapid decline); the two novae RS Oph and V407 Cyg as RS Oph type (circumstellar matter (CSM) shock); and the two novae U Sco and CI Aql as U Sco type (normal decline). The V light curves of these novae almost overlap with each other in the same group, if we properly stretch in the time direction (timescaling law). We apply our classification method to the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and M31 novae. YY Dor, LMC N 2009a, and SMC N 2016 belong to the normal-decline type, LMC N 2013 to the CSM-shock type, and LMC N 2012a and M31 N 2008-12a to the rapid-decline type. We obtained the distance to SMC N 2016 to be d = 20 ± 2 kpc, suggesting that SMC N 2016 is a member of our Galaxy. Rapid-decline type novae have very massive WDs of M_WD = 1.37-1.385 M_☉ and are promising candidates for SN Ia progenitors. Novae of this type are much fainter than the maximum magnitude versus rate of decline relations.