The UBV Color Evolution of Classical Novae. IV. Time-stretched (U − B)<sub>0</sub>–(M <sub> B </sub> − 2.5 log f <sub>s</sub>) and (V − I)<sub>0</sub>–(M <sub> I </sub> − 2.5 log f <sub>s</sub>) Color–Magnitude Diagrams of Novae in Outbursts
Izumi Hachisu, Mariko Kato
Abstract
Abstract Light curves and color evolutions of two classical novae can be largely overlapped if we properly squeeze or stretch the timescale of a target nova against that of a template nova by . Then, the brightness of the target nova is related to the brightness of the template nova by , where M [ t ] is the absolute magnitude and a function of time t , and f s is the ratio of timescales between the target and template novae. In the previous papers of this series, we show that many novae broadly overlap in the time-stretched ( B − V ) 0 – color–magnitude diagram. In the present paper, we propose two other ( U − B ) 0 – and ( V − I ) 0 – diagrams and show that their tracks overlap for 16 and 52 novae, respectively. Here ( U − B ) 0 , ( B − V ) 0 , and ( V − I ) 0 are the intrinsic U − B , B − V , and V − I colors and not changed by the time stretch, and M B , M V , and M I are the absolute B , V , and I magnitudes. Using these properties, we considerably refine the previous estimates of their distance and reddening. The obtained distances are in reasonable agreement with those of the Gaia Data Release 2 catalog.