Identification of a Superbright Nova in Our Galaxy: Revisiting the Light-curve Analyses of the Candidate Novae CP Lac, CP Pup, V838 Her, V597 Pup, V5583 Sgr, and V5589 Sgr

Abstract The two very fast novae in our Galaxy, V1500 Cyg and V1674 Her, have reached the absolute V magnitude of M V , max ≈ − 10.4 . These brightest novae are identified as superbright novae. Such superbrightnesses are realized if an optically thick shocked shell forms far outside the nova (white dwarf (WD)) photosphere and expands at a velocity of a few thousand kilometers per second. We have analyzed V light curves of six candidate novae, CP Lac, CP Pup, V838 Her, V597 Pup, V5583 Sgr, and V5589 Sgr, by comparing them with our model nova light curves of 1.25 and 1.35 M ⊙ WDs calculated with the free–free emission from a nova wind. Analyzing the data with our method, we obtain M V , max = − 10 for V838 Her, and we suggest that its large peak optical luminosity is due to the ejection of an optically thick shell, as we have suggested for the case of V1674 Her. The light curves of the other five novae, CP Lac, CP Pup, V597 Pup, V5583 Sgr, and V5589 Sgr, are reproduced only with the free–free emission model V light curves without an optically thick shocked shell. Their M V , max are fainter than −10 mag. We conclude that these five are not superbright novae.