Multiwavelength Photometry and Progenitor Analysis of the Nova V906 Car

We present optical and infrared photometry of the classical nova V906 Car, also known as Nova Car 2018 and ASASSN-18fv, which was discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) on 2018 March 16.32 UT (MJD 58193.0). The nova reached its maximum on MJD 58222.56 at V _max = 5.84 ± 0.09 mag, and had decline times of $t_{2,V}=26.2$ days and $t_{3,V}=33.0$ days. The data from Evryscope shows that the nova had already brightened to $g^{\prime }\simeq 13$ mag five days before discovery, as compared with its quiescent magnitude of g = 20.13 ± 0.03. The extinction toward the nova, as derived from high-resolution spectroscopy, shows an estimate consistent with foreground extinction to the Carina Nebula of $A_V={1.11}_{-0.39}^{+0.54}$. The light curve resembles a rare C (cusp) class nova with a steep decline slope of α = −3.94 post-cusp flare. From the light-curve decline rate, we estimate the mass of the white dwarf to be M _WD = <0.8M _⊙, consistent with $M_{WD}={0.71}_{-0.19}^{+0.23}$ derived from modeling the accretion disk of the system in quiescence. The donor star is likely a K-M dwarf of 0.23–0.43 $M_{\odot }$, which is heated by its companion.