Spectroscopic and photometric insights into the early evolution of Nova V6594 Sgr

ABSTRACT We present multi-epoch optical photometric and spectroscopic observations of the Nova V6594 Sgr, discovered in outburst on 2021 March 25.29 ut. The light curve analysis reveals the characteristics of a fast nova, with decline time-scales of $t_2 = 25$ and $t_3 = 39$ d. A moderate reddening value of $E(B-V) = 0.36 \pm 0.04$ is estimated. A progenitor is identified in archival surveys with an effective temperature of approximately 7200 K. Dust formation is observed around 40–45 d post-outburst. On day 178 following the outburst, the dust temperature is estimated to be around $T_{\mathrm{ dust}} \sim 795$ K. Dust masses for amorphous carbon and graphite are estimated to be $M_{AC} = (2.40 \pm 1.04) D_{\text{kpc}}^2 \times 10^{-10}$ M$_{\odot }$ and $M_{GR} = (5.18 \pm 2.36) D_{\text{kpc}}^2 \times 10^{-10}$ M$_{\odot }$, respectively, where D is the distance of the Nova V6594 Sgr in kpc. Spectroscopic evolution of the P-Cygni line profiles reveals significant changes in the absorption velocity. Additionally, the continuum transitions from a non-blackbody to a blackbody origin. The H$\alpha$ profile decomposition also suggests the origins intrinsic to the novae ejecta that cause such changes. These three probes offer valuable clues about the complex physical processes during the early evolution of the nova, prior to the optical peak, after which the nova follows a more typical evolutionary path. A rudimentary photoionization model using cloudy is also discussed.