Optical observations of the fast nova V1674 Herculis

ABSTRACT We present the evolution of optical spectra and light curves of the fast nova V1674 Herculis during 150 d past its eruption. Using the post-eruption AAVSO light curve, we have calculated the orbital period of V1674 Her to be 0.153 d. There is no unambiguous white dwarf spin period in our data. The optical spectra show that the ionization increases with time. A morphokinematic analysis of the H$\alpha$ line profile indicates a bipolar morphology with polar blobs and an equatorial ring. Lyman beta fluorescence is found to be the dominant mechanism for the excitation of neutral oxygen. On day 19.87, [Ne iii] and [Ne v] lines are present, indicating the presence of the ONe white dwarf. On day 147.66, the nebular lines are still present, implying that the nova had not gone into quiescence yet; this spectrum is accretion-dominated.