Nova Herculi 2021 as an intermediate polar

Abstract

. We report the results of observations of Nova Herculi 2021 - V1674 Her. The object is characterized by several exceptional properties. The progenitor was identified as an intermediate polar. The speed of the outflow reached 10000 km s − 1 . The brightness decline was exceptionally rapid: t 2 ∼ = 1 . 2 d , t 3 ∼ = 3 d . The pulse spin signal was detected in photometry soon after the nova eruption. Extremely fast spin-up of the white dwarf rotation was measured. Despite challenges in cycle counting, we successfully constructed the O - C diagram of spin pulse maxima based on three seasons of observations. The result suggests a stable spin acceleration, with an anticipated gradual decline over the next decades. Additionally, we investigated the evolution of the orbital period.