2008MNRAS.387..289L

Photometric observations of V4633Sgr (Nova Sagittarii 1998) during 1998-2005 reveal the presence of a stable photometric periodicity at P₁= 180.8min which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for 6yr. Shortly after the nova eruption it was measured as P₂= 185.6min. It has decreased monotonically in the following few years reaching the value P₂= 183.9min in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rotates nearly synchronously with the orbital revolution. According to our interpretation, the post-eruption evolution of NovaV4633Sgr follows a track similar to the one taken by V1500Cyg (Nova Cygni 1975) after that nova eruption, on a somewhat longer time-scale. The asynchronism is probably the result of the nova outburst that led to a considerable expansion of the white dwarf's photosphere. The increase in the moment of inertia of the star was associated with a corresponding decrease in its spin rate. Our observations have followed the spinning-up of the white dwarf resulting from the contraction of its outer envelope as the star is slowly returning to its pre-outburst state. It is thus the second known asynchronous polar classical nova.