The symbiotic nova remains at maximum for one or a few decades, and then declines towards its original luminosity.
Variables of this type are double star systems with one red giant, which probably is a Mira variable,[1] and one a hot compact object (usually a white dwarf), with markedly contrasting spectra and whose proximity and mass characteristics indicate it as a symbiotic star.
They are divided into D-type (dusty) or S-type (stellar), depending on whether the giant is a Mira variable or not.
[2] The red giant fills its Roche lobe so that matter is transferred to the white dwarf and accumulates until a nova-like outburst occurs, caused by ignition of thermonuclear fusion.
The slow luminosity increase would then be simply due to time needed for growth of the ionization front in the outburst.