SS Cygni: The mass accretion rate behaviour in quiescence and in outburst

Abstract

From the HeII λ1640 emission line equivalent width values in all good available IUE low resolution spectra, we have deduced the correspondent mass accretion rate values Mdot for SS Cygni, using the optically thick boundary-layer model by Patterson and Raymond 1985. The Mdot behaviour can be distinguished as follows:

1) in the rising and declining phase of an outburst, Mdot is not inconsistent with the commonly accepted theoretical models on the quiescence-outburst optical behaviour of dwarf novae, which suppose the luminosity depending only on the rate Mdot at which matter is accreted;

2) Mdot in outburst is < Mdot in quiscence and suggests that the accretion is not the only energy release mechanism responsible for the higher luminosity. In this paper we will discuss the results searching for alternative and/or additive mechanism in producing the highest luminosities associated with the outbursts.