Can the Friction of the Nova Envelope Account for the Extra Angular Momentum Loss in Cataclysmic Variables

It has been shown that the rate of angular momentum loss (AML) in cataclysmic variables (CVs) below the period gap is about 2.47 times that caused by gravitational radiation (GR), suggesting an extra AML mechanism aside from GR. Several potential mechanisms have been proposed but none of them has been verified. In this work, we examine whether AML caused by friction between the expanding nova envelope and the donor star can account for the required AML rate. By adopting various expanding velocities of the envelope, we have calculated the evolution of CVs with typical initial parameters. Our results show that this friction interaction unlikely solves the extra AML problem unless the expanding velocities are extremely low. Thus, there should be a more efficient AML mechanism that plays a role in CV evolution.