On Orbital Period Changes in Nova Outbursts

TL;DR

This paper introduces a new mechanism explaining orbital period changes during nova outbursts, highlighting the role of magnetic fields on the secondary star and predicting possible decreases in orbital periods.

Contribution

The study proposes a novel magnetic mechanism that can cause orbital period decreases during nova outbursts, challenging previous assumptions.

Findings

Magnetic fields on the secondary star can induce orbital period decreases.

The mechanism can produce negative orbital period changes during nova outbursts.

Application to U Sco supports the proposed model.

Abstract

We propose a new mechanism that produces an orbital period change during a nova outburst. When the ejected material carries away the specific angular momentum of the white dwarf, the orbital period increases. A magnetic field on the surface of the secondary star forces a fraction of the ejected material to corotate with the star, and hence the binary system. The ejected material thus takes angular momentum from the binary orbit and the orbital period decreases. We show that for sufficiently strong magnetic fields on the surface of the secondary star, the total change to the orbital period could even be negative during a nova outburst, contrary to previous expectations. Accurate determinations of pre- and post-outburst orbital periods of recurrent nova systems could test the new mechanism, in addition to providing meaningful constraints on otherwise difficult to measure physical quantities. We apply our mechanism to outbursts of the recurrent nova U Sco.