The Magnetic Nature of the Cataclysmic Variable Period Gap
C. Garraffo, J. J. Drake, J. D. Alvarado-Gomez, S. P. Moschou, and O., Cohen

TL;DR
This paper investigates the magnetic properties of secondary stars in cataclysmic variables and proposes that increased magnetic complexity near the period gap causes a decline in angular momentum loss, explaining the observed gap.
Contribution
It introduces a magnetic complexity-based explanation for the CV period gap, supported by observational data and synthetic population modeling.
Findings
Magnetic complexity of M dwarfs increases with faster rotation.
Higher magnetic complexity correlates with reduced angular momentum loss.
The period gap can be explained by a rise in magnetic complexity near 3 hours.
Abstract
One of the most important problems in the context of cataclysmic variables (CVs) is the lack of observations of systems with periods between 2 and 3.12 hours, known as the period gap. The orbital evolution of CVs with periods shorter than those in the gap is dominated by gravitational radiation while for periods exceeding those of the gap it is dominated by magnetic braking of the secondary star. Spruit & Ritter (1983) showed that as periods approach 3 hours and secondary stars become fully convective a sharp decline in magnetic dynamo and braking efficiency would result in such a gap. Recent X-ray observations finding coronal magnetic energy dissipation is similar in fully convective and partly radiative M dwarfs cast this theory into doubt. In this work, we use Zeeman-Doppler imaging observations culled from the literature to show that the complexity of the surface magnetic fields of…
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