Applegate Mechanism
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Eclipsing Time Variation Calculator


This module allows to calculate whether eclipsing time variations of a given magnitude can be produced via magnetic activity, specifically by what is referred to as the Applegate mechanism. This formalism considers changes in the stellar quadrupole moment, arising as a result of angular momentum redistribution due to magnetic activity. The change in the quadrupole moment couples to the binary orbit via gravity, thus inducing the period change. The calculation below assesses the required energy for the change in the quadrupole moment, which is compared to the energy that is produced by the star. The latter is crucial to assess the feasibility of the Applegate mechanism within a specific system.

The formalism employed here is based on the two-zone model by Voelschow et al. (2016), A&A, 587, A34. Any publications using results from this calculator should include both a citation to the paper and a reference to the web module in the acknowledgement.

Test Sources

Source Parameters

Binary Period (Pbin) days
Binary semi-major axis (abin) R
Modulation Period (Pmod) yr
Observed period change (ΔP/Pbin)
Mass of the magnetically active star (Msec) M
Radius of the magnetically active star (Rsec) R
Luminosity of the magnetically active star (Lsec) L
Temperature of the magnetically active star (Tsec) K
Parameter k1
Parameter k2
Radio Luminosity/SFR Calculator