Period versus mass ratio evolution models for HIP 15429 assuming isotropic re-emission. The estimated present-day period is shown as the grey dashed line, while the range of tested initial parameters of the pre-mass transfer system are indicated as the grey-shaded region. Theoretical tracks for the case of fully (non-) conservative mass transfer are shown as (dashed) dotted black lines. They are chosen to match the estimated present-day binary properties. Coloured lines indicate binary evolution models computed with varying initial periods, mass ratios and mass accretion efficiencies, β (see models M3a to M3d in Table C1). Time evolves from left to right, with the left-most point representing the initial values. The evolutionary tracks assume circularised orbits during mass transfer. For discussion of eccentric mass transfer scenarios (see Sect. 9).