Observations of three pre-cataclysmic variables from the Edinburgh-Cape blue object survey

Aims: This study aims at determining the parameters of the three candidate pre-cataclysmic binaries EC 12477–1738, EC 13349–3237, and EC 14329–1625, most importantly their orbital period. Methods: Time-series photometry reveals orbital modulation in the form of sinusoidal variation due to the reflection effect. Photometric observations are complemented by time-resolved spectroscopy that yields radial velocities of the H$\alpha$ emission line. The combination of both methods allows us to unambiguously determine the orbital periods. The average spectra are used to estimate physical parameters of the primary and secondary stellar components. Results: We determine the orbital period for EC 12477–1738 as 0.362 d, thus confirming the value previously reported. A similar period, P=0.350 d, is found for EC 14329–1625. Both systems incorporate a medium-hot white dwarf ( $T = 15\,000{-}20\,000$ K) and an M3V secondary star. The third pre-CV, EC 13349–3237, is the youngest of the three, with a hot WD ( $T \sim 35\,000$ K), and it also has the longest period P=0.469 d. It furthermore turns out to be one of the still rare pre-CVs with a comparatively early-type, M1V, secondary star, which will eventually evolve into a CV above the period gap.