Abstract

Aims. System parameters of the object LTT 560 are determined in order to clarify its nature and evolutionary status. Methods. We apply time-series photometry to reveal orbital modulations of the light curve, time-series spectroscopy to measure radial velocities of features from both the primary and the secondary star, and flux-calibrated spectroscopy to derive temperatures of both components. Results. We find that LTT 560 is composed of a low temperature (T ∼ 7500 K) DA white dwarf as the primary and an M5.5 ±1 main-sequence star as the secondary component. The current orbital period is P orb = 3.54(07) h. We derive a mass ratio M sec/M wd = 0.36(03) and estimate the distance to d = 25-40 pc. Long-term variation of the orbital light curve and an additional Hα emission component on the white dwarf indicate activity in the system, probably in the form of flaring and/or accretion events. © ESO 2007.