Field RR Lyrae stars

Secondary components were found to be predominantly low-mass objects. However, for two of the stars, RZ Cet and AT Ser, the mass of the suspected companion of more than one solar mass suggests that it is a massive white dwarf, a neutron star or even a black hole. We found that the semi-major axes of the proposed orbits are between 1 and 20au.

Because the studied stars belong to the closest RR Lyraes, maximal angular distances between components during orbit should at least be between 1 and 13mas and this improves the chance to detect both stars using current telescopes and interferometers. However, our interpretation of the O-C diagrams as a consequence of the LiTE should be considered as preliminary without reliable spectroscopic measurements. On the other hand, our models give a prediction of the period and radial velocity evolution which should be sufficient for plausible proof of binarity.