On the formation of close binaries – an interferometric look on Algol(s)

Abstract

Both theoretical and indirect observational evidences suggest that most of the closest binary stars with orbital periods of few days (as well as hot Jupiter-type exoplanets) formed with an original separation larger by 1-2 orders of magnitude than the present one. Consequently, an orbital shrinking mechanism(s) must be present that extracts the angular momentum from a primordial binary. From the possible mechanisms studied in the literature we describe the so-called 'Kozai cycles combined with tidal friction' (KCTF), which gives some definite predictions for the statistical properties of the orbital elements in such close binaries. Due to the recent powerful observing techniques, such as optical and radio (VLBI) interferometry, we can already peer inside such close binaries, so we have some opportunity to check these predictions. We examine the practical details, constraints, restrictions about the inquiring of the necessary information from specific triple systems by interferometric (as well as polarimetric) observations. Finally, to illustrate this we give a brief description of our recent combined optical and radio interferometric measurements of Algol.