  Pre-main sequence (PMS) binaries are surrounded by circumbinary disks from
which matter falls onto both components. The material dragged from the
circumbinary disk flows onto each star through independent streams channelled
by the variable gravitational field. The action of the bar-like potential is
most prominent in high eccentricity systems made of two equal mass stars. AK
Sco is a unique PMS system composed of two F5 stars in an orbit with e=0.47.
Henceforth, it is an ideal laboratory to study matter infall in binaries and
its role in orbit circularization. In this letter, we report the detection of a
1.3mHz ultra low frequency oscillation in the ultraviolet light curve at
periastron passage. This oscillation last 7 ks being most likely fed by the
gravitational energy released when the streams tails spiralling onto each star
get in contact at periastron passage enhancing the accretion flow; this unveils
a new mechanism for angular momentum loss during pre-main sequence evolution
and a new type of interacting binary.
