Evidence of accretion triggered oscillations in the pre-main-sequence interacting binary AK Sco

TL;DR

This study reports the detection of a low-frequency ultraviolet oscillation in the pre-main sequence binary AK Sco, linked to accretion processes at periastron, revealing new insights into binary star evolution.

Contribution

It provides the first observational evidence of accretion-triggered oscillations in a PMS binary, highlighting a novel mechanism for angular momentum loss.

Findings

Detected a 1.3mHz oscillation at periastron

Oscillation linked to accretion flow interactions

Suggests a new binary evolution mechanism

Abstract

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.