Evolution of contact binary systems close to the orbital period cut-off
G. Loukaidou, K. Gazeas, S. Palafouta, D. Athanasopoulos, S. Zola, A. Liakos, P. Niarchos, P. Hakala, A. Essam and D. Hatzidimitriou
Ultra-short orbital period contact binaries (P < 0.26 d) host some of the smallest and less massive stars.
These systems are faint and rare, and it is believed that they have reached a contact configuration after
several Gyrs of evolution via angular momentum loss, mass transfer and mass loss through stellar wind processes.
This study is conducted in the frame of Contact Binaries Towards Merging (CoBiToM) Project and
presents the results
from light curve and orbital analysis of 30 ultra-short orbital period contact binaries with the aim to investigate
the possibility of them being red nova progenitors eventually producing merger events.
Approximately half of the systems
exhibit orbital period modulations, as a result of mass transfer or mass loss processes.
Although in contact,
their fill-out factor is low (less than 30 per cent), while their mass ratio is larger than longer period contact binaries.
The present study investigates the orbital stability of these systems, with the aid of correlation diagrams and examines
their physical and orbital parameters in comparison to those of the entire sample of known and well-studied contact binaries,
based on a combined spectroscopic and photometric analysis.
It is found that ultra-short orbital period contact binaries have
very stable orbits, while very often additional components move in wide orbits around the central binary system.
that the evolution of such systems appears to be very slow, which explains why the components of ultra-short orbital period
systems still exist as main sequence stars after several Gyrs of evolution.
Reference: Loukaidou et al., 2022, MNRAS, 514, 5528