Photometry and Hα studies of a low-mass-ratio overcontact binary ASAS J082243+1927.0

Both high-precision CCD photometric and Hα line studies are presented for an overcontact binary ASAS J082243+1927.0. The light curve exhibits a total eclipse at secondary minima along with an O'Connell effect. The light curve was modelled using the Wilson-Devinney code and the best solution provides the mass ratio q ∼ 0.106 and fill-out factor f ∼ 72 per cent. These parameters indicate that the system is a low-mass-ratio overcontact binary with a high degree of geometrical contact. The Hα line equivalent width varied at different phases and it is found that the line is possibly filled in at secondary minima. From a small sample of overcontact binaries, we found a correlation between the orbital period and Hα line equivalent width of the primary component. Based on a sample of high filling factor and low-mass-ratio contact binaries, a mass ratio cut-off is observed at q_critical = 0.085 in the mass-ratio-period plane. It was observed that for q_critical < 0.085, the period decreases with an increase of q, and above it the period increases as the mass ratio increases. Interestingly, the observed mass ratio cut-off value lies close to the critical mass ratio range as predicted in the literature. The observational evidence of the cut-off of the mass ratio and its variation with orbital period are discussed in terms of mass transfer and angular momentum loss. Based on the results, we suggest that, ASAS J082243+1927.0 is at the verge of merger, eventually forming a fast rotating star.