The O’Connell effect is a phenomenon found in eclipsing binaries where the maxima between eclipses are not equally bright. It was first described by Roberts (1906), codified by O’Connell (1951), and named the O’Connell effect by Milone (1968). Despite being known for over a century, however, the physical processes underlying the O’Connell effect are still shrouded in mystery. Wilsey & Beaky (2009) suspects that there are in fact several different processes (most prominently starspots and the effects of mass transfer) that can cause the O’Connell effect and that different processes are at work in different systems. My own research on Kepler eclipsing binaries shows that over 7% of eclipsing binaries exhibit the O’Connell effect and that the effect is stable over long periods of time in some systems while it varies considerably in a matter of days in other systems.
One constant found is that the O’Connell effect is only found in short period systems where the stars are close enough to significantly affect each other. Such close binaries are very important: low-mass examples may host habitable exoplanets or be progenitors of type Ia supernovae, while high-mass examples are the natural progenitors of the recently detected gravitational wave events. Since mass transfer is a possible cause of the O’Connell effect, studying and understanding the O’Connell effect can give insight into the evolution of these systems. Furthermore, understanding what systems show the O’Connell effect will allow us to better understand the data we receive from future large surveys such as the LSST at the Vera Rubin Observatory. Many of the systems in my sample have a V magnitude brighter than 13 and all have a period under 10 days. They are targets ripe for observing, and these observations will allow us to better understand the mystery of the O’Connell effect.
O'Connell Effect Target List (37 KB .csv file)
Milone, E. E. 1968, AJ, 73, 708, doi: 10.1086/110682
O’Connell, D. J. K. 1951, Publications of the Riverview College Observatory, 2, 85
Roberts, A. W. 1906, MNRAS, 66, 123, doi: 10.1093/mnras/66.3.123
Wilsey, N. J., & Beaky, M. M. 2009, Society for Astronomical Sciences Annual Symposium, 28, 107