Eclipsing binaries in extrasolar planet transit surveys: the case of SuperWASP

Abstract

Extrasolar planet transit surveys will also detect eclipsing binaries. Using a comprehensive binary population synthesis scheme, we investigate the statistical properties of a sample of eclipsing binaries that is detectable by an idealized extrasolar planet transit survey with specifications broadly similar to those of the Wide Angle Search for Planets (SuperWASP) project. In this idealized survey, the total number of detectable single stars in the Galactic disc is of the order of 106-107, while, for a flat initial mass ratio distribution, the total number of detectable eclipsing binaries is of the order of 104-105. The majority of the population of detectable single stars is made up of main-sequence stars (~60 per cent), horizontal-branch stars (~20 per cent), and giant-branch stars (~10 per cent). The largest contributions to the population of detectable eclipsing binaries stem from detached double main-sequence star binaries (~60 per cent), detached giant-branch main-sequence star binaries (~20 per cent), and detached horizontal-branch main-sequence star binaries (~10 per cent). White dwarf main-sequence star binaries make up approximately 0.3 per cent of the sample. The ratio of the number of eclipsing binaries to the number of single stars detectable by the idealized SuperWASP survey varies by less than a factor of 2.5 across the sky, and decreases with increasing Galactic latitude. It is found to be largest in the direction of the Galactic longitude l=-7 b 5 and the Galactic latitude b=-22 b 5. We also show that the fractions of systems in different subgroups of eclipsing binaries are sensitive to the adopted initial mass ratio or initial secondary mass distribution, which is one of the poorest constrained input parameters in present-day binary population synthesis calculations. This suggests that once statistically meaningful results from transit surveys are available, they will be able to significantly improve the predictive power of population synthesis studies of interacting binaries and related objects.