False positives and shallow eclipsing binaries in transiting exoplanet surveys

Abstract

PLATO (PLAnetary Transits and Oscillations of stars), ESA’s M3 mission, is due to launch in 2026. It will aim to detect transits by exoplanets around bright nearby stars and, where possible, to characterise those stars using asteroseismology. With 24 cameras arranged in four overlapping groups, PLATO will have an excellent signal to noise ratio, making the detection of an Earth-like planet in an Earth-like orbit around a Sun-like star a real possibility. However, the pixel size is large: at 15, there is an increased risk of blends with background eclipsing binaries. This work aims to quantify that risk. Data from Kepler has been used to calibrate the distribution of planets and eclipsing binaries detectable in a transiting exoplanet survey using the population synthesis code, BiSEPS. The calibrated synthetic populations have then been used to predict the numbers of exoplanets and eclipsing binaries mimicking planets that PLATO is likely to detect. Other forms of false positive, such as instrumental effects and stellar variability, are beyond the current scope of this project. My work offers insights into short period (P < 10 day) eclipsing binaries detectable in transiting exoplanet surveys, both in terms of initial mass ratio distribution and initial period distribution. From confirmed Kepler planets in Kepler Data Release 25, I derive two intrinsic exoplanet distributions which bracket the likely true distribution. These distributions converge at planet radius 0 < log R/R⊕ < 0.2. For the two proposed Long Look fields from Rauer et al. (2014), I find that more exoplanets are likely to be detected in the Southern field, while more blended eclipsing binaries are likely to contaminate observations of the Northern field. My methods can be extended to other transiting exoplanet surveys, by incorporating the detection parameters of the relevant observatory into the code.