Probing the Spatial Distribution of Extrasolar Planets with Gravitational Microlensing

Abstract

Under the current microlensing planet search strategy of monitoring events caused by stellar-mass lenses, only planets located within a narrow region of separations from central stars can be effectively detected. However, with the dramatic increase of the monitoring frequency, two additional populations of free-floating and wide-orbit planets can be detected. In this paper, we investigate the lensing properties of events caused by wide-orbit planets and find that the light curves of a significant fraction of these events will exhibit signatures of central stars, enabling one to distinguish them from those caused by free-floating planets. Due to the large primary/planet mass ratio, the effect of the central star endures to considerable separations. We find that for a Jupiter-mass planet the signatures of the central star can be detected with fractional deviations of > 5% from the best-fitting single-lens light curves for > 80% of events caused by bound planets with separations < 10 AU and the probability is still substantial for planets with separations up to 20 AU. Therefore, detecting a large sample of these events will provide useful information about the distribution of extrasolar planets around their central stars. Proper estimation of the probability of distinguishing events caused by wide-orbit planets from those caused by free-floating planets will be important for the correct determination of the frequency of free-floating planets, whose microlensing sample will be contaminated by wide-orbits planets.

total 7 pages, including 4 figures, ApJ, submitted

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• A Neptune-mass Free-floating Planet Candidate Discovered by Microlensing Surveys
• Microlensing Characterization of Wide-Separation Planets
• Constraining the Frequency of Free-Floating Planets from a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results
• A free-floating or wide-orbit planet in the microlensing event OGLE-2019-BLG-0551
• Secure Identification of Free-Floating Planets
• Microlensing Detections of Planets in Binary Stellar Systems
• Characterization of Microlensing Planets with Moderately Wide Separations
• Microlensing by a wide-separation planet: detectability and boundness
• OGLE-2016-BLG-1227L: A Wide-separation Planet from a Very Short-timescale Microlensing Event
• Free-floating or wide-orbit? Keck adaptive-optics observations of free-floating planet candidates detected with gravitational microlensing
• Exoplanet Occurrence Rates from Microlensing Surveys