The abundance of Galactic planets from OGLE-III 2002 microlensing data

Abstract

From the 389 OGLE-III 2002 observations of Galactic bulge microlensing events, we select 321 that are well described by a point-source point-lens light-curve model. From this sample we identify one event, 2002-BLG-055, that we regard as a strong planetary lensing candidate, and another, 2002-BLG-140, that is a possible candidate. If each of the 321 lens stars has one planet with a mass ratio q = m/M = 10-3 and orbit radius a = RE, the Einstein ring radius, analysis of detection efficiencies indicates that 14 planets should have been detectable with Δχ2 > 25. Assuming our candidate is due to planetary lensing, then the abundance of planets with q = 10-3 and a = RE is np ≈ n/14 = 7 per cent. Conversion to physical units (Jupiter masses, M Jup, and astronomical units, au) gives the abundance of 'cool Jupiters' (m ≈ MJup, a ≈ 4 au) per lens star as np ≈ n/5.5 = 18 per cent. The detection probability scales roughly with q and (Δχ2)-1/2, and drops off from a peak at a ≈ 4 au like a Gaussian with a dispersion of 0.4 dex.