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

Snodgrass, Colin; Horne, Keith and Tsapras, Yiannis (2004). The abundance of Galactic planets from OGLE-III 2002 microlensing data. Monthly Notices of the Royal Astronomical Society, 351(3) pp. 967–975.

DOI: https://doi.org/10.1111/j.1365-2966.2004.07839.x

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=R_E, the Einstein ring radius, analysis of detection efficiencies indicates that 14 planets should have been detectable with ² > 25. Assuming our candidate is due to planetary lensing, then the abundance of planets with q= 10^-3 and a=R_E is n_p≈n/14 = 7 per cent. Conversion to physical units (Jupiter masses, M_Jup, and astronomical units, au) gives the abundance of ‘cool Jupiters’(m≈M_Jup, a≈ 4 au) per lens star as n_p≈n/5.5 = 18 per cent. The detection probability scales roughly with q and (²)^-1/2, and drops off from a peak at a≈ 4 au like a Gaussian with a dispersion of 0.4 dex.

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