Is There a Planet in that Microlensing Event?

The fundamental scale in microlensing is the Einstein ring whose size is proportional to the square root of the mass of the lens. Given that planets are 10^-3 to 10^-5 times less massive than their host stars, a microlensing event is dominated by the signal from the lens star. Because a planet is so much smaller than its host star, its microlensing signal will be a much smaller perturbation superposed on the light curve of the host star.

Exercise

Some of the following light curves have planetary signals, and some do not. Can you tell which ones are planets?

MOA-1998-BLG-033

Lightcurve of MOA-1998-BLG-033 Gaudi et al. 2002.

Is there a planet?

Yes No

OGLE-1998-BLG-014

Lightcurve of OGLE-1998-BLG-014 Gaudi et al.2002.

Is there a planet?

Yes No

OGLE-1999-BLG-036

Lightcurve of OGLE-1999-BLG-036 Bond et al.2004

Is there a planet?

Yes No

OGLE-2005-BLG-390

Lightcurve of OGLE-2005-BLG-390 Beaulieu et al.2006

Is there a planet?

Yes No

References:

Gaudi et al. (2002), ApJ, 566, 463
Gaudi et al. (2002), ApJ, 566, 463
Bond, Udalski, Jaroszyński, et al. (2004), ApJL, 606, 155
Beaulieu, Bennett, Fouqué, et al. (2006), Nature, 439, 437