# Is There a Planet in that Microlensing Event?

by Jennifer Yee

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?

### OGLE-1998-BLG-014

#### Lightcurve of OGLE-1998-BLG-014

Gaudi et al.2002.

Is there a planet?

### OGLE-1999-BLG-036

#### Lightcurve of OGLE-1999-BLG-036

Bond et al.2004

Is there a planet?

### OGLE-2005-BLG-390

#### Lightcurve of OGLE-2005-BLG-390

Beaulieu et al.2006

Is there a planet?

### 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