We present the analysis of the first circumbinary planet microlensing event , OGLE-2007-BLG-349 .
This event has a strong planetary signal that is best fit with a mass ratio of q \approx 3.4 \times 10 ^ { -4 } , but there is an additional signal due to an additional lens mass , either another planet or another star .
We find acceptable light curve fits with two classes of models : 2-planet models ( with a single host star ) and circumbinary planet models .
The light curve also reveals a significant microlensing parallax effect , which constrains the mass of the lens system to be M _ { L } \approx 0.7 M _ { \odot } .
Hubble Space Telescope images resolve the lens and source stars from their neighbors and indicate excess flux due to the star ( s ) in the lens system .
This is consistent with the predicted flux from the circumbinary models , where the lens mass is shared between two stars , but there is not enough flux to be consistent with the 2-planet , 1-star models .
So , only the circumbinary models are consistent with the HST data .
They indicate a planet of mass m _ { c } = 80 \pm 13 { M _ { \oplus } } , orbiting a pair of M-dwarfs with masses of M _ { A } = 0.41 \pm 0.07 M _ { \odot } and M _ { B } = 0.30 \pm 0.07 M _ { \odot } , which makes this the lowest mass circumbinary planet system known .
The ratio of the separation between the planet and the center-of-mass to the separations of the two stars is \sim 40 , so unlike most of the circumbinary planets found by Kepler , the planet does not orbit near the stability limit .