In this paper , we explore the astrophysical implications of near-field microlensing and its effects on stellar transit observations , with a special emphasis on the Kepler mission . Kepler is a NASA-approved mission whose goal is to detect a large number of extrasolar , earth-like planets by obtaining near-continuous photometry of > 100 , 000 F , G , and K dwarfs for four years .
The expected photometric precision of Kepler is 90 \mu mag ( achieved in 15 minute samples ) , at which the effect of microlensing by a transiting companion can be significant .
For example , for a solar-type primary transited by a white-dwarf secondary , the maximum depth of the transit is 0.01 % , which is almost entirely compensated by the microlensing amplification when the white dwarf is at \sim 0.05 AU .
The combined effect of microlensing and transit increases to a net amplification of 150 \mu mag at an orbital separation of 0.1 AU , and 2.4 millimag at an orbital separation of 1 AU .
Thus , the effect of microlensing can be used to break the degeneracy between a planetary-mass object for which the microlensing effect is negligible , and a more massive object of the same size .
For brown dwarfs at orbital separations of a few AU , the effect of microlensing is several percent of the transit depth , and hence the microlensing effect must be taken into account in deriving the physical parameters of the brown dwarf .
The microlensing signal caused by a neutron star or a black hole in a binary can be several millimag , far exceeding the transit depth , and potentially detectable even from ground-based observations . Kepler will be sensitive to white dwarfs , neutron stars , and black holes in binaries through their microlensing signatures .
These observations can be used to derive the frequency of such compact objects in binaries , and to determine their masses .