MODERN COSMOLOGY

Galactic microlensing 401

Figure 14.3. The set-up of a gravitational lens situation: The lens L located between
source S and observer O produces two images S 1 and S 2 of the background source.Dd
is the distance between the observer and the lens,Dsbetween the observer and the source
andDdsbetween the lens and the source.

Figure 14.4.Einstein ring (broken curve) and some possible relative orbits of a background
star with projected minimal distancesp=r/RE= 0. 1 , 0. 3 ,..., 1 .1 from a MACHO M
(from [22]).