3. Point-mass lens and binary source
For a binary source, according to Griest & Hu (1992), two values of and defining the closest approach to the first and to the second source object are used, which imply two functions and . With and being the luminosities of the two parts and the luminosity offset ratio
so that the light curve is a superposition of two light curves for point sources behind point-mass lenses.
Since the two components of the binary source may be located on the same side or on opposite sides of the lens trajectory without changing the distance functions and , two different physical configurations producing the same light curve exist. I call the case where the components are on the same side the cis -configuration, the case where the components are on opposite sides the trans -configuration.
Let denote the distance between the closest approaches of the lens to the two components and denote the distance between the source components, both measured in projected Einstein radii . It follows that
The angle between the direction from source component 1 to source component 2 and the lens trajectory is given by
where the upper sign refers to the trans-configuration and the lower sign refers to the cis-configuration. The half-distance between the components follows as
© European Southern Observatory (ESO) 1998
Online publication: April 28, 1998