6. Secondary caustics in binary lensing
In this section, we specify our results for the binary case where simple analytical formulae can be written. Let's consider two masses placed on the horizontal axis and let's choose the origin in the centre of mass. We call the separation between the masses a, then we have and . Eq. (9) is of second degree. Its solutions are
They are always simple and lie on a circle of radius centered in the middle of the two masses.
The radius of the two ovals is the same:
Its maximum value is reached when the two masses are equal, in fact, in this case, their distance from the two masses is maximum.
The two caustics are given by the following expression:
Their cusps are at positions
Their area is
reaching the maximum value in the equal masses case.
© European Southern Observatory (ESO) 2000
Online publication: June 30, 2000