## 2. Information from a fit of a galactic microlensing event
From a fit of the light curve to the observed data of a galactic
microlensing event, the only dimensional parameters are the point of
time when the event occurs and the
characteristic timescale related to its
duration. While the point of time does not yield
any relevant information, all physical quantities related to the
observed event which involve a dimension depend on
. This is true not only for the `standard model'
of Galactic microlensing - a point-mass lens and a point source -, but
also for `anomalous' events (binary sources and lenses, parallax
effects, blending, finite size of the source and the lens).
With and , can be written as where The characteristic time scale is given by where is the transverse velocity of the lens relative to the line-of-sight source-observer. Note that motions of the source and the observer are also absorbed into this quantity. For a given , the mass therefore follows as where is a characteristic velocity and
. One sees that depends
on the timescale as well as on © European Southern Observatory (ESO) 1998 Online publication: January 27, 1998 |