  We establish the multiparameter quantum Cram\'er-Rao bound for simultaneously
estimating the centroid, the separation, and the relative intensities of two
incoherent optical point sources using alinear imaging system. For equally
bright sources, the Cram\'er-Rao bound is independent of the source separation,
which confirms that the Rayleigh resolution limit is just an artifact of the
conventional direct imaging and can be overcome with an adequate strategy. For
the general case of unequally bright sources, the amount of information one can
gain about the separation falls to zero, but we show that there is always a
quadratic improvement in an optimal detection in comparison with the intensity
measurements. This advantage can be of utmost important in realistic scenarios,
such as observational astronomy.
