Population Clustering as a Signal for Deconfinement in Accreting Compact Stars

We study the evolution of the rotation frequency for accreting compact stars.The discontinuous change of the moment of inertia of a rapidly rotating stardue to the possible quark core appearance entails a characteristic change inthe spin evolution. Numerical solutions have been performed using a modelequation of state describing the deconfinement phase transition. Trajectoriesof spin evolution are discussed in the angular velocity - baryon number plane(phase diagram) for different accretion scenarios defined by the initial valuesof mass and magnetic field of the star, as well as mass accretion rate andmagnetic field decay time. We observe a characteristic increase in the waitingtime when a configuration enters the quark core regime. Overclustering of thepopulation of Z sources of LMXBs in the phase diagram is suggested as a directmeasurement of the critical line for the deconfinement phase transition sinceit is related to the behaviour of the moment of inertia of the compact star.Comment: 6 pages, 4 figures, uses aastex.cls (included), text and figures revised, references update