Optical spectral variability of PG QSOs

In previous studies we have shown that the optical variability of quasars increases, on average, with redshift. We explained this dependance in terms of a hardening of the spectrum during bright phases, coupled with the increase of the rest-frame frequency for increasing red-shift. We re-analize now these correlations on the basis of new light curves of PG quasars, recently published by the Wise Observatory group.