[WKK93] Star 5 , the SIMBAD biblio

We report the detection of variability in the recently discovered double QSO HE 1104-1805 (z=2.319) over a time span of 20 months. Component A has faded in B magnitude from 16.65 to 17.06, component B from 18.57 to 18.91. The variation is entirely due to a dimming of the QSO continua, with no discernible changes in emission line fluxes. The continuum slope of A has become significantly softer, while the slope of B has become harder. The gravitational lens nature of the system is corroborated, but the proposed microlensing component can no longer be uniquely identified due to the interference of intrinsic variability. We propose strategies for a long-term photometric and spectroscopic monitoring.