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We present a new determination of the time delay of the gravitational lenssystem HE1104-1805 ('Double Hamburger') based on a previously unpublisheddataset. We argue that the previously published value of dt_(A-B)=0.73 yearswas affected by a bias of the employed method. We determine a new value ofdt_(A-B)=0.85+/-0.05 years (2 sigma confidence level), using six differenttechniques based on non interpolation methods in the time domain. The resultdemonstrates that even in the case of poorly sampled lightcurves, usefulinformation can be obtained with regard to the time delay. The error estimateswere calculated through Monte Carlo simulations. With two already existingmodels for the lens and using its recently determined redshift, we infer arange of values of the Hubble parameter: Ho=48+/-4 km/s Mpc^-1 (2 sigma) for asingular isothermal ellipsoid (SIE) and Ho=62+/-4 km/s Mpc^-1 (2 sigma) for aconstant mass-to-light ratio plus shear model (M/L+gamma). The possibly muchlarger errors due to systematic uncertainties in modeling the lens potentialare not included in this error estimate.Comment: 11 pages, 15 figures, accepted by Astronomy and Astrophysic

The Double Quasar HE 1104–1805: A case study for time delay determination with poorly sampled lightcurves