Abstract. Today most of existing personalization systems (e.g. content recommenders, or targeted ad) focus on individual users and ignore the social situation in which the services are consumed. However, many human activities are social and involve several individuals whose tastes and expectations must be taken into account by the service providers. When a group profile is not available, different profile aggregation strategies can be applied to recommend adequate content and services to a group of users based on their individual profiles. In this paper, we consider an approach intended to determine the factors that influence the choice of an aggregation strategy. We present a preliminary evaluation made on a real large-scale dataset of TV viewings, showing how group interests can be predicted by combining individual user profiles through an appropriate strategy. The conducted experiments compare the group profiles obtained by aggregating individual user profiles according to various strategies to the "reference" group profile obtained by directly analyzing group consumptions.

Measuring solar‐like oscillations in an ensemble of stars in a cluster, holds promise for testing stellar structure and evolution more stringently than just fitting parameters to single field stars. The most‐ambitious attempt to pursue these prospects was by Gilliland et al. who targeted 11 turn‐off stars in the open cluster M67 (NGC 2682), but the oscillation amplitudes were too small (<20 μmag) to obtain unambiguous detections. Like Gilliland et al. we also aim at detecting solar‐like oscillations in M67, but we target red giant stars with expected amplitudes in the range 50–500 μmag and periods of 1 to 8 h. We analyse our recently published photometry measurements, obtained during a six‐week multisite campaign using nine telescopes around the world. The observations are compared with simulations and with estimated properties of the stellar oscillations. Noise levels in the Fourier spectra as low as 27 μmag are obtained for single sites, while the combined data reach 19 μmag, making this the best photometric time series of an ensemble of red giant stars. These data enable us to make the first test of the scaling relations (used to estimate frequency and amplitude) with an homogeneous ensemble of stars. The detected excess power is consistent with the expected signal from stellar oscillations, both in terms of its frequency range and amplitude. However, our results are limited by apparent high levels of non‐white noise, which cannot be clearly separated from the stellar signal.

We have made an asteroseismic analysis of the variable blue stragglers in the open cluster M67. The data set consists of photometric time‐series from eight sites using nine 0.6–2.1 m telescopes with a time‐baseline of 43 d. In two stars, EW Cnc and EX Cnc, we detect the highest number of frequencies (41 and 26) detected in δ Scuti stars belonging to a stellar cluster, and EW Cnc has the second highest number of frequencies detected in any δ Scuti star. We have computed a grid of pulsation models that take the effects of rotation into account. The distribution of observed and theoretical frequencies shows that in a wide frequency range a significant fraction of the radial and non‐radial low‐degree modes are excited to detectable amplitudes. Despite the large number of observed frequencies we cannot constrain the fundamental parameters of the stars. To make progress we need to identify the degrees of some of the modes from either multicolour photometry or spectroscopy.

We obtained high-precision time-series observations of stars in the open cluster NGC 1817 in order to find d Scuti stars among the cluster members. The detection of 12 d Scuti stars, of which our data suggest that 11 are cluster members, makes NGC 1817 a key target for asteroseismology of 1.5Ϫ2.5 M , stars. One of the cluster member d Scuti stars is also an eclipsing binary, potentially offering very strong constraints for theoretical modeling. In addition, we find one d Scuti star candidate, a g Dor candidate, two variables of currently unknown type, and two eclipsing binary systems. We also describe a method for combining the oscillation frequencies of several d Scuti stars in a single cluster to obtain information about the order n of the excited modes. This method will eventually be used to constrain the theoretical models to be compared with precise oscillation frequencies determined from a future multisite campaign (asteroseismology).

We report on an ambitious multisite campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time series photometry. We outline here the data acquisition and reduction, with emphasis on the optimization of the signal-to-noise ratio of the low-amplitude (50-500 μmag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultrahigh precision (∼10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 μmag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and δ Scuti stars.