1 Introduction

The remarkable scientific potentials of the Hubble Space Telescope Fine Guidance Sensor (HST-FGS) archival data for determining microvariability in a large sample of stars have been discussed by Kuschnig et al. (1997). The authors indicate some instrumental problems which are typical for photometry in space and their study was extended by Zwintz et al. (2000). Future photometric satellite projects, like the CNES-lead asteroseismology experiment COROT, the Canadian micro-satellite project MOST or the Danish project MONS can also benefit from the investigation of instrumental and environmental problems encountered when performing photometry from a space-borne platform. Another powerful data base for investigating various effects which impede the determination of intrinsic photometric characteristics of stars is provided by the HIPPARCOS mission. Despite all efforts to calibrate an instrument before launch and to develop reliable instrumental models already in the design stage, it always will be necessary to determine and/or check such model parameters independently, based on real data.

Triggered by publications claiming detection of low-level photometric variability of stars we tried to determine the relevant instrumental characteristics of this satellite from archival data only. In particular we were interested in frequencies induced in the analysis of light curves by the instrumental properties of HIPPARCOS.