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Using a simple model based on the characteristics of sunspots and faculae in solar active regions, the effects of surface brightness inhomogeneities on the position of the photocentre of the disk of a solar-like, magnetically active star, are studied. A general law is introduced, giving the maximum amplitude of the photocentre excursion produced by a distribution of active regions with a given surface filling factor. The consequences for the detection of extrasolar planets by means of the astrometric method are investigated with some applications to forthcoming space missions, such as GAIA and SIM, as well as to ground-based interferometric measurements. Spurious detections of extrasolar planets can indeed be caused by activity-induced photocentre oscillations, requiring a simultaneous monitoring of the optical flux and a determination of the rotation period and of the level of activity of the target stars for an appropriate discrimination.
In order to understand the exoplanet, you need to understand its parent star. Astrophysical parameters of extrasolar planets are directly and indirectly dependent on the properties of their respective host stars. These host stars are very frequently
We present the work in progress of a study based on photometric and spectroscopic observations of young Weak-line T Tauri and Post T Tauri stars just attiving on the Zero Age Main Sequence. This study is part of a project based on high-resolution spe
The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsat
Astrometry can detect rocky planets in a broad range of masses and orbital distances and measure their masses and three-dimensional orbital parameters, including eccentricity and inclination, to provide the properties of terrestrial planets. The mass
We present the discovery of four new long-period planets within the HARPS high-precision sample: object{HD137388}b ($Msin{i}$ = 0.22 $M_J$), object{HD204941}b ($Msin{i}$ = 0.27 $M_J$), object{HD7199}b ($Msin{i}$ = 0.29 $M_J$), object{HD7449}b ($Msin{