The SARG Exo - Planets Search: Scientific Aims

The issue concerning the presence of planets around other stars was resolved since 1995 when the first planet (51 Peg) was discovered by Geneva team (Mayor & Queloz 1995, Nature, 378, 355). Up to day there are a number greater than 60 of discovered extrasolar planets. However, understanding the frequency and the properties of the planets as a function of some fundamental parameters (mass, chemical composition of parent star, dynamical environment) cannot easily inferred from current surveys. In particular, a crucial point is the following:

is the high metallicity of the parent star the cause or the effect of the presence of the planets?

Binary systems are ideal laboratoris to identify possible chemical anomalies of the star with the planet, by comparing the chemical composition of the component. If the high metallicity of the parent stars of planets is the result of planets or planetesimal ingestion (Gonzalez 1997) some systematic differences are expected between members of a binary system with and without planetary companions.  

In the figure the histogram of metallicities of stars bearing planets (solid line) compared to a volume limited sample of 77 G dwarfs within 20 pc (dashed area) is shown (from Butler R.P, Vogt S.S., Marcy G.W., Fischer D.A., Henry G.W. & Apps K. 2000, ApJ 545, 504).

Furthermore, the discovery of planets in binary systems may allow to study the dynamical effects on planetary systems due to the presence of the stellar companion, providing basic data about the minimum binary separation for planet formation and possible perturbations of planetary orbits.