Direct determination of physical parameters for main sequence stars

The environment of planetary formation and evolution is mainly characterized by its host star's physical properties. Until recently most fundamental stellar parameters, like e. g. the star's radius and effective temperature, have only been estimated indirectly; but with advances in interferometric observing technique it is now possible to obtain a direct estimate of them. In this poster we present preliminary results from measured interferometric fringe visibilities of main-sequence stars. These visibilities were collected using the four-beam combiner VLTI/PIONIER instrument and the 1.8m Auxiliary Telescopes (ATs) in A1-G1-K0-J3 quadruplet configuration. We bracketed each science target with different calibrators to ensure reducing the systematic errors in our data. For each target star, the data reduction was performed several hundred times, each time randomizing the set of fringes by the bootstrap method and the calibrators' diameters. This allowed us to take into account error correlations across spectral channels, between consecutive observations, and overnight. Each result was least-squares fitted by a uniform disc, yielding a value for the target's diameter. From the distribution of diameters we assessed the statistical error in the respective measurement. Using the HIPPARCOS parallax we estimated the distance and obtained the star's linear radius. Combined with the bolometric flux we obtained a direct quantification of the effective temperature from the Stefan-Boltzmann equation. Finally, these direct determinations of stellar radii and effective temperatures enable us to better characterize planets around main-sequence stars.