First step to detect an extrasolar planet using differential interferometric observations – Perspectives for Dome C

Performed in November 2007, the observation of the hot Jupiter-like exoplanet Gliese 86b constituted the first attempt of exoplanet detection with MIDI, and also the first VLTI observation using AMBER and MIDI simultaneously. Fringes were obtained for both instruments with the aim to correct the interferometric phase in N -band from the wet dispersion using the fringes in K -band. In N -band, it appears that the theoretical interferometric phase would be a curved-like function with an amplitude of about 0.04°. According to the MIDI phase measurements of the calibrator HD 9362, we roughly estimate that a precision of about 0.33° is currently reached. The AMBER data, obtained in parallel, were too noisy for correcting the corresponding dispersion in N band, the correction accuracy standing at factor 10 above the detection. Dome C presents a very low absolute humidity level. In homogeneous humidity conditions, the curvature amplitude of the phase term due to water vapor, is also ten times smaller than the MIDI one, and may stand below the planetary phase signature. However differential humidity measurements would be required to completely validate the potential of this site.