Didier Queloz

PRIMA: study for a dual-beam instrument for the VLT Interferometer

PRIMA (instrument for Phase-Referenced Imaging and Microarcsecond Astrometry) is a conceptual study for a single-baseline dual-feed instrument for the Very Large Telescope Interferometer (VLTI), which is under construction by the European Southern Observatory on Cerro Paranal in Chile. The goals of PRIMA include narrow-angle astrometry with a precision of 10 μas over an arc of 10, and imaging of faint sources with the full sensitivity of the 8 m telescopes in the VLT array. Key scientific programs that can be carried out with PRIMA in imaging mode include observations of active galactic nuclei, the Galactic Center, stars, and circumstellar matter. Scientific drivers for the astrometry are searches for planets and low-mass stellar companions, binary stars, dynamics of clusters, and (relative) parallaxes. We list the main performance requirements for PRIMA, present system architectures for the dual-beam system, and discuss limitations of the interferometric field-of-view.

Atmospheric signatures by transit of HD209458 with VLT/UVES

In our search for clues as to the nature of the exosphere of HD209458 (Moutou et al., 2001 ; Moutou et al., 2003, Iro et al., 2004), we have acquired VLT/UVES data during an ambitious observational campaign performed in June-September 2002 and covering 6 transits of the exoplanet. The resolving power was R=100000 in the 0.475-0.68 micron range. We search for ions and neutral molecules (such as H2O+, CO+, CH+, etc) originating in the planets exosphere and located in the evaporated material around the planet, occulting its primary star. We present in this paper a tentative search in the spectral regions where features of sodium or H2O + can be present.

First attempt in searching for HD209458b's exosphere

The transit of the planet orbiting HD209458 has been observed using VLT/UVES, in search for faint signatures of an extended envelope of gas possibly surrounding the planet, called exosphere. Preliminary results are shown and described. They show no evidence so far of exospheric signatures.

Transmission Spectroscopy for Extrasolar-Planet Studies: UVES Search and Future Prospects

Following the discovery of the first transit of an extra-solar planet we made a high-resolution follow-up of this event, in the goal of recovering the transmission spectrum of the planet’s atmosphere. UVES on the VLT was used to get high-quality spectra but no detection can be claimed so far. We also describe prospects in this field of investigation, for the next instrumentation.

Outer Disc Rotation from Cepheid Variables

We have measured radial velocities for a large number of classical cepheids of the Galaxy, particularly in the outer disc. We determine the rotation curve up to a galactocentric radius of 16 kpc. The results are then compared to similar studies using HII regions. We also consider some possible complications.