The ESPRI project: astrometric exoplanet search with PRIMA
I. Instrument description and performance of first light observations⋆
Observatoire de Genève, Université de Genève, 51 chemin Des Maillettes, 1290
2 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
3 Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
4 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
5 European Southern Observatory, Alonso de Córdova 3107, Vitacura-Santiago, Chile
6 Automatic Control Laboratory, École Polytechnique Fédérale de Lausanne, Switzerland
7 Laboratoire de Systèmes Robotiques, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
8 École d’ingénieur ARC, 2610 St. Imier, Switzerland
9 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, 86001 Arizona, USA
10 Centre Suisse d’Électronique et Microtechnique, 2007 Neuchâtel, Switzerland
Accepted: 5 December 2012
Context. The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for discovering and studying planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years to detect their barycentric motions due to orbiting planets. We present the operation’s principle, the instrument’s implementation, and the results of a first series of test observations.
Aims. We give a comprehensive overview of the instrument infrastructure and present the observation strategy for dual-field relative astrometry in the infrared K-band. We describe the differential delay lines, a key component of the PRIMA facility that was delivered by the ESPRI consortium, and discuss their performance within the facility. This paper serves as reference for future ESPRI publications and for the users of the PRIMA facility.
Methods. Observations of bright visual binaries were used to test the observation procedures and to establish the instrument’s astrometric precision and accuracy. The data reduction strategy for the astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO were used as an independent verification of PRIMA astrometric observations.
Results. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 μas was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain that is not monitored by the internal metrology system.
Conclusions. Our observations led to defining corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.
Key words: instrumentation: interferometers / techniques: interferometric / astrometry / planetary systems / binaries: visual / stars: general
Part of this work is based on technical observations collected at the European Southern Observatory at Paranal, Chile. The raw data is publicly accessible at the ESO Science Archive Facility (http://archive.eso.org/).
© ESO, 2013