Nulling interferometry: performance comparison between space and ground-based sites for exozodiacal disc detection

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, 17 Allée du Six Août, 4000 Liège, Belgium e-mail: defrere@astro.ulg.ac.be
² LAOG–UMR 5571, CNRS and Université Joseph Fourier, BP 53, 38041 Grenoble, France
³ LESIA, Observatoire de Paris-Meudon, CNRS, 5 place Jules Janssen, 92195 Meudon, France
⁴ NASA Goddard Space Flight Center, 8800, Greenbelt Road, Greenbelt, MD 20771, USA
⁵ Science Payloads and Advanced Concepts Office, ESA/ESTEC, postbus 299, 2200 AG Noordwijk, The Netherlands

Received: 22 May 2008
Accepted: 11 August 2008

Abstract

Context. Characterising the circumstellar dust around nearby main sequence stars is a necessary step in understanding the planetary formation process and is crucial for future life-finding space missions such as ESA's Darwin or NASA's terrestrial planet finder (TPF). Besides paving the technological way to Darwin/TPF, the space-based infrared interferometers Pegase and FKSI (Fourier-Kelvin Stellar Interferometer) will be valuable scientific precursors.

Aims. We investigate the performance of Pegase and FKSI for exozodiacal disc detection and compare the results with ground-based nulling interferometers.

Methods. We used the GENIEsim software (Absil et al. 2006, A&A, 448, 787) which was designed and validated to study the performance of ground-based nulling interferometers. The software has been adapted to simulate the performance of space-based nulling interferometers by disabling all atmospheric effects and by thoroughly implementing the perturbations induced by payload vibrations in the ambient space environment.

Results. Despite using relatively small telescopes (≤0.5 m), Pegase and FKSI are very efficient for exozodiacal disc detection. They are capable of detecting exozodiacal discs 5 and 1 time respectively, as dense as the solar zodiacal cloud, and they outperform any ground-based instrument. Unlike Pegase, FKSI can achieve this sensitivity for most targets of the Darwin/TPF catalogue thanks to an appropriate combination of baseline length and observing wavelength. The sensitivity of Pegase could, however, be significantly boosted by considering a shorter interferometric baseline length.

Conclusions. Besides their main scientific goal (characterising hot giant extrasolar planets), the space-based nulling interferometers Pegase and FKSI will be very efficient in assessing within a few minutes the level of circumstellar dust in the habitable zone around nearby main sequence stars down to the density of the solar zodiacal cloud. These space-based interferometers would be complementary to Antarctica-based instruments in terms of sky coverage and would be ideal instruments for preparing future life-finding space missions.