PEGASE: a free flying interferometer for the spectroscopy of giant exo-planets

This paper presents a summary of the phase-0 performed in 2005 for the Pegase mission. The main scientific goal is the spectroscopy of hot Jupiters (Pegasides) and brown dwarfs from 2.5 to 5 μm. The mission can extend to the exploration of the inner part of protoplanetary disks, the study of dust clouds around AGN,. The instrument is basically a two-aperture (D=40 cm) interferometer composed of two siderostats and one beam-combiner. The formation is linear and orbits around L2, pointing in the anti-solar direction within a +/-30° cone. The baseline is adjustable from 50 to 500 m in both nulling and visibility measurement modes. The angular resolution ranges from 1 to 20 mas and the spectral resolution is 60. in the nulling mode, a 2.5 nm rms stability of the optical path difference (OPD) and a pointing stability of 30 mas rms impose a two level control architecture. It combines control loops implemented at satellite level and control loops operating inside the payload using fine mechanisms. According to our preliminary study, this mission is feasible within an 8 to 9 years development plan using existing or slightly improved space components, but its cost requires international cooperation. Pegase could be a valuable Darwin/TPF-I pathfinder, with a less demanding, but still ambitious, technological challenge and a highly associated scientific return. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only

Real-time optical path difference compensation at the Plateau de Calern I2T interferometer

The fringe tracker system of the ASSI (Active Stabilization in Stellar Interferometry) beam combining table at the I2T interferometer is described and its performance evaluated. A new real-time algorithm for the optical path difference (OPD) measurement is derived and validated. It is based on a sinusoidal phase modulation whose amplitude is optimized. It also allows automatic fringe detection at the beginning of an observation when scanning the OPD. The fringe tracker servo-loop bandwidth is adjusted by a numerical gain and ranges between 20 and 50 Hz in the reported experiments. On stars, fringe-locked sequences are limited to 20 s due to fringe jumps. However, the fringe tracker is able to recover the coherence area after a few seconds. Such a fringe tracker operation can last more than one hour. A fringe tracking accuracy of 85 nm is achieved for visibility ranging between 7 and 24% , a turbulence coherence time of approximately 9 ms at 0.85 μm, a Fried parameter of around 14 cm at 0.5 μm and an average light level of 100 000 photoevents/s, (typically visual magnitude 2 in the conditions of the experiment). Visibility losses are evaluated and are found to be mainly due to turbulent wavefront fluctuations on the two telescopes and to the static aberrations of the optical train. The measurements of OPD and angle of arrival are reduced to derive turbulence parameters: the coherence time, the average wind speed, the Fried parameter and the outer scale. Our estimations for the outer scale range between 20 and 120 m, with an average value of the order of 40 m. Both OPD and angle of arrival data, obtained on 15 m baseline and a 26 cm telescope diameter respectively, are fully compatible with the same modified Kolmogorov spectrum of the turbulence, taking into account a finite outer scale

Performance of the angle of arrival correction system of the I2T + ASSI stellar interferometer

The Active Sta bi li zation in Stellar Inter fero me try (ASSI) recombining table, developed at Office National d'Etudes et de Recherches Aérospatiales (ONERA), France, was implemented on the two-Telescope Interferometer (I2T) of the Observatoire de la Côte d'Azur (OCA) in 1993, compensating for the atmospheric turbulence wavefront fluctuations. Initial fringe observations were made in June 1994 with a 11 m North-South baseline. In this paper, we report the performance of the ASSI table servo system for correction of the angle of arrival. Tracking accuracy of about $\pm0.24$ arcsec was achieved in typical seeing conditions ($r_0\geq 10$ cm) and on mv=2 sources. Collected data allows to compare theoretical with observed temporal power spectra of the angle of arrival fluctuations, using Kolmogorov model. Spatio-temporal seeing parameters met during observations (Fried parameter r0 and coherence time t0) are estimated

Elements-cles de la conception d'un instrument spatial a synthese= d'ouverture optique

Communication to : Colloque international sur l'optique spatiale,= Toulouse (France), 2-4 decembre 1997Available from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1997 n.215 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Stabilisation active de la phase en synthese d'ouverture

Tire de : Congres ICSO'91, Toulouse, 25-27 septembre 91SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1991 n.199 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Multiple-aperture optical telescopes: cophasing sensor testbed

International audienc

Multiple-aperture optical telescopes: cophasing sensor testbed

International audienc

Multiple-aperture optical telescopes: cophasing sensor testbed

International audienc