V. Coudé du Foresto (DESPA, Obs. Paris-Meudon),
F. Malbet (LAOG, Obs. Grenoble), responsable du groupe
D. Mékarnia (Fresnel, Obs. Nice),
R. Petrov (Astrophysique, Univ. Nice),
F. Reynaud (IRCOM, Univ. Limoges),
M. Tallon (CRAL, Obs. Lyon)
Date: 7 mars 1997
This report covers the different points that have been addressed by the Working Group on the near-IR/red instrumentation of VLTI and GI2T. The mandate of our group was to study an interferometric instrument that:
could become operational on VLTI in a 2-beam version as soon as
the first two UTs come in-line (early 2000);
could be used in that version to provide unique scientific
results within the 30 nights reserved on the UTs for interferometric
could easily be upgraded to accommodate 3 beams (the ATs) when
they come in-line (mid-2001);
could be developed fully within the French community and for a
budget envelope of 3-4MF, even though an international collaboration is
most likely to occur;
could possibly be used and/or tested on GI2T.
Our work is to be inspired from the previous works and documents released on the topic (Interferometry Panels and ISAC at ESO, IVOIRE group in France, trilateral ESO/MPG/INSU Memorandum on VLTI). An additional assumption is made that the instrument will benefit from a low-cost adaptive optics system (whose feasibility is studied in parallel by another Working Group), so that single-mode operation with decent efficiency can be considered for the UTs in K and the ATs in the red.
Our group realized that the interferometric combination of two UTs is
unique essentially for the sensitivity it provides, and therefore identified as a priority target for the UTs the study of the central core of active galactic nuclei, whose observation at decametric baselines can lead to important new science in relatively little telescope time. Major science objectives for the ATs are the study of low-mass objects (brown dwarfs and "hot Jupiter" exoplanets), the circumstellar environment of YSOs (also a backup program with spectral resolution on the UTs), stellar surface structures and Be stars, and AGBs with their circumstellar environment at high spectral resolution.
Based on numerical simulations and the observed behavior of PUE’O (the CFHT adaptive optics bonnette), we have analyzed the performance of the low-cost, 31-actuator curvature-sensing AO system proposed by the AO Working Group. For the UTs the maximum correction will be achieved at magnitudes V<12. The average Strehl ratio in K would then be in the range 0.1-0.3. For the 20% best seeings, the Strehl ratio would still be 0.2 at V=14. With the ATs, the average Strehl would be best at 0.8—0.9 in K and 0.05-0.2 in H-alpha, for magnitudes V<10.
The time and budget constraints and the expected performance of the adaptive optics lead us to recommend a simple instrument single-mode,
single-field) for the K band (non-thermal IR), based on proven designs with a capacity for spectral resolution of up to 10000. It features spatial filters and photometric calibration to provide high precision visibility measurements. The instrument is upgradable towards the red. Such an instrument has the capability to perform the recommended science programs; it is clear, however, that in a cophased mode its sensitivity t low spectral resolutions will be limited by the fringe sensor. The faintest sources can only be observed in coherent mode.
We present a preliminary work breakdown structure and a census of the
internal resources (expertise and manpower) in each of the laboratories affiliated to the National Program for High Angular Resolution. They are found to be sufficient in most domains to undertake the project fully within the community, with the exception of a relative lack of computer scientists/programmers.