Report - School of Physics
Report - School of Physics
Report - School of Physics
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3.2.2 The Darwin Ground-Based Precursor: GENIE<br />
GENIE is a nulling interferometer under development by ESA and ESO for the<br />
VLTI. GENIE will allow the development and demonstration <strong>of</strong> the technology required<br />
for nulling interferometry, allowing testing <strong>of</strong> the Darwin technology in an<br />
integrated and operational system (amplitude control loops, high-accuracy optical<br />
path difference control loop, dispersion control, polarisation compensation, background<br />
subtraction, and internal modulation). GENIE is considered by the Darwin<br />
project as necessary for demonstrating these technical concepts in advance <strong>of</strong> launch.<br />
Two competitive instrument definition studies were due for completion by the end<br />
<strong>of</strong> 2004, with the scientific case being prepared in collaboration between ESO and<br />
ESA. GENIE will be considered by the ESO Council in April 2005, and could be<br />
operational by mid-2008. If not accepted by ESO, a separate laboratory technology<br />
demonstrator would be needed to validate the Darwin concepts.<br />
GENIE is also considered mandatory as a specific instrumental configuration to<br />
survey southern-hemisphere target candidates, in order to decide which targets are<br />
most suitable for observation by Darwin, and specifically to characterise the level <strong>of</strong><br />
exo-zodiacal light, which must be below certain limits necessary for exo-planetary<br />
detections. A corresponding programme is planned to be undertaken at the Keck<br />
telescope in the northern hemisphere for preparations for TPF. Studies by den Hartog<br />
et al. (2004) show that the capabilities <strong>of</strong> GENIE are sufficient to detect the<br />
planet around τ Boo within 1 hour, and by inference some 5 other candidate ‘hot<br />
Jupiter’ planets. GENIE could use either the VLT UTs or ATs, at a wavelength <strong>of</strong><br />
3.6 µm, and will require a significant number <strong>of</strong> observing nights (<strong>of</strong> order 50).<br />
The main limiting factors for GENIE are the phase and thermal background stability<br />
on Paranal, as well as system complexity issues involved with its integration<br />
into the existing VLTI environment. If GENIE were located on the high Antarctic<br />
plateau (Dome C) where the thermal background is lower, and the seeing both better<br />
and slower (see Section 3.1.2), the performance required to perform its science<br />
programme could perhaps be achieved using smaller (<strong>of</strong> order 1 m) telescopes and a<br />
simpler, dedicated system architecture. This has to be balanced against the reduced<br />
sky coverage at −75 ◦ latitude, and probably more complex logistics.<br />
Table 9: Darwin: integration times for detection <strong>of</strong> Earth-like planets at S/N = 5, and spectroscopy<br />
at S/N = 7 in the faintest part <strong>of</strong> the spectrum (in hours). See text for details.<br />
Stellar type 10 pc 20 pc 30 pc<br />
G2V 18–33 28–54 109–173<br />
G5V 12–22 27–46 105–166<br />
K2V 4–9 26–37 104–157<br />
K5V 4–6 26–35 249–155<br />
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