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A Terra Hunting Experiment at the INT
Rationale
To detect smaller mass planets (down to 1Mе) using the radial velocity technique, we need to be able to retrieve a signal in the limit of stellar variability noise. One way to improve this retrieval is to modify the frequency and duration of the data sample ­ i.e. a dedicated campaign of regular, daily observations for as long as is required to determine the orbital period. Such an observing program is not feasible with a non-dedicated telescope. To address this, we are proposing a "Terra Hunting Experiment" to be performed using a close-copy of the HARPS spectrograph installed on the 2.5m Isaac Newton Telescope (INT) in La Palma. The survey, operating over a minimum of 5 years, will target the nearest, brightest, solar-like stars. We intend to commence survey operations during 2018, providing synergy with other planet-finding surveys such as Gaia and PLATO.

Timescale
Summer 2014 - Establish consortium 2015-2016 - Manufacturing phase 2017 - Assembly, integration and verification 2018-2023 - Survey operations

The site
The INT is located on La Palma in the Canary Islands. It is a 2.5 m telescope at the Roque de los Muchachos; an altitude of ~2400 m. The median seeing is estimated to be ~1.2 arcsec with 20-25% of the year being clouded. The size of the seeing disc is well suited to our purpose.
Photo courtesy of the Isaac Newton Group of Telescopes, La Palma.

The instrument
The design of the high stability spectrograph will be a close-copy of the HARPS (north and south) spectrographs. These instruments have an excellent track-record, providing a lower risk solution than a new design concept. The 3D model (shown above) illustrates the main spectrograph components housed within a vacuum chamber and mounted on a rail system. The light path is shown in yellow. A large 700mm parabolic mirror is located at the left-end of the vacuum chamber. The spectrograph is fed via 2 fibres coupled to the telescope at the Cassegrain focus (not shown). The exact specifications are under review, but the approximate wavelength range will be 380-680 nm with an R ~ 100000. The high stability design in conjunction with Fabry-Perot/Thorium-Argon calibration sources should allow an RV precision of better than 1 ms-1.
Image credit: Observatoire Astronomique de l'UniversitИ de GenХve

Scientific merit
Statistics from the Kepler mission results indicate the presence of low-mass planets, but we have yet to find an Earth-like planet. A radial velocity signal from an Earth-like planet would be buried in the stellar variability noise. However, a change in the way we collect radial velocity data can help us recover a smaller signal: if the signal sampling is on the order of a day and sampled for as long as we need to recover the period of the planet then there is a significant reduction in signal aliasing allowing a low amplitude planetary signal to be detected. The figure shows a simulation of 120 nights of observations, assuming 80% good weather, stellar noise of 1.25 ms-1 and 4 small mass planets with orbit: (1/days): [0.232,0.104, 0.057,0.026] (indicated by arrows Credit: D. Segransan, UniversitИ de GenХve (priv comm) on the diagram), k1 amplitude smaller than the noise: respectively [0.88,1.17,1.16,0.80] (ms-1), ecc=0. The top left graph shows the FFT analysis of the intense, daily observing strategy, the bottom left the same number of measurements but spread over 180 days. The structure of alias in each observing scenario is displayed on right side diagrams; the intense observation strategy is cleaner with better defined detections.

Current status
We are putting together a proposal for the ING Board to review in June. Given the current status of the INT we welcome community support and input into this proposal. We are in the process of establishing the consortium for the project; the current members are: University of Cambridge (UK) - PI institute University of Exeter (UK) UniversitИ de GenХve (Switzerland) Please contact us (see contact information below) for further information.

Contacts:

Didier Queloz (PI) - dq212@cam.ac.uk Samantha Thompson - sjt20@cam.ac.uk