HARPS3 and the Terra Hunting Experiment
We present the current status and a project description of the Terra Hunting Experiment with HARPS3 - a new instrument being built for the Isaac Newton Telescope. HARPS3 is planned to be installed on an upgraded and roboticized Isaac Newton Telescope by 2020. HARPS3 will be a high resolution (R = 115,000) echelle spectrograph with a wavelength range from 380-690nm. It is being built as part of the Terra Hunting Experiment – a future 10 year radial velocity measurement programme to discover "Earth-twins". The instrument design is based on the successful HARPS spectrograph on the 3.6m ESO telescope and HARPS-N on the TNG telescope. The main changes to the design in HARPS3 will be: a customised fibre adapter at the Cassegrain focus providing a stabilised beam feed, dual-beam full-Stokes polarimeter and an on-sky fibre diameter ~ 1.4 arcsec, the implementation of a new continuous flow cryostat to keep the CCD temperature very stable, characterisation of the HARPS3 CCD to map the effective pixel positions and thus provide an improved accuracy wavelength solution and the instrument integrated into a robotic operation. The robotic operation will optimise our programme which requires our target stars to be measured on a daily basis.