The COsmical Dynamics EXperiment (CODEX)
L. Pasquini¹, CODEX TEAM ^2
1 European Southern Observatory ² The CODEX concept study is a collaboration between ESO, IoA Cambrige, Observatoire de Geneve, INAF-Trieste
CODEX is a proposed array of high resolution spectrographs fed by OWL, exceptionally stable, and which will use a novel laser technique to obtain an ultra precise absolute wavelength calibration. CODEX is conceived to measure wavelength differences which correspond to an unprecedented radial velocity accuracy (1 cm/sec over 10 years or longer) with the primary aim of performing for the first time a direct measurement of cosmic dynamics. This will be obtained by observing many lines of sight towards Z ~ 1.5 to Z ~ 4 quasars, and measuring the Doppler acceleration occurred between two epochs in the intervening Lya and metallic lines due to the cosmic expansion. CODEX is the only experiment aiming at a direct measurement of the dynamical effects of the elusive dark energy, which has become part of the current cosmological standard model, without making any assumption about the physics and on the evolution of the objects involved. The longer the experiment's time-base, the larger the cosmic signal is, and CODEX will further provide a set of legacy QSO spectra with a precise absolute wavelength calibration which can be used by future generations of astronomers to obtain highly accurate constraints on the evolution of dark energy between the red shift range Z=1.5-4 and the present. The improvement with respect to the existing facilities is challenging, but feasible. The set of R=150000, S/N  2000 spectra for  40 QSOs will constitute an unique dataset which can be exploited for other purposes; it will be possible, among other things, to determine the variation of the fine structure constant to an accuracy of 10^-8 over an Hubble time, or 2 orders of magnitude more precisely than at present. As an high resolution optical spectrograph at OWL, CODEX will have a tremendous impact on many branches of astrophysics. Thanks to its extremely high precision, it will be able to confirm, characterize and discover earth masses planets in habitable zones around other stars and it will be able to determine with exquisite accuracy the abundance of the primordial elements and their isotopes.We present here a conceptual design study which uses detailed simulations to assess the expected accuracy. CODEX could be fully developed in as little as 12 years, including the development of a full prototype and its testing for 3 years at the VLT.

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On 20 Oct 2005, 17:41.