Exploring variations in the fundamental constants with ELTs: The CODEX spectrograph on OWL
Paolo Molaro¹, Michael T. Murphy², Sergei A. Levshakov^3
1 Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy
² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
³ Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia Cosmological variations in the fine structure constant, a, can be probed through precise velocity measurements of metallic absorption lines from intervening gas clouds seen in spectra of distant quasars. Data from the Keck/HIRES instrument support a variation in a of 6 parts per million. Such a variation would have profound implications, possibly providing a window into the extra spatial dimensions required by unified theories such as string/M-theory. However, recent results from VLT/UVES suggest no variation in a. Here, after comparing the present Keck and VLT datasets, we put forward the requirements for a high resolution spectrograph on an ELT if it is to significantly improve upon the present results. The foremost requirements are 0.1 m s^-1 wavelength calibration precision and resolution high enough to properly resolve even the narrowest of metallic absorption lines, R > 150 000 (FWHM < 2 km s^-1). With such a resolution the COsmic Dynamics EXperiment (CODEX) spectrograph currently being designed for the ESO OWL telescope will achieve a 2-to-3 order-of-magnitude precision increase in Da/a. This will rival the precision available from the Oklo natural fission reactor and upcoming satellite-borne atomic clock experiments. Given the vital constraints on fundamental physics possible, the ELT community must consider such a high-resolution optical spectrograph like CODEX.

---

File translated from T_EX by T_TH, version 3.33.
On 20 Oct 2005, 17:41.