6dF: A very efficient multi-object spectroscopy system for the UK Schmidt Telescope

Multi-object spectroscopy at the Anglo-Australian Observatory's 1.2-m UK Schmidt Telescope (UKST) is carried out with the FLAIR multi-fibre system. The FLAIR front-end feeds an optically-efficient, all-Schmidt spectrograph mounted on the dome floor. However, positioning of the 92 available fibres within the 40 sq.deg. field of the telescope is essentially a manual operation, and can take from four to six hours. Typical observations of sufficient signal-to-noise usually take much less than this (e.g. about an hour for galaxy redshifts to B ∼ 17). Clearly, therefore, the system is working at well under its potential efficiency for survey-type observations where repeated reconfigurations of fibres are required. To address the imbalance between reconfiguration time and observing time, a fully-automated, off telescope, pick-place fibre-postioning system known as 6dF has been proposed. It will allow 150 fibres to be reconfigured across a 6-degree circular field in under an hour. Three field plates will be available with a 10-15 minute field-plate changeover anticipated. The resulting factor of 10 improvement in observing efficiency will deliver, for the first time, an effective means of tackling major, full-hemisphere, spectroscopic surveys. An all southern sky near-infrared-selected galaxy redshift survey is one high-priority example. The estimated cost of 6dF is $A450k. A design study has been completed and substantial funding is already in place to build the instrument over a two-year timescale.