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The HERMES Project: Connecting to the 2dF facility


The 2dF facility is a robotic multi-object pick-up system installed at the prime focus of the AAT. A tumbler unit holds two identical field plates on opposite sides. During night-time operation, one configured plate field is positioned at prime focus for astronomical observations, while the other is reconfigured in about 40 minutes by the fiber positioner, with up to 400 fibers put on as many astronomical targets in a two-degree field diameter. This prevents losing precious telescope time when going to another field or when selecting different objects in the same field. The available spectral range is limited by the facility field corrector glasses to the ‘optical’ domain (365nm-1100 nm).

2dF in AAT dome

The 2dF top end mounted on the AAT (Click for full resolution image. Photo: Barnaby Norris)

2dF positioner being tested at the AAT
The 2dF positioner configuring a test field. The fibres run from the edge to locations corresponding to the target objects. (Click for full resolution image. Photo: Barnaby Norris)

The 2dF system is currently feeding the AAOmega spectrograph. This provides a powerful survey capability in the optical domain (0.37 to 0.95 μm) at low (1,000) to moderate (up to 10,000) spectral resolutions. An improved throughput fiber feed, with dual fibres for each target, will be installed to connect 2dF to both the HERMES spectrograph, and to AAOmega, in the coudé laboratory. (It is only intended to use one spectrograph at a time, although this is a mainly a limitation of the detector infrastructure, and having dual fibres does make simultaneous observation in the future a theoretical possibility.) Each 140 μm diameter fiber core covers 2 arcsecond on the sky. Two 400-fibre bundles (one for each field plate) will be connected to two interchangeable input slits in the HERMES slit assembly.