SSO News

Published in the RSAA Lunations
Vol1 Issue2 1–31 March 2020

Upgrade to the Two Degree Field Facility

The Two Degree Field facility (2dF) on the AAT at Siding Spring Observatory provides a two degree window on the sky and the ability to position up to 400 optical fibres precisely using a purpose built pick and place robot. These long flexible fibres carry the faint signals from many stars and galaxies to either one of two purpose built spectrographs which analyse the light.

Currently the robot is undergoing an upgrade with the replacement of its two field plates.

The performance and efficiency of the instrument robotics depends on its ability to accurately place the optical fibres. The replacement of the previous one magnetic stainless steel and one experimental invar plates with high precision and thermally stable invar field plates will provide a more accurate and thermally stable field on which to place the magnetically held optical fibres.

Invar is a very difficult material to accurately machine large flat surfaces. The Department of Physics Workshop at Oxford University possessed the capability, expertise and metrology to undertake the manufacture of these plates. The plates are 540 mm in diameter and weight approximately 20kg.

The image shows the field plate after the fiducial fibres have been fitted. The fiducial fibres are embedded in the field plate and are illuminated by LEDs when required to allow the machine vision system of the positioner robot to accurately calibrate the field plate. The original field plates only had 21 fiducial fibres fitted and a number were often obscured by fibres placed on the field. The new plates have a total of 77 fiducial fibres which will provide more numerous measurement points during the calibration process. In April 2020 the field plates will be taken to AAO - Macquarie for accurate measurement of the 77 fiducial fibres for incorporation into the instrument configuration.

It is believed that the improved dimensional accuracy, thermal stability and additional fiducial fibres will improve the calibration of the robot and enhance the precision with which the optical fibres can be placed to capture the faint light from the astronomical objects.

Chris McCowage, Kristin Fiegert